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How a Tesla Coil Works

Posted by on February 22, 2011

The Tesla Coil we use in our show is a modern version of a classic device invented by Nikola Tesla. Our coil is called a DDSSTC (Dual Resonant Solid State Tesla Coil). This means the coil is controlled by transistors, just like in the computer you are reading this on. This is a modern upgrade to the device Tesla created, called the SSTC (Spark Gap Tesla Coil). But how does it work?

Nikola Tesla is not a well known man, but he is the father of our electric age. He was the pioneer of Alternating Current (AC) the type of electricity that comes out of your wall socket. This is different from Direct Current (DC) the type of electricity that comes from a battery. Tesla knew that AC was a much better way to deliver electricity to your house, and he helped design the electrical grid we use today.

Though Tesla didn’t like they way the world would look with so many wires running about to deliver power. He started work on a way to deliver power wirelessly so that there would be no need to run so many wires around the planet. His work lead him to the invention of the Tesla Coil.

A Tesla Coil works much in the same way your cell phone charger works, but in reverse. Instead of reducing voltage, it increases it. This is called a transformer. It has two main sets of windings, a primary winding and a secondary winding. The difference in the number of turns in each winding determines if the voltage out will be higher or lower then the voltage in and by how much. A Tesla Coil has very few turns on the primary (input) side, and many turns on the secondary (output) side. This increases the voltage tremendously.

But a Tesla Coil does much more then increase voltage, it increases frequency.  You can see a schematic of a Spark Gap Tesla Coil above. The capacitor and spark gap work together to create a very high frequency pulse to drive the primary coil. Tesla designed it this way because once you create very high voltage electricity at a very high frequency, you can create a field of energy with which to transmit power.

Here is a video of our Tesla Coil transmitting enough power to light up a Florescent light bulb.

Our Tesla Coil is different the the schematic above in that it has no spark gap. Instead, a series of transistors ‘switch’ current on and off at a very high frequency. This means we can control the Tesla Coil at different frequencies, and even produce sounds.

Here’s a video of two Dual Resonant Solid State Tesla Coils playing a song.

So this is how a Tesla Coil works. It creates high-voltage electricity at a high frequency. And when you produce this kind of electricity, you can do cool things like power light-bulbs with no wires.


28 Responses to How a Tesla Coil Works

  1. Karen Lee

    Totally Awesome!!!!! This is what the students in my class and my own children thought about your presentation today. We loved it!!! Thank you so much and we hope to see you again next year!
    Happy Easter!

    Karen Lee
    Breakfast Point Academy

  2. Mrs. Gomes

    Your demonstration was amazing! We were most impressed with the use of the Tesla Coil and how it made plasma energy. My students were talking about this display for days. Thank you Science Brothers!!!! We appreciate your dedication to study of Science.

    ~Lisa Gomes

  3. cole

    what would happen if lightning hits dry ice ps go science + Dan

    • Bill Science

      The ‘lighting’ is made up of hot plasma, so it would melt the dry ice faster.

  4. Steve

    If someone is desiring to hit a specific frequency what formula would be applicable in this situation?



    • Bill Science

      My coil is a digital DRSSTC so there’s no formula. I send the signal as a pulse train of a certain frequency and that’s the audio frequency I get out.

  5. Austin

    Does any body know weather or not tesla coils are still in use today?

  6. joe


    • Bill Science

      The spark doesn’t need to travel that far, just the EM field the coil produces.


    Can this be used to create free energy by using an electric genarator that has charge already then using the incressed voltage produced by the teslor coil to mantain its initial power with excess enrgy to supply somthing else

  8. Damien

    Hello already left a message with you today but i come to check and it aint there so I’ll try again. could you not power a tesla coil with an electric powered generator an then using the amplified voltage from tesla coil power the generator with enough waste energy or unused energy to power a second generator thus creating a free source of energy cause if so then we have had free energy from the beginning and you guys with education money and a facility to use and you chose to make music and light shows use your resources and make a difference i don’t have the luxury of any resources at present but books and the internet and i know it can be done so please.

  9. John

    How do the primary and secondary windings work?

  10. gabriel

    Hey, nice article. Why tesla’s coild won’t work to power a laptop or a smartphone? Thanks.

    • Bill Science

      Much like a radio receiver picks up weak stations, a tesla receiver would pick up the transmitted energy and convert it into a more useful form.

  11. Joseph Moore

    If I were to build a tesla coil how would I make sure that the electricity went into things that I wanted it to and nothing else? Also would I be able to charge my laptop with it once it was built?

    • Bill Science

      Efficient power transmission with a Tesla Coil requires a tuned receiver. Much like a radio receiver picks up weak stations, a tesla receiver would pick up the transmitted energy and convert it into a more useful form.

  12. Rupert

    I have a question that is probably very silly – please explain why the capacitor continues to charge through the negative cycle of the AC. I would have thought that the capacitor charges for half the cycle and discharges for the other half and so there is no net build up of charge. Obviously that’s not the case, since it does have a build up, but it would be great if someone explained why. Thanks in advance.

    • Bill Science

      Connecting a capacitor to an AC source does very different things than when connected to DC. Connecting to AC creates a shift in power factor, a concept that is tough to explain. The capacitor in the Tesla coil forms an LC tank circuit with the inductor that makes up the Tesla coil primary. See

  13. Alex

    dear scientist brothers!

    thanks for your help!
    I needed this website (made by you) to make a science project!
    I am very happy to have this website!
    thanks for your help again!
    do you ever saw a person or hear die because the tesla coil?



  14. Alex

    Another questions:
    how dangerous is the tesla coil?
    can it be a weapon?
    can it blow up if you do something wrong?
    how far away you need to be from the tesla coil that you are safe?

  15. Alex

    more questions:
    how many tesla coils did you build in your life?
    is the tesla coil made to be a weapon too?
    are tesla coil and death ray “brothers”?

  16. Cam

    you said that the number of turns on the input side is less than those of the output… yet in the diagram it looks like the turns are more on the input and less on the output, why is that?

  17. Cam

    Nevermind, I was looking at the square with the wires wrapped around it and not the diagram below it… could you explain the square though?

  18. kirubasankar


    exactly what i needed

    much informative

  19. THANKS!!!

    Exactly What I Needed.

  20. sahaj

    I have made the same for my science exhibition and I am a student of class VIII its awesome

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