I'm using 6 boards with my 14.4kV pig, but I'm also running it through a
home-made stack of 2 paralleled 20A+ variacs on each leg (4 total variacs ganged
on 1 shaft). I'm using a homemade fixed ballast choke as well to limit the
pig current to 60A. Haven't tripped the 50A breaker feeding my control box
yet. But I can put 280V into the pig to get the voltage out for 6 SISG4 boards
to work.
It's weird to ramp up the variac until all hell breaks loose. It sounds
nice and smooth, like a synch gap, at the "breakover" point. About 30A draw
with .150 uF primary cap. Cranking just a bit more, and up to the max on the
variacs, suddenly gives the streamers a mean, obnoxious, metallic ringing
tone, and makes the streamers dart out much more chaotically (doesn't seem to
support sustained arcs as well). The Pig current draw maxes as well.
It would be nice if you could do some breakrate measurements with your
setup and verify that the bps is going through the roof when this happens.
Probably not good for the SISG (or the primary caps!). Maybe if we were clever
we could find a way to pulse this voltage in, but sustain the streamer with a
normal rate. Only seems to make a 15% increase in streamer length, but boy
does it look angry!
Are there any coil specific issues? For example, can I use a standard
8.5" x 40" coil with 9"x30" spun toroid? This coil is a bit lossy (wound
with 24 awg at 1790 turns).
With a 6" coil, I had to eliminate my strike rail or the secondary would
arc to it (from a bunch of points from halfway up to the top). The SISG
doesn't seem to care one bit about primary strikes. But I'm so overpowering the
6" coil that the secondary streamers are reaching around under the primary and
killing electronics under there. Maybe put everything under the primary in a
big steel box, like Bunnikiller does with his 30kV pig coil!
See my next post for a simpler solution that I tried and works really
well!
Are there any preferences for cap sizes? If
I use the pig, I'll likely go with my 60kV pulse caps at 0.06uF tank size.
My understanding is that primary current over 800A is lossy through the
IGBTs. They really start to heat up if you push things past the "breakover" point
or jack up the primary current too much. I set another board on fire a few
weeks ago, and I chalk *that* failure up to overheating.
My original plan (bought the 6 pcbs from Mark about a year ago) was to
use 4 boards for an sisg coil and 2 boards to power my attempt at
Tesla's flat coil at 1/2 scale.
I'm making a twin 6" setup with two SISG4 boards. I'm trying to be
conservative on the design.
So, if there are some "coil LC preferences", then that would likely
dictate a new coil.
I think keeping it around 130kHz and 800A peak on the primary would make the
SISG happy. Nobody has reliable data yet on how to "tweak" the resistances
for performance, efficiency, or longevity. Might want an to at least do some
temp monitoring on the heatsinks to see what works.
I haven't been scientific in my approach, just fooling around trying to
break the darn thing!
-Phil LaBudde
Center for the Advanced Study of Ballistic Improbabilities
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