Robert Adams Pulsed Electric Motor Generator

Robert Adams Pulsed Electric Motor Generator: Theory & Tips

In 1975 the Chairman of the New Zealand Institute of Electrical Engineers, Robert Adams, filed for a patent on a new type of highly efficient motor / generator that utilized the power of permanent magnets.

However, his patent was denied, and he was subsequently pressured by the prime minister and several large companies to keep his invention to himself.

After 20 years of this, Adams, now in his seventies, felt he didn’t have much to lose, and so he decided to publish his invention in a 1994 edition of Nexus Magazine.

Since then, thousands of experimenters around the world have replicated Adams’ revolutionary device, some with incredible results.

Unfortunately, there is a lot of confusion and misinformation out there about the Adams Motor, which I aim to clear up in this article by mainly referring to the inventor’s own words.

What makes the Adams Motor so special?

In short, the Adams motor uses only a small amount of power to rotate permanent magnets, it then recaptures some of this power to keep its supply battery (partially) charged, and then uses generator coils to extract additional useful power to run loads.

These claims might seem ridiculous to some readers, but I have a working model running in my shed that does just this, and I only studied this stuff for two weeks before I built it!

It’s not rocket science, you just need an open mind and learn why it works, without violating any established laws of physics.

Now on to the detailed answer 🙂

But first, a short detour, as I need to clarify the term “back EMF” before we can continue, since even Robert Adams himself does not always use it in the clearest way.

Back EMF 101

It is important to know that there are 3 types of electromotive force, or EMF, present in an Adams Motor circuit:

  1. Supply EMF
    The voltage supplied by a power supply or a battery.
  2. Counter EMF
    A voltage induced in a motor coil by a moving magnet, opposing the supply voltage.
  3. Flyback EMF
    A high voltage spike produced by a collapsing magnetic field.

As you can see I did not use the term “back EMF” in the list above, as some people use that term for #2, while others use it for #3 in the list, or both!

This is the source of a lot of confusion and misunderstanding.

That is why I use the wording from the 1954 Basic Electricity manual, which was used to teach army cadets about electricity and electric motors:

Counter EMF

Here is an excerpt from that excellent book:

In a DC motor, as the armature rotates, the armature coils cut the magnetic field, inducing a voltage or electromotive force in these coils. Since this induced voltage opposes the applied terminal voltage, it is called the “counter electromotive force”, or “counter-emf.”

There you have it; counter EMF is induced in a coil when a magnet passes by, and is in opposite direction to the supply voltage.

Counter EMF is displayed as a battery opposing the source voltage

It continues:

This counter-emf depends on the same factors as the generated emf in a generator–the speed and direction of rotation, and the field strength. The stronger the field and the faster the rotating speed, the larger will be the counter-emf.

An electric motor is at the same time a generator, and the generator output of a motor is the counter EMF.

Now here comes the really interesting part that was an eye-opener for me:

What actually moves the armature current through the armature coils is the difference between the voltage applied to the motor (Ea) minus the counter-emf (Ec).

Ohm’s Law states that

current = voltage / resistance

But for DC motors, this is changed to

current = (supply voltage - counter EMF) / resistance

Since counter EMF increases as the motor speeds up, this explains why the current draw of an electric motor decreases with speed, which is further explained in the next section:

The internal resistance of the armature of a DC motor is very low, usually less than one ohm [10-20 ohm in an Adams motor]. If this resistance were all that limited the armature current, this current would be very high… However, the counter-emf is in opposition to the applied voltage and limits the value of the armature current that can flow.

And from another source:

As the motor turns faster and faster, the [counter] emf grows, always opposing the driving emf, and reduces the voltage across the coil and the amount of current it draws… if there is no mechanical load on the motor, it will increase its angular velocity ω until the [counter] emf is nearly equal to the driving emf. Then the motor uses only enough energy to overcome friction.

Lumen Learning

Soooo, long story short: if you want to use the least amount of current to spin a rotor, you let it run at maximum speed, without a mechanical load, to maximize counter EMF.

Robert Adams had this to say about it:

For efficient running the [counter] E.M.F. must be nearly equal to the applied E.M.F.

So what then is the flyback EMF that others sometimes mistakenly call “back EMF”?

Well, when current flows through a coil, this current establishes a magnetic field around the coil.

If you then suddenly disconnect the coil, there will no longer be any current flowing to support the magnetic field, and so it rapidly collapses in on itself.

And we know that a changing magnetic field induces a voltage, and the formula it follows is

Voltage = Inductance / Rate of change of current

In other words, the faster you cut off the supply current, the higher the resulting voltage spike.

In a regular DC motor, this high voltage flyback EMF is being diverted using a flyback diode to protect the windings, essentially wasting this energy.

In an Adams Motor, the flyback EMF is instead “captured” in a capacitor, and then used to (partially) recharge the supply battery.

I hope it is now clear what the difference is between the three types of EMF present in an Adams Motor.

For more information on counter EMF, and how you can engineer an electric motor that does not generate any counter EMF, I highly recommend you check out Peter Lindemann’s brilliant Electric Motor Secrets presentations.

Features and advantages

In his publication “The Adams Pulsed Motor Generator Manual“, Adams mentions a long list of features and advantages of his device.

I will now quote these and add comments where needed.

It overcomes back EMF, which is the big problem in all conventional machines

In this case, back EMF refers to counter EMF.

Adams mentioned that “as Lenz’s Law states, the induced [counter] EMF is in such a direction as to oppose the rotation which is producing it.”

This is called Lenz drag, and results in wasted power.

An Adams Motor is pulsed at the exact right time so the Lenz drag is cancelled out, allowing the rotor to keep spinning freely.

It, in turn, (due to its unique design) harnesses the effect of back EMF, I.E., the collapsing magnetic field, thereby increasing torque and decreasing power input

In this case, back EMF refers to flyback EMF.

The flyback voltage spike pushes the magnet along, increasing torque.

The flyback EMF is also siphoned back to the supply battery, thereby decreasing net power input.

It does not require a separate motor in the motor/generator mode to produce electrical output energy

It utilizes one common rotor which runs the machine and generates output power

Conventional machines need drive coils around the entire rotor circumference to pull it through its full range of motion, while an Adams Motor only needs two or even just one drive coil.

This leaves room to place generator coils around the same rotor, removing the need for a second generator rotor.

All it’s rotor poles are of similar polarity, I.E., all south going or all north going

Traditional electric motors use an alternating north-south magnet configuration, while in an Adams Motor all magnetic pole faces are of the same polarity.

It’s drive (stator) winding and pole requirements are small

While you are not restricted to using any particular wire gauge, there are in fact a couple of guidelines you should follow to create optimal drive coils, which I’ll discuss later.

The air gap is not critical

Whether the gap between the coil core and the rotor magnet is 1mm or 2mm is not super important, “however reduction will increase torque and also increase input power in proportion.”

It requires no cooling fan

The motor and switching circuit run cool (~40º), because they use only a very small amount of current, applied during brief pulses.

The machine does not require constant current power input

The motor is ideally pulsed with a 25% duty cycle, which means no current flows for 75% of the time, while conventional electric motors have a current flowing continuously.

The unique design of the machine is such that:
a. It feeds energy back into its battery supply
b. There is virtually zero magnetic drag
c. It’s temperature, under full load conditions, is less than half that of any conventional machine
d. Regarding mechanical switching mode, the “tapered star contactor disc” which the inventor conceived, is a means of governing and/or altering the duty cycle, which, in turn, gives an automatic means of varying speed, current, and torque

A lot to unpack here.

The high voltage flyback EMF is fed back to the supply battery, allowing it to (partially) recharge.

Magnetic drag is nullified by a perfectly timed pulse.

The small amount of current in the system allows the motor to run cooler.

Duty cycle is used to adjust speed, current, and torque of the motor.

The machine, in high efficiency mode, I.E., beyond unity, is producing energy from space, viz., (electrostatic scalar potential)

This claim is a questionable one for several reasons.

First of all, the term “beyond unity” or “overunity” will immediately disqualify this invention in the minds of many, since nothing can be more than 100% efficient, and neither is the Adams Motor.

A better term to use would be “Coefficient of Performance” or “COP”, as this compares power input from the power supply with power output by the device.

Since some rotational energy comes from the permanent rotor magnets being attracted to the iron coil cores, energy which is not coming from the power supply, a properly constructed Adams Motor can actually achieve a COP > 1.

Since this energy comes from the magnets, the claim that energy is produced “from space” seems to be incorrect.

The vague term “electrostatic scalar potential” also seems to be unnecessary to explain the functioning of this device.

Contrary to conventional machines, the slower the speed, the greater the efficiency, the greater the torque, the lower the input power

This statement confuses me a little, as in conventional machines it is in fact the case that slower speed equals higher torque, but also higher current draw in proportion.

I did notice that my most efficient Adams Motor ran at a slower speed, and used much less power, but I haven’t yet been able to measure if it had in fact greater torque.

As there is no power factor loss in the machine there are constant power and torque characteristics (machine in resonance mode)

Adams writes “there is no power factor loss because the Adams machine runs in a state of resonance.”

The phase angle of the voltage and current in a series resonant circuit is zero at the resonant frequency, and if phase angle is zero, power factor is unity, see: https://www.electronics-tutorials.ws/accircuits/series-resonance.html

As there is no change in the direction of supply energy there are no eddy current or hysteresis losses sustained

This same claim is made in a patent of another pulsed motor, called the Keppe Motor, and explains the reasoning behind it in a bit more detail:

“Zero hysteresis, since the feeding current is a direct and pulsed current, so there is no polarity alternation of the source. Minimized eddy currents, because… the magnetic fields created inside the coil –both during power supply and back energy supply are parallel to the body of the motor, thus yielding close-to-zero induced currents.”

The machine, in all modes of operation, is self-protective from any likely adverse conditions occurring; therefore no protective ancillary devices are required

Can be run without a load without running itself to destruction, due to the self-regulating effects of counter EMF vs speed.

High speeds with their attendant problems are not necessary

Even a slowly spinning permanent magnet rotor is able to generate power, and the flyback EMF which recharges the source battery is also not dependent on rotational speed.

The machine can be electrically loaded simultaneously with a further increase in output energy of upwards from 50% to beyond 100% without overload or heating above its normal operating temperature

Adding properly designed generator coils to the Adams Motor allows extra power to be extracted, without much additional current draw.

The machine lends itself admirably to simple and inexpensive speed control

All you need to do is tweak the pulse duration.

How does it work?

Now that we know why this motor is so special, let’s look at how it actually works.

In his patent application, Adams describes his devices as follows:

…a direct current electric motor… which draws current only when the most effective use can be made of it, thus allowing the motor to run very efficiently.

Robert Adams, provisional patent application

The following series of drawings from Robert Adams’ patent application show a full cycle of the motor, which will help explain how it works:

Different stages of drive pulse vs rotor rotation

Here is what Robert Adams had to say about these drawings (I will highlight some important parts in bold):

Figures 1 to 4 show, in diagrammatic form, a motor according to the present invention, the rotor being at a different stage of its revolution in each of the various figures, and

Figures 1a to 4a [the bottom left corner of each drawing] show a representation of the current flow in each of the stages shown in Figures 1 to 4.

The drawings show a form of motor according to the invention which has a rotor [A] comprising four permanent magnets, 1 to 4, and a stator [B] comprising of two coil windings. The motor can be operated when the coil windings are connected to an appropriate DC voltage source.

The voltage source can be a bench power supply, but most often rechargeable lead-acid batteries are used.

The rotor magnets can be of any type, but Adams said that “there will be much disappointment to a lot of people out there to learn that magnet energy product does not govern efficiency in any way whatsoever.”

Stronger magnets require more input power to achieve the same amount of rotation, and so efficiency remains the same, although torque increases.

So to start, build a 12-24V device, and use lower strength ferrite magnets before upgrading to higher voltages and neodymium magnets.

The supply of current to the windings is controlled by a current controller shown diagrammatically in the drawings as a switch [S]. The current controller is operated in synchronism with the rotation of the rotor [A], so that current is supplied to the stator windings [B] only when the magnets 1 to 4 have just past their central point of alignment with the stator windings.

While Robert Adams himself preferred to use a brush commutator as his current controller, he also included drawings for transistor switches triggered by, for example, photo interrupters, Hall sensors, or trigger windings.

NOTE
I’ve seen many websites mention that you should only use MOSFETs for switching, as their internal body diode will create a path for the “back EMF” to flow back to the battery. This is WRONG, and another clear example of people not understanding the concept of counter EMF! You do NOT want the counter EMF to flow that way, you only want the flyback EMF to flow that way. None of Robert Adams’ drawings show MOSFETs, only regular transistors, although he does mention MOSFETs in an 2001 article written on his website.

As is shown in Figure 1 the stator windings are activated to produce a north magnetic pole adjacent the ends of the rotor magnet, 1 & 3. As indicated in Figure 1a, this is the point at which the current is first permitted to pass through the windings. Thus there is a magnetic field repulsion established between the stator and the rotor which causes the rotor to rotate in the direction indicated by the arrow. The magnetic repulsion is commenced when the rotor is at a small angle x degrees past the point of alignment with the stator windings.

Then, as shown in Figure 2, the current is maintained in the stator windings until the rotor has moved to an angle of y degrees past the point of alignment with the stator windings. Then at this point the current controller [S] cuts off the supply of current to the windings [B]. The resulting collapsing magnetic field now reverses magnetic polarity attracting on-coming rotor poles, thereby stator windings are pulsed again repeating the cycle.

You see that pulse timing is everything in this motor, in order to maximize the effect of the repulsion and attraction forces.

You need a way to precisely control the start time of the pulse, as well as its duty cycle, or your results will most likely not be very impressive.

This is why I decided to use a microcontroller to have direct control over the pulse timing and duty cycle.

Also, another force that is acting on the rotor, mentioned in another text, is the attraction of the approaching rotor magnet to the iron cores of the drive coils.

This attraction normally results in drag when the rotor magnets moves past the coils, but since that is the exact time the coils are pulsed, this nullifies the drag on the rotor, allowing it to continue to spin freely!

Figure 3 shows the motor with the rotor [A] having just past the position shown in Figure 2 and there is no supply electric current remaining in the stator windings [B]. The rotor is continuing to rotate under its angular momentum. This continues until the position shown in Figure 4 is reached. The pole 1 of the rotor is now at an angle of z degrees passed its point of alignment… Thus the pole 4 of the rotor [A] has almost reached the position of the pole 1 in Figure 1. In other words, the current controller [S] is just about to allow current to flow through the stator windings once more.

The cycle is then repeated, four times for each revolution of the rotor [A].

You’ll want the rotor to have a decent amount of mass, in order for it to act as a flywheel to maintain its angular momentum when the pulse is OFF.

Sooo, now that you know how the Adams Motor works, you can see why this motor is so efficient, as current is only applied “when the most effective use can be made of it”, just like when pushing someone on a swing, instead of being applied continuously, as in a regular DC motor.

But here is the biggest secret of this motor, in the words of Adams:

In all, the machine benefits from [three] different force actions per revolution and paying a minuscule toll fee for only one.

…the rotor magnet is mutually attracted to the stator (gets away without paying for that)

…from the repulsion pulse of the stator at point ‘x‘.

…the rotor is given a further pulse from the collapsing field (a few degrees after point ‘x‘)

Adams Update

Brilliant!

Now, the collapsing field is harnessed not just to give the rotor a boost, but also to recharge the supply battery, as Adams depicts in the following drawing (be sure to read the notes!):

Adams motor battery recharging

All that seems to be needed is a diode and a capacitor!

(Still trying to figure out exactly how the above circuit works)

It’s an exceptionally ingenious device, yet no laws of physics are being broken.

Coil resistance

Now, there is one more aspect of the drive coils that needs our attention:

Wind stators with a resistance in the range of ten to twenty ohms each for a small model.

Robert Adams, The Revelation of the Century

It might seem crazy to the average electrical engineer to wind stator coils with such high resistance, but Adams said that using stator coils of low resistance is the main reason many experimenters see lousy results:

The cardinal mistake being made here is that most of these experimenters are concerned about I2R losses!

IceStuff Adams Motor Guide

Our goal is an efficient motor, and so we want to draw as little current as possible, and so a higher resistance coil makes sense.

But less current equals a weaker magnetic field, and we need a strong magnetic field to achieve the greatest possible torque and RPM…

So what’s the solution?

Magnetomotive force (MMF) is measured in Ampere-Turns, which is based on the following observations:

  1. If the current is increased and the number of turns remains the same, the magnetic field strength is increased.
  2. If the number of turns of a coil is increased and the current remains the same, the magnetic field strength is increased.

Based on #2 above, we can see that if less current flows because our drive coil has a higher resistance, then we’d need to increase the number of turns to achieve our desired magnetic field strength.

A few turns of thin wire on the left, many turns of thick wire on the right, identical resistance

A 10 Ω coil with many turns of thick wire will establish a much stronger magnetic field for the same amount of current draw than a 10 Ω coil with few turns of thin wire, and will result in a much stronger flyback EMF from the collapsing magnetic field, which we can use to (partially) recharge our battery.

So while the high-ohm drive coils suggested by Adams will reduce current draw, they also force you to use more copper, resulting in more energy being available to be recaptured.

Now this is all absolutely within the current laws of Physics.

But once I state it as “more energy being available” now that we have more copper involved, some people will start to feel uncomfortable.

“Where does this additional energy come from?!”

Not sure, but it is exactly what the well established Ampere-Turns rule predicts, so it shouldn’t be news to any electrical engineer.

It seems that only Joseph Newman, who became batshit crazy, but who had some brilliant original thoughts earlier in his life, has an explanation for it in his book “The Energy Machine of Joseph Newman“.

He postulates that:

Energy input to make a magnet has absolutely nothing to do with energy within a magnetic field — catalytic effect only.

Joseph Newman, The Energy Machine of Joseph Newman

And:

The facts further demonstrated that the strength of the magnetic field was observed to increase as more atoms within the material became aligned!

Joseph Newman, The Energy Machine of Joseph Newman

So Newman says that the more atoms you can align, the stronger the magnetic field, and you only need a relatively small input current to achieve this, as it is purely a catalyst to force atoms into alignment.

From this it follows that having more copper in a coil gives us more atoms to align, and thus a stronger magnetic field results.

This is why his motor was HUGE, and had 90.000 (!!) turns of 5-gauge copper wire!

Was Newman correct?

I don’t know, but his is the only explanation I’ve found so far that makes any logical sense, and which completely fits the experimental evidence.

In our Adams motor, we don’t need an infinitely strong magnetic field.

It should just be strong enough to overcome the attraction of the rotor magnet to the stator core, and ideally provide enough flyback EMF to recharge our battery.

So we can use much, MUCH smaller coils than in the Newman motor 🙂

I’ve found that using 0.35 mm copper wire works very well, and based on some forum posts, this is also what Adams preferred to use for his low voltage machines, while he supposedly used 0.5 mm wire on his high power ones.

Generator

We have discussed the Adams “motor” in detail, but wasn’t there also a “generator” part to it?

There is indeed!

Luckily the generator is a lot simpler than the motor bit, although there are still a few things to keep in mind.

Here are some quotes by Robert Adams pertaining to the generator coils:

Ideal cores can be built cheaply and quickly by dismantling a spare power or audio transformer and utilizing the “I” section laminations, obtain winding former to fit same and it is ready for winding. Turns and gauge will depend on what voltage and current you choose. Remember, at this stage, you should only be building a demonstration model, so to speak.

After a few changes, corrections, and/or general modifications you will be ready to put a mechanical and/or electrical load on the machine. For an electrical load it is suggested you firstly wire up a bank of 6 – 12 LEDs. If everything is go, then switch over to torch lamps. Later on with a bigger machine – car lamps, or maybe household lamps and a mechanical load simultaneously.

Robert Adams – The Adams Pulsed Motor Generator Manual, p.27

Adams clearly mentions here that he uses laminated cores for his generator coils, which makes sense, as these minimize eddy currents.

I plan to try these Dayton Audio crossover coils as generator coils, as they already have laminated cores.

We read before that Adams mentioned:

It does not require a separate motor in the motor/generator mode to produce electrical output energy

It utilizes one common rotor which runs the machine and generates output power

Robert Adams

In the drawing below, we see 2 slim drive coils, spaced 180º apart, and 4 fatter generator coils, spaced 90º apart, all placed around a single rotor.

Adams Motor Generator Setup
4 rotatable “fat” generator coils directly hooked up to a load and ammeter

Actual dimensions

The drawing notes mention a 1/2 scale, but what paper size was used?

New Zealand uses ISO standards, so it could realistically be either A4 or A3.

I started out by assuming it was A4, but the measurements were all a bit odd and random.

Then I read somewhere that Adams preferred to use 3/4 inch (20mm) magnets, and 0.35 mm wire.

When I scaled the image to A3, the magnets were indeed 10mm wide, and at a 1/2 scale, that means in actuality they were 20mm!

Since it would be easier to get the direct measurements instead of having to multiply everything by 2, I scaled the image again to an A2 size (which is 2x A3), and did the same for the other technical drawings from the manual.

Now I could directly read the dimensions of all the parts by drawing over them, and this is what I found:

Rotor: 20 cm diameter, 2 cm thick, very light materials used, tiny amount of spacing between rotor and stators.

