Nikola Tesla

Tesla Anti Theft protection

This is a simple Tesla Coil design. The neon sign transformer provides current to the capacitor which stores a charge. As the voltage and current reach their peak, an arc forms across the spark gaps which allows all the stored energy to transfer to the primary coil. The primary coil creates a magnetic field which is absorbed and stepped up by the secondary coil. The magnetic field in the primary then collapses and its energy is transferred back to the capacitor and the process repeats until resistance in the circuit depletes all the stored energy. This transfer of energy from the capacitor to the primary is called resonance and it's frequency is determined by the values of both the capacitor and the primary (inductor). For every arc, which occurs 120 times a second (one for every positive and negative sine wave) there are thousands of cycles of charging and discharging between the primary and capacitor, so not only does the Tesla coil step up the voltage, it also steps up the frequency as well. Tesla coils can operate in the range of 50,000 to 500,000 Hertz depending on how they are tuned.

The secret to creating the greatest output is in tuning. A person on a swing mimics a Tesla coil in operation. If you give someone a push they will swing back and forth until resistance due to friction causes them to stop. If you push them on every cycle the amplitude of the swinging will increase each time provided that each push is greater then friction which causes them to slow down. If you can time the arc in a Tesla coil to coincide with the waves in the resonant circuit, you will increase the output exponentially. This is done by adding or decreasing the number of turns in the primary, changing the value of the capacitor, or increasing the frequency of the neon sign transformer. In our classroom design, the easiest way was to use an alligator clip on the end of the wire to attach to the primary. Depending on where we attached the wire to the coil varied the size of the coil and therefore changed the tuning of the coil.

Tesla Coil Slideshow

Our First Coil

This was a group class project by the students in my 4th year apprenticeship class. Every year I gave Nikola Tesla a plug since I always found it unfair that the creator of every AC electric motor that we use today, plus all of the other inventions i.e. radio, radar, x-rays, blade-less turbines etc. went unnoticed while lesser inventors like Thomas Edison literally stole the spotlight. I was a little hesitant to build one since in the past it was difficult to find construction information, but it was the Internet to the rescue. After a lot of research and experimentation we came up with our final design. The primary coil was #8 copper ground wire wrapped around a plastic bucket, and the secondary was a six-inch PVC pipe with 1000 turns of #22 gauge wire. We used a neon sign transformer to feed the resonant circuit at 15,000 volts. I estimated the final voltage output at 750,000 volts at 50,000 Hertz.

In the photo you can see a student (right) holding a florescent lamp which is in no way connected to the circuit itself, but lighting because of the electricity flowing through the air, and another student (left) holding a copper rod drawing an arc from the antenna. Even though the charge was 750 kV, the shock was barely felt because the discharge was in the micro amps, and because the high frequency increased the "skin effect" which is the tendency for electrons to migrate closer to the surface of a conductor. The higher the frequency the greater the effect, so at 50,000 Hertz, most of the electrons were traveling over the surface of the person and not through him. All this knowledge still didn't comfort me when I was the first one to poke a rod next to the antenna.

Tesla's original concept was to build a large Coil to transmit electricity wirelessly though the air to receiving coils elsewhere across the earth. In Tesla's final design the Earth itself was the capacitor and the ionosphere was the return path for the current. All one needed was a receiving coil and you could have wireless power anywhere in the world you went. Cars wouldn't need batteries, your cordless drills would never need recharging, no more ugly transmission lines criss crossing the country, there was only one fly in the ointment: How do you charge people for the electricity. Tesla's dream of wireless transmission of power (and communications) ended when funding for the project was discontinued after the Wardencliff tower was almost completed.

Our first topload was a dryer hose placed on top of a board to hold it's shape. What looks like hair is sparks from the topload during a long exposure by the camera.

The Telsa coil needs a capacitor to store a charge and to form a resonant circuit with the primary coil in order to boost the frequency up (50,000 Hertz). After a failed attempt at using glass plates and aluminum foil, I discovered another "coiler" was using a salt water capacitor. The salt water, since it is conductive, acts like a plate in a capacitor, and the glass is the dielectric insulator between the two plates. One plate is in the bottle, and the other is the pool of saltwater outside the bottle. We used a copper pipe to bring the current to the capacitor. In later designs we used multiple smaller glass bottles because it increased the surface area of the capacitor thus making it larger. There are of course much more efficient designs, but we had limited time and money and it did serve it's purpose.

This shows the capacitor under operation. The light you see is spark discharge inside the bottle. This was probably not the most efficient operation since a lot of energy is being lost here, but it made an impressive display.

Antenna "Top load" made from two heavy duty pie tins and dryer hose with metallic tape over the surface. The Top Load has dual functions, it acts like a capacitor storing a charge between arcs, adding capacitance to help create a resonant circuit, and transmitting the electricity through the air to a receiver antenna.

Steve (Doc) Bernard putting the final touches on the primary coil which consisted of twenty turns of 1/4 copper tubing.

Secondary coil after the final coat of varish. The secondary consisted of 1000 turns of 22 gauge magnetic wire.

Close-up of Spark Gap

Electricians will recognize the parts used to make the spark gaps. Fender washers, 1/4-20 nuts, barrel nut and a Hilti concrete pin for the point. I used angle brackets to mount them on a board and to form a series circuit.

The spark gaps are arranged in series. Our original design only had a single spark gap, but after doing some research I found that multiple spark gaps increased the power of the coil, probably because the arc quenches faster. It also keeps the unit cooler since the arcs are spread over multiple points. Our original spark gap used to get red hot.

Photo of spark gaps during operation. The fan has a dual purpose of cooling the spark gaps and blowing out the arc after the gap has fired.

View of primary and secondary coils

Aluminum foil covered plastic ball. Tesla's original coil used a polished metal sphere as the top load and later used a toroid.

Mercury Vapor Lamp as the "Top Load"

Zapping a belt buckle