Ignition system

[Mecke]

if i build one with an capasitor, what size and model would be best?

[Petitlu]

capacity is not really important, I put 80uf.
With 0.22UF it will work!
the difference is in the recharge time of the capacitor.

[jimmy101]

The diode suppresses the inductive back emf which can be a higher voltage than the switches can handle. Think of a higher voltage arc.

See this explanation:
http://en.wikipedia.org/wiki/File:FlybackExample.GIF

I don't think you want to use a snubber diode in an HV ignition circuit, indeed I think it'll make the circuit not work.

You want the field energy to collapse into the coil's secondary winding and not be snubbed (dumped, absorbed, wasted) by the diode across the primary winding. That is why car ignition circuits use a capacitor (condenser) and not a diode. The cap sources enough current to keep the voltage across the switch (car's ignition points) from exceeding the break down voltage.

edit: engrish

[dewey-1]

jimmy101;

I never stated to use on an ignition coil.
It was in reference to the relay coil.

[Mecke]

Hey again! I have tried with other metods to fire up my ignition coil but with no success. I belive that its maybe broken or something... I have read that you van measure the ohm betwen - and +, and also - + and the middle. I would appreciate if someone could measure the ohm values on their coil and post them here!

[Petitlu]

+- coil : 15 ohms

+ / middle : 2.4ko

- / middel : 2.4ko

[Mecke]

Thanks!

[Petitlu]

I disassembled my ignition to take measures!

[Mecke]

Thanks again, your awsome!

[jimmy101]

jimmy101;

I never stated to use on an ignition coil.
It was in reference to the relay coil.

Sorry, but you didn't actually specify which coil you meant. Since the OP is about an ignition coil and a simple switch that is what I assumed you were talking about.

For a buzz coil circuit a cap or diode across the relay's coil isn't needed. A cap across the HV coil's primary is needed and a diode in the same place will make the circuit not work.

[Mecke]

it is working now!
I bought a new ignition coil and made an buzz coil and now i get a nice 5 mm spark

[Petitlu]

Excellent !

I'm happy for you! !