Magnets: 20x20x80 mm magnets with N poles facing out, and rounded edges. This 4:1 length to width ratio for the magnets supports the hypothesis that Adams used Alnico magnets in this particular design:

Typical open circuit Alnico 5 applications require a long magnetic length to pole surface ratio (usually 4:1 or greater) to insure good magnetic performance.

Adams Magnetic Products

Drive coils: 20 mm wide, 30 mm long, 10 mm solid iron core. If Adams used 0.35 mm wire, the coil would end up being ~10 Ohm, which is what he recommends, so this further solidifies these dimensions.

Generator coils: 30 mm wide, 30 mm long, 20 mm core with 15 mm of laminated core sticking out the back. ~15 Ohm if 0.35 mm wire is used, however, this resistance value seems unreasonably high, so you might want to experiment with generator coils with much thicker wire and lower ohmic resistance.

Shaft: 10 mm brass shaft, with 8mm ends for bearings (measurements differ slightly per drawing, so this is my best guess).

Structure: ~50 cm wide.

Switch: A custom star wheel commutator disk, 50mm wide.

A few additional things stand out from the drawing:

  1. The drive coil cores are 1/2 the width of the rotor magnet, while the generator cores have the same width as the rotor magnet
  2. The generator cores stick out about 50% further than the end of the coil
  3. The generator coils can be rotated around the rotor between 25º and 45º for finding the point of maximum power generation
  4. A switch to turn the current flow from the generator coils ON or OFF

Now, point #2 above requires some additional explanation.

Heel end slug

A core sticking out the back of a coil is called a “heel end slug”, and was used in relays like the GPO Relay 3000 to create a slower release.

A heel end slug affects the collapse of the magnetic field when the energising current is switched off. The collapsing field cuts the slug to produce an eddy current which in turn has its own magnetic field which opposes the collapse. ie It assists the field and attempts to maintain it around the complete magnetic circuit and therefore holds the armature in… The relay becomes practically normal to operate but slow to release.

Dean Forest Railway Telecoms

In the case of a generator coil, its function is slightly different, yet significant.

When a rotor magnet approaches a generator coil, the coil effectively turns into an electromagnet, with a North and a South pole, and a neutral zone in the middle.

If we add a heel end by making the core longer than the coil, the neutral zone will still be in the middle of the core, and so will have moved further up the coil.

Left, a regular generator coil. Right, a generator coil with a 50% heel end.

The result?

A heel ended generator coil will produce a much higher voltage for 2 reasons:

  1. More coil windings are exposed to the same magnetic polarity
  2. Higher inductance due to the additional iron

While this is a plausible explanation, Robert Adams never actually mentions this requirement, and it could just be that having the laminations stick out the back made it easier for him to mount the generator coils, as they have a bolt through them in the drawing.

Switching the generator coils

While the drawing appears to show a regular switch, Robert Adams may in fact have used a more advanced switching mechanism, as he used the same symbol in other drawings to represent various commutation methods.

Some experimenters claim that by precisely switching the generator coils, just like we did with the drive coils, magnetic drag can be minimized, and power output maximized.

Surprisingly, the output coils are switched Off for most of the time.

This sounds mad but it most definitely isn’t mad.

With the output coils disconnected, the approaching rotor magnets generate a voltage in the output coil windings but no current can flow.

As no current is flowing, no magnetic field is generated and so the rotor magnets just pull directly towards the output coil iron cores.

The maximum output coil voltage is when the rotor magnets are aligned with the output coil cores.

At that instant the output switch is closed and a strong pulse of current is drawn off and then the switch is opened again, cutting off the output current.

The output switch is closed for only three degrees or so of the rotor’s rotation and it is off again for the next eighty seven degrees, but the opening of the switch has a major effect.

The switch being opened cuts off the current flowing in the output coils and that causes a major reverse voltage spike causing a major magnetic field which pushes the rotor on its way.

That voltage spike is rectified and passed back to the battery.

Patrick J. Kelly

Keep in mind that again, Robert Adams himself never mentioned the need to switch the generator coils to achieve his results.

In fact, it seems that a lot of people are convinced they need to try all sorts of esoteric “low-drag” generator coil setups, while Adams managed to make his motor so efficient that he could achieve his results with any old generator, as is evidenced from this excerpt from his UK patent GB2282708A:

It seems preferable to regard the machine as a motor and maximize its efficiency in that capacity whilst using a mechanical coupling to an alternator of conventional design for the electrical power generation function.

Robert Adams & Harold Aspden – Patent GB2282708A, p. 24

The MOTOR is the invention.

However, the generator does have a clear function in demonstrating the peculiar properties of this device, as mentioned in the same patent:

The machine is able to demonstrate the excess power delivery from the ferromagnetic system by virtue of electrical power generation charging a battery at a greater rate than a supply battery is discharged.

Robert Adams & Harold Aspden – Patent GB2282708A, p. 19

So this is how Adams tried to prove his motor displayed power in excess of that supplied by the source battery: by charging a second battery from the generator output at a rate faster than the source battery was discharged.

Source of excess energy

So where does this “excess energy” come from?

We’ll let Robert Adams describe it in his own words:

There is massive trapped energy in many natural materials, especially metals. Latent magnetic energy is ever present in these materials and this energy I describe within the structures of electric motors is found to play an important role together with that of the energy harnessed from the small air gap between the rotor and stator sections; this applies to both motors and generators alike.

Power source applied to electric motors expands the ever present covert electromagnetic flux of the metal materials, i.e., the iron core and copper windings. It is not the impressed energy applied to the motor that creates the inductive field, as taught in universities and colleges alike; the magnetic flux field “already” exists in its natural state within the stator system; the application of energy into the system simply “expands” the natural latent inherent inductive energy residing therein.

This expanded inductive energy, in conjunction with the energy harnessed at the air gap between the rotor and stators, provides the driving power of the motor.

Robert Adams – Applied Modern 20th Century Aether Science

When Adams talks about “the energy in the air gap”, he means energy from the aether, or what quantum physicists nowadays call the zero-point field, which he strongly believed in.

As proof of this excess energy flowing into his air gap, he refers to a simple but fascinating experiment, both in his UK patent and in his book The Revelation of the Century, from The Principles of Electromagnetism (1955) by E.B. Moullin.

The first thing to remember is this:

The flux density in the gap represents the mechanically available energy.

Next, here’s what you do:

Take some transformer E laminations and wind a primary and a small secondary onto the middle as shown above in Fig. 1.

Use a variable AC power supply to adjust the input power supplied to the primary.

Use strips of cardboard or plastic between the E and I laminations to simulate an “air gap” of various thicknesses.

Now you want to measure both the amps that go into the primary, as well as the voltage in the secondary / search coil.

Each time you increase the gap by placing another strip of material in between, you adjust the power supply so that the voltage in the secondary remains the same, which means the flux density, or magnetic field strength on “the other side of the gap” remains constant, and thus the mechanical energy available remains constant.

Now here comes the kicker: if you plot the input current versus the gap size, you’ll clearly see it curves down!

Remember, we kept the voltage across the gap the same, so the same mechanical power is present, yet we need less and less current to establish that same amount of mechanical power the larger the gap becomes!

So where is that additional energy coming from?!

All we know is that it is clearly NOT coming from our power supply 🙂

This is why your air gap should not be too small, as that will limit this excess gap energy from being harnessed.

Adams mentions in several places that ideally the gap should be 1 to 1.25mm wide.

Replication tips

In this article you learned several things to keep in mind when trying to replicate this device, but Robert Adams was also kind enough to leave us a list of recommendations in his book The Revelation of the Century.

Some of his tips only apply if you use brush commutation, so I highlighted the parts I feel are most important, regardless of commutation method.

VALUABLE HINTS ON REPLICATION

  1. Use only pure iron for the stator/drive windings, not laminated steel core.
  2. Wind stators with a resistance in the range of ten to twenty ohms each for a small model.
  3. For 2) above, use voltages of between 12 and 36.
  4. For small machine make contactor star disk one inch maximum diameter.
  5. Keep wiring short and of low resistance.
  6. For small machine install fuse/holder 500m.a. to 1 amp.
  7. Install switch for convenience and safety.
  8. Use small bearings. Do not use sealed bearings as these are pre-packed with a dense grease which causes severe drag.
  9. Use only silver contacts for pulse switch.
  10. If using high-energy-product magnets, vibration becomes a serious problem if constructional materials and design are faulty.
  11. Air gap is not critical; however reduction will increase torque and also increase input power in proportion.
  12. For higher speed, lower current, series-connected stators recommended.
  13. a) If machine stator windings are of low resistance and drawing high current at higher input voltage, it is advisable to install a switching transistor which will completely eliminate sparking at points.

    b) On calculating input power, however, the transistor switch burden must be subtracted from total input.
  14. a) Points tuning and pressure are vitally important; experiment will indicate optimum settings.

    b) If, however, all electronic switching process is preferred, i.e., using photo, magnetic, hall effect, etc., then the above in a) is completely eliminated.
  15. If constructing a large model involving large super-power magnets, note the following:- The greater the magnetic energy product, the greater the power required to drive the machine, the greater the torque, the greater the vibration problem, greater copper content, greater cost etc.

Further tips were given by Adams, and again, I highlight the important points:

If contemplating the construction of a proving machine – note as follows :

1) Don’t purchase expensive powerful ‘neodymium’ or ‘samarium cobalt’ magnets without first having experience with cheap easy-to-get ‘alnico’ magnets, for if you commence with powerful magnets you will find yourself facing powerful problems. Using powerful magnets will not prove anything beyond what alnico will do. However, given this, if you feel you MUST choose powerful magnets, for whatever your reasons, take heed -great care is required in the handling of them to preclude personal injury.

2) For a proving machine do not use less than 10 ohms each for two stators at 180 degrees apart; recommend series mode for first attempt. Don’t be concerned about start windings initially and, remember, what can be achieved MICROscopically can be achieved MACROscopically and so I strongly suggest – walk before you run.

3) Should you experience any difficulty in designing and constructing the tapered disc contactor (machining, etc.) then use electronic switching, i.e. photo, Hall effect, or inductor effect, with switching current transistor, etc. The machine, correctly constructed, should still deliver a minimum 107% efficiency. The charging effect will, of course, be lost, and the input current to supply the electronic switching will raise the total input quite steeply. The point to be made here is that in using electronic switching, in a larger machine, the degree of loss due to this use of electronic switching is negligible.
—————————————————————————-
However, for those who are seeking greater efficiency figures, it is advised to stay with the tapered disc contactor method and build a small wattage unit, i.e. 0.25 to 1 watt. This is the area of power rating within which you will gain quicker and better results which, in turn, will provide the necessary experience for designing and building a larger unit.

Once again the inventor cannot stress the importance enough, for those who wish to construct a successful device, to start at the bottom rung and listen to what the device is saying to you as you go along.

The above statements make it really clear that for the best results, don’t use transistors, but use a brush commutator instead.

Only once you’ve achieved good results with the contactor disk should you progress to transistors or other means of switching.

Other pulsed motors

Was Robert Adams the only person who thought about pulsing a motor?

Not really, although it seems he was the first!

Adams invented his pulsed electric motor generator in 1970, filed for a patent in 1975, but didn’t publish his work publicly until 1994.

Joseph Newman

Then there is the infamous Joseph Newman, who developed a pulsed motor of gigantic proportions to prove his theory and patent claims were valid.

Joseph Newman Motor
Joseph Newman standing next to his enormous motor / generator

Newman filed for a US patent titled “Energy Generation System Having Higher Energy Output Than Input” in 1980, and released a book titled “The Energy Machine of Joseph Newman” in 1984, in which he explains the theory behind his motor/generator in detail.

The general idea is that he pulsed a coil consisting of 90.000 turns of thick 5-gauge wire with just 9V (6 1.5V AA batteries), which then generated a very strong magnetic field, which in turn spun the heavy permanent magnet rotor around, and generated huge flyback currents when the pulse ceased, which he then used to power loads.

Newman was not granted a patent, so he went to court, grew more and more frustrated over the years, and slowly went crazy.

I recommend you watch this documentary to find out what happened exactly.

John Bedini

Newman, amongst others, inspired John Bedini, who successfully replicated the Newman motor, developed his own pulsed motors, and published his theories in a 1984 book titled “Bedini’s Free Energy Generator“.

But while Newman used a massive amount of copper in order to create a VERY strong magnetic field, the Bedini motor only needed a magnetic field strong enough to offset the attraction of the rotor magnet to the stator core, which is why the Bedini motor is a LOT smaller.

John Bedini motor
John Bedini next to one of his pulsed motors

In 2001, John Bedini filed for a patent titled “Device and method for utilizing a monopole motor to create back EMF to charge batteries“, which was granted in 2003.

He helped a 10-year old girl create one of his motors for a school science project, and this circuit turned into the most replicated motor in the alternative energy community, called the Bedini SG (SG stands for School Girl).

So while Newman and Bedini published their ideas before Robert Adams did, we see that Adams already filed a patent years before that.

Lutec 1000

In 1999, the Australian duo Lou Brits and John Christie from the company Lutec, filed for a patent titled “System for controlling a rotary device“.

If you read the patent, you’ll soon find out that they use the exact same methods Robert Adams used, and Adams made it very clear he felt they were stealing his ideas.

Lutec 1000 motor prototype
Image on the Lutec home page of their latest prototype, before the site went offline

There has been a lot of controversy around the Lutec 1000 motor, and the Australian Sceptics Society ripped them apart in their article “Free Energy? Not From Lutec“.

Keppe Motor

The last pulsed motor I want to discuss is a very interesting one, as it is the only one discussed here that has actually been implemented into a consumer product!

It is called the Keppe Motor.

The Keppe Motor is a highly efficient motor that uses the principle of electromagnetic resonance to optimize its efficiency. It was developed by three researchers, Carlos Cesar Soós, Alexandre Frascari and Roberto Heitor Frascari, based on the discoveries of the scientist Norberto da Rocha Keppe, set forth in his book “The New Physics Derived From A Disinverted Metaphysics,” first published in France, 1996.

Keppe Motor Website

While their explanation of how the motor works seems a bit odd and metaphysical from time to time, the fact of the matter is that you can buy a table fan from their website which is just as powerful as a store-bought fan, but uses up to 80% less power to run and doesn’t heat up!

Keppe motor table fan
The Keppe motor table fan

They also achieve this by pulsing the motor at the exact right time, although the details differ slightly from the Adams motor, as Adams used rotor magnets of identical polarity, while the Keppe motor uses both North and South poles.

In their FAQ they explain how the Keppe motor works:

Electric motors transform electric energy into mechanical energy, and electric generators do the opposite, i.e., transform mechanical energy into electric energy. The Keppe Motor comprises a motor feature (electricity being transformed into mechanical energy) and a generator feature (mechanical energy being transformed into electricity) in balance at the point of resonance of the system.

System’s highest efficiency is reached when the resonance between the two components of action (motor feature) and complementation (generator feature) takes place. The resonant point of this system includes the electric power supply (domestic grid or battery) and the load on the shaft.

The Keppe Motor contains a magnetic rotor with permanent magnets which rotates inside the stator coils. When the magnet is set in motion by the supply voltage applied to the coil (motor feature), it creates additional voltage in the coil terminals (generator feature), increasing the magnetic energy stored in it. This energy enters in resonance with the power grid’s energy through pulses of varying intervals determined by the Keppe Motor itself and this is the nature of its high efficiency. As consequence, one of the best advantages of the Keppe Motor is that it runs cold, which is an indication of its high efficiency and guarantee of durability.

Nevertheless, for all this to occur, it is not enough to make a motor with a different design – you must also change the power supply, otherwise, resonance cannot be achieved.

The best way to reach resonance is to let the motor interrupt its own power supply according to its own structure, without interfering with its operation. Because of that, the typical and necessary power supply of the Keppe Motor is PDC (Pulsed Direct Current), the only supply that allows the system to reach resonance. Depending on the motor design and parameters, such as wire gauge, presence or absence of an iron core, type of magnet, coil inductance, etc., the entire system will automatically search for its point of resonance for the load and voltage specified. At this point the electrical current decreases to the minimum necessary to perform the desired work. This minimum is always lower than that required by conventional direct or alternating current to perform the same task.

The Keppe team was granted a US patent in 2013, titled “Electromagnetic motor and equipment to generate work torque“.

Closing thoughts

This article was meant to clear up some confusion that exists among experimenters attempting to replicate Robert Adams’ device.

The idea was to use the words of Adams himself to explain what he was and wasn’t trying to do, and I hope you gained some clarity from this.

I also urge you to study the other pulsed motors I discussed in this article, as certain patterns will become clear to you, and a lot can be learned from them.

Especially study the Bedini motor, as there is a lot of educational material available for that one.

As for me, I’ve been working for months on perfecting my own Adams Motor / Generator replication (follow my progress on YouTube).

Right now, I’ve settled on a final design for the drive coils and drive circuit (check out my Arduino Pulsed Motor Driver on Github), and am now going to add the generator coils.

Once everything is working as advertised, I will create a PCB and make plans and kits available through this website.

My goal is to have this ready halfway through 2021.

Are you working on an Adams motor replication? Shoot me an email at [email protected], because I’d love to hear how it’s going!

Tesla Coil Experiments

7 Impressive Tesla Coil Experiments

When most people think of a Tesla Coil, they think of big sparks.

This frustrates me to no end…

There are a ton of other cool experiments that can be performed with Tesla Coils, especially if you have a matching pair of them.

In this article I cover 7 cool Tesla Coil experiments for you to try.

1. Sparks (with a twist)

Yes, let’s just start with the most basic and obvious one, but with a little twist.

Modern day Tesla Coilers mainly aim to discharge the longest possible spark straight into the air.

Not very creative.

Nikola Tesla, especially in his early days, used his coils to create beautiful sparks in many different variations.

6 creative ways in which Tesla discharged his coils (1982)

He added all kinds of wire shapes, bulbs, and other accessories to the ends of his coils so he could study different discharge patterns.

Tesla would also hold sparking coils in his hands for a spectacular effect.

Nikola Tesla holding a coil while sparks emanate from it

Later, he would take the now famous pictures of sparks emanating from his Colorado Springs Magnifying Transmitter.

Tesla in front of his Extra Coil in Colorado Springs
Tesla in front of his Extra Coil in Colorado Springs

This photoshoot was mainly so he had something to wow his investors with.

Sparks were not Tesla’s main purpose.

In fact, he tried everything he could to suppress sparks, as they were considered losses in his system.

So get yourself a Tesla Coil, add a sharp metal point, like a piece of wire or a nail to the top of your coil, and push enough power into the system to create a spark.

Just don’t stop with the boring “straight into the air” sparks.

Get creative!

2. Flame speaker

Now let’s do something awesome; let’s make our sparks sing!

And I don’t mean those silly 8-bit Super Mario tunes you always hear from your friendly neighbourhood coiler.

No, I mean real music coming from the spark!

Eric Dollard held a brilliant demonstration of this “flame speaker” at the 2019 Energy Science & Technology Conference.

To achieve this, you need to be able to apply Amplitude Modulation (AM) to your input signal that enters the Tesla Coil primary.

I do this using an FY6900 function generator, which has AM modulation built-in.

On my phone I play a song through Spotify, which goes into a tiny 5V audio amplifier, which then enters my function generator’s VCO IN port.

I then set the function generator to amplitude modulation, and use the VCO IN port as the modulation source.

Finally, I run the signal generator output through an FYA2050S 20W amplifier to have enough power to generate a (small) spark.

Music, real music, can be heard playing from the spark ⚡🎶

Now you’re officially one of the cool kids!

3. Radio reception

Not many people realise it, but the main purpose of Tesla’s research with his coils focused on transmitting power and radio signals.

Just not the type of radio signals we are used to today.

In his brilliant article The True Wireless, Tesla explains that traditional radios radiate waves into the air.

Only a billionth of the transmitted power is received and then has to be amplified again before the signal can be used to play over your speakers.

Tesla intended to transmit his radio signals through the earth, in which case hardly any power was lost during transmission.

He therefore did everything he could to minimize the amount of radiated waves, as these were seen by Tesla as system losses.

… [my] wireless transmitter is one in which the Hertz-wave radiation is an entirely negligible quantity as compared with the whole energy

Tesla, N. (1919). My Inventions: The autobiography of Nikola Tesla. New York, NY: Cosimo Classics

So while the Tesla Coil is on purpose terrible at transmitting radio waves through the air, you can still receive them if you’re close enough.

We’ll need the same setup from the flame speaker experiment + an AM radio (I found an old Grundig Yacht Boy 217 in my parents’ house).

Then we’ll need to tune our Tesla Coil to within the AM frequency band supported by our radio, which is 520 – 1610 kHz in my case.

When you now push your amplitude modulated wave through your coil and tune your radio to the same frequency, you’ll hear the song coming from your radio!

Video of my Tesla Coil AM radio transmission

Pretty neat, huh?!

Now if you want to follow Tesla more closely, you could ram a few 3 meter long ground rods into your backyard, and connect your Tesla Coil to it to transmit into the ground.

You could now use your radio, with its antenna connected to a ground rod further away, to receive the signal through the ground.

In fact, if you have an AM radio station nearby, you could even receive their signal, and even some of their broadcast power, through the ground, using a Tesla Coil tuned to their frequency.

For more on this, check out Eric Dollard’s Crystal Radio Initiative.

4. Voltage & current gradient

When a Tesla Coil is in resonance, the voltage peak is situated near the coil’s top load, which is why sparks discharge from there.

A nice way to visualize the actual voltage rise along the coil is by attaching a small neon bulb to the end of a non-conducting stick.

