I'm trying to make a Tesla coil with approximately 200 turns in the secondary coil using 28 gauge enameled copper wire. My primary coil has 3-6 turns with a thicker wire. I've made all the connections according to the schematic and yet, my Tesla coil doesn't work. What am I doing wrong? The current flows through the primary coil but there's no response in secondary coil and thus the CFL doesn't glow

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  • \$\begingroup\$ doesn't work is not a good description of the observed results .... please use more detail in your description ..... what measurements have you done? .... what were the results of those measurements? ..... also, your schematic is unreadable \$\endgroup\$
    – jsotola
    Dec 2 '18 at 1:46
  • 3
    \$\begingroup\$ You're dealing with dangerous levels of electricity in a Tesla coil and you don't know what is happening? We can't understand your schematics to help you either. It will be most prudent to just stop what you're currently doing and save your life. \$\endgroup\$
    – shimofuri
    Dec 2 '18 at 2:22
  • \$\begingroup\$ It may have been called a Tesla coil, but the image you've shown is not. Do some research, find out what it's called, and then ask the right question. Compare it with C_Elegans' drawing (which is a long way short of a TC, but shows more of the features), and you'll see his C2, which is a fundamental part of a TC. The good news, with your PP3 power supply and non-TC circuit, you can ignore the 'you'll kill yourself' doom mongers. \$\endgroup\$
    – Neil_UK
    Dec 2 '18 at 6:00
  • \$\begingroup\$ Sorry about fuzzy screen. Uploaded clear and new circuit diag that I used as reference. Here are few more details.. Transistor: 2N2222A; Resistor: 20kOhms. Current is flowing in primary coil, but not through diode/LED which turns on the transistor. Can I assume my circuit or connection is correct? \$\endgroup\$
    – Tiger 28
    Dec 2 '18 at 17:58

A tesla coil is essentially a transformer with a really large ratio of turns, connected to a high frequency AC source. The problem with your circuit is that you're essentially, just letting DC current flow through the primary of your coil, which will not work.

The simplest tesla coil design might look something like this (note, values are approximate, you should not attempt to build anything resembling this circuit without a thorough understanding of how everything works, and more importantly how anything can go wrong and KILL YOU)

How it works:

  • Initially, V1 charges the capacitor C1 through its output resistance (R1) until it reaches a high enough voltage to arc across the spark gap
  • When an arc forms across the spark gap, it momentarily shorts C1 to C2, charging C2 until the voltage across the spark gap is no longer high enough for a spark to be sustained
  • C2 begins to discharge into L3, increasing the magnetic field inside it as well as the current through it. When C2 reaches 0V, L3 still has a current flowing through it, so it begins to charge C2 up to a negative voltage, until the magnetic field collapses. At this point C2 begins to discharge through L3 again, and the cycle repeats until the energy stored in C2 dissipates due to resistance in the wires or losses in the transformer. C2 and L3 form what's called a tank circuit, which when given a pulse of energy, oscillates until the energy stored in the capacitor and inductor runs out.
  • The alternating current in L3 induces a high voltage in L4, making sparks and doing the tesla coil thing.


simulate this circuit – Schematic created using CircuitLab

The tank circuit formed by L3 and C2, and some way to periodically provide energy to it are integral to making a Tesla coil, you cannot build one without them.

Finally, as I said above, do not try to build this without a thorough understanding of how to work with high voltage. While the output of the Tesla coil is likely not deadly, C1 most certainly is.

  • \$\begingroup\$ Single transistor tesla coils are a thing. The circuit given in the question can oscillate if everything is setup correctly. It depends on a lot of unwritten assumptions (inductance of the coils, parasitic capacitances, amplification of the transistor, etc.) It probably worked for whoever built it because he got it all close enough. A small change anywhere in the circuit or construction (physical layout) could cause it to fail. \$\endgroup\$
    – JRE
    Dec 2 '18 at 11:17
  • \$\begingroup\$ Yes, indeed they can, if setup properly. However, I thought a spark gap Tesla coil would be easier to explain how it worked, and it also had the side benefit of only working if a high voltage supply is available. \$\endgroup\$
    – C_Elegans
    Dec 2 '18 at 15:15

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