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.
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.
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.
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!!
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.
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.
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!
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”.
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.
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.
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.
There are several famous pictures of Tesla holding a wirelessly illuminated lamp in its hand, like the one below.
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.
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…
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.
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
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:
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
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:
“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
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.
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:
Wireless light (room-scale)
Single wire energy transmission
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…