One leg of the bulb should point outward, and the other should ideally be connected to the stick with aluminium tape, which then creates a mini top load for the bulb so a voltage difference will appear across its legs.

When you now move the bulb’s pointy leg along the length of the coil, you will see it light up brighter and brighter as it nears the top.

Tesla Coil voltage gradient visualized with a neon bulb

We can do a similar thing with the current in the coil.

For this, we need a magnetic pickup, which is basically a coil of wire on an iron core, and an oscilloscope.

Connect the pickup to your scope and move it along the length of the coil, like we did with the bulb.

This time, you will find that the current peak is actually near the ground terminal of your coil, and the current low point near the top load.

Standing Waves and Resonance | Transmission Lines | Electronics Textbook
1/4 wave transmission line has its voltage (E) and current (I) peaks on opposite ends

The reason for this is that voltage and current are 90º out of phase, and since the Tesla Coil is a 1/4 wave resonator, current and voltage peaks end up on opposite sides.

So while this may not be the most exciting experiment you’ve ever done, it definitely is an educational one.

5. Wireless light

Another favorite pastime of coilers is to hold a fluorescent bulb or tube near their coils to see them light up in their hands, without any direct electrical connection.

I admit, this is fun to do, and Tesla performed similar demonstrations.

How to Build a Wireless Energy Transfer Array to Power Light Bulbs Without  Plugging Them In « Fear Of Lightning :: WonderHowTo
Nikola Tesla holding a light bulb that is illuminated wirelessly

It is important to note here that Tesla did not intend to use this method of wireless power on a scale larger than inside a room, as it is highly inefficient.

It was used more as a party trick.

6. Single wire light

Now on to some rather peculiar experiments whose results are not so easy to explain.

So, you know how they always teach you that current only flows if there is a closed circuit?

Well, we’re going to light an incandescent light bulb from a single wire, without a return!!

Simon from Tesla Scientific shows several cool ways in which to light a bulb with a single wire from a Tesla Coil’s ground connection

Why not use LEDs or neon bulbs?

Because an incandescent bulb is harder to light, and needs a reasonable amount of current to flow, so is much more impressive.

It will show that loads can be powered with an open circuit!

For a coil powered with just a signal generator, you can use tiny 1.5V or 3V grain of rice bulbs.

If you have a bit more power at your disposal, try using 240V 15W oven bulbs.

Hold the bulb against the ground connection of your running coil andddd…. nothing happens…

Now, attach a piece of wire or aluminium foil to the other terminal of the lamp and behold, it lights up!

The piece of wire or foil acts as a capacity, or “elastic reservoir” as Tesla described it, allowing the current to oscillate back and forth through the load.

Single Wire Power Transmission Analog

Click here to learn more about single wire electricity

NOTE: this will NOT work with a Slayer Exciter type circuit, as those use the ground connection of the secondary for feedback, and so it is not free to attach a bulb to. You will need a traditional Tesla Coil setup, where the ground terminal is actually connected to the ground.

7. Single wire power transmission

In the previous experiment we already saw that we could light an incandescent bulb from a single wire without a return.

Now we take that a step further and transmit power to a second receiver coil.

There we convert it back to a regular closed circuit current and power a small motor with it.

Single wire power transmission using two tuned Tesla Coils

The cheapest and fastest way to create a transmitter / receiver pair of Tesla Coils is to purchase some PCB coils, like this one or this one.

You will also need some capacitors (ideally a variable capacitor as well) to tune the primary coils to the same frequency as the secondary coils for optimal efficiency in power transfer.

Place the coils a good distance apart and connect their ground connections using a single wire.

On the receiver end, add a full-wave bridge rectifier with a smoothing capacitor to convert the high-frequency current to DC.

I recommend using 1N4148 diodes for the bridge rectifier of low power coils, as they are fast enough to handle a few MHz.

Finally, connect a small 12V computer fan to it as a load, or any other small DC load of your choosing, and see it come to life when you get the tuning of your coils exactly right!

Congrats, you just proved it is possible to transmit power over a single wire without a return, and then use it to power a regular load!

Closing thoughts

If you would replace the single wire between the two coils with the earth, then you get what Tesla’s ultimate goal was with this technology.

He wanted to transmit power around the world using the earth as the “wire”.

This was his True Wireless.

After reading and performing these Tesla Coil experiments, I hope you now realize that Tesla didn’t invent his coils just to make sparks.

Single Wire Power Transmission Analog

4 Methods for Single Wire Power Transmission

Today’s 3-phase power grid uses 3 or 4 wires to transmit electrical energy. This article describes 4 innovative methods, some over 100 years old, which use only a single wire to transmit the same amount of power or more, without a return wire!

These methods hold the promise to drastically reduce costs and lower line losses, and imply that our Electrical Engineering textbooks might be due for an update.

In order of increasing exoticness, these are the methods we will cover in this article:

  1. Single-Wire Earth Return (SWER)
  2. B-Line or Single Line Electricity (SLE)
  3. Tesla’s Single Wire Transmission Without Return
  4. Avramenko / Strebkov Single-Wire Electric Power System (SWEPS)

Before we dive in, let’s take a quick look at what makes our current power transmission system less than ideal.

3-Phase: why we use it, and why it is flawed

The 3-phase system has been used to transmit power for more than 120 years now, and hasn’t changed much since. So why use 3-phase? There are a few good reasons:

  1. A minimum of 3-phases are required to establish a smooth rotating magnetic field, which is needed to achieve optimal torque in electric motors. Nikola Tesla, who played a key role in designing our current power system, invented the AC induction motor 1, and was therefore a strong proponent of a 3-phase system.
  2. Another major benefit of 3 phases is that since each phase is 120º apart, they add up to zero at each point in time. This is why we can transmit 3-phases without needing 3 return wires as well. As long as the loads are balanced between phases, we can combine the returning currents into one, which then cancel each other out, mitigating the need for a return wire, or using only a single, relatively small return wire if the phases aren’t perfectly balanced.

If you want a more entertaining explanation, see the video below.

It’s a pretty nifty system. However, there are several major downsides as well:

  • 3 or 4 wires are needed for power transmission
  • Large support towers for the wires
  • Very expensive to place underground, since wires need to be spaced sufficiently far apart
  • Significant energy losses
  • Constant reactive power compensation needed
  • Complex load balancing
  • Risk of phase-to-phase faults due to wind

So is there no better way? Back in the day, not really. AC was chosen over DC mainly because transformers could be used to easily step-up and step-down the currents.

This was needed because transmission losses are smaller at higher voltages, but you can’t push hundreds of kilovolt into someone’s household appliances, so conversion was needed.

Thanks to solid-state technology, this is now also possible for DC, albeit at much greater costs and lower reliability, which is why High-Voltage DC (HVDC) lines are currently mainly used for very large distances or to connect two AC systems, even though HVDC promises to reduce line losses and requires less conductors than a 3-phase AC system.

What follows are 4 alternative systems that only need a single conductor to transmit power, and which solve most, if not all, of the above mentioned issues.

Since many people will say outright that single wire power transmission is impossible, I will try to offer as much credible evidence as I can, and will make it clear how these results can be replicated for easy verification.

Single-Wire Earth Return (SWER)

The first system we’ll describe, SWER, is also the only one in the list that is currently in active service.

This system, which supplies single-phase power over one conductor while using the earth (or the ocean) as a return path, was developed around 1925 in New Zealand for the economical electrification of thinly populated rural areas. Today SWER is actively used in New Zealand, Australia, Alaska, Canada, Brazil, and Africa, as well as in HVDC submarine power cables 2.

SWER circuit diagram

Interactive SWER circuit diagram. Click on the open switches to close them and see the current flowing through the circuit.

The main benefit of this system is its affordability, since SWER only uses one instead of two conductors, and because current drawn by these rural customers is relatively small, thinner cables, and therefore fewer and smaller poles can be used to hold the cable up.

19kV Single-Wire Earth Return wire in Australia

The downside is that these lines are not very efficient, and they often experience significant voltage drops. However, the main issue is that currents of up to 8 amps can flow through the ground near the earth points, so there is a danger of shocking people and animals if the earth connection is faulty.

And while SWER systems are great to economically transmit relatively small amounts of power to thinly populated areas, they cannot be used to provide cities and industry of power, so their use case is fairly limited.

The next single-wire power transmission method we will discuss solves some of the problems inherent to SWER, and does away with the need for a return current through the ground altogether.

B-Line or Single Line Electricity (SLE)

Professor Michael Bank from the Jerusalem College of Technology devised a highly interesting way to enable single-wire power transmission by creating equal phase currents in the live wire and the return wire, which then allows these wires to be combined into one 3.

His system, which he calls a B-Line, achieves this by using a 180º phase shifter after the source, combining the two wires into one transmission line, and then transforming this back to a regular two wire current before the load by using another 180º phase shifter. Both load and generator won’t “see” the difference!

The phase shift is achieved by using a reverse connected 1:1 transformer, and for higher frequencies a half period delay line could be used. The following interactive circuit diagram should make this idea more clear.


Interactive B-Line circuit diagram

If you look at the current graph in the interactive circuit above, you’ll see that the current in the single-wire transmission line is twice that of the source, because the two wires are combined into one.

This means that to transmit the same amount of power, the single transmission line needs to have half the resistance, hence a more expensive wire is needed, but at least you’ll only need one!

A major benefit of the B-Line over a SWER system is that the B-Line does not use the ground as a return circuit!

Yes, it seems in the animation above that the ground is involved, but since the current in the single transmission line is doubled in this system, and the current between source and load adheres to Ohm’s law, no other current can exist! Ground current does not exist here, since it is all kept inside the circuit.

Professor Bank ran two experiments to further prove that ground is not involved in this circuit.

  1. He used a 300 kHz signal, which then allowed him to replace the grounded inverter coil by a 500m long, half period delay line without a connection to the ground. The system still functioned as before.
  2. In the chapter Zeroing without the current injection into the ground, Bank describes a device which he calls a “nullifier” which offers an adequate zero-voltage reference level, and can therefore replace a ground connection. His transmission system still worked when the ground connection was replaced with a nullifier, further proving that no current flows through the ground in this circuit.
Nullifier as designed by Professor Michael Bank, which offers a zero-voltage reference level adequate to zero a current. It is an aerial consisting of a considerable quantity of monopoles, with length much smaller than a quarter of a wavelength.

Bank mentions that the downside of using his system is that his single wire creates a stronger EM field than a 3-phase system, which offers compensating polarity, and so has a larger effect on humans. This downside is countered by the fact that a single conductor requires way less space, and is therefore much cheaper to place underground where is can’t harm humans.

The delay line also needs to be adjusted when the frequency changes to keep the phase shift equal to 180º. However, the major drawback of this system seems to be the fact that double the current needs to be transferred over a single conductor, creating larger transmission losses due to heat dissipation (I²R losses), unless more expensive, lower resistance cables are employed.

The next system, which is very easy to replicate, solves the high-current problem of the B-Line, and is the first in the list that seems to defy explanation by today’s Electrical Engineering models.

Tesla’s Single Wire Transmission Without Return

“I had already proved in my lecture at Columbia College that I could transmit energy through one wire” 4

All the way back in 1891, during a lecture at Columbia College in front of the American Institute of Electrical Engineers, Nikola Tesla was the first to demonstrate definitively that electrical energy can be transmitted through a single wire without a return, and be used to power loads, like incandescent lamps.

“In several demonstrative lectures before scientific societies… I showed that it was not necessary to use two wires in transmitting electrical energy, but that one only might be employed equally well.” 5

In its most basic form, Tesla’s single wire system is simply a grounded alternator with the other terminal connected to a capacitance, like a large metallic object. Tesla explains the workings of this system using an illuminating analog in his article “The True Wireless”.

Tesla electric transmission through two wires and hydraulic analog
Fig. 3. — Electric Transmission Thru Two Wires and Hydraulic Analog.
Tesla diagram showing electric transmission through a single wire hydraulic analog
Fig. 4. — Electric Transmission Thru a Single Wire Hydraulic Analog.

“The operation of devices thru a single wire without return was puzzling at first because of its novelty, but can be readily explained by suitable analogs. For this purpose reference is made to Figs. 3 and 4.

In the former the low resistance electrical conductors are represented by pipes of large section, the alternator by an oscillating piston and the filament of an incandescent lamp by a minute channel connecting the pipes. It will be clear from a glance at the diagram that very slight excursions of the piston would cause the fluid to rush with high velocity thru the small channel and that virtually all the energy of movement would be transformed into heat by friction, similarly to that of the electric current in the lamp filament.

The second diagram will now be self-explanatory. Corresponding to the terminal capacity of the electric system an elastic reservoir is employed which dispenses with the necessity of a return pipe. As the piston oscillates the bag expands and contracts, and the fluid is made to surge thru the restricted passage with great speed, this resulting in the generation of heat as in the incandescent lamp. Theoretically considered, the efficiency of conversion of energy should be the same in both cases.” 6

This basic single wire system was further perfected by Tesla over the years, culminating in the development of Tesla’s Magnifying Transmitter, which would use the entire globe as the “wire”. In the image below, Tesla shows us the evolution of his device.

Evolution of Nikola Tesla’s single wire system 4

First an inductor is added (2), then this inductor becomes a variable inductor (3), and then a step-up transformer is introduced (4), effectively creating the famous Tesla Coil setup. This is then further perfected to generate the highest possible efficiency and voltage by using tuned circuits and resonance.

Tesla planned to transmit large amounts of power through the earth, essentially removing the need for transmission lines altogether. However, in the core it is still a single wire transmission system, and instead of the earth, you can use two tuned Tesla coils connected by a single wire to transmit electrical energy the way Tesla originally intended.

Three ways to power loads from a single wire transmission line coming off of a Tesla Coil

The diagrams above show the following:

  1. High-voltage, high-frequency loads can be directly powered from the single wire transmission line, as long as a capacitance is present at the end of the line
  2. A second Tesla Coil acts as a receiver and steps down the voltage of the transmission line to power low-voltage, high-frequency loads
  3. After step-down, the high-frequency electricity is rectified using a full-wave bridge rectifier with smoothing capacitor to power low-voltage DC loads

As you can see, Tesla’s transmission system is highly versatile, and capable of powering a wide variety of loads from a single wire. Unfortunately, it was never taken into service, because Tesla put all his efforts into his “wireless” power transmission through the earth.

It is crazy to think that Tesla already called the “necessity of a return circuit for the conveyance of electrical energy in any considerable amount” an “old notion” back in 1898! 5 That’s why I was elated to find that a group of Russian scientists is finally pushing this technology forward and is actually integrating it into the power grid. On top of that, they found that these single wire currents posses some curious properties…

Avramenko / Strebkov Single-Wire Electric Power System (SWEPS)

In 1993, the Russian duo Stanislav and Konstantin Avramenko filed for a patent titled “Method and Apparatus for Single Line Electrical Transmission6, which was granted to them on August 15, 2000.

I’ll let the authors describe the function of the apparatus described in the patent.

“Transformation of electrical energy… into the energy of oscillation of a field of free electrical charges such as the displacement current or longitudinal wave of an electric field, the density of which varies in time, and the transmission of the energy via a transmission line which does not form a closed circuit comprising a single-wire transmission line and, where necessary, its transformation into the electromagnetic energy of conduction currents.”

That snippet might need some explanation.

Essentially, Avramenko is saying that their apparatus transforms a regular conduction current into an oscillating electric field. This oscillating electric field is what is then transmitted along a single conductor transmission line, and finally at the end of the line transformed once more back into a regular conduction current.

They refer to their transformer as a “alternating density generator”, since it creates a wave by varying the density of the electric field, or a “monovibrator”, since only a single terminal is connected to the line.

Avramenko’s Alternating Density Generator is simply a secondary coil with one terminal disconnected, or alternatively connected to the other terminal with or without a series capacitance.

In the end though, any ol’ transformer can be used, “with or without a ferromagnetic core”, as long as only one terminal of the secondary is connected to the transmission line, although the authors recommend that for the best efficiency tuned transmitter and receiver coils should be used, in other words: Tesla Coils.

So far, the devices in the Avramenko patent are identical to Nikola Tesla’s, apart from the fact that they were given a different name. The fact that they describe what they believe is the nature of the single wire current is something that is valuable though.

Avramenko Diode Plug

Besides transformer coils, one unique apparatus is introduced to transform the single wire current into a regular conduction current: the Avramenko diode plug.

Avramenko’s diode plug can power a load with regular pulsed DC, directly from a single wire line

This device is really nothing more than a half-wave rectifier setup with the input terminals of the two diodes connected to the single wire transmission line, but it enables some thought-provoking results.

For example, when traditional magnetoelectric or thermoelectric milliammeter are used on the single-wire line, no current is measured, but when these same meters are connected to the Avramenko plug circuit, current is measured 7

Also, placing a 10 kΩ resistor, a capacitor, or an inductor in series with the single wire line, does not affect the current measured in the Avramenko plug circuit at the end of the line! 8 The single wire current seems to completely “ignore” those components, hinting at superconductive properties! They do not seem to adhere to Ohm’s Law or Kirchoff’s Laws.

Knowing this, the following claim from the Avramenko patent makes sense.

“The invention will make possible a sharp reduction in the costs involved in transmitting electrical energy over long distances, and a sharp reduction in the losses of Joulean heat from transmission lines.”

These results substantiate Avramenko’s claim that the single wire currents, which he and his colleagues Zaev and Lisin call “polarization currents” in their 2012 paper, differ fundamentally from conduction currents, and that they are longitudinal rather than transverse in nature.

Improved Avramenko plug, with a full-wave bridge rectifier setup, a capacitance connected to the end of it, and a magnetoelectric milliammeter connected across, as suggested by Kasyanov (2015)

Other authors come to the same conclusions, but also mention that the Avramenko plug’s efficiency can be improved by using a full-wave bridge rectifier setup 9 10.

Implementation into the Russian power grid

The overwhelming experimental evidence suggests that single wire power transmission is possible and is much cheaper and more efficient than our ancient 3-phase power grid, because it uses less wires of smaller diameter, therefore less poles will be needed, smaller transformers can be used due to the higher frequency, less energy is lost during transmission, transmission distance and capacity are increased, and the danger of short-circuits is removed.

And while Western scientists still scoff at the feasibility of single wire currents, the Russian government has been funding research into this field for years now, with the goal to seriously upgrade over 1 million kilometers of outdated overhead transmission lines in the coming 15 years 11

In a 2018 paper, the Federal Scientific Agroengineering Center VIM of Russia proposes to use this technology to enable…

“Direct solar energy conversion and transcontinental terawatt power transmission with the use of resonant wave-guide technology developed by N. Tesla” 11

Besides worldwide power transmission, the paper continues to describe other applications of Tesla’s technology, some of which have already been patented by the authors, including:

  • Electric rockets
  • Chlorine-free ways to build solar cells
  • 10x lower electrolysis costs, to make hydrogen
  • Batteryless electric cars
  • Contactless power for trains
  • Underground cables to replace the overhead ones

If the US and Europe want to stay competitive, it seems high time to start taking this revolutionary technology seriously, and to start pouring some serious R&D power into its development.

What about 3-phase motors?!

After reading this article, I hope the viability and revolutionary nature of single wire power transmission has become apparent. However, only 1 phase can be transmitted over a single wire, which is fine for most residential customers, but we learned in the beginning that 3-phase power is needed to run industrial motors…

Luckily there are several solutions to create 3-phase power from a single phase line.

Creating 3-phase power from a single wire line, as proposed by Michael Bank
  1. TRiiiON offers plug & play 3-phase power solutions
  2. The inventor of the B-Line mentioned in this article also offers a solution: split the single wire line into three lines at the customer end, then use simple L & C filters to shift 2 phases by 60º and 1 phase by 180º using an inverter coil, resulting in a 3-phase current 3

Closing thoughts

This article described 4 methods to transmit electrical power over a single wire, without a return.

It turns out that the effect is ridiculously easy to replicate: take any transformer and only use one terminal of the secondary. That’s it! You can then further increase transmission efficiency by running the transformer at its resonant frequency.

With replication being so incredibly simple, and the potential for room-temperature superconductivity being so blatantly obvious, it honestly baffles me that this technology is not pursued at full force by researchers around the world. It seems only Russia is taking this seriously.

I urge everyone who reads this to start experimenting and finding ways to get this technology out there. My guess is that it will not be accepted until a fully developed product or method is made available that saves businesses or consumers so much money that they will almost be forced to adopt it.

If you know any methods to achieve single wire power transmission that were not mentioned in this article, please share in the comments!

Nikola Tesla World System for Wireless Energy Transmission

Nikola Tesla’s Transmission Systems

My previous writings have laid the foundation needed to understand this article, in which I will give a brief overview of how the current power grid evolved, and how Tesla planned to radically change this.

Evolution of electric power transmission

In the beginning there was direct current, or DC. However, there was not one single universal power line as we know it today, since DC is not so easy to “transform” into different voltage ratings. So instead, there were different lines for different purposes, since arc lights needed around 10kV, while street cars used 500V for example. Another major downside was that DC, especially at lower voltages, could not be transmitted very far or the losses became too great, and so the generating plant usually had to be within 1 mile from the point of consumption.

