question about ignition coil circuit (fwd)

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Date: Sun, 14 Nov 2004 15:32:13 -0500
From: Jack Vandam <snotoir7674g@xxxxxxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: question about ignition coil circuit

Thanks again for your response to my previous inquiries....

I have just built a small ignition coil circuit driven by what essentially
is a lamp dimmer (triac and diac circuit) and capacitor.  Although some
quite robust sparks are being produced (up to 2"), I find that spark length
drops off after about 30 sec or so.  I think this may be partially caused by
components in the circuit heating.  At first, I wasn't heatsinking the
triac/ diac, but since I have I can get the longer sparks for a greater
period of time.  However, as I said, there is still dropoff.  What else
could I do to improve the consistency?  Should I switch to a NPO ceramic
capacitor and use metal oxide resistors in the triac/diac circuit?  What
about the larger polypropylene output cap (although it isn't heating from
what I can tell)?

Thanks,
Jack