I was recently building a larger slayer exciter. I've been trying out different coil ratios, coil materials, different transistors and many circuit variation, most of them just excited a fluoroscent bulb, just at different a brightness. But the last one gave me small arcs.

The most recent one I made had about 850 turns in the secondary to 4 turns in the primary. I ran it at 40V with an old power adapter[I made that by soldering two 20V DC power bricks in series](I don't own/can't afford a Lab Bench power supply).

I was using a TIP41C, and burnt 1 out, because careless me left it powered on for a long time without a heat sink. This one gave me half cm arcs when I leave the free end of the coil in air.

Then I switched to a MJE3055T. It worked pretty well, and added 2mm to my 5mm arc, but Looking at all those pictures of 2 inch arcs on youtube, I was not that happy with mine. I recently bought 1500 meters of 37AWG magnet wire(for about 9$) and I really need some advice from experts/professionals/engineers, to build another one, which can give me large arcs with my 40V supply, a 40KV ceramic capacitor, 18AWG primary coil and a TO-220 type transistor I guess(TIP41C, MJE3055T, and I've got a few other high voltage transistors that I salvaged).

Thanks a lot for any help guys! Would really appreciate some advice!

  • 2
    \$\begingroup\$ Best advice you'll get about this: buy a fire extinguisher and some insurance. \$\endgroup\$ May 11, 2017 at 10:39
  • \$\begingroup\$ better than that - I would stay away from furniture and flammable substances while working on it.. \$\endgroup\$ May 11, 2017 at 10:41
  • 1
    \$\begingroup\$ This isn't really the site for open-ended advice. It's an electrical engineering design question and answer site. If you can ask a particular question that has enough embedded information to make it answerable then that should be fine. \$\endgroup\$
    – Andy aka
    May 11, 2017 at 10:53
  • \$\begingroup\$ The slayer exciter isn't really designed for large arcs. You should do some research and see about building an actual Tesla Coil. By the way, 37AWG is very fine, probably much too fine for a Slayer Exciter or Tesla Coil. The resistance will likely be too high and will cause very inefficient operation. \$\endgroup\$
    – DerStrom8
    May 11, 2017 at 11:50

3 Answers 3


Slayer exciter circuits are by design very inefficient. It is nothing more then a simple resonant circuit operating in a lossy manner. To get bigger sparks you need something more like a Tesla coil operating as a class D amplifier. Adding more turns will add resistance and reduce the resonant Q factor of the circuit, eventually giving you even less voltage gains for exponentially increasing amounts of power.

I would suggest you spend some time reading up on Tesla coils. Basically you are switching FETs or IGBTs on and off, not partially driving them in a class A style like the slayer exciter does.

A small half bridge Tesla coil can get you 1-2 ft arks and cost under $50 to build if you keep it simple. That being said, if you are not aware of the dangers of working with high voltages, building a Tesla coil is a good way to toast yourself.


Try 4000 turns on a secondary coil 1.5 inches in diameter, use an ultra fast switching diode like a byv 600 and an audio amplifier transistor such as an nte36, happy sparking đź‘Ť p.s. up the resistance alot to save the transistor from overheating, use a large heat sink and try a primary of 12 turns at a 3 inch diameter and insulate between the primary and secondary to avoid losses.


The last guy said more windings make for more resistance...this is true but it's not a Tesla coil and as a lossy circuit in the first place makes little difference. Try 4000 turns of your 36 AWG wire around a 1.5-2 inch pipe, loosely coupled with a primary of 10-12 turns of 12 AWG at a 2.5-3 inch diameter respectively.

The transistor's gain is very important. The higher gain and switching frequency will bring larger arcs because the more breaks per second mean an easier path for the discharge to flow, since previous arcs are still present.

3 more tips:

  1. Tuning can be done on the primary coil (try bare wire spread apart enough that you can move an alligator clip along the coil to try different settings, when it is tuned well wind that coil from insulated wire).

  2. With two equal transistors, try a dual primary coil sharing power supply and feedback (but with their own primary coil and diode). On that note, throw out your diode unless it's of the ultra-fast switching type (try a BYV600).

  3. Unless it's a variation of the slayer exciter, you don't need a capacitor (in circuit drawings, a cap between the HV end of the secondary and ground is a natural occurrence, as air is the dielectric).

Good luck.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.