inconsistent performance from high voltage ignition coil/ lamp dimmer circuit

[Jack Walston]

I recently built a robust lamp dimmer to drive an ignition coil. The dimmer
circuit uses both a triac and diac along with a capacitor, resistor, and
variable resistor. The dimmer feeds a 1 uF AC capacitor which in turn
drives the coil. I have the coil in a mineral oil bath to provide greater
output voltages without arcovers and I have sometimes been able to achieve
2.5" sparks to ground. However, I am finding output very inconsistent,
especially after the unit has been running for a minute or so. Both the
triac/diac are heatsinked, which helped a lot but I still can't achieve
consistent output. If I leave the unit off for a while and then come back
and turn on, sometimes I'll get the longer sparks and sometimes not. Any
idea what's going on? I've been thinking of switching to a NPO capacitor
and metal oxide resistor, but is this really necessary or is there something
else that could be done to improve output consistency?

Thanks,
Jack

 

[NSM]

| I recently built a robust lamp dimmer to drive an ignition coil. The
dimmer
....
| else that could be done to improve output consistency?

1) Why?

2) Perhaps search for Tesla Coils?

N

 

[James Sweet]

| I recently built a robust lamp dimmer to drive an ignition coil. The
dimmer
...
| else that could be done to improve output consistency?

1) Why?

2) Perhaps search for Tesla Coils?

N

I got very impressive results by driving an old monitor flyback with the
output from one of those cheap Advance F32T8 electronic fluorescent
ballasts. Wire both outputs in parallel and connect them to the primary
winding of a flyback, I could strike the arc at more than an inch and draw
it out to 3" or more.