Nevertheless, Thomas Edison, who invented a reliable incandescent light bulb in 1879, wanted to replace gas lamps and candles in people’s homes by electric light. On Thursday, June 8, 1882, the Edison Electric Company lit up their first house: the house of banker J. P. Morgan. Edison then continued to launch the first electric utility company that same year, with 85 launching customers. It was an impressive feat, although there were still some teething problems to overcome. It is also interesting to note that Edison used a 3-wire system, so he could transmit power at 110V as well as 220V, since not all motors required the same voltage.

On the other side of the ocean, the focus was instead on alternating current (AC), since the consensus seemed to be that Edison’s low voltage DC system was highly impractical for long-distance power transmission. To distribute power efficiently, high voltages were required, which in turn called for electrical transformers, and economically viable transformers only existed for AC. In 1886, George Westinghouse and others used this affordable step-up / step-down technology to create the basis for the modern power grid.

However, Westinghouse and his companions had one major flaw in their system: there was no motor in the world that could run on their beloved AC power! This meant AC could be used to light lamps, but not used to power machines or street cars, while DC could. Luckily, their problems were solved when in 1887 Nikola Tesla invented his revolutionary induction motor, for which he received a patent in 1888 1. In fact, Tesla was granted 7 patents on May 1st 1888 2, which did not just cover the electric motor, but also a way to use this invention in the electrical transmission of power. This technology was licensed by Westinghouse in that same year.

Plaque at the Niagara Falls hydroelectric power plant, showing 9 Tesla patents
Plaque at the Niagara Falls hydroelectric power plant, showing 9 Tesla patents

The Tesla / Westinghouse AC system was used in 1893 to power the entire Chicago World Fair, and in 1895 this dynamic duo created the first large-scale hydroelectric power plant in the US at Niagara Falls. These were decisive blows against DC.

In the end, the War of the Currents was won by AC because it was more efficient, could be transmitted over larger distances, could be served from a central power plant instead of requiring a power plant per square mile, could easily be transformed into different voltages, and ultimately because it was a heck of a lot cheaper due to economies of scale and more affordable apparatus.

More than 100 years later, our modern power grid still uses the same principles to transmit power, except that the voltage at which power is transmitted has increased significantly, from 4000V on the first AC power line in the US, to 110kV or sometimes even 765kV on today’s long-distance power lines.

This was of course a very brief summary, and many more people were involved in the development of electrical power transmission, but for the sake of this article, the above introduction should suffice. For a more detailed history, I highly recommend you read Empires of Light by Jill Jonnes.

Fresh ideas

So not much has fundamentally changed over the past 100 years when it comes to long-distance power transmission, but this does not mean that no radical improvements were envisioned during that period. In fact, 10 years after coming up with his AC motor, Nikola Tesla made several ingenious inventions capable of revolutionizing the industry once more. These inventions made his earlier groundbreaking work on AC pale in comparison, but were never implemented for a variety of reasons.

The most important reason being that the whole industry had just spent over a decade investing in AC power lines, and so they did not really feel like starting from scratch again. Also, Tesla was a great inventor, but a poor business man, and was not able to bring his inventions to market in an economically viable manner. His AC inventions were only commercialized properly thanks to George Westinghouse.

We will now have a look at the radical ideas Tesla had regarding the transmission of electrical energy.

Wireless light

During his lecture back in 1891 titled “Experiments With Alternate Currents of Very High Frequency And Their Application To Methods of Artificial Illumination“, Tesla displayed, amongst other spectacular phenomena, that he could light up an “exhausted tube” without having any wires connected to the lamp. The following diagram shows one of these setups, in which two metal plates were connected to the terminals of a Tesla Coil, creating a high-voltage, high-frequency electrostatic field in the room which excited the molecules in the exhausted tubes, causing them to light up.

Original caption: "Ideal method of lighting a room. Tubes devoid of any electrodes rendered brilliant in an electrostatic field.
Original caption: “Ideal method of lighting a room. Tubes devoid of any electrodes rendered brilliant in an electrostatic field.”

There are several famous pictures of Tesla holding a wirelessly illuminated lamp in its hand, like the one below.

Nikola Tesla holding a wireless light bulb.
Nikola Tesla holding a wireless light bulb.

Lighting fluorescent tubes by holding them close to a Tesla Coil is still something many people enjoy doing, and it is a cool effect for sure. However, some believe that this was Tesla’s big “wireless energy” idea, and then say that this would never have worked over long distances. Indeed, the field created by Tesla’s coils does not reach very far, which is exactly why he never intended to use this method as a way to transmit energy over long distances, but only to light up rooms. In fact, Tesla believed sending waves through the air was a losing strategy, since power will not get very far due to the inverse-square law.

“Through ages past man has attempted to project in some way or other energy into space. In all his attempts, no matter what agent he employed, he was hampered by the inexorable law of nature which says every effect diminishes with distance, generally as the square of the same, sometimes more rapidly.” 3

Tesla often negatively referred to this type of energy transmission as Hertz wave radiation, which he in fact saw as an energy loss in his own system, and therefore tried to minimize. Yes, Tesla wanted as little energy as possible to “escape” into the air.

“It will be of interest to compare my system as first described in a Belgian patent of 1897 with the Hertz-wave system of that period. The significant differences between them will be observed at a glance. The first enables us to transmit economically energy to any distance and is of inestimable value; the latter is capable of a radius of only a few miles and is worthless… the amount of energy which may be transmitted [with my system] is billions of times greater than with the Hertzian.” 4

In the rather blunt statement above, Tesla clearly states that he devised a method of energy transmission far superior to sending electromagnetic waves through the air. So what exactly was this superior system he is referring to?

Single wire energy transmission

We see the first version of Tesla’s unique transmission system in an 1897 “Electrical Transformer” patent, in which Tesla describes his invention as follows:

“What I claim as my invention is a system for the conversion and transmission of electrical energy, the combination of two transformers, one for raising, the other for lowering, the potential of the currents, the said transformers having one terminal of the longer or fine-wire coils connected to line, and the other terminals adjacent to the shorter coils electrically connected therewith and to earth.” 5

This sounds an awful lot like the AC transmission system used by Westinghouse, so what’s so radical about this invention? The accompanying diagram depicted below might make the difference clear.

Single wire energy transmission system using two iron core Tesla Coils
First single wire energy transmission patent (1897): “a diagram illustrating the plan of winding and connection which I employ in constructing my improved coils and the manner of using them for the transmission of energy over long distances.”

What we see here are two flat spiral coils connected by a single wire, without a return! Yes, no return wire is necessary to transmit power. This is the radical improvement Tesla made over traditional 2-wire energy transmission, drastically reducing the costs of constructing long-distance transmission lines.

The transmitter coil is a step-up transformer of a special kind, invented by Tesla to reach higher voltages than were possible with traditional transformers of the day:

“The improvement involves a novel form of transformer or induction-coil and a system for the transmission of electrical energy by means of the same in which the energy of the source is raised to a much higher potential for transmission over the line than has ever been practically employed heretofore.” 5

The receiver is an identical coil, which functions as a step-down transformer, to which lamps H and motors K are connected. The high voltage allowed energy to be transmitted with more efficiency, and, more importantly, this new type of coil enabled energy to be transmitted over a single wire, without a return. 6 years earlier, Tesla already used these coils to light incandescent bulbs with a single wire:

“I have discovered that if I connect to either of the terminals of the secondary coil or source of current of high potential the leading-in wires of such a device, for example, as an ordinary incandescent lamp, the carbon may be brought to and maintained at incandescence, or, in general, that any body capable of conducting the high-tension current described and properly enclosed in a rarefied or exhausted receiver may be rendered luminous or incandescent, either when connected directly with one terminal of the secondary source of energy or placed in the vicinity of such terminals so as to be acted upon inductively.” 6

And in 1898 he said:

“Among the various noteworthy features of these currents there is one which lends itself especially to many valuable uses. It is the facility which they afford for conveying large amounts of electrical energy to a body entirely insulated in space. The practicability of this method of energy transmission, which is already receiving useful applications and promises to become of great importance in the near future, has helped to dispel the old notion assuming the necessity of a return circuit for the conveyance of electrical energy in any considerable amount.” 7

Unfortunately, today, over 100 years later, electrical engineers still believe the “old notion” of a return wire is a necessity, even though it is extremely simple to connect two small Tesla Coils and replicate Tesla’s results. I have transmitted power over a single wire, and so have thousands of others around the world, and it works. It’s time electrical engineering courses start including this knowledge into their curriculums, for it is a great shame that this promising branch of research has been completely neglected by Universities and engineers for over a century now. The cost savings from requiring only a single wire could finally make it economically viable to connect millions of people in rural areas to the grid who have so far had to do without electricity.

One final thing to note about the transmission system described in the patent above, is that the transmission line is above ground, and mounted on tall, insulated poles to contain the high voltage current:

“The line-wire should be supported in such manner as to avoid loss by the current jumping from line to objects in its vicinity and in contact with earth—as, for example, by means of long insulators, mounted, preferably, on metal poles, so that in case of leakage from the line it will pass harmlessly to earth.” 5

This setup would change very soon, for instead of bringing this innovative invention to market, it was later that same year, 1897, that Tesla made yet another major improvement to his transmission system, even more radical than single wire energy transmission, which aimed to do away with transmission lines altogether…

“Wireless” energy

While single wire energy transmission already goes way beyond traditional electrical engineering practices, Tesla had bigger plans. He wanted to remove transmission lines from the equation by using the “natural medium” as a conductor instead. He had two different mediums in mind for this.

Atmospheric currents

Tesla’s brainwave was that the transmission line could be made obsolete if current was transmitted through the atmosphere instead of a wire, which he believed was possible if the voltage was high enough and the coils were properly tuned. He filed for two patents on this idea in 1897, which were granted in 1900 and numbered 649,621 and 645,576.

“The invention which forms the subject of my present application comprises a transmitting coil or conductor in which electrical currents or oscillations are produced and which is arranged to cause such currents or oscillations to be propagated by conduction through the natural medium from one point to another remote therefrom and a receiving coil or conductor at such distant point adapted to be excited by the oscillations or currents propagated from the transmitter.” 6

First wireless transmission system, using flat spiral coils as both a transmitter and a receiver, and the earth as a conductor
First wireless transmission system, using flat spiral coils as both a transmitter and a receiver, and the atmosphere used as a conductor

In the image above we see a circuit similar to the single wire transmission circuit discussed earlier, with one big difference: there is no wire connecting the transmitter and the receiver coils! Instead of a power line, the voltage would be pushed so high that a conducting path between the two elevated terminal was established in the upper air strata!

“If the potential be sufficiently high and the terminals of the coils be maintained at the proper elevation where the atmosphere is rarefied the stratum of air will serve as a conducting medium for the current produced and the latter will be transmitted through the air, with, it may be, even less resistance than through an ordinary conductor.” 6

To make this arrangement work, the transmitter and receiver coil needed to be tuned to the same resonant frequency.

And “the best conditions for resonance between the transmitting and receiving circuits are attained [when] the points of highest potential are made to coincide with the elevated terminals D D‘” 6. In other words, “the capacity and inductance in each of the circuits [need to] have such values as to secure the most perfect condition of synchronism with the impressed oscillations”. So these coils were tuned resonant transformers.

Later in his life, Tesla shared the setup he used to proof to the patent examiner that this mode of energy transmission actually worked:

Experimental demonstration in the Houston Street laboratory, before G.D. Seeley, Examiner in Chief, U.S. Patent Office, January 23, 1898, of the practicability of transmission of electrical energy in industrial amounts by the method and apparatus described in U.S. Patents No. 645,576 and No. 649,621. Applications filed September 2, 1897.
Experimental demonstration in the Houston Street laboratory, before G.D. Seeley, Examiner in Chief, U.S. Patent Office, January 23, 1898, of the practicability of transmission of electrical energy in industrial amounts by the method and apparatus described in U.S. Patents No. 645,576 and No. 649,621. Applications filed September 2, 1897.

Tesla had the following to say about this:

“In experimenting with these high potential discharges which I was always producing, I discovered a wonderful thing. I found, namely, that the air, which had been behaving before like an insulator, suddenly became like a conductor; that is, when subjected to these great electrical stresses, it broke down and I obtained discharges which were not accountable for by the theory that the air was an insulator.  When I calculated the effects, I concluded that this must be due to the potential gradient at a distance from the electrified body, and subsequently I came to the conviction that it would be ultimately possible, without any elevated antenna — with very small elevation — to break down the upper stratum of the air and transmit the current by conduction.

…I took a tube 50 feet long, in which I established conditions such as would exist in the atmosphere at a height of about 4 1/2 miles, a height which could be reached in a commercial enterprise.

…I used that coil which is shown in my patent application of September 2, 1897 (Patent No. 645,576 of March 20, 1900), the primary as described, the receiving circuit, and lamps in the secondary transforming circuit, exactly as illustrated there.

And when I turned on the current, I showed that through a stratum of air at a pressure of 135 millimeters, when my four circuits were tuned, several incandescent lamps were lighted.” 7

The patent examiner must have been impressed by the demonstration, since the patents were granted.

It is once more important to note that Tesla was not “radiating” energy into the air, but was actually establishing a conducting path between the transmitter and the receiver:

“It is to be noted that the phenomenon here involved in the transmission of electrical energy is one of true conduction and is not to be confounded with the phenomena of electrical radiation which have heretofore been observed and which from the very nature and mode of propagation would render practically impossible the transmission of any appreciable amount of energy to such distances as are of practical importance.” 6

Earth currents

While atmospheric currents were one option, Tesla had in fact a more promising candidate lined up: earth currents. In a February 1901 Collier’s Weekly article titled “Talking With The Planets” Tesla described his “system of energy transmission and of telegraphy without the use of wires” as:

“(using) the Earth itself as the medium for conducting the currents, thus dispensing with wires and all other artificial conductors … a machine which, to explain its operation in plain language, resembled a pump in its action, drawing electricity from the Earth and driving it back into the same at an enormous rate, thus creating ripples or disturbances which, spreading through the Earth as through a wire, could be detected at great distances by carefully attuned receiving circuits. In this manner I was able to transmit to a distance, not only feeble effects for the purposes of signaling, but considerable amounts of energy, and later discoveries I made convinced me that I shall ultimately succeed in conveying power without wires, for industrial purposes, with high economy, and to any distance, however great.”

In the following statement it is made clear that ever since his 1893 lecture, Tesla had been thinking about the possibility of transmitting signals and power using the earth as a conductor:

“I do firmly believe that it is practicable to disturb by means of powerful machines the electrostatic condition of the earth and thus transmit intelligible signals and perhaps power. In fact, what is there against the carrying out of such a scheme? We now know that electric vibration may be transmitted through a single conductor. Why then not try to avail ourselves of the earth for this purpose?” 7

In the same article, Tesla foresees that the earth and the atmosphere could function as a giant condenser, in which case he expects that the earth’s “period of vibration might be very low”, which later turned out to be true. He proposed “to seek for the period by means of an electrical oscillator”, which he eventually did, and which led Tesla to the conclusion that the earth’s resonant frequency was around 11.78Hz, as mentioned in his Canadian patent from 1906 (calculated by using his .084840 seconds for an electric pulse to travel the earth’s diameter and back). He also noted already that “in order to displace a considerable quantity [of electricity], the potential of the source must be excessive.”, which is why he pushed his Magnifying Transmitter to ultimately generate 30 million volts!

What is a Magnifying Transmitter you might ask? I’ll let Tesla describe his self-declared “best invention” to you:

Patent drawing of the Tesla Magnifying Transmitter
Patent drawing of the Tesla Magnifying Transmitter

“It is a resonant transformer with a secondary in which the parts, charged to a high potential, are of considerable area and arranged in space along ideal enveloping surfaces of very large radii of curvature, and at proper distances from one another thereby insuring a small electric surface density everywhere so that no leak can occur even if the conductor is bare.

… this wireless transmitter is one in which the Hertz-wave radiation is an entirely negligible quantity as compared with the whole energy, under which condition the damping factor is extremely small and an enormous charge is stored in the elevated capacity. Such a circuit may then be excited with impulses of any kind, even of low frequency and it will yield sinusoidal and continuous oscillations like those of an alternator.

… Taken in the narrowest significance of the term, however, it is a resonant transformer which, besides possessing these qualities, is accurately proportioned to fit the globe and its electrical constants and properties, by virtue of which design it becomes highly efficient and effective in the wireless transmission of energy. Distance is then absolutely eliminated, there being no diminution in the intensity of the transmitted impulses. It is even possible to make the actions increase with the distance from the plant according to an exact mathematical law.” 8

In short, Tesla’s idea was to determine the resonant frequency of the earth, then create a powerful oscillator, the Magnifying Transmitter, which pushed enormous potentials into the earth at exactly the right frequency in order to create electrical standing waves inside the earth, which then allowed energy to be received at the nodal points of the standing waves, with very little transmission loss. Power would be pushed into the earth through the ground connection at the transmitter, conducted through the earth, and collected again from the earth at the receiver end.

A lot of misunderstanding exists regarding the resonant frequency of the earth Tesla was referring to. The reason is that when you Google for “earth resonant frequency”, the first articles all mention the Schumann resonance of 7.83Hz, which then leads people to conclude that Tesla’s calculations were way off. However, the Schumann resonance is not the frequency of interest here, as my friend Simon from Tesla Scientific once explained to me:

“The original frequency [of the Tesla Magnifying Transmitter] is around 45 kHz, not the Schumann frequency. Tesla’s idea was to use harmonic frequencies or maybe “beat frequencies”, otherwise the coil would have to be ¼ the size of the earth! But the frequency that’s of interest is the earth’s frequency itself, not the Schumann resonance, since the Schumann resonance deals with the cavity that exists between the earth’s surface and the ionosphere, but the energy travels through the earth, and the resonant frequency of the earth is around 11.78Hz.”

Everyone I tell about this bold plan to transmit energy through the earth mentions how much resistance the earth has compared to a normal conductor, but Tesla disagrees and believed the earth is an “ideal conductor”:

“It is difficult for a layman to grasp how an electric current can be propagated to distances of thousands of miles without diminution of intention. But it is simple after all. Distance is only a relative conception, a reflection in the mind of physical limitation. A view of electrical phenomena must be free of this delusive impression. However surprising, it is a fact that a sphere of the size of a little marble offers a greater impediment to the passage of a current than the whole earth. Every experiment, then, which can be performed with such a small sphere can likewise be carried out, and much more perfectly, with the immense globe on which we live. This is not merely a theory, but a truth established in numerous and carefully conducted experiments… This mode of conveying electrical energy to a distance is not ‘wireless’ in the popular sense, but a transmission through a conductor, and one which is incomparably more perfect than any artificial one. All impediments of conduction arise from confinement of the electric and magnetic fluxes to narrow channels. The globe is free of such cramping and hinderment. It is an ideal conductor because of its immensity, isolation in space, and geometrical form.” 9

Of course it is correct to say that a handful of soil has more electrical resistance than a copper wire, which is why Tesla had to use millions of volts and had to create an extremely elaborate grounding system:

“In this system that I have invented it is necessary for the machine to get a grip of the earth, otherwise it cannot shake the earth. It has to have a grip on the earth so that the whole of this globe can quiver.” 10

For a detailed analysis of the grounding system Tesla employed, I can recommend reading this article on Open Tesla Research.

Semi-finished Wardenclyffe Tower in Shoreham, New York
Semi-finished Wardenclyffe Tower before it was torn down

An experimental setup of the Magnifying Transmitter was erected in Tesla’s Colorado Spring laboratory between 1899 and 1900. Tesla then continued to develop the first commercial power station based on his earth transmission system in Shoreham, New York, called the Wardenclyffe Tower. In his autobiography, Tesla referred to his global energy transmission scheme as his “World System”. The Wardenclyffe project would have been the crown on Tesla’s work, but was unfortunately never finished due to a myriad of reasons, and Tesla never really managed to recover from this blow (read more about this in my previous post on the history of the Tesla Coil). In 1917 the tower was demolished, since the US government suspected it was being used by German spies for radio transmission 11.

Conclusion

The goal of this article was to clear up the confusion surrounding Tesla’s “wireless” energy. It turned out he meant “conduction without wires” instead of “wirelessly radiating through the air”. There were a few ingenious transmission systems Tesla experimented with, in chronological order:

  1. Wireless light (room-scale)
  2. Single wire energy transmission
  3. Atmospheric currents
  4. Earth currents

The only serious effort I know of at this moment to develop wireless power transmission is the company WiTricity, but they work on a variation of #1 above and are therefore limited to very small distances. Earth currents were dubbed by Tesla to be his “best invention”, but we might never know if his World System would have worked in practice, since modern Electrical Engineers do not spend any time researching this fascinating technology, and because I am quite certain that with all the sensitive electronic equipment in use today it will not be allowed to push millions of volts into the earth on the off-chance that all those devices will be fried.

However, even if transmission through the earth on a global scale is out of the question, or you believe it would not work for any number of reasons, then one question still remains:

Why are we not researching single wire energy transmission?

Tesla showed in countless easy-to-replicate experiments that energy can be transmitted over a single wire without a return, so why are we still using two wires more than 100 years later?

Let’s park the tricky earth currents for now, start with the simple basics, and build our knowledge from there. Single wire energy transmission deserves to become an active research field, since it promises to cut the money spent on electric wiring in half, and could therefore finally make it economically viable to connect “the last billion” to the electricity grid. It seems wrong not to pursue this noble task, especially since Nikola Tesla has already done most of the hard work for us. If only we tried…

History of the Tesla Coil and its geometries

History of the Tesla Coil and its Geometries

The first time I ever heard about a Tesla Coil, was actually while playing the video game Red Alert during my teenage years. In the game, the coil was a powerful weapon which shot massive bolts of lightning at the enemy. Shooting big sparks is actually the main association people have with the Tesla Coil, since that is what modern “coilers” use it for.

