Folks-
Last night I finally got around to running the SISG on my 12" secondary
"pig" coil. Previously I had reported on running the SISG on a 6" coil, but
with a 10kVA pig. That coil was a bit small for the power.
I only ran for about 30 seconds before I saw a flash from the
electronics under the primary and the coil quit working. Once again, a section of one
of the rectifier legs blew out (diodes vaporized, the string in several
pieces).
After investigating today, I found that during that brief run one of the
SISG boards was damaged. One SIDAC vaporized, its two brethren cracked, and
the IGBT in that section shorted as well. Although the IGBT has 10 ohms of DC
resistance from gate to C and E, the collector and emitter are a dead short.
The SIDACS explode, but you can't tell a dead IGBT without a meter.
FWIW, I'm still running the same .220 uF total primary tank. Calculated
~55 uH of primary, 50kHz Fres calc and measured. Pig ballasted to 60A max,
variac'ed for 280V out. I didn't crank the variacs past where the gap fired
rhythmically, since I'm running STR and I didn't want the BPS to run away (easy
with a SISG). Six SISG-4 boards for 21.6kV firing point.
I had just finished doing some runs with the same setup with the RSG. I
had just finished my "Terry Filter" for the pig earlier that day, and it
appeared to eliminate much of the kickback I was having to the control panel. I
simply removed the ARSG and installed the SISG and rectifier.
Based on my experience so far, I wouldn't push the IRGPS60B120KDP IGBTs
past 5kVA. The instantaneous currents seem to cause damage very quickly.
All my previous caveats about high-powered SISG coils still apply as well.
FWIW I was getting 10'+ sparks from it before it died, around 10kVA
input (based on the panel volt and ammeters for the pig input). I haven't
bothered fine-tuning the coil yet, as I'm working on other issues.
-Phil LaBudde
Center for the Advanced Study of Ballistic Improbabilities
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