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I'm researching about Tesla coils and I made a prototype for myself two days ago. I benefited from other topics on this website, and Instructables and Quora.

Despite all my trying it didn't work. I've been trying new combinations, components, cables etc. since yesterday (about 34 hours,) but it seems I am cursed.

This is my setup on breadboard:

enter image description here

My troubleshooting attempts:

  • I thought "maybe wrong transistor," so I tried different NPN transistors such as 2N2222A, BD243C, BD139 and N-type MOSFETs (Z44 and IRF540.) Nothing worked.
  • I thought "maybe wrong power supply," so I tried a 12V-1A adapter, 12V7Ah battery, 12V2A adapter. Nothing worked.
  • I thought "maybe I should use a Schotky diode (1N4001) instead of LED on the base of the transistor." Didn't work.

Other combinations

  • I tried changing primar coil polarity countless times
  • I tried it with 10kohm, 22kohm, also with 50k potentiometer

This circuit does not work despite all my efforts.

  • Vin was always 12V
  • The transistors warmed up but my primary coil current is 0.00 amperes.

I changed the breadboard but it didn't affect my results.

My primary coil trials were with 3mm, 1mm and 0.8mm => 2 turns, 4 turns, 6 turns.

My secondary coil trials are with 0.4 mm => ~240 turns and ~550 turns (the one in picture.)

These are the circuits I tried:

circ#1

circ#2

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  • \$\begingroup\$ Have you seen this electronics.stackexchange.com/questions/630289/… . These kind of oscillator are weird. Have you tried also swapping the 3 turns inductor? I should use a classic generator driving an H-bridge. \$\endgroup\$
    – Antonio51
    Commented Nov 11, 2022 at 16:58
  • \$\begingroup\$ yes absolutely i see and and checked over your this topic but i really confused. how can i overcome this oscillations? if you mean primary coil as 3 turns conductor, yes i changed wire, tried different diameter wires with different turn numbers. \$\endgroup\$ Commented Nov 11, 2022 at 18:32
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    \$\begingroup\$ I've had better luck driving the primary of my tesla coil with a VCO and a H-bridge (classic solid-state tesla coil arrangement). The VCO allows fine-tuning of the primary frequency to match the secondary's resonant frequency. The aspect ratio of your secondary also seems wrong to me; ideally, it should be about 3:1 to 4:1 (length:diameter). Your secondary is too long and thin. \$\endgroup\$ Commented Nov 11, 2022 at 19:19
  • \$\begingroup\$ hmm as i understand, i should make or buy a VCO circuit and make a new coil 3:1 secondary. so how should the primary one be? and i dont get where the H bridge must be. will it be in VCO? \$\endgroup\$ Commented Nov 11, 2022 at 20:07
  • \$\begingroup\$ i looked out, VCO circuits are a little bit complex 😅 can i use 555 for it? do i need a square wave or sine wave like AC? \$\endgroup\$ Commented Nov 11, 2022 at 20:19

2 Answers 2

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Just from looking at your setup, I think the following is happening: you are not seeing primary current because it's high frequency AC and your meter is reading the average of zero; your transistors are warming up so current is likely going through them.

Tesla coils are extremely sensitive to changes in parameters and your 240 and 550 turn secondaries are almost certainly nowhere near the proper value for your primary so you're not seeing any output.

The "schematics" you got off of Pinterest are not helpful; your capacitor could be +/- 20% out of the box and small changes in the primary inductor that are unavoidable without precisely specifying the dimensions will make your primary frequency change wildly.

You'll need to measure or calculate the inductances and resonant frequencies of your primary and secondary circuits to get any sort of predicable behavior. And even then, your calculations can give you results that are off by 10s of %. That's why many coils are made with an adjustable primary coil.

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  • \$\begingroup\$ okey i see, i've two questions right now; i dont have a device to measure frequency. Where can i find the way for these calculations about resonances and inductances? 2nd one is that how must the secondary be? \$\endgroup\$ Commented Nov 11, 2022 at 20:00
  • \$\begingroup\$ I would look on a dedicated Tesla coil site. Some of the equations won't be applicable since your primary is being driven rather than free resonating through a spark gap but the equations for the secondary should work. \$\endgroup\$
    – vir
    Commented Nov 11, 2022 at 20:02
  • \$\begingroup\$ which site can help me? i'm open your advices. \$\endgroup\$ Commented Nov 11, 2022 at 20:09
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    \$\begingroup\$ teslamap.com/download.html teslacoildesign.com tesla.nu/programs/javatc/javatc.html \$\endgroup\$
    – Antonio51
    Commented Nov 12, 2022 at 7:34
  • \$\begingroup\$ okey, thanks a lot. i saw "javatc" but it seems very confusing. my researches are continuing nowadays, i'm gonna obtain these sites \$\endgroup\$ Commented Nov 12, 2022 at 16:54
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That's a "Slayer exciter", not a Tesla coil.

Loose the solderless breadboard, it doesn't work well for powerful circuits, or for fast circuits, and this device is both fast and powerful. Use solder, or screw, connections instead.

If it doesn't start, try reversing the three turn primary.

If you're using one of those little 9v batteries to power this it may just not be strong enough, use something stronger, like 8 AA cells connected in series.

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  • \$\begingroup\$ hmm okey i'm gonna try this. actually i tried 12V big battery but it didn't work but i didn't prefer 9V or other cells. and sure i'll tranfer to plate with solder. Finally, i saw this sentence a lot times "this is not a real tesla coil". i wonder what i should do for "real tesla coil". \$\endgroup\$ Commented Nov 12, 2022 at 17:00
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    \$\begingroup\$ Teslas design used a supply greater than 1000V and a spark gap. see wikipedia page. \$\endgroup\$ Commented Nov 12, 2022 at 19:05

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