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I made a Tesla coil using the circuit from this video.

The MOSFET seems to be getting hot and current passes through the primary but I get no response from the secondary.

enter image description here

Here are the dimensions of the coil:

  1. Secondary winding: 1.5 inch 670 turns
  2. Primary winding: 3 turns
  3. MOSFET: IRFZ44N (fresh)
  4. Capacitor: 3.3uf 50v
  5. Power supply: 15V @2000mA

Please help me with this project as I am an amateur in electronics.

JRE
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Gishopan Sivakumar
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3 Answers3

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This is "not quite" the definitive Slayer Exciter SE EE reference BUT it should serve as a useful guide to Slayer Seekers. If it seems useful I'll add to it.

A "Slayer Exciter" implementation of a Tesla Coil is a somewhat hit & miss affair at the best of times. Some work well, or sometimes work well, or ... . Many are not designed or poorly designed. And as with anything found on the internet - some will never have worked for the maker, no matter how convincing their video or text may (or may not) be, and no amount of copying correctly will make your version of their fraudulent material work.

Your example is suspect in using a a MOSFET (very unusual, not impossible) and lacking the usual base (or gate) to ground reverse connected diode, which is an essential part of most such circuits.

His long winded and unnecessarily detailsed warnings about destroying the MOSFET gate are correct but his chosen component values are dangerously bizarre given his warnings. His suggested range of operating voltages are unnecessarily high.
All told, while his circuit MAY in fact have worked for him, it's not by design, and I'd suggest you look through a few dozen of the hundreds available on web and choose one more liable to be a good one.

All that said:

"Dotting" or relative winding direction and plarity of the two inductors is CRUCIAL. In my incomplete skim of his video he did not seem to mention this and did not show it on his diagram - an utterly inexcusable omission.
If both coil are wound in the same direction on the former then the bottom of the low voltage one should connect to the transistor collector / drain. This is sort-of-if-you-are-lucky implied by his diagram. That's not good enough.
Reversing the primary polarity may make the difference.

Operation from 12V should be possible. This may even save your FET gate from dying.
A few turns on the primary may help. Or not.
A diode from gate to ground (cathode / bar end to gate) may help.

Here is an excellent SE EE Q&A re Slayer Exciters

Here are 46 SEEE Slayer Exciter posts in descending order of votes.

Hare are agh agh agh!!! 100's of the brutes.

Screen capture from his video.
Dots by me.
Build another version.

enter image description here

Russell McMahon
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  • Thank you sir but that the same schematic i'm using!.And are you telling me that Keystone Science is fake – Gishopan Sivakumar Nov 20 '19 at 23:01
  • will 672 turns around a 1.5'' pipe be inappropriate? – Gishopan Sivakumar Nov 20 '19 at 23:39
  • @GishopanSivakumar I copied that image from your linked video. | Have you checked the coil polarities as I suggested? | Where is the clear well lit well focused photo of your device? | Have you read the 2 year old SE EE Q&A that goes with the circuit link that yuou posted - here https://electronics.stackexchange.com/questions/339770/how-does-this-tesla-coil-design-work | Did you know that that is where the circuit came from? || I am saying what I said already. If you read what I said you will see what I said. PART of what I said is ... – Russell McMahon Nov 21 '19 at 03:39
  • ... " ...Your example is suspect in using a a MOSFET (very unusual, not impossible) and lacking the usual base (or gate) to ground reverse connected diode, which is an essential part of most such circuits. ... his chosen component values are dangerously bizarre given his warnings. ... his circuit MAY in fact have worked for him, it's not by design, and I'd suggest you look through a few dozen of the hundreds available on web and choose one more liable to be a good one...." – Russell McMahon Nov 21 '19 at 03:39
  • Did you look at my links? Did you do the things I suggested? – Russell McMahon Nov 21 '19 at 03:40
  • Output coil spec is very flexible. Input coil may want to be a few turns. BUT given the effort you will expend overall, choosing one of the dozens and dozens circuits that are well done is a good idea. This one is su[per marginal and suspect. a good – Russell McMahon Nov 21 '19 at 07:03
  • @RusselMcMahon Thank you for your advice,I made some minor tweaks & just replaced the Z44 with a F18KM which gave me about 6mm of arcs and wireless lighting.I have got many BJT-Slayer exciter circuits from the internet which I'm going to try out and will opt for a powerfull(er) FET like the IRFP260 or IRFP250 – Gishopan Sivakumar Nov 21 '19 at 11:48
  • I read through https://electronics.stackexchange.com/questions/339770/how-does-this-tesla-coil-design-work & i kind of understood why a slayer exciter is not a weekend project. – Gishopan Sivakumar Nov 21 '19 at 11:51
  • @GishopanSivakumar IMPORTANT - A "good" Slayer Exciter circuit IS a weekend project. What is NOT a weekend project is a circuit that is utterly undesigned, like this one is, that uses MOSFETS without proper attention to how they are driven, as this one does (while almost all others use bipolar transistors or take special care to account for the MOSFETs 'needs'*), that does not consider the crucial matter of coil polarities, as this one doesn't, ... . | MANY other SE ccts should more or less "just work". This one is a mess. Try another one. || * MOSFETs will be excellent when used correctly. – Russell McMahon Nov 21 '19 at 18:52
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IRFZ needs 5V to start conducting. Won't be fully open, but that's enough to start your oscillation. If total resistance is 1050 Ohms at 20V PSU you will have around 0.2A running through resistors. That is 1V on your 50 Ohm resistor, and you have 19V on Gate-Source and that's fairly close to manufacturer's limit. I'm going to build it myself soon, and I will start with 1k instead of your 50. Not sure about resistor between G-S but 100 Ohms should be sufficient using only 12V PSU. If your transistor is getting hot, it means it's open and draining your full power to source. I would start with the already mentioned polarity of your coils, as that's what starts oscillation. 1k resistor could be lowered for more juice in your circuit once you get it going.

Old Navy
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  • Just checked data-sheet and there is no need to go over 5V on Gate as at 5V it is capable of 20A which is not going to be needed in this setup. Keep it low as that would save you journey to buy another one. – Old Navy Apr 01 '22 at 00:55
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I believe your main issue is your gate voltage is too high, you only 50 and 1kohms in your divider. Even a BJT driven unit uses R values of about 10kohms, that's your main problem. Mosfets are voltage driven therefore your get is basically being slammed on somewhat and the negative pulse from the secondary (while missing the reverse bias gate pulldown diode which is usually an led due to how they turn on) is unable to turn off the fet. Try increasing the values of your gate Voltage Divider values (such as a pot on one leg of the divider to allow tuning.

Anthony Lee Volkman
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