Jamie t writes:

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.

http://webpages.charter.net/jamie_5"

If he's measuring a constant 300 V on the HV input, then that's not
the problem.

You really need an oscilloscope to see what's happening at the junction
of R1 and C1 - it should be sawtooth as C1 charges and eventually
triggers QD1. You can also AC-couple your DMM if it doesn't already
have a blocking capacitor on the AC range and see if there's any
activity there.

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