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Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Simon wrote ...
In theory a spark gap might be able to do the job. Have a spark gap after your output resistance and put your load in parallel with the gap. Any of the more practical minded members have thoughts?
It wouldn't be efficient and it might not regulate all that well. Simple, though. :)
SPark gap has a negative resistance and would likely form a relaxation oscillator with filter cap unless very big series resistor is used, and it would waste a lot of power. But would work too..
Measuring one typical iggy I have here, it has primary resistance of 3 ohms and secondary resistance of 7 kiloohms (wich is good considering 30kiloohms for 400VA obit I have here)
If driven properly those little thingies may make a nice high-power HVDC supply. Most worrying are actually core losses with iron. Could end on my projects list one nice day...
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
That 3 Ohm resistance is common for the lowest end of ignition coils; better are the type that have an external resistor that's bypassed for cold-start or ignition coils designed for electronic ignition.
My coil has a primary resistance of less than 1 Ohm when hot.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
You could try connecting that NPN transistor to the 555's control voltage pin (the one you're normally supposed to decouple to ground with a capacitor) instead of the reset pin.
I fancy trying this now since I've got all the parts except the ignition coil It would make a great low-powered rugged HV supply for testing things with, and it would be easy to have switchable polarity for the output, by swapping the iggy primary terminals and turning the diode round.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
You could try connecting that NPN transistor to the 555's control voltage pin (the one you're normally supposed to decouple to ground with a capacitor) instead of the reset pin.
I already mentioned something similar few posts above, exscept I just directly used phototransistor from optocoupler, in place of one duty-cycle resistors.
Pin 5 could also work but it seems somehow limited in range.
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Regulating Ignition Coil HV
It would make a great low-powered rugged HV supply for testing things with, and it would be easy to have switchable polarity for the output, by swapping the iggy primary terminals and turning the diode round.