OL-DRSSTC 9 - Better trigger!!

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Terry Fritz <vardin@xxxxxxxxxxxxxxxxxxxxxxx>

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