John Grafton wrote:

Came across this circuit to be used as a dual coil ignition coil driver
recently and tried building it. However, despite all efforts, I can't get
it to work:

http://www.capturedlightning.org/hot...dracDriver.pdf

If you read the description, you'll see that the included line voltage
doubler is required if the circuit is to be operated from 120 v line.
Therefore, I am using the doubler also.

Here's all I can get from the circuit. I use between a 25 and 60 watt
incandescent in series with the 120 v input to the doubler for protection of
the circuit. When I plug in the circuit, I hear no sparks nor is there any
hum of the included ignition coil. Sometimes the 60 watt bulb will light
brightly as the circuit is plugged in; othertimes the bulb does not light at
all. Adjusting the variable resistor has no effect on the brightness of the
light bulb if it's on and if no light bulb, pot adjustment won't light it
either. I've been told that the top and middle leads of QD1 need switched
(in other words QD1 top goes to ground and QD1 middle goes to R2/diode
junction). Tried that and still no response.

This seems like it should be a simple circuit to troubleshoot, but I am out
of practice for some time and not sure where to start. I've checked L1 out
of circuit and it still has the proper resistance. I've also replaced the
pot since adjusting it was getting me nothing, and still nothing with a new
pot. The output from the doubler is correct at 300+ volts. Tried switching
ignition primary wires, but still no effect. Instinct tells me that QD1
might be bad. Is there any way I can measure it out of circuit to be sure?
What would resistances be between terminals?

Any suggestions would be greatly appreciated.

Thanks,
John

You do realize, using a voltage doubler like that, the low side must be
floating on the circuit? or at least away from the mains.

In other words, you can not have your (-) of that circuit to the
common of the supply.

Putting that aside..

It's possible your light bulb load is not allowing the cap to
charge long enough before the trigger circuit fires.




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