Re: [TCML] Frequencies

[jimlux <jimlux@xxxxxxxxxxxxx>]

Rhys Sage wrote:
> I've considered a whole load of alternatives for driving the ignition coil. I decided in the end to play safe and optically isolate the coil from the 555 pulse generator. To that end I'll employ an IR emitter-detector pair.
>
> I discovered a capacitor plus a resistor across the coil should, according to one website, foil any surges from the coil while a diode in series should foil any kickback.
The problem is that a snubber and diode (which is what you describe) 
suppresses the kickback.  The kickback is what you need.  A auto 
ignition coil is a transformer about 100:1 turns ratio, so feeding it 
with a 12V pulse makes a 1200V output pulse.

What the ignition really does, though, is run current through the 
inductance of the primary until it gets to around 5A, then turns off 
really fast.  Since V = L di/dt, and di/dt is really big, you get a 
voltage across the primary of about 400V, or 40kV at the secondary.

Clamp the (would-be) 400V pulse to 12V, and it doesn't work.


> I have a pretty mundane coil at the moment. It's a cheapie coil that I bought just to try things with. I expect it won't be powerful enough to use for anything other than experimentation - which is fine right now.
>
> 400 hertz is quite slow. Using a simple electric motor running at 6000 rpm and a spinning disk with 4 segments of alternate block and clear combined with an interrupter would give me about 200 pulses a second. Doubling the segments to 8 would give 400 hertz. That's achievable with a simple piece of cardboard!
>
>
>
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