Ignition coils can handle quite high power levels.

Bipolar ignition coils. 70V input voltage with 20000uF smoothing cap and MOSFET (IRF740) switching. Significant current draw - primary peak 20A. What might not be apparent from the video is that the arc is very loud. I'm letting the voltage fly after switching. The output voltage is approximately 80kV.

I've collected info to this page:

http://www.niksula.hut.fi/~plahteen/misc/old_projects/ignition/ignition.html

In order to get long sparks you need to feed the coil enough power for each pulse (meaning long enough on-time to build the current). You also need to switch the current off fast at it's peak. That will result in inductive kick which will rise to infinity regardless of input voltage as long as enough current is flowing at the switch off time. However it will be limited by the switching device maximum voltage (and other practical reasons such as capacitance). We want the voltage to fly as high as possible within safe limits. Secondary voltage is usually multiplied over 100x the primary so 400V kick should be around 40kV at the secondary.

These coils are anti-parallel so the spark is between -40kV and +40kV terminals. That's why 80kV.

The circuit I used is here:

circuit2.gif (file lost, will replace when I find it)

Be warned however that this is only a quick and dirty way. High voltage spikes may destroy the MOSFET in the long run. The cap should be rated well over 400V and 100n is pretty critical (compromise between high current and high voltage spikes).

The MOSFET avalanching at around 400V offers a natural clipping limit. As long as that pulse energy is (s)low enough it will survive. The parallel capacitor (s)lows down the kick and helps to protect the MOSFET. Too large capacitor will however result in too large short at the moment of switch-on.

I however didn't use any protection with this specific circuit. The component values may be quite critical. I used it with two different coils (primary inductances 5mH and 9mH).

Better circuit here:

http://www.niksula.hut.fi/~plahteen/misc/old_projects/ignition/circuit1.gif

C should be determined so that the primary voltage swing after the switch-off remains below the safe limit. R should be determined so that discharging of C is slow enough while getting maximum current to flow through the inductor. These values depend on your coil and switching device and can be determined in practice with an oscilloscope. The gate diode ensures that switch-off is as fast a possible. They are not too critical though. R may be in the range of some 100kohm.

Here is one possibility too:

http://www.niksula.hut.fi/~plahteen/misc/old_projects/ignition/circuit6.gif

R and C determined so that the voltage is low enough to be safe but as high as possible to give long sparks. R will become hot.

I've tested the basic circuit up to 200V and it will work up to a point but voltages much more than 24V aren't too safe in the long run without some of the suggested solutions. If you are out of luck you may destroy the MOSFET even with 12V. The parallel capacitor may get destroyed too if it's of low quality. It sees high voltages and get's discharged very rapidly.

Low voltages such as 12V will limit the primary current due to internal resistance too much and aren't very impressive. So at least 24V is typically required for good results.

Best solution would be a full bridge like the ones on a solid state tesla coils. However that would require higher voltage to operate and/or a resonant capacitor since it's not allowed to fly. More complex in any case.

Category:

Howto & Style

Tags:

• HV
• kilovolt
• spark
• electricity
• kV
• high
• voltage
• streamer
• tesla
• coil
• ignition
• bipolar

[ppsjsh]

i use 24v AC @ 1A on my ignition coil, not long arcs though but i think it steps up the amps and voltage a lil. it can melt aluminuim and small copper wire in just a few secs. im tired of using realys cause of the constant buzzing and looking to put more power in it. im trying to make a zvs driver but cant find the plans. do u know where i might can find them? thanks

[decod31]

@ppsjsh This video was done using a flyback circuit. Where current is "charged" and then disconnected by the fet (a pulse) and let fly to about 400V at primary. Peak current was about 20A.. There are some schems in the description, but not zvs. For zvs you need some tesla coil circuit (like steve wards).

AC is not good for switching and as a standalone drive you would need high frequency and relatively high voltage (400V) AC to get the same results as here.

[decod31]

@ppsjsh BTW. to speak of stepping up both amps and volts is a bit misleading since that would be against conservation of energy (as a mean value). For both zvs and flyback you build up low voltage high current and transform it to high voltage low current. What also happens is that a temporally long "charge" (either resonant -zvs or flyback) is released in short amount of time conserving the total energy.

Zvs you can find by googling steve ward tesla, but it's a bit overkill (DRSSTC).

[decod31]

@ppsjsh BTW. to speak of stepping up both amps and volts is a bit misleading since that would be against conservation of energy (as a mean value). For both zvs and flyback you build up low voltage high current and transform it to high voltage low current. What also happens is that a temporally long "charge" (either resonant -zvs or flyback) is released in short amount of time conserving the total energy.

Zvs you can find by googling steve ward tesla, but it's a bit overkill (DRSSTC).

[juniortore1]

Why is it only off and on, cant you run it constant?

(ignoring the problems the ignition coils might have)

[decod31]

@juniortore1 Sure, it can run continuously and I have run it continuously for several minutes, but for more controlled arcs (less change of a coil breakdown due to overvoltage). Tapping it on and off like I did here is less likely to cause a problem when the circumstances are not well controlled. Say due to an arc channel forming inside the insulator in the coil or simply overheating. This allows time for it to cool down and hopefully prevent it from breaking entirely.

[MegaMaxyKing]

nice arcs, but my ingition coils can handle 2000 Watt

no joke, look at my vids

[juniortore1]

@juniortore1 Ohhhhh, My ignition coiles arced over on the inside, the plastic got burnt from an arc, and shorted the secondary inside. I now took the coils themselves out of the can. I will stick them under some oil, and vacuum the air out, then make some high power driver... like this eventually, And since they are out of the can, I will make a center tap for ZVS to power it just for long purple arcs :)

[BarneySaysHi]

Ah, I didn't see that one yet, sorry.

[decod31]

I kinda did it already in my video "PRF modulated ignition coil".