Modern Tesla Coil (left) versus Tesla's original Colorado Springs "Magnifying Transmitter" coil (right)
Figure 1. Modern table top Tesla Coil (left) versus Tesla’s original Colorado Springs “Magnifying Transmitter” coil (right)

However, Nikola Tesla, it’s original inventor, had many practical uses for these high voltage, high frequency coils besides shooting sparks, and it actually came in many shapes and forms, all with their own characteristics and use cases. This article shows how the Tesla Coil evolved over time, and what it was used for.

Where it all began

In 1887, Heinrich Hertz created the first experimental proof of the electromagnetic waves predicted by Maxwell’s theory. This created a lot of buzz around high frequency currents and sparked Tesla’s curiosity as well, who had up till then mainly been working on his AC motors and transmission system, as is evident from his patent history.

Today we are used to hearing “gigahertz” being thrown around, which is equal to 1 BILLION oscillations per second, while in Tesla’s time 20 to 30 THOUSAND oscillations was considered a very high frequency. The reason is that we have transistors now, which switch on an atomic scale, while bulky mechanical oscillators were used in the late 1800’s, and there was just no good way to make them run much faster.

However, Tesla wanted to push beyond the 30 kHz limitation, and in 1891 he patented his Method and Apparatus for Electrical Conversion and Distribution, in which Tesla described how he created rapidly oscillating currents without a mechanical oscillator:

“I have thus succeeded in producing a system or method of conversion radically different from what has been done heretofore—first, with respect to the number of impulses, alternations, or oscillations of current per unit of time, and, second, with respect to the manner in which the impulses are obtained. To express this result, I define the working current as one of an excessively small period or of an excessively large number of impulses or alternation or oscillations per unit of time, by which I mean not a thousand or even twenty or thirty thousand per second, but many times that number, and one which is made intermittent, alternating, or oscillating of itself without the employment of mechanical devices.” 1

So how did Tesla achieve this impressive feat?

“I employ a generator, preferably, of very high tension and capable of yielding either direct or alternating currents. This generator I connect up with a condenser or conductor of some capacity and discharge the accumulated electrical energy disruptively through an air-space or otherwise into a working circuit containing translating devices.” 1

In other words, Tesla found practical use for Lord Kelvin’s condenser discharge – who he regularly credited 2 – and patented it. Tesla now had a way to create high frequency currents.

The first application of this high frequency setup is found in another patent granted to Tesla in 1891, titled System of Electric Lighting 3. In this key patent, we see the first ever diagram and description of a complete Tesla Coil circuit, and the text contains a revealing passage about the reason why this device was invented:

“For a better understanding of the invention it may be stated, first, that heretofore I have produced and employed currents for very high frequency for operating translating devices, such as electric lamps, and, second, that currents of high potential have also been produced and employed for obtaining luminous effects, and this, in a broad sense, may be regarded for purposes of this case as the prior state of the art; but I have discovered that results of the most useful character may be secured under entirely practicable conditions by means of electric currents in which both the above-described conditions of high frequency and great difference of potential are present. In other words, I have made the discovery that an electrical current of an excessively small period and very high potential may be utilized economically and practicably to great advantage for the production of light.” 3

So the very first Tesla Coil ever was used to produce light using not just high frequency currents, not just high voltage currents, but both high frequency and high voltage at the same time! The Tesla Coil essentially expands the high frequency circuit mentioned earlier with a high voltage step up transformer to achieve “enormous frequency and excessively high potential”.

Another telling passage from the patent text mentions how Tesla noticed that a single wire could be used to light a bulb:

“I have discovered that if I connect to either of the terminals of the secondary coil or source of current of high potential the leading-in wires of such a device, for example, as an ordinary incandescent lamp, the carbon may be brought to and maintained at incandescence, or, in general, that any body capable of conducting the high-tension current described and properly enclosed in a rarefied or exhausted receiver may be rendered luminous or incandescent, either when connected directly with one terminal of the secondary source of energy or placed in the vicinity of such terminals so as to be acted upon inductively.” 3

The diagram in the patent shows two bulbs connected by a single wire (the other end of the coil connected to a conducting wall), and Tesla even shows two custom single wire bulbs which he used in these lighting experiments. All very interesting stuff, and no mention of large sparks yet! So what did this first coil look like? And did it have other uses besides lighting?

Bipolar coil (1891)

The first drawing of a Tesla Coil are found in Tesla’s 1891 lecture before the American Institute of Electrical Engineers, in which various experiments are shown utilizing the coil, including an extensive study of “discharge phenomena”, or sparks.

Study of discharge phenomena using a bipolar Tesla Coil during a lecture in 1891
Figure 2. Study of discharge phenomena using a bipolar Tesla Coil during a lecture in 1891

Something that stands out immediately is that this coil is placed horizontally, not vertically like “modern” Tesla Coils. Also, there is no “terminal capacitance” on one end, and a ground connection on the other, like you usually see in a Tesla Coil. This setup is what is now known as a “Bipolar” Tesla Coil.

Another interesting fact is that the primary coil is actually placed inside the secondary coil, as can be seen in the image below. Tesla instructed to “introduce it from one side of the tube, until the streams begin to appear.” 4

Bipolar Tesla Coil with primary located inside the secondary
Figure 3. Bipolar Tesla Coil with primary located inside the secondary

Modern Tesla Coils have an air core, but these early models had their primary wound on top of an iron core:

“In many of these experiments, when powerful effects are wanted for a short time, it is advantageous to use iron cores with the primaries.” 4

Iron cores increase magnetic fields, resulting in more powerful induction effects. However, these iron cores had a major drawback:

“In these experiments if an iron core is used it should be carefully watched, as it is apt to get excessively hot in an incredibly short time.” 4

And at the end of the lecture Tesla already predicted that using iron cores would become a thing of the past:

“In the present systems of electrical distribution, the employment of the iron with its wonderful magnetic properties allows us to reduce considerably the size of the apparatus; but, in spite of this, it is still very cumbersome.  The more we progress in the study of electric and magnetic phenomena, the more we become convinced that the present methods will be short-lived.” 4

In the lecture, Tesla describes how he used his coil to study, amongst other things:

  1. Discharge phenomena
  2. Single wire & wireless light
  3. HF / HV electrical insulation
  4. Impedance phenomena

It is interesting to read that Tesla did not have any math at hand to calculate the ideal primary length and capacitance, he simply said that “the length of the primary should be determined by experiment.”4 Also, no mention of resonance between the primary and secondary is mentioned in the lecture, so it seems like Tesla’s 1891 coil was still a tightly coupled, “normal” induction coil.

Now, was this bipolar coil used often, or only during the 1891 lecture? Well, years later, in an article in the Electrical Experimenter of July 1919, Tesla shared a whole range of bipolar coils and the things he used them for.

Tesla Oscillators from the Electrical Experimenter from July 1919
Figure 4. Tesla Oscillators from the Electrical Experimenter from July 1919

It is clear from the picture above that Tesla used this type of coil extensively, and came up with all sorts of ingenious improvement. Further, it is funny to note that Tesla sometimes calls this device a “Tesla Coil”, and other times a “Tesla Transformer” or even a “Tesla Oscillator”.

Some of the uses of these coils mentioned in the article:

  • Gas engine ignition
  • Wireless
  • Ozone production
  • Creation of undamped waves

A very versatile device!

After reading all this info, I wondered how big these coils actually were, since size is hard to gauge from the pictures and drawings above. Luckily I found an image of an original coil displayed in the Tesla museum in Belgrade, powering an original Tesla light tube, and which has someone standing next to it, providing a good estimate of the size.

Original Tesla Transformer as displayed in the Tesla museum
Figure 5. Original Tesla Transformer as displayed in the Tesla museum

Conical coil (1894)

After the 1891 lecture, Tesla gave several other lectures on high frequency, high voltage devices, and in 1893 Tesla got involved in developing the world’s first hydroelectric power plant at Niagara Falls, together with George Westinghouse. We see that during that period Tesla filed for several generator, motor, and power transmission patents. However, on the side he kept developing his coil, resulting in the massive conical Tesla Coil shown below.

Conical Tesla Coil
Figure 6. Conical Tesla Coil from 1894

“This coil, which I have subsequently shown in my patents Nos. 645,576 and 649,621, in the form of a spiral, was, as you see, [earlier] in the form of a cone.” 5

The cone shape was chosen to minimize the potential difference between the turns near the top of the coil, so there was less risk of damaging the insulation of the wires. In his comment, Tesla references two of his most famous wireless energy transmission patents, saying that he first used a conical geometry, and later a spiral one, but that in essence they were one and the same device.

Inspired to “develop electric forces of the order of those in nature”, this conical coil was Tesla’s first to reach 1 million volts:

“The first gratifying result was obtained in the spring of the succeeding year when I reached tensions of about 1,000,000 volts with my conical coil. That was not much in the light of the present art, but it was then considered a feat.” 6

This cone shaped coil was a very significant step in the development of the Tesla Coil, since we now for the first time see an upright coil with one end connected to ground. This is what Tesla had to say about this coil:

“This [Figure 6] shows the first single step I made toward the evolution of an apparatus which, given primary oscillations, will transform them into oscillations capable of penetrating the medium. That experiment, which was marvelous at the time it was performed, was shown for the first time in 1894.” 5

So Tesla was figuring out a way to create waves that could penetrate the surrounding medium, and his setup was as follows:

“The idea was to put the coil, with reference to the primary, in an inductive connection which was not close—we call it now a loose coupling—but free to permit a great resonant rise. That was the first single step, as I say, toward the evolution of an invention which I have called my “magnifying transmitter.” That means, a circuit connected to ground and to the antenna, of a tremendous electromagnetic momentum and small damping factor, with all the conditions so determined that an immense accumulation of electrical energy can take place. It was along this line that I finally arrived at the results described in my article in the Century Magazine of June 1900.” 5

According to Tesla’s words, this coil was the first of his coils to implement a loose coupling between the primary and the secondary, and the reason for this was to allow the secondary to vibrate more freely without being weighed down by the primary, thus allowing for much greater voltages at the top of the coil, resulting in beautiful discharges.

“The discharge there was 5 or 6 feet, comparatively small to what I subsequently obtained.” 5

We encounter this conical coil once more in an 1897 “Electrical Transformer” patent.

Conical Tesla Coil from 1897 patent
Figure 7. Conical Tesla Coil from 1897 patent

Tesla mentions how different shapes can be used for the same purpose:

“Instead of winding the coils in the form of a flat spiral the secondary may be wound on a support in the shape of a frustum of a cone and the primary wound around its base, as shown in Fig. [7].” 6

In another drawing from the same patent, it becomes clear how Tesla intended to use these coils to transmit energy at extremely high voltages over a single wire, stepping it up at the transmission end, and stepping it down at the receiver end to power loads.

Single wire energy transmission system using two iron core Tesla Coils
Figure 8. Single wire energy transmission system using two iron core Tesla Coils

In this drawing we also see that a magnetic core is still part of the design.

Flat spiral coil (1897)

In the same patent discussed above, Tesla mentions that around 1897 he usually worked with flat spiral coils:

“The type of coil in which the last-named features are present is the flat spiral, and this form I generally employ, winding the primary on the outside of the secondary and taking off the current from the latter at the center or inner end of the spiral. I may depart from or vary this form, however.” 6

So Tesla generally used a flat spiral coil, but said other geometries worked as well.

In one of the most famous pictures ever made of Nikola Tesla, we can see the inventor sitting in front of a humongous flat spiral coil in his lab on Houston Street, New York
Figure 9. In one of the most famous pictures ever made of Nikola Tesla, we can see the inventor sitting in front of a humongous flat spiral coil in his lab on Houston Street, New York

The main reason Tesla started using flat spiral coils was because they better suppressed the sparks, which were essentially losses in the circuit, allowing him to achieve higher voltages:

“In carrying on tests with a secondary in the form of a flat spiral, as illustrated in my patents, the absence of streamers surprised me, and it was not long before I discovered that this was due to the position of the turns and their mutual action.” 7

Another major benefit of using flat coils is that they are relatively safe, since the highest potential terminal is at the center, out of reach:

“Those portions of the wire or apparatus which are highly charged will be out of reach, while those parts of the same which are liable to be approached, touched, or handled will be at or nearly the same potential as the adjacent portions of the ground, this insuring, both in the transmitting and receiving apparatus and regardless of the magnitude of the electrical pressure used, perfect personal safety, which is best evidenced by the fact that although such extreme pressures of many millions of volts have been for a number of years continuously experimented with no injury has been sustained neither by myself or any of my assistants.” 8

The “transmitting and receiving apparatus” referred to in the quote above are from two patents filed in 1897 for a revolutionary “wireless” energy transmission system, which planned to use the earth as a conductor.

First wireless transmission system patent, using flat spiral coils as both a transmitter and a receiver, and the earth as a conductor
Figure 10. First wireless transmission system patent, using flat spiral coils as both a transmitter and a receiver, and the earth as a conductor

From the patent drawing it is clear that iron cores were not longer being used at this point. We also see a new part being introduced: an “elevated terminal… preferably of large surface”. This terminal acted as a capacitance, and Tesla tweaked his circuit so that the point of highest potential would coincide with these elevated terminals:

“It will be readily understood that when the above-prescribed relations exist the best conditions for resonance between the transmitting and receiving circuits are attained, and owing to the fact that the points of highest potential in the coils or conductors A A are coincident with the elevated terminals the maximum flow of current will take place in the two coils, and this, further, necessarily implies that the capacity and inductance in each of the circuits have such values as to secure the most perfect condition of synchronism with the impressed oscillations.” 9

Here we see clearly that the Tesla Coil has officially evolved from a traditional, magnetically coupled transformer, into a resonant transformer, based on resonant inductive coupling. This is a crucial point in which Tesla Coils differ from regular transformers. It’s all about tuning the primary circuit to the secondary, and the receiver to the transmitter.

Bifilar spiral coil

Tesla's bifilar flat pancake coil from 1893
Figure 11. Tesla’s bifilar pancake coil from 1893

As early as 1893, Tesla already patented a very unique flat spiral coil design, now commonly known as the “bifilar pancake coil”. This coil was wound using two parallel wires, and then connecting the end of one to the beginning of the other wire. This setup resulted in a larger difference in potential between the turns, and therefore a much larger self-capacitance in the coil, with the goal to do away with expensive capacitors altogether, and let the coil itself contain all the capacitance it needs to oscillate at a certain frequency:

“My present invention has for its object to avoid the employment of condensers which are expensive, cumbersome and difficult to maintain in perfect condition, and to so construct the coils themselves as to accomplish the same ultimate object.” 10

However, Tesla kept using capacitors, mainly Leyden jars, in many of his later experiments. So even though the idea behind the bifilar coil is brilliant, it seems like Tesla did not find it useful enough in practise.

Helical coil (1899)

It’s interesting that we’ve already discussed 3 different coil geometries, none of which resembles the “modern” helical Tesla Coil. So did Tesla himself even use this shape at all? Yes, he sure did, as you can see from the beautifully preserved original below, as displayed in the Tesla museum in Belgrade.

Original 500KV helical Tesla Coil in the Tesla Museum in Belgrade
Figure 12. Original 500KV helical Tesla Coil inside the Tesla Museum in Belgrade

In the picture above we see the familiar thin helical coil shape with a toroid as terminal capacitance, as well as three 10-turn primaries, which could most likely be connected in series to vary the operating frequency of the coil.

While this is the shape that first comes to mind for most people when they think of a Tesla Coil, Tesla did not actually write much or anything about this geometry in particular. However, we do see this coil shape return on multiple occasions in pictures taken around 1899 inside Tesla’s Houston Street and Colorado Springs laboratories. These helical coils are sometimes wide and short instead of thin and tall.

Houston Street lab, showing a spiral coil on the wall and a wide, short helical coil in the foreground
Figure 13. Houston Street lab, showing a spiral coil on the wall and a wide, short helical coil in the foreground

Nikola Tesla holding a helical receiver coil
Figure 14. Nikola Tesla holding a helical receiver coil

Wide helical receiver coil tuned to receive electrical energy from a transmitter elsewhere in the lab
Figure 15. Wide helical receiver coil tuned to receive electrical energy from a transmitter elsewhere in the lab, showing sparks between two condenser plates

Helical coils bombarded with sparks from the Colorado Springs Magnifying Transmitter
Figure 16. Helical coils bombarded with sparks from the Colorado Springs Magnifying Transmitter

Helical receiver coil outside of the Colorado Springs lab, tuned to the Magnifying Transmitter, lighting a single bulb
Figure 17. Helical receiver coil outside of the Colorado Springs lab, tuned to the Magnifying Transmitter,”wirelessly” lighting a single bulb

More helical Tesla Coils used in Colorado Springs
Figure 18. More helical Tesla Coils used in Colorado Springs

From the pictures above, and especially the Colorado Springs pictures, it seems like Tesla used a wide selection of helical receiver coils for experimentation purposes. Many of them even come without a primary and terminal capacitance, which suggests that this was not the “final form”, but merely a simple-to-put-together version of a coil used for testing purposes. We also see that the Houston Street coils were wide and short, while the Colorado Springs coils were of the thin and tall variety.

Magnifying Transmitter (> 1899)

Patent drawing of the Tesla Magnifying Transmitter
Figure 19. Patent drawing of the Tesla Magnifying Transmitter

We have now arrived at the final and most advanced Tesla Coil ever created: the Tesla Magnifying Transmitter (TMT). This coil, developed in Colorado Springs and patented in 1902, was intended to transmit ultra high voltage electrical energy around the globe, by using the earth as a conductor. In his autobiography, Tesla explained the TMT in the following way:

“It is a resonant transformer with a secondary in which the parts, charged to a high potential, are of considerable area and arranged in space along ideal enveloping surfaces of very large radii of curvature, and at proper distances from one another thereby insuring a small electric surface density everywhere so that no leak can occur even if the conductor is bare.

… this wireless transmitter is one in which the Hertz-wave radiation is an entirely negligible quantity as compared with the whole energy, under which condition the damping factor is extremely small and an enormous charge is stored in the elevated capacity. Such a circuit may then be excited with impulses of any kind, even of low frequency and it will yield sinusoidal and continuous oscillations like those of an alternator.

… Taken in the narrowest significance of the term, however, it is a resonant transformer which, besides possessing these qualities, is accurately proportioned to fit the globe and its electrical constants and properties, by virtue of which design it becomes highly efficient and effective in the wireless transmission of energy. Distance is then absolutely eliminated, there being no diminution in the intensity of the transmitted impulses. It is even possible to make the actions increase with the distance from the plant according to an exact mathematical law.” 7

As you can read in the above excerpt, the TMT was created to reach as high of a voltage as possible by spacing the conductors appropriately and in large circles, an insight he gleaned from working with his flat spiral coils 8, whereas on a modern Tesla Coil secondary the conductors are always wound close together. Also, Tesla’s intention was to minimize “Hertz-wave radiation” (electromagnetic radio waves), because he wanted to focus all the energy of the coil into the earth for his “wireless” energy transmission scheme. This massive coil’s dimensions were such that it would oscillate with the earth’s natural electric charge to enable this energy transmission, as Tesla explains in more detail in a short 1908 article:

“When the earth is struck mechanically, as is the case in some powerful terrestrial upheaval, it vibrates like a bell, its period being measured in hours. When it is struck electrically, the charge oscillates, approximately, twelve times a second. By impressing upon it current waves of certain lengths, definitely related to its diameter, the globe is thrown into resonant vibration like a wire, forming stationary waves.” 9

Extra coil

But was the only difference between a “regular” Tesla Coil and a Magnifying Transmitter the fact that the conductors were properly spaced? Not exactly. The biggest difference in fact is the addition of another coil into the circuit. Whereas a Tesla Coil has a primary and a secondary coil, the Magnifying Transmitter has a third, freely oscillating coil, which Tesla simply called the “extra coil” (in the patent drawing above).

Tesla in front of his Extra Coil in Colorado Springs
Figure 20. Tesla in front of his Extra Coil in Colorado Springs

Tesla explains the purpose of the extra coil as follows in his Colorado Spring Notes:

“It is a notable observation that these “extra coils” with one of the terminals free, enable the obtainment of practically any e.m.f. the limits being so far remote, that I would not hesitate in undertaking to produce sparks of thousands of feet in length in this manner.

Owing to this feature I expect that this method of raising the e.m.f. with an open coil will be recognized later as a material and beautiful advance in the art.” 10

So the extra coil is what allowed the TMT to reach such immense voltages, but how? The primary coil and secondary coil oscillate at an identical frequency and are therefore resonantly coupled. While this coupling is key to induce current from the primary into the secondary, it also weighs the oscillations down. It adds a certain damping factor, since the secondary coil is not 100% free to oscillate as it pleases. Tesla’s brilliant insight here was that he would have a resonantly coupled primary and secondary, but then add an extra coil which is not tuned to the same exact frequency and can therefore oscillate more freely, allowing the voltage to rise to even greater heights.

