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RE: OLTC II Even bigger arcs
Original poster: "Steve Conner" <steve.conner-at-optosci-dot-com>
>You mention that at one point you had to use a breakout point on your
>(smooth) 8" x 24" toroid. That interests me because, (when my SSTC was
>working), I didn't need one.
Yes, I did use a breakout point. The OLTC is like a classic spark-gap coil,
it starts with a fixed amount of bang energy stored in its tank capacitor,
and if that isn't enough to cause breakout, then tough luck :( However a
SSTC will just keep pumping in energy until it either breaks out, flashes
over, or explodes.
Later, I was able to get it to break out without a breakout point, but I
still used one, because it gave me more tuning options. To get breakout, I
had to tune for maximum output voltage in the absence of streamers, and this
is not the same tuning as for maximum streamer length. (Because of detuning
by the streamer capacitance.) I tried various breakout points