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Re: OL-DRSSTC 9 - Better trigger!!



Original poster: "D.C. Cox" <resonance@xxxxxxxxxx>


Terry --- any photos yet of the spark output?

Dr. Resonance


Hi All,
The OL-DRSSTC coil now triggers at any input voltage so the power can be "fully" controlled by a variac! I went to a "fully resonant tuned" trigger pulse and it will now fire "anything"!!
http://hot-streamer.com/temp/OL-DRSSTC-2005-10-11-001.gif
The trigger pulse is a big 35 amp 96kHz decrement sinewave now that lasts for about 8 cycles! It will start up any lazy ol-DRSSTC :o)) It could probably even power a little Tesla coil all by itself, but it is only 5.3mJ/bang or 0.32 watts. Almost 1 inch by the Freau equation... Might be useful for "enyweeny" coils:
http://www.roffesoft.co.uk/tesla/enyweeny/enyweeny.htm
The drive circuit is here in the upper right:
http://hot-streamer.com/temp/OL-DRSSTC-08.gif
I took out the 2.7ohm resistor and added a reverse diode across the SIDAC. I added a loop of "primary" wire to the trigger loop so I could tune it right to the Fo frequency of the primary coil. So it runs much like the original OLTC did. There is not much to it (it really only needs "one" cap...):
http://hot-streamer.com/temp/OL-DRSSTC-2005-10-11-005.jpg
One could probably fiddle with the part values as you please. The SIDAC "could" probably push 80 amps!! Peak current is controlled by the firing voltage and primary loop impedance. The voltage ringup is able to keep the circuit in conduction until the cap energy is used up. Really cool!! ;-))


With a test load, the circuit fires right up! Yellow is primary current and blue is the trigger circuit loop current.
http://hot-streamer.com/temp/OL-DRSSTC-2005-10-11-002.gif
At 60BPS, this heated the IGBTs to about 40C with the fan in place (could use a "better" instead of the "cheapest" fan...).
I hooked it to the full coil and tuned it for some nasty primary currents and it started and ran fine:
http://hot-streamer.com/temp/OL-DRSSTC-2005-10-11-003.gif
The firing pulse train looks like this:
http://hot-streamer.com/temp/OL-DRSSTC-2005-10-11-004.gif
So that is where I am... Things to do...
A simple inrush current limiter could replace the big blocking inductor for less power but a far smaller size...
The fan needs to be "better"... Maybe a big CPU fan, but I don't have the low voltage to run it...
I need to put back in the 150nF primary cap and 16uH primary to optimize it all much better.
I need to get a few more parts from DigiKey....
BTW - I think DK# P12241-ND 2.4uF 400V poly caps could directly replace the 2.5uF caps from Richardson...


Cheers,
Terry