Extra Coil circuit diagram
Figure 21. Extra Coil circuit diagram from Tesla’s Colorado Spring notes

“It is found best to make [the] extra coil 3/4 wave length and the secondary 1/4 for obvious reasons.” 11

Since we’re talking about geometries in this article, it is also crucial to note that the extra coil had a 1:1 length to diameter ratio. The reason is that a coil’s self-capacitance is at its lowest at a 1:1 ratio, as was later determined through research by Medhurst 12

Table of H values for the self-capacitance formula Capacitance in pF = H x Diameter, as measured by Medhurst. Self-capacitance is at its lowest at H = 1, where H is length / diameter.
Figure 22. Table of H values for the self-capacitance formula Capacitance in pF = H x Diameter, as measured by Medhurst. Self-capacitance is at its lowest at H = 1, where H is length / diameter. Source: Radiotron Designers Handbook 

Anyone who has ever experimented with Tesla Coils know how sensitive the circuit is. For example, if you put your hand close to the coil, the frequency immediately drops due to the extra capacitance your body adds to the circuit, without even touching it! So the lower the self-capacitance, the less the circuit is weighed down, and the higher the voltage rise that is attainable.

Wardenclyffe

Semi-finished Wardenclyffe Tower in Shoreham, New York
Figure 23. Semi-finished Wardenclyffe Tower before it was torn down

Once Tesla finished up his research in Colorado Spring, he started working on his first full-scale transmitting tower in Shoreham, New York, called the Wardenclyffe Tower. Construction was never completed, and only scattered notebook drawings remain, so we have no idea if Tesla’s groundbreaking wireless transmission system would have worked in practise.

Many “conspiracies” have popped up over time that big industry and banking powers did not want Tesla to transmit “free” energy all over the globe and therefore shut the project down. You often read that J.P. Morgan, who financed the initial construction of the Wardenclyffe tower, said something along the lines of “you can’t put a meter on that”, and therefore cut the funding. In fact, reading this very statement fueled my quest into the world of Nikola Tesla. However, Tesla himself felt that Morgan lived up to all his promises and was not to blame:

“I would further add, in view of various rumors which have reached me, that Mr. J. Pierpont Morgan did not interest himself with me in a business way but in the same large spirit in which he has assisted many other pioneers. He carried out his generous promise to the letter and it would have been most unreasonable to expect from him anything more. He had the highest regard for my attainments and gave me every evidence of his complete faith in my ability to ultimately achieve what I had set out to do. I am unwilling to accord to some small-minded and jealous individuals the satisfaction of having thwarted my efforts. These men are to me nothing more than microbes of a nasty disease. My project was retarded by laws of nature. The world was not prepared for it. It was too far ahead of time. But the same laws will prevail in the end and make it a triumphal success.” 7

However, when one reads the letters between Tesla and J.P. Morgan from that time, it does appear that J.P. Morgan might not have been as helpful as he could have been, and that in the above statement Tesla simply did not wish to speak ill of him in public.

Despite that, Tesla’s energy was not “free”, as some claim. Tesla had to put in thousands of horsepower to kick his transmitter into motion, and even fried the power station near his Colorado lab once because he was using so much energy. However, his system being an open system, like a windmill or solar panel, rather than a traditional closed circuit, it is not impossible to conceive that energy already present in the earth or the ambient medium, which oscillated at the same frequency, could be resonantly coupled in to reinforce his input.

Also, once an oscillating current was established in the earth, a lot less energy would be required to keep it going, just like how you need a lot of power to push someone on a swing, but once they are going you only have to give a tiny push to keep them swinging about.

Magnifying Transmitter Design Sheet
The TMT is a complex device and therefore harder to replicate than a Tesla Coil, which is why I was ecstatic to find a Colorado Spring Magnifying Transmitter Design Sheet, created by Simon from Tesla Scientific. There are designs for several operating frequencies, and you can even request a custom frequency design. Click here to check it out.

Modern coils

Modern Tesla Coil
Figure 24. Modern Tesla Coil

After discussing the Magnifying Transmitter and its bold purpose to transmit power across the globe, it feels like a gigantic step backward to now talk about how modern “Coilers” apply some of Tesla’s ideas, simply to create big sparks and light fluorescent tubes in their hands. However, this is the current state of the Tesla Coil, and the reason why many people are unaware of the original grand purpose of these coils.

On a positive note, thanks to the active coiling community, modern Tesla Coil calculators like TeslaMap have emerged, which make coil calculations a whole lot easier. These coils are almost exclusively helical coils with one terminal grounded and a toroidal terminal capacitance on the top end.

Another very interesting development is that today’s Tesla Coils are not always powered by spark gaps anymore, like in Tesla’s time, but often by electronics. Such coils are called Solid State Tesla Coils (SSTC), or Dual Resonant Solid State Tesla Coils (DRSSTC), and their circuit diagrams are mental, but work very well.

DRSSTC circuit diagram
Figure 25. DRSSTC circuit diagram

The only thing I find funny is that the community’s general solution to creating larger sparks is to add more turns on the secondary and push more power through the circuit, while a much smaller coil, designed according to the Magnifying Transmitter specifications, would result in way larger discharges.

Closing thoughts

The goal of this article was  to clear up some of the confusion surrounding the use cases for these high frequency, high voltage coils, as well as to show the various stages of development they went through and the different shapes they came in, as each of the geometries had their own pros and cons. Tesla himself called his Magnifying Transmitter his best invention, and solely based on that fact it is worth researching in more detail, which I plan to do in the future.

I hope you enjoyed this little journey through time! In my next article I dive deeper into the various electrical transmission systems Tesla devised over his lifetime.

Tesla Hairpin Circuit Stout Copper Bars Replication

Tesla Hairpin Circuit Replication & Experimental Results

After more than a year of research and development, I am excited to finally share my Tesla Hairpin replication and experimental results! I share things that worked, and things that didn’t work, as well as why. This article also contains a detailed parts list, so you can easily replicate my setup and experiments.

This article will be pretty hands on, and assumes you have read my foundational articles, A Brief History of the Tesla Hairpin Circuit and Impedance, the Skin Effect, and their Implications in High Frequency Circuits. If you haven’t, I highly recommend you check them out first, as we will build upon that knowledge here.

Why the Hairpin circuit?

You might rightly ask yourself why I spent so much time researching this seemingly simple circuit. Isn’t it obvious what it does? It clearly isn’t, judging from the lack of proper replications out there and the unsubstantiated claims around this device. But isn’t the Hairpin overshadowed by the much more impressive feats of the Tesla Coil and Magnifying Transmitter? Sure, but these devices have different purposes, and their working cannot be understood properly without first understanding the Hairpin, out of which these more advanced devices evolved. Thoroughly understanding the Magnifying Transmitter, Tesla’s “best invention”, is what made me start this journey, and the Hairpin is the first step of the way.

My journey so far

My journey started when I watched a 10-part series of YouTube videos where Karl Palsness presented his Hairpin replication. He showed single wire energy transmission over a very thin wire, a bulb lit while submerged in water, and Karl touching the copper bars without getting hurt, even though thousands of volts pulsed through the circuit, a result he attributed to “scalar waves”. I was very impressed!

I did my best to find out more about his particular setup, and found an article on Transformacomm in which many practical details were shared. The article mentions the following parts:

Nothing fancy there! This gave me the confidence to create my own replication, even though all I had seen or read about this circuit was contained in the Transformacomm article and the previously mentioned video series. I purchased the same capacitors Karl used, the first affordable 10kV power supply I could find, copper bars of similar dimensions, and attached a basic spark gap consisting of two bolts facing each other. The end result can be seen in the picture below.

Version 1 of my Tesla Hairpin replication
Figure 1. Version 1 of my Tesla Hairpin replication

Unfortunately, the circuit did not work. In fact, the spark gap even refused to fire! I asked for help on the Energetic Forum and simultaneously started to perform more research, since I felt my knowledge, even of basic electrical concepts, was severely lacking.

Based on what I learned, I continually tweaked and improved my Hairpin, until I was able to perform a true replication of Tesla’s experimental results, at which point I had upgraded every single part of my initial circuit…

The right power supply for the job

As mentioned previously, Karl Palsness used a 10kV oven transformer, and I naively thought that all transformers are the same, which is why I ended up buying the first affordable 10kV transformer I could find: a Seletti 10kV neon sign transformer (NST).

I was impressed when I connected the transformer to my super simple spark gap and saw sparks flying across, but was sorely disappointed when I added the rest of my Hairpin circuit to the mix, and all sparking ceased. Why did this happen? The main difference between the transformer Karl used versus mine, is that his ran at 60Hz and mine at no less than 34kHz!! This turned out to make all the difference in the world.

Soon after my post on the Energetic Forum about this issue, I came across the concept of capacitive reactance (explained in detail here), which makes capacitors let more current “through” the higher the frequency of that current. This is the same effect high-pass filters use in audio applications.

In other words, the 34kHz current coming from my NST was not charging the capacitors and then discharging these capacitors through the spark gap, but instead, due to capacitive reactance, the high frequency input current directly passed through the capacitors, creating a short circuit, and preventing the gap from firing at all.

My first idea was to try to reduce the 34kHz current to a lower frequency. One of the solutions I came across was to use a full-wave bridge rectifier (FWBR) setup to convert the alternating current to a direct current, and so I purchased some high voltage, high frequency rectifier diodes, which were capable of withstanding 100mA at 30kV. I created my bridge setup, as shown in the image below, and I was excited that my spark gap finally fired, albeit with a deafening noise (DC sparks are apparently louder than AC sparks).

30kV full-wave bridge rectifier (FWBR)
Figure 2. 30kV full-wave bridge rectifier (FWBR)

Before my excitement had fully settled in, sparks already started to fly from one side of a diode to the other side, causing it to catch on fire… This wasn’t going to work: the only way forward was a lower frequency power supply.

On AliExpress I found a proper 10kV neon sign transformer which ran at the European power line frequency of 50Hz. This one also specifically mentions “no GFI”, which stands for Ground Fault Interrupter. A GFI shuts off an electric power circuit when it detects that current is flowing along an unintended path. So a GFI makes an NST safer, but in the case of a Tesla circuit, it can also prevent your device from functioning properly, which is why a “no GFI” NST is recommended. This does mean you have to be extra careful of course.

When I received my NST a few weeks later, it turned out they shipped me a 15kV version instead of the 10kV one I ordered. First I was annoyed, because I thought I might now not be able to achieve the same results as Karl Palsness, but then I read the following words by Nikola Tesla:

“A large capacity and small self-inductance is the poorest kind of circuit which can be constructed; it gives a very small resonant effect.”1

And:

“The higher the tension of the generator, the smaller need be the capacity of the condensers, and for this reason, principally, it is of advantage to employ a generator of very high tension.” 2

In other words, a small capacity and large inductance is preferable, and the higher the voltage of an NST, the higher the inductance, since more turns of wire are used. So in the end, a 15kV transformer should actually achieve even better results than a 10kV one. And indeed, it worked like a charm!

Spark gap upgrade

While my new 15kV NST produced beautiful sparks through my simple spark gap, I was not getting the same results Tesla described:

“When a large induction coil is employed it is easy to obtain nodes on the bar, which are rendered evident by the different degree of brilliancy of the lamps.” 3

My Hairpin did not show any nodes; it simply showed a maximum voltage, minimum current near the bottom, and maximum current, minimum voltage near the top of the bars, which is to be expected if you compare the Hairpin to a shorted transmission line.

Half wave standing wave pattern on a 1/4 wave shorted transmission line
Figure 3. Half wave standing wave pattern on a 1/4 wave shorted transmission line

However, I figured that if the spark hit the other side of the gap with enough force, it would shock the circuit into a higher order resonance, creating the enigmatic “nodes on the bar”. I took one good look at my current spark gap, consisting of two opposing bolts glued to the wooden base, and I knew that this was not a setup worthy to be called a true replication of Tesla’s work.

Super simple static spark gap
Figure 4. My super simple static spark gap

I knew Tesla had experimented with some advanced spark gap designs, and so I decided to perform a detailed literature analysis to figure out which type of spark gap Tesla used in his original Hairpin demonstrations. After much research, I came to the conclusion that it was most likely an air quenched spark gap, of which I then created a modern replication.

Tesla air quenched spark gap replication
Figure 5. My air quenched spark gap

This spark gap functions really well, as long as you keep the tips of the aluminum electrodes clean. I was able to push the spark gap distance to over 25mm, which significantly increased the rate of change of voltage in the circuit, and therefore led to more impressive impedance effects. However, still no nodes on the bar, and so I looked at the next possible culprit: the bars themselves!

Thicker bars

Thanks to my new NST and improved spark gap, my Hairpin was functioning quite well, but the “nodes on the bar” Tesla mentioned were still not showing up. By now I had a hunch that the skin effect, also referred to as the “thick wire effect”, might have something to do with the nodes, and so I looked into ways to maximize this phenomenon. It turns out that the ticker you make the bar, the larger its surface area becomes, and the more pronounced the skin effect will be. I then read the following words by Tesla:

“The thicker the copper bar… the better it is for the success of the experiments, as they appear more striking.” 3

I decided that it was time to make a trip to the hardware store for a thicker bar! My original bar was a 12mm copper pipe, which I upgraded to a 22mm copper pipe of about 220cm in total.

Shorter connections

While upgrading my Hairpin’s copper bar, I also decided to upgrade some of the wired connections in the circuit, since I was afraid that part of the wave generated by the spark gap was reflected back due to an impedance mismatch. To learn more about impedance mismatches, I strongly recommend you watch the following highly informative video:

I initially used the excess high voltage wires from 10kV Seletti NST to connect each component. However, these wires were not rated for the 80kV surging through my circuit, and so I considered using multiple wires instead of a single wire for some of the connections. While using more wires lowers impedance, it is even more effective to do away with the wires completely, and so I connected my capacitors directly to the base of the bar, similar to the Karl Palsness setup.

Capacitor connection
Figure 6. Capacitor connection

Achieving resonance

While describing the Hairpin experiment during his 1893 lecture, Tesla mentioned that “electrical resonance… has to be always observed in carrying out these experiments.” 2. However, I did not really know what electrical resonance meant and how to achieve it in this circuit, so I sort of skipped over it. Then I started watching some YouTube videos of other experimenters who replicated the Hairpin circuit, and came across the highly informative circuit analysis below by Fred B.

In this video, Fred shows us that the Hairpin circuit can be simplified into an LC circuit, which is a very common type of circuit capable of generating oscillating currents when in resonance! 

Hairpin circuit simplified into a resonant LC circuit, energized by the primary of the transformer
Figure 7. Hairpin circuit simplified into a resonant LC circuit, energized by the secondary of the transformer

Resonance occurs at a specific wave frequency, where the inductive reactance of an inductor becomes equal in value to the capacitive reactance of a capacitor, resulting in nearly zero impedance 3.

Pfew!! That’s a lot of terminology being thrown around… just remember that when a circuit is resonating, the current oscillates between the inductor and the capacitor, as explained in the video below.

So to establish resonance in a circuit, there are three essential components to take into account:

  1. Inductance (L)
  2. Capacitance (C)
  3. Frequency (F)

This is captured in the formula for the resonant frequency:

resonant \thinspace frequency \thinspace in \thinspace hertz = 1/2\pi \sqrt{inductance \thinspace in \thinspace henries \times capacitance \thinspace in \thinspace farads}

Now, since we are using an off-the-shelf neon sign transformer which runs off of mains power, both the frequency and the inductance of our circuit are unchangeable. Therefore, we will have to find the correct capacitor value that will resonate with the inductance of our coil, at the mains frequency of 50 or 60Hz, depending on where on this beautiful planet you live. This proved to be much harder than I had envisioned…

Finding the ideal capacitor value

Unfortunately, Tesla himself did not specify the specific capacitance values he used in his Hairpin circuit, but in figure 2 we can spot two “six-pack” Leyden Jar capacitors, and from the always trusty Wikipedia we learn that “a typical Leyden jar of one pint size has a capacitance of about 1 nF”, which is equal to 1000pF, while Tesla himself uses 0.003mfd, or 3000pF, as mentioned in his Colorado Springs Notes calculations4.

This suggests that one six-pack of parallel connected Leyden Jars could yield a capacitance of up to 18,000pF. Two of these arrays connected in series, like in the Hairpin circuit, would result in a total series capacitance of 9000pF, which is a lot more than the 17.7pF Lecher used in his circuit, and also way more than the 1000pF my initial UHV-9A caps yielded. The same article also mentions the energy stored in a Leyden Jar “may be as high as 35,000 volts.” If we again place two of these arrays in series, the combined voltage rating of the capacitors could be an impressive 70kV, again, much more than the 24kV Lecher discharged. This makes sense, because while Lecher merely studied resonance effects and therefore did not need as much power, Tesla tried to achieve the highest rate of change possible in his circuit to maximize impedance effects.

Since I had not much to go on, I simply used the same capacitors Karl Palsness used in the first version of my Hairpin replication, which were two UHV-9A caps rated at 40kV 2000pF, without having any clue as to why he used these particular values. Since these two capacitors are placed in series in the Hairpin circuit, the effective total capacitance is 1000pF. So is this the capacitance required to resonate with my 15kV 50Hz NST?

According to the Fred B video discussed earlier, a 15kV 60Hz NST requires ~1.8nF, or 1800pF, to achieve resonance. This was almost twice the amount of capacitance my two caps were providing! However it is not completely clear from the video how he arrived at this figure, and my NST runs at 50Hz instead of 60Hz, which is why I decided to measure the inductance of my NST, so I could calculate the ideal capacitor value myself.

I tried three different ways to measure the inductance of the NST’s secondary coil, but despite numerous attempts, I got such wildly different results that I could not rely on their accuracy. I then bought an LCR meter, but the inductance of my NST appeared to fall outside of the range of the meter, resulting in overload errors on the display.

Finally I thought, why not use one of the available Tesla Coil design calculators out there, since they also include calculations for ideal capacitor size. Below you find the calculators I used and the results:

Very interesting results, and all way higher than the 1000pF Karl Palsness used and the 1800pF Fred B suggested in his video, even when we take into account that they run their circuits at 60Hz instead of the 50Hz NST I used in these calculations. But why does TeslaMap give us a value that is so much higher than the other two calculators?

This is because the value TeslaMap returns is a so called Larger Than Resonant (LTR) capacitance, which is explained as follows by Kevin Wilson from TeslaCoilDesign.com:

“A resonant sized cap can cause a condition known as resonant rise which causes voltages in the primary circuit to increase far above normal levels. These high voltages can easily damage a NST, so NSTs should only be used with Larger Than Resonant (LTR) primary capacitors. To minimize the risk of a resonant condition in the primary circuit I use a MMC at 1.618 times the resonate size. The ratio of 1:1.618 is known as pi or the golden ratio. Any two numbers in this ratio will have the fewest common multiples which will result in virtually no chance of resonance. ” 5

Wow, “virtually no chance of resonance” is not what we are aiming for here! Of course he has a point, because resonant rise is definitely a real thing, and can result in hundreds of kilovolts running through your circuit, even though your input is “only” 15kV 6. However, the spark gap essentially acts as a current limiting device in the Hairpin circuit, protecting your capacitors from overvoltage, as long as you don’t make the spark gap too wide.

Still, at these enormous pressures, there is always a risk of damaging your NST and capacitors. But if you’re aiming to replicate Tesla’s original experiments, and Tesla says that “electrical resonance… has to be always observed”, it doesn’t make any sense to me to pick a capacitor size “which will result in virtually no chance of resonance”! And I will mention here again what Tesla said about using a large capacitance:

“A large capacity and small self-inductance is the poorest kind of circuit which can be constructed; it gives a very small resonant effect.” 7

Since the LTR size is 1.618 times the actual capacitance required for resonance, this means TeslaMap calculated 10300pF / 1.618 = 6388pF to be the ideal size, which is exactly in between the results of the other two calculators, and so I assumed that this was a good value to aim for.

Finding the ideal capacitor

Now that I knew what value to look for, the next challenge was to find and procure two capacitors with (approximately) this value when placed in series, which could also withstand the extreme voltages present in the circuit. You essentially have three options:

  1. Purchase two big and expensive capacitors
  2. Assemble a Multi-Mini Capacitor (MMC)
  3. Build your own capacitors from scratch (e.g. Leyden Jars or variable capacitors)

MMC capacitor bank, source: hvtesla.com
Figure 8. MMC capacitor bank

A MMC consists of several high voltage capacitors connected in series and parallel to achieve the desired capacitance and voltage rating, and is very popular under Tesla Coilers. TeslaMap has a nice tool to help you create one. However, it seemed like an awful lot of work to create these, and while MMC’s are known to be cheaper than purchasing a single big capacitor, two MMC’s with the capacitance and voltage rating I was looking for would cost me well over $200!

For these reasons I decided to settle for a cheaper and much simpler approach: purchasing two 40kV 10000pF capacitors. This yielded a series capacitance of 5000pF, which is a significant improvement over the 1000pF I was using at the time, and came close enough to the 6300pF we were aiming for to see if it had any positive effects on the results of the experiment. Not ideal, but at least this Less Than Resonant capacitance provided my caps and NST with some extra protection from damage due to voltage spikes caused by extreme resonant rise effects, while heeding Tesla’s advice to use a capacitor that is smaller rather than larger.

However, I did not get to perform many experiments with these brand new caps, because one caught fire after just 10 seconds of operation… Guess polystyrene film capacitors are just not up to the job.

Capacitor burned through after 4 seconds of operation
Figure 9. Blurry image of exploded capacitor

During that brief instant of operation, I noticed that the sparks in my gap were a lot “fatter” when using this larger capacitance (see video below), implying more current was being passed. I do not know, though, if this is preferable, since it appears that the goal is to maximize the time rate of change of voltage, and not necessarily of current. I could be wrong, and more testing is required to confirm this suspicion.

