OL-DRSSTC 7 - It's Alive!

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Terry Fritz <vardin@xxxxxxxxxxxxxxxxxxxxxxx>

Hi All,

I was not able to work on the OL-DRSSTC concept thing for the last 
few days, but today I am back at it.

It seems to work fine!!!!!

I am just running in a "single shot" mode right now and there is a 1 
ohm damping resistor in the primary loop just to keep things 
pleasantly under control for testing.

Here is the first time the primary only system fired where the CT 
feedback fully "takes over" the IGBT gate drive.  The primary was a 
56uH coil, 37.5uF cap and the 1 ohm "load" resistor.  The 440uF 
storage cap was charged to 200VDC:

http://hot-streamer.com/temp/OL-DRSSTC-2005-10-09-01-First-Fire!.gif

Primary loop current is in yellow and gate drive voltage is in blue.

At about 40 amps of primary current, the gate drive voltage locked in 
solid and was nicely clipped at 25 volts by the gate transorbs.

Here is the entire burst:

http://hot-streamer.com/temp/OL-DRSSTC-2005-10-09-02.gif

Here is the tail:

http://hot-streamer.com/temp/OL-DRSSTC-2005-10-09-03.gif

Here is the start:

http://hot-streamer.com/temp/OL-DRSSTC-2005-10-09-04.gif

Here is primary current (yellow) and buss cap voltage (blue).

http://hot-streamer.com/temp/OL-DRSSTC-2005-10-09-05.gif

Here is the first time I fired the full coil with the secondary in 
place. This is a very significant firing in that it simply "did not blow up "

http://hot-streamer.com/temp/OL-DRSSTC-2005-10-09-06.gif

The coil was pretty out of tune so I took a turn of the primary:

http://hot-streamer.com/temp/OL-DRSSTC-2005-10-09-07.gif

I took another turn of the primary and hooked the plane wave antenna 
to the blue channel.  Top voltage is about 80kV:

http://hot-streamer.com/temp/OL-DRSSTC-2005-10-09-08.gif

Here is the first time it arced to a grounded object.  Just a 
grounded rod a foot away.  Nothing blew up :-)))

http://hot-streamer.com/temp/OL-DRSSTC-2005-10-09-09.gif

Since I am firing single shoot I could not get an arc "picture", but 
trust me :o))

Here is the bench setup"

http://hot-streamer.com/temp/OL-DRSSTC-2005-10-09-10.jpg

The OL-DRSSTC "guts":

http://hot-streamer.com/temp/OL-DRSSTC-2005-10-09-11.jpg

The coil side:

http://hot-streamer.com/temp/OL-DRSSTC-2005-10-09-12.jpg

Here is the latest schematic.  Not much changed other than the 
trigger circuit is using a 0.47uF cap and I changed back to the old 
primary cap and inductance since it was easier to fiddle with right now.

http://hot-streamer.com/temp/OL-DRSSTC-06.gif

The trigger circuit still needs work.  The "cheap" caps get hot so it 
needs nice foil poly caps too!!  I think you need to "tune" it so 
that the trigger pulse is also a resonant circuit near the coil's 
frequency.  It takes a good powerful pulse to start the thing.  It 
"could" be more sensitive, but I am afraid it might not turn off well 
if it were too easy to trigger.  Modeling suggests that "turning off" 
could be a significant problem...

The trigger loop through the CTs acts like and inductor.  The trigger 
circuit cap and SIDAC are just like a coil's primary circuit.  The 
2.7 ohm resistor could be lowered too give more "bang' too...  The 
tiny SIDAC seems to run stone cold and loves this service!

It does take a primary voltage over about 200V to get the coil to 
trigger.  It would be nice if that were lower so it could run under 
power control with a variac...  I was also using a 100 ohm resistor 
"tapped" across the bridge output to give extra kick for manual 
firing.  Interesting since that opens up some possibilities for 
120BPS and other very simple BPS controls.

BTW - I know many are interested in the Gate drive and I forgot to 
get a scope picture of it, so I went and did it now:

http://hot-streamer.com/temp/OL-DRSSTC-2005-10-09-GateDrive.gif

Yellow is primary current and blue is a gate voltage.  Between 15 and 
16uS you can see the dead time glitches.

http://hot-streamer.com/temp/OL-DRSSTC-2005-10-09-GateDrive1.gif

timing seems pretty late, but the peak current is low so the gate 
drive is low and slow too:

http://hot-streamer.com/temp/OL-DRSSTC-2005-10-09-GateDrive2.gif

http://hot-streamer.com/temp/OL-DRSSTC-2005-10-09-GateDrive3.gif

http://hot-streamer.com/temp/OL-DRSSTC-2005-10-09-GateDrive4.gif

In general, it seems to work fine!  Some technology certainly need to 
be worked out, but there is no fundamental problem at all...  And, it 
makes foot+ sparks "easily" even the "first time" ;-))

Cheers,

	Terry