trouble getting this hv circuit to work

[John Grafton]

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-streamer/temp/Old2001Files/2001-12/QuadracDriver.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

[Bert Hickman]

Hi John,

It sounds like the Quadrac is not "firing" or is no longer functional.
The schematic drawing you referenced does indeed have an error - the top
(MT1) and middle (MT2) pins or the Quadrac need to be swapped in order
for the circuit to operate correctly. The bottom terminal is correctly
shown as the trigger (T). The component specs for the Teccor device can
be found here:

http://rocky.digikey.com/WebLib/Teccor/Web%20Data/Quadrac%20(4-15%20Amps).pdf

Make sure that all diodes are polarized properly and that your circuit
matches the schematic (with MT1 and MT2 leads of the Quadrac reversed).
If all of these are correct, replace the Quadrac. You could also measure
the voltage across C1 - it should increase/decrease as you change the
pot setting, and as you increase the pot setting, you may also see it
change abruptly as the the internal DIAC (inside the Quadrac) fires.

Good luck,

Bert
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[John Grafton]

Thanks, Bert, for your fast reply. The problem was indeed the quadrac and
the schematic error. Once corrected, everything worked. I have another
question if you don't mind. I'd like to run two ignition coils in parallel
for more spark output. The description calls for GM HEI coils, which I
have, but one coil is a bit different from the other and I'm not sure how to
ground the HV ground. Better to show an image than to explain:
http://img212.imageshack.us/img212/4968/heicoil1ip2.jpg

Thanks,
John

"Bert Hickman" <bert-h...@comcast.net> wrote in message
news:n8Sdnb7xSdK1D_zU...@giganews.com...

[Bert Hickman]

Hi John,

Excellent! BTW, be very careful with this circuit - the high current
output pulses can knock you into the next county if you get zapped... :^)

I suspect that the other end of the secondary on coil 2 is simply the
core (which would normally be grounded to the car's chassis when
mounted). Have you tried measuring the resistance between the HV output
and the core?

Bert

[John Grafton]

Bert,

That was one of the first things I checked, resistance between output and
core. It's infinite, so there doesn't appear to be any connection. That's
what was throwing me off too (and is making me wonder whether or not I
should connect the cores together too).

I wanted to make sure I had the hookup correct because I'll be placing these
coils under oil soon.

Does it look good to you? Any changes/ mods to be made?

Thanks again,
John

"Bert Hickman" <bert-h...@comcast.net> wrote in message

news:mpOdnW0b_awNgv_U...@giganews.com...

[Bert Hickman]

Hi John,

No - otherwise, it looks good! You also should have the option of
connecting the outputs in series to obtain higher output voltage by
reversing the phasing of one of the LV windings. You may also want to
try increasing the size of C2 to increase "bang" size when using two HEI
coils.

Good luck and play safely,

Bert
--
***************************************************
We specialize in UNIQUE items! Coins shrunk by huge
magnetic fields, Lichtenberg Figures (our "Captured
Lightning") and out of print technical Books. Visit
Stoneridge Engineering at http://www.teslamania.com
***************************************************