So while I am still unable to tell you what the perfect capacitor value is for a 15kV NST, my capacitor fund was empty after the explosion of my higher value ones, and so I was forced to switch back to using my original UHV-9A capacitors. Luckily, these capacitors perform very well, and easily achieve resonance in the circuit, although an ideal capacitor might offer more power throughput.

Replicating Tesla’s experiments

Now that almost every part of my Hairpin circuit was upgraded, I felt ready to attempt a replication of Tesla’s original experiments as described in his Philadelphia lecture.

Nikola Tesla hairpin circuit stout copper bars 1893 lecture
Figure 10. Tesla Hairpin experiment from his Philadelphia lecture

“The bars B and B1 were joined at the top by a low-voltage lamp l3 a little lower was placed by means of clamps C C, a 50-volt lamp l2; and still lower another 100-volt lamp l1; and finally, at a certain distance below the latter lamp, an exhausted tube T. By carefully determining the positions of these devices it was found practicable to maintain them all at their proper illuminating power. Yet they were all connected in multiple arc to the two stout copper bars and required widely different pressures. This experiment requires of course some time for adjustment but is quite easily performed.”2

So in this experiment, Tesla used four different incandescent light bulbs:

  1. “Low-voltage lamp” (l3)
  2. 50-volt lamp (l2)
  3. 100-volt lamp (l1)
  4. Exhausted tube (T)

It was not easy to procure these bulbs, since they have an unusual voltage rating, and because incandescent bulbs are no longer sold in Europe. However, the internet is an amazing place, and I was able to purchase the following bulbs to run this experiment with (same order as listed above):

  1. 12V, 10W car bulb
  2. 50-volt, 40W incandescent bulb
  3. 110-volt, 40W incandescent bulb
  4. 8W fluorescent tube

I connected the bulbs to the bar using a lamp fitting wired to two car battery charging clamps, which made them easy to move up and down the bar. When I fired up the circuit, the bulbs lit up, and after some careful adjustment I was able to make all four lights light up at full brightness! Success!!

Experimental results

Below you find a video with all the experiments I ran, including Tesla’s original experiments, as well as me touching the bars, lighting a bulb underwater, and single wire energy transmission.

Besides the experiments in the video, I have some other findings to share. For example, it is preferable to use high-wattage bulbs. So if you have the choice between a 110v 25w, or 110v 40w bulb, go for the 40w one, because it will work better in this circuit. Initially I (naively) thought: “40w requires more power than 25w, so it will be easier to light the 25w bulb.” However, a lower wattage only means that the resistance of the filament is higher, letting less current through, and thus resulting in a lower wattage for the same voltage rating. Higher wattage equals lower resistance, and this has worked better in my experiments.

For a successful result, it is also crucial that you adhere to the order Tesla uses for his lamps, so the lower voltage lamp at the top, and the highest voltage lamp at the bottom. If you change the order around, not all lamps will light up.

It is possible to light a fluorescent tube by simply holding it near the bars, or with a single thin wire connected near the capacitor end of the bar. If you move the tube over the bar from the bottom to the top, you notice that it lights up brightly near the capacitors, and turns off near the top. This is because, when the short bar is connected at the top, the Hairpin functions as a quarter wave shorted transmission line, resulting in a half wave standing wave pattern on the bar. This means voltage is maximum near the capacitors, and minimum near the top, while current is minimum near the capacitors, and maximum near the top, due to voltage and current being out of phase with each other.

In other words, we’re dealing with a single node. The “nodes on the bar” Tesla described in his lectures are possibly higher-order standing wave patterns. To achieve this higher-order resonance, I might need to use an even more powerful NST, since Tesla said:

“When a large induction coil is employed it is easy to obtain nodes on the bar.” 3

For this reason, I was very curious to know the frequency of the waves in my Hairpin. I used a simple frequency counter, which showed a frequency between 45 and 60 kHz.

Frequency counter result
Figure 11. Frequency counter result

I also measured the inductance of my copper bars with an LCR meter, which turned out to be 182.23uH. Since I used 1000pF total series capacitance, the self-resonant frequency equals:

    \[\frac{10^6}{2\pi\sqrt{182.23uH \times 1000pF}} = 372.8kHz\]

This is a lot higher than the frequency measured by my frequency counter. Of course, the larger you make the capacitance, the lower becomes the self-resonant frequency, possibly making it easier to push the bars into a harmonic resonance. For example, using 6300pF capacitance lowers the resonant frequency to just 148kHz. This is worth exploring further.

Besides the frequency, I was curious what the wave actually looked like. However, I was unable to find a good way to connect an oscilloscope to an 80kV circuit without frying it, which is why I simply placed a scope probe close to the bar and fired up the circuit, which resulted in the following image:

Hairpin oscilloscope result shows 50Hz input wave with superimposed high-frequency wave
Figure 12. Hairpin oscilloscope result shows 50Hz input wave with high-frequency wave superimposed upon it

You can clearly see the 50Hz input current, with a high frequency wave superimposed upon it. This is exactly what Tesla described when he discussed using spark gaps to achieve high frequency currents:

“Most generally there is an oscillation superimposed upon the fundamental vibration of the current.” 2

Those were some of the notable observations I was able to make while testing this circuit.

Parts list

In case you wish to replicate my setup, here are the parts I used, with links to where I purchased them:

Concluding remarks

For the past year I have been working towards publishing this article, so I am stoked to finally be able to make it public. I hope that this article, together with my previous foundational articles, will allow you to replicate Tesla’s Hairpin experiments and save you a lot of time, money, and frustration in the process. My research will now focus on the theory and application of the Tesla Coil, and ultimately of the Tesla Magnifying Transmitter. Exciting stuff ahead!

Impedance, the Skin Effect, and how they apply to Nikola Tesla

Impedance, the Skin Effect, and their Implications in High Frequency Circuits

Many of the famous experiments Nikola Tesla performed involved high frequency alternating- or impulse currents. At these high frequencies, something interesting happens: these rapidly vibrating currents pass with great difficulty through a seemingly low resistance conductor. This effect is caused by impedance, or the opposition of a conductor to the flow of alternating current. This article explains impedance in detail, since it plays a crucial role in understanding high frequency circuits, and because the subject has more layers of complexity to it that one might expect.

Let’s start by defining some key terms:

Resistance R: friction against DC

Reactance X: inertia against AC

Impedance Z: combination of resistance and reactance

Of course these short definitions don’t tell you too much, but it does show you that these three concepts are intertwined, and so we will structure the rest of our exploration of impedance around them, starting with the easiest one: resistance.

Resistance

Most people are familiar with resistance, which has the symbol R, is measured in ohm Ω, and is a way to state how difficult it is for a direct current to pass through a conductor. For example, copper has a very low resistance, so you don’t need a lot of pressure (voltage) to push a current through it, whereas lead, which is conductive, has about 12 times more resistance, and therefore requires 12 times more voltage to push the same amount of current through it.

This relation between resistance, voltage, and current is expressed in the formula for resistance:

resistance = \frac {voltage}{current}

Besides the type of material that is being used, the shape of the conductor also has a large influence on resistance. For example, a thin, long wire has a higher resistance than a thick, short wire, just like it is harder to push water through a thin, long straw compared to a short, thick pipe.

It is very important to reiterate that resistance applies to DC currents only, since the opposition against alternating currents is called reactance, which we will cover next.

Reactance

I just mentioned reactance is inertia against AC currents, but more precisely, it is the opposition of a circuit element to a change in voltage, and since AC changes its voltage constantly, reactance mainly applies to AC.

Changing currents, especially of high frequency, have a significant effect both on capacitors, as well as on inductors, so there are two parts to this puzzle:

  1. Capacitive reactance
  2. Inductive reactance

We will discuss both of these in detail, since each produces unique effects that are crucial in understanding some of Nikola Tesla’s experimental results.

Capacitive reactance

When you apply a DC current to a capacitor, the capacitor will simply charge until it reaches the level of the supply voltage. In such a case there is no current at all flowing “through” the capacitor. The flow of current ends on one plate of the capacitor, never reaching the other side. However, when a high frequency current is applied, things change dramatically, as mentioned by Tesla:

“Another equally remarkable feature of high frequency impulses was found in the facility with which they are transmitted through condensers [capacitors], moderate electromotive forces and very small capacities being required to enable currents of considerable volume to pass.” 1

The reason high frequency currents pass through a capacitor with such ease, is because of something called capacitive reactance, which describes the opposition of a capacitor to a change in voltage. The amount of current passed through a capacitor is related to the capacitance and the rate of voltage change, according to the following formula:

current\thinspace through\thinspace capacitor = capacitance\thinspace in\thinspace farads \times \frac {change \thinspace in\thinspace voltage}{change\thinspace in\thinspace time}

Since voltage does not change for a steady DC current, apart from when the current is first switched on, the current through the capacitor equals zero. However, as frequency increases, the rate of change of voltage over time increases, letting more current pass the higher the rate of change.

Some feel it is incorrect to say that currents pass through a capacitor, since electrons do not actually move from plate to plate. However, when I read up on what it is then that causes a current to appear on the other side of the capacitor when high frequency currents are applied, wildly different explanations were offered.

The explanation that made the most intuitive sense to me, was that one could view the dielectric between the capacitor plates as a flexible membrane, that, when hit with a large pressure, can oscillate. This, then, would not actually let any current through, but it would apply pressure to the other side of the capacitor by pushing into it and then retreating again, setting up a wave. This would also explain why a DC current does not create a current on the other side of the capacitor, since a steady pressure does not make the membrane oscillate.

Oscillating membrane
Figure 1. Oscillating membrane

Not sure if this explanation is wholly accurate of what actually happens, but it gives us a decent mental model to understand the behavior of capacitive reactance.

The formula for capacitive reactance itself is:

capacitive \thinspace reactance \thinspace in \thinspace ohms = \frac {1}{2\pi \times frequency \thinspace in \thinspace hertz  \times capacitance \thinspace in \thinspace farads}

If you fill in 0Hz in the above formula, which describes a DC current, capacitive reactance approaches infinity, therefore blocking DC. However, if you fill in higher and higher frequencies, capacitive reactance starts to approach zero, therefore acting as a short circuit, letting the alternating current pass.

High pass filters

In audio engineering, a high-pass filter is a circuit which blocks low frequency signals from the waveform, and only lets high frequency signals through. As you might have guessed, high pass filters work by making use of the effects of capacitive reactance. Only above a certain frequency, called the cut-off frequency, the reactance of the capacitor in the circuit becomes low enough for a signal to pass.

This cut-off frequency can be calculated as follows:

cut-off \thinspace frequency \thinspace in \thinspace hz = \frac {1} { 2\pi \times resistance \thinspace in \thinspace ohms \times capacitance \thinspace in \thinspace farads}

In this sense, we could say that the capacitors in a Tesla Hairpin circuit act as high pass filters, blocking the 50 or 60Hz input signal coming from the transformer, allowing the capacitors to charge, but letting the high frequency pulses from the spark gap through with ease.

Frequency vs rate of change

So far I’ve used the terms “frequency” and “rate of change” interchangeably, but there is in fact a subtle distinction that should be made between the two, which becomes clear when Tesla describes his Hairpin circuit:

“These results, as I have pointed out previously, should not be considered to be due exactly to frequency but rather to the time rate of change which may be great, even with low frequencies.” 2

We already saw before that the “time rate of change” is calculated by:

\frac {change \thinspace in \thinspace voltage}{change \thinspace in \thinspace time}

For example, if we assume we have a 10kV, 50Hz power supply, then each cycle takes 0.02 seconds (1 second / 50Hz). The rate of change is then 500kV/s (10kV / 0.02). Now, this calculation assumes we’re working with a sine wave, but if we instead disruptively discharge a condenser 50 times per second, where each discharge only takes 0.01 seconds, so half the time of one sine wave oscillation, the rate of change increases from 500kV/s to 1000kV/s, while the frequency is still 50Hz!

We can also achieve a 1000kV/s rate of change with a sine wave, but then we either have to double the voltage at 50Hz, or double the frequency to 100Hz, using the original 10kV. These calculations clearly show that, yes, a higher frequency leads to a higher rate of change, but that by using rapid discharges we can achieve a “time rate of change which may be great, even with low frequencies.” With discharges, frequency is the time between pulses, while the rate of change is determined by the duration of a single pulse.

This also has implications for the capacitive reactance formula mentioned before, which contained frequency in Hz as one of its denominators. This formula works as long as we’re dealing with sine waves, but for disruptive discharges we have to replace 2\pi \times frequency with \frac {2\pi}{duration \thinspace of \thinspace discharge}, also known as angular velocity. This results in the following adjusted formula:

capacitive \thinspace reactance \thinspace in \thinspace ohms = \frac {1}{\frac {2\pi}{duration\thinspace of\thinspace discharge\thinspace in\thinspace secs} \times capacitance\thinspace in\thinspace farads}

We will see a similar theme when we describe the next component of reactance: inductive reactance.

As you can probably tell, I have a strong aversion to the traditional notation of mathematical formulas, especially variable names, since they trade off understandability for compactness, making them completely unreadable for the uninitiated. One is expected to know what a random Greek letter stands for, and also the unit used is often only implied (are we dealing with Hz or kHz, ohms or milliohms?), or, if one is lucky, the unit can be found in the text near the formula.

I develop software and so I work with variables all the time. HOWEVER, coding conventions state that one should “avoid ambiguous and small [variable] names which are hard to understand. Names should be descriptive such that it should tell what it is for” 3.  This is the reason why I use more verbose variables in my formulas. They are far from perfect as well, but at least it is clear what each variable stands for.

Inductive reactance

Where capacitors let more current through the higher the frequency, conductors and inductors behave in exactly the opposite way, providing more opposition to current flowing as frequency and/or inductance increase. The reduction of current flow in a conductor due to induction is called inductive reactance 4.

So why does a conductor oppose the flow of AC current at all? The reason can be found in Lenz’s law, which states that “an induced current has a direction such that its magnetic field opposes the change in magnetic field that induced the current.” 4 In other words, when a current is passed through a conductor, a magnetic field is created, which in turn induces a current in the same conductor (self-induction) in the exact opposite direction, a so-called “back emf”, thereby opposing the initial current that generated the magnetic field in the first place.

Since a changing magnetic field induces a voltage that is directly proportional to the rate of change of the current producing it, this means that when the rate of change is doubled, the self-induced back emf is doubled, reducing the flow of current through the conductor accordingly. This is captured in the following formula for inductive reactance:

inductive \thinspace reactance = 2\pi \times frequency \thinspace in \thinspace hertz \times inductance \thinspace in \thinspace henrys

As you can see from the formula, if frequency or inductance is increased, so is inductive reactance. Similar to the capacitive reactance formulas, the above formula can also be rewritten to apply better to pulse currents, like so:

inductive \thinspace reactance = \frac {2\pi}{duration \thinspace of \thinspace discharge \thinspace in \thinspace secs} \times inductance \thinspace in \thinspace henrys

So the shorter the discharge time, the stronger the effect of inductive reactance.

Tesla once mentioned:

“One of the prominent characteristics of high frequency or, to be more general, of rapidly varying currents, is that they pass with difficulty through stout conductors of high self-induction.” 1

We already learned that high frequency currents have a high rate of change, and therefore set up a strong back emf, causing the current to “pass with great difficulty” through a conductor.

Tesla also mentions that this effect is present in “stout conductors of high self-induction”, and on another occasion he said that “the thicker the copper bar… the better it is for the success of the [impedance] experiments” 2. Why? Because the thicker the bar, the larger the surface area, the greater the self-inductance 3, and the more powerful the effect of inductive reactance, or inertia to AC.

The skin effect

 

Skin effect visualization
Figure 2. Cross-section of a wire showing the Skin Effect, where the orange stands for the amount of current flow

We’ve seen how circuits behave differently to DC versus high frequency AC. One of the most curious effects is the so-called “skin effect”, which causes alternating currents to flow closer to the surface, rather than through the centre of a conductor, effectively increasing the resistance, since less volume is available for the current to flow through. In fact:

“For sufficiently high frequencies… the conductor might as well have a hollow core, as the central region of the conductor carries essentially none of the current.” 4

A 50kW radio transmitter, using hollow copper tubes coated with silver, to have great conductivity at the “skin”, where most of the current will be flowing.
Figure 3. A 50kW radio transmitter, using hollow copper tubes coated with silver, to have great conductivity at the “skin”, where most of the current will be flowing.

As the image above shows, the skin effect is a well known phenomena which has practical implications. This is also why stranded Litz wire is often used to transmit radio frequency AC, since it maximizes surface area of the conductor(s) and therefore minimizes losses due to the skin effect.

The first to mention of the skin effect, sometimes called the “thick wire effect”, was mathematical genius Oliver Heaviside around 1883. Heaviside also championed the idea of induction, and is the one who transformed Maxwell’s original quaternion equations into their vector form still used today by engineers around the world, so he was a real heaviweight (pun intended). To understand Heaviside’s explanation of the skin effect, we must, however, first understand how he, like John Henry Poynting, believed that all energy propagation along the direction of the wire takes place outside of the wire instead of through it:

“[Energy transfer] takes place in the vicinity of the wire, very nearly parallel to it, with a slight slope towards the wire… It causes the convergence of energy into the wire.” 4

What Heaviside is saying is that the energy is induced into the wire from the dielectric surrounding it. This leads him to the following explanations of the skin effect:

“Since on starting a current the energy reaches the wire from the medium without, it may be expected that the electric current in the wire is first set up in the outer part, and takes time to penetrate to the middle. This I have verified by investigating special cases. Increase the conductivity of a wire enormously, still keeping it finite, however. Let it, for instance, take minutes to set up current at the axis. Thus, ordinary rapid signalling ‘through the wire’ would be accomplished by a surface current only, penetrating but a small depth.” 4

And:

“Having been, so far as I know, the first to correctly describe the way the current rises in a wire, viz, by diffusion from its boundary, and the consequent approximation, under certain circumstances, to mere surface conduction.” 4

So if we accept that energy is induced into a conductor from without, then Heaviside’s explanation makes sense: the energy reaches the outer skin of the conductor first, and does not have the time to penetrate deeply into it when oscillating at high frequencies.

Now let’s see what a modern textbook tells us about the skin effect:

“Skin effect: The tendency of alternating current (ac) to flow near the surface of a conductor, thereby (a) restricting the current to a small part of the total cross-sectional area and (b) increasing the resistance to the flow of current.” 5

A fair definition. Now what can the book tell us about the cause of the skin effect?

“Skin effect is caused by the inductance of the conductor, which causes an increase in the inductive reactance especially at high frequencies. The inner filaments of the conductor experience an inductive reactance with all the surrounding filaments, their reactance thus being higher than the outer filaments. Thus, the current tends toward the lower reactance filaments, i.e. the outside filaments. At high frequencies, the circumference is a better measure of resistance than the cross-sectional area. The depth of penetration of current at thigh frequencies can be very small compared to the diameter. Skin effect must be taken into account when designing antennas and metallic waveguides.” 5

So instead of Heaviside saying the current starts at the outside of the wire and does not have time to reach the centre, this explanation says that the skin effect is caused by a stronger inductive reactance at the centre of the conductor compared to the outside of the conductor, effectively pushing the current towards “the path of least reactance”, which is near the surface.

Disagreement on the cause of the Skin Effect
Figure 4. Disagreement on the cause of the Skin Effect

On Wikipedia I found yet another explanation, which highlighted eddy currents as the cause:

“The skin effect is due to opposing eddy currents induced by the changing magnetic field resulting from the alternating current.”

We know how to perform accurate calculations with electricity, but still don’t have a clue what electricity actually “is”. In the same vein, we can calculate the skin depth at any given frequency, but don’t seem to agree on what causes the phenomenon in the first place. This twilight zone seems to be the unfortunate fate of science in general, and physics in particular. While all explanations we just discussed of what causes the skin effect seem plausible, “the mere absence of nonsense may not be sufficient to make something true”, as Nassim Taleb once aptly said.

Thus, we are left with uncertainty about the exact cause of the skin effect, but at least everyone agrees that it increases resistance to current flow significantly at high frequencies. This is why I believe that the skin effect is a major cause for the unique Impedance Phenomena Nikola Tesla showcased in his Hairpin experiments.

Impedance

Well, that was quite the journey to finally arrive at the overarching phenomenon of impedance, another term coined by Oliver Heaviside 6. We already learned that when applying direct current (DC) to a circuit, there is no distinction between impedance and resistance. However, when an alternating current (AC) is applied, reactance leads to an increase in opposition to current flow. I tried to capture the relationships of these concepts in the image below.

Impedance infographic
Figure 5. Impedance infographic

The formula for impedance provides another way to show these relationships:

impedance = \sqrt{resistance \thinspace in \thinspace ohms^2 + (inductive \thinspace reactance \thinspace in \thinspace ohms - capacitive \thinspace reactance \thinspace in \thinspace ohms)^2}

It is important to mention that for a series resonant circuit, like the Tesla Hairpin circuit, impedance is at its minimum and current at its maximum at the resonant frequency. Conversely, for a parallel resonant circuit, impedance is at its maximum and current at its minimum at the resonant frequency:

“The resonance of a series RLC circuit occurs when the inductive and capacitive reactances are equal in magnitude but cancel each other because they are 180 degrees apart in phase.” 7

To wrap things up, I would like to share with you an old but must-see video demonstration, titled Similarities of Wave Behavior. In this video, the presenter uses a physical wave device to show, amongst other highly interesting things, the way (electric) waves reflect when they encounter a conductor with a different impedance:

Concluding words

We covered a lot of ground in this article, but I feel that a detailed understanding of impedance is a necessary prerequisite to understanding the behavior of high frequency circuits. It seems that we have now covered enough fundamental subject matter to take an informed shot at properly replicating Nikola Tesla’s Hairpin circuit and its curious effects. The next blog post will describe my own Hairpin replication, including a parts list, experimental results, and a detailed circuit analysis, so everyone will be able to follow along and duplicate the results. Feel free to leave some honest feedback in the comments below!

Nikola Tesla hairpin circuit stout copper bars 1893 lecture

A Brief History of the Tesla Hairpin Circuit / Stout Copper Bars

In his autobiography, Nikola Tesla called the Magnifying Transmitter (TMT) his “best invention” 1, but it is also one of his most complex and misunderstood inventions. I decided that the only way to truly understand the TMT, was to retrace all the steps that led up to this invention, and the Hairpin circuit, which is covered in detail in this post, seems to be at the root of it all. This seemingly simple circuit contained more surprises and subtle complexities than I anticipated, so let’s dive in and see what we can learn from the inventor himself!

A journey back in time

Before we discuss how to replicate this unique device, it is important to trace its origin. Tesla first described the Hairpin circuit during his 1891 lecture in New York:

Nikola Tesla hairpin stout copper bars circuit from his 1891 lecture
Figure 1. First mention of Hairpin circuit by Tesla during his 1891 lecture

“In operating devices on the above plan I have observed curious phenomena of impedance which are of interest. For instance if a thick copper bar be bent, as indicated in Fig. [1], and shunted by ordinary incandescent lamps, then, by passing the discharge between the knobs, the lamps may be brought to incandescence although they are short-circuited. When a large induction coil is employed it is easy to obtain nodes on the bar, which are rendered evident by the different degree of brilliancy of the lamps, as shown roughly in Fig. [1]. The nodes are never clearly defined, but they are simply maxima and minima of potentials along the bar. This is probably due to the irregularity of the arc between the knobs.

In general when the above-described plan of conversion from high to low tension is used, the behavior of the disruptive discharge may be closely studied. The nodes may also be investigated by means of an ordinary Cardew voltmeter which should be well insulated. Geissler tubes may also be lighted across the points of the bent bar; in this case, of course, it is better to employ smaller capacities. I have found it practicable to light up in this manner a lamp, and even a Geissler tube, shunted by a short, heavy block of metal, and this result seems at first very curious. In fact, the thicker the copper bar in Fig. [1], the better it is for the success of the experiments, as they appear more striking. When lamps with long slender filaments are used it will be often noted that the filaments are from time to time violently vibrated, the vibration being smallest at the nodal points. This vibration seems to be due to an electrostatic action between the filament and the glass of the bulb.” 2

As you can see from figure 1 and Tesla’s description, this device mainly consists of thick copper bars, hooked up to a high voltage power source, which charges capacitors until they reach a high enough voltage to make them discharge disruptively through a spark gap. Looks like a rather simple circuit, right? Well, there is more to it than meets the eye, and the effects of “nodes on the bar”, hinting at electrical standing waves, and lighting lamps while they’re short circuited, are curious enough results to make this device worth investigating.

Nikola Tesla Chicago World Fair 1893 Hairpin Circuit
Figure 2. A picture taken at the Chicago World Fair of 1893, showing a Hairpin with bulbs connected to it on the right, and “six-pack” Leyden Jar capacitors on the table in the back

The next time Tesla mentioned this circuit was during a lecture two years later in Philadelphia, showing a slightly different setup:

Nikola Tesla hairpin circuit stout copper bars 1893 lecture
Figure 3. Tesla “stout copper bars” circuit from his 1893 lecture

“Referring to Fig. [3]a, B and B1 are very stout copper bars connected at their lower ends to plates C and C1, respectively, of a condenser, the opposite plates of the latter being connected to the terminals of the secondary S of a high-tension transformer, the primary P of which is supplied with alternating currents from an ordinary low-frequency dynamo G or distribution circuit. The condenser discharges through an adjustable gap d d as usual. By establishing a rapid vibration it was found quite easy to perform the following curious experiment. The bars B and B1 were joined at the top by a low-voltage lamp l3 a little lower was placed by means of clamps C C, a 50-volt lamp l2; and still lower another 100-volt lamp l1; and finally, at a certain distance below the latter lamp, an exhausted tube T. By carefully determining the positions of these devices it was found practicable to maintain them all at their proper illuminating power. Yet they were all connected in multiple arc to the two stout copper bars and required widely different pressures. This experiment requires of course some time for adjustment but is quite easily performed.

In Figs. [3]b and [3]c, two other experiments are illustrated which, unlike the previous experiment, do not require very careful adjustments. In Fig. [3]b, two lamps, l1 and l2, the former a 100-volt and the latter a 50-volt are placed in certain positions as indicated, the 100-volt lamp being below the 50-volt lamp. When the arc is playing at d d and the sudden discharges are passed through the bars B B1, the 50-volt lamp will, as a rule, burn brightly, or at least this result is easily secured, while the 100-volt lamp will burn very low or remain quite dark, Fig. [3]b. Now the bars B B1 may be joined at the top by a thick cross bar B2 and it is quite easy to maintain the 100-volt lamp at full candle-power while the 50-volt lamp remains dark, Fig. [3]c. These results, as I have pointed out previously, should not be considered to be due exactly to frequency but rather to the time rate of change which may be great, even with low frequencies. A great many other results of the same kind, equally interesting, especially to those who are only used to manipulate steady currents, may be obtained and they afford precious clues in investigating the nature of electric currents.

In the preceding experiments I have already had occasion to show some light phenomena and it would now be proper to study these in particular; but to make this investigation more complete I think it necessary to make first a few remarks on the subject of electrical resonance which has to be always observed in carrying out these experiments.” 3

You may notice that this time, the capacitors and spark gap have switched place in the circuit compared to the 1891 version. Also, the top shunt bar is now detachable, allowing for more types of experiments to be performed. Tesla also goes into much more detail here explaining his experiments with this device, achieving fascinating results, like lighting several lamps of different voltage ratings at full brightness… while they’re short circuited!

One thing to note is that Nikola Tesla himself never used the term “Hairpin circuit”. In fact, he never really seems to have given this device a name at all, but only refers to it as “stout copper bars”. Wherever the name Hairpin originated, it’s catchy, a lot of people use it already to describe this device, and it is easier to write, which is why I use the name Hairpin in this article.

There is one other time Tesla mentioned the Hairpin circuit, in an 1898 article on the electro-therapeutic benefits of high frequency currents, and it is possibly the most interesting article out of all the ones mentioned here.

“One of the early observed and remarkable features of the high frequency currents, and one which was chiefly of interest to the physician, was their apparent harmlessness which made it possible to pass relatively great amounts of electrical energy through the body of a person without causing pain or serious discomfort… these currents would lend themselves particularly to electro-therapeutic uses.” 4

So the high frequency currents generated from the capacitor discharges were so harmless that they were actually passed through the bodies of real patients, without pain! This explains how experimenters like Karl Palsness, whose Hairpin replication we will discuss at length later on, are able to hold the copper bars while the spark gap is firing, and even light a lamp while its submerged in water and then touching the water, without receiving as much as a shock.

“Now, why is it that in a space in which such violent turmoil is going on living tissue remains uninjured?”, Tesla asks the reader. He continues:

“One might say the currents cannot pass because of the great self-induction offered by the large conducting mass. But this it cannot be, because a mass of metal offers a still higher self-induction and is heated just the same. One might argue the tissues offer too great a resistance. But this again cannot be the reason, for all evidence shows that the tissues conduct well enough, and besides, bodies of approximately the same resistance are raised to a high temperature. One might attribute the apparent harmlessness of the oscillations to the high specific heat of the tissue, but even a rough quantitative estimate from experiments with other bodies shows that this view is untenable. The only plausible explanation I have so far found is that the tissues are condensers. This only can account for the absence of injurious action.” 4

So while Tesla does not seem to have a conclusive explanation for the apparent harmlessness of his high frequency currents, it does help to hear his reasoning and insight on the matter, since I’ve heard many people say in forum posts that “it’s just RF”, suggesting that it is simply a characteristic of radio frequency currents to not injure the human body. However, do not try this at home, because there is also something called Electrosurgery, which is “the application of a high-frequency (radio frequency) alternating polarity, electrical current to biological tissue as a means to cut, coagulate, desiccate, or fulgurate tissue.” Not sure what those last three things are, but they sound awful! Be careful.

Also crucial to note is how Tesla never attributes his peculiar results to an exotic type of energy. There is no mention of scalar waves, longitudinal energy, cold electricity, or any of that stuff people love to throw around. He is simply talking about high voltage, high frequency currents.

So what does his electro-therapy device look like? Tesla actually shows us several different setups in the article, as shown in figure 4 below.

Tesla high frequency oscillators for electro-therapy hairpin circuit
Figure 4. Eight “modes of connection” for Tesla’s electro-therapeutic device

The circuits in figure 4 might be a bit much to take in at one time, so I would like to point your attention now to figure 4.3 specifically, which is in fact a circuit identical to the Hairpin! Let’s see what Tesla had to say about that particular setup..

“One of the prominent characteristics of high frequency or, to be more general, of rapidly varying currents, is that they pass with difficulty through stout conductors of high self-induction. So great is the obstruction which self-induction offers to their passage that it was found practicable, as shown in the early experiments to which reference has been made [The Hairpin from his lectures?], to maintain differences of potential of many thousands of volts between two points — not more than a few inches apart — of a thick copper bar of inappreciable resistance. This observation naturally suggested the disposition illustrated in Fig. [4.3]. The source of high frequency impulses is in this instance a familiar type of transformer which may be supplied from a generator G of ordinary direct or alternating currents. The transformer comprises a primary P, a secondary S, two condensers C C which are joined in series, a loop or coil of very thick wire L and a circuit interrupting device at break b. The currents are derived from the loop L by two contacts c c’, one or both of which are capable of displacement along the wire L. By varying the distance between these contacts, any difference of potential, from a few volts to many thousands, is readily obtained on the terminals or handles T T. This mode of using the currents is entirely safe and particularly convenient, but it requires a very uniform working of the break b employed for charging and discharging the condenser.” 4

So two movable contacts were connected to the conductors, the terminals of which which were then applied to the patient’s skin in an “entirely safe” way! Tesla does mention that the spark gap has to operate very consistently for this to work, or else the waves created on the conductors, and therefore the voltage applied to the patient’s skin, will start to vary. The fact that Tesla required a very uniform working of the spark gap to achieve his results, is what made me research Tesla’s spark gaps in detail, and led me to create a modern version of his air quenched spark gap.

Tesla also mentions another revolutionary effect he could achieve with this device: single wire energy transmission!

“Among the various noteworthy features of these currents there is one which lends itself especially to many valuable uses. It is the facility which they afford for conveying large amounts of electrical energy to a body entirely insulated in space. The practicability of this method of energy transmission, which is already receiving useful applications and promises to become of great importance in the near future, has helped to dispel the old notion assuming the necessity of a return circuit for the conveyance of electrical energy in any considerable amount.” 4

Wow… Tesla already called the need for a return wire an “old notion” in 1898, and still all our electronics require a return wire more than a hundred years later!!

This 1898 article is full of revelations and gives us valuable insight into completely new uses of the Hairpin circuit, but possibly the most interesting part of it is how Tesla shows several different setups of what he seems to view as the same device: some with just one loop of wire, like in figure 4.3, but many come with both a primary and a secondary, like figure 4.2 and 4.4. Yet, the most telling schematic of the bunch is shown in figure 4.5, about which Tesla had the following to say:

“The circuit connections as usually made are illustrated schematically in Fig. [4.5], which, with reference to the diagrams before shown, is self-explanatory. The condensers C C, connected in series, are preferably charged by a step-up transformer… The primary p, through which the high frequency discharges of the condensers are passed, consists of very few turns of cable of as low resistance as possible, and the secondary s, preferably at some distance from the primary to facilitate free oscillation, has one of its ends–that is the one which is nearer to the primary–connected to the ground, while the other end leads to an insulated terminal T, with which the body of the patient is connected. It is of importance in this case to establish synchronism between the oscillations in the primary and secondary circuits p and s respectively.” 4

This sounds an awful lot like a Tesla Coil, complete with a resonantly coupled primary and secondary, where the secondary has one end connected to ground and the other to an insulated terminal. And the most astonishing thing is that Tesla mentions this device in one breath with the Hairpin circuit from figure 4.3! The reason this is of such importance, is because it is like finding a transitional fossil, which describes how the Hairpin eventually evolved into the Tesla Coil.

This might be the reason why some people claim the Hairpin circuit is “just a single turn primary of a Tesla Coil”. Though this might seem like a valid point at first, the Hairpin was clearly used to experiment with electrical standing waves, hence the “nodes on the bar” 2, while standing waves are not required in a Tesla Coil primary, as well as impedance phenomena, which is also not the purpose of a Tesla Coil. So yes, the Hairpin definitely has things in common with a single turn Tesla Coil primary, but they have completely different use cases.

Lecher Lines

When reading forum posts and watching YouTube videos on the Hairpin circuit, there is always someone screaming in ALL CAPS that Tesla is a fraud, because he did not invent this circuit, Ernst Lecher did in 1888 when he invented the Lecher Line. Even though Tesla never actually claims to have invented this circuit, I decided to dig into Lecher’s original paper to see if these assertions had any merit, but when I found out the title was Eine Studie über elektrische Resonanzerscheinungen, I knew I would first have to brush up my German! I even looked into hiring a native speaker to perform the translation, but at 21 pages, that would have cost me a small fortune. Luckily I am Dutch, so German comes fairly naturally to me, and I have several German friends who could help me out with the tricky parts.

It took me a tremendous amount of time, but I finally managed to translate the entire paper (click here for the full translation), which contains a wealth of useful information, and really helps to get a better understanding of the Hairpin circuit. Let’s see how Lecher describes his setup “in its simplest form”:

Orignal Lecher Lines schematic
Figure 5. Lecher Lines schematic taken from the original 1890 article by Ernst Lecher

“A and A’ are square sheet metal plates with 40cm sides; they are connected by means of a 100 cm long wire segment, which is cut in the middle and at F two brass balls of 3 cm in diameter are added (in Fig. 1, only the cross-section of the square plates is drawn). The two brass balls are at a distance of 0,75 cm from each other and are connected using thin wires to the poles of a very strong inductor, whose coil has a length of 35 cm and a diameter of 18 cm; the inductor is fed by four powerful accumulators [batteries], and in some cases by a dynamo. A Foucault mercury interrupter serves as electric break. Across from the plates A and A’ are two plates B and B’ of identical size at a distance of around 4 cm. From these plates B, B’ run two wires against s and s’ and from there parallel until t and t’. The distance between the parallel wires (s to s’) is 10-50 cm; the length st (s’ t’) on the other hand should be at least 400 cm. The diameter of these parallel wires is here and for all experiments in this publication 1 mm. For this first experiment we assume the length [of the wire] to be about 600 cm (drawn too short in the figure ), and the distance of the parallel wires from each other 30 cm. At the end of the parallel wires (t and t’) a cord is connected to each, which extends the length of the wires by about 100 cm and allows for a gentle and comfortable tensioning thereof… Over the wire ends t and t’ I now lay an exhausted glas tube without electrodes g g’, ideally filled with nitrogen and a trace of turpentine vapor; this glass tube starts to light up due to the electrical vibrations in the wires.” 3

It is great that Lecher described his setup in such detail. The “Foucault mercury interrupter” mentioned by Lecher is not to be confused for the spark gap; its function was merely “to rapidly connect and disconnect a direct electric current to create the changing magnetic field needed for induction coils.” 4 In other words, it took the direct current from the batteries and turned it into a pulse current, which then powered the “very strong inductor”.

The metal plates A A’ and B B’ function as the two capacitors we also find in the Hairpin circuit, and because Lecher mentions their specific dimensions and distance from each other, we are even able to calculate their capacitance. Two plates of 40×40 cm, placed at a distance of 4 cm from each other, have a capacitance of 35.4 pF. Since they are placed in series in this circuit, given the short x x’ is present, the total series capacitance in Lecher’s circuit was around 17.7 pF. Lecher also mentions his spark gap was 0,75 cm wide, and since the dielectric strength of air at 25ºC and ordinary atmospheric pressure is 31.300V per cm 5, we can assume that Lecher discharged around 0,75 * 31.300 ≈ 23.500V through his spark gap. Fun facts.

Difference between Lecher Lines and Hairpin circuit

By comparing Lecher’s paper with the writings of Nikola Tesla, we learn that while the circuit diagrams of the Hairpin circuit and the Lecher Lines look similar, and Lecher also lit up lights with it, there are some significant differences. For starters, Lecher did not use “stout copper bars” like Tesla did, but instead used 1 mm wires. Lecher also mentions his wire was more than two times 600 cm, or more than 12 meters, long. Later in the paper he even uses 2 x 20 meter long wires! If we compare this to the Hairpin image in figure 2 at the beginning of this article, we see that Tesla’s bars were a lot shorter than that (looks like the bar is approximately 14 light bulb lengths long, which most definitely is shorter than 12 meter).

Besides, Tesla mentioned that “electromotive forces of many thousand volts are maintained between two points of a conducting bar or loop only a few inches long6, suggesting that his conductors did not need to be that long, possibly because Tesla was able to achieve higher frequencies, and therefore shorter wavelengths, by perfecting the condenser discharge process through the invention of advanced spark gap designs, whereas Lecher used a simple static gap with two brass balls as electrodes.

Finally, the main difference between the Lecher Lines and the Hairpin circuit — and this took me a long time to figure out — is in their purpose: Lecher studied resonance phenomena with his Lecher Lines, while Tesla studied impedance phenomena with his Hairpin circuit. Therefore, Lecher used an electrodeless exhausted tube, which did not have an electrical connection to his conductors, assuring the standing waves were not disturbed, but lit up due to the vibrations in the wires. Tesla, on the other hand, used several incandescent lamps of various voltage ratings, and did connect them electrically to his conductors, since he was showing how high-frequency currents “pass with difficulty through stout conductors”6, causing the current to prefer the resistive path of an incandescent lamp filament over the normally inappreciable resistance of the copper bars.

So did Lecher feel like he invented this circuit? Not really..

“This part of my arrangement is similar to that stated in the beautiful work of Hertz, and was also used in the experiments of Sarasin and De la Rive.”3

Lecher actually credits Hertz, Sarasin and De la Rive for a similar circuit, so the internet crusaders who are fighting to protect Lecher’s primacy and honor at every mention of the Hairpin circuit can hopefully calm down now.

Concluding remarks

In this article we learned that Tesla used his Hairpin circuit to display curious impedance phenomena, single wire energy transmission, apply apparently harmless currents to patients for medical purposes, and, finally, to “create pulsations through metal bars, or pipes, and test for harmonic frequencies and standing waves.”4, as one biographer put it.

We also learned that Tesla does not ascribe these effects to any exotic form of energy. He simply talks about high voltage, high frequency currents. It also became clear that the Hairpin eventually evolved into the Tesla Coil, but that the Hairpin cannot simply be seen as a single turn primary, since the use cases are totally different. The same goes for Lecher Lines, which look similar to the Hairpin in many respects, but differs in several crucial ways, mainly again in its use case.

The information in this article gives us a solid foundation in the journey to understand and eventually replicate the Hairpin circuit, according to Nikola Tesla’s own specifications. There is still one thing we have to cover in more detail before we start the replication and experimentation, one thing which plays a crucial role in understanding why the Hairpin works the way it does, and that is impedance, specifically the so-called “skin effect”. This innocuous sounding term has far reaching consequences for high frequency systems, and also has a surprisingly bumpy past. Click here to read all about impedance and the skin effect.

Orignal Lecher Lines schematic

Lecher Lines: A Translation of the Original Paper by Ernst Lecher

While reading up on Nikola Tesla‘s Hairpin circuit, I constantly came across people saying that Tesla’s circuit was identical to Lecher Lines, invented by the Austrian physicist Ernst Lecher around 1890, which was an apparatus used to measure the wavelength of high frequency electric waves by creating standing waves on two parallel wires, and then measuring the distance between the antinodes. However, apart from a Wikipedia article and some obscure blog posts, there was not a lot of information available on Lecher Lines, how to use them, and the values of the circuit components. That’s why I decided to look up the original Lecher Lines paper, written by its inventor, Ernst Lecher, titled  Eine Studie über electrische Resonanzerscheinungen 1.Read more…

Tesla air quenched spark gap replication

Tesla Air Quenched Spark Gap Replication

In a previous post I performed a detailed literature review on the various types of spark gaps Tesla employed in his experiments. My motivation for that research was that I am trying to replicate Tesla’s stout copper bars, or  ‘hairpin’, circuit, and I wanted to figure out which type of spark gap he was most likely using for that particular experiment. My conclusion, based on the research I performed, was that he most likely used an air quenched spark gap. In this article I show you my replication of Tesla’s air quenched spark gap design from his 1893 lecture with a modern twist, including a parts list and my laser cutter ready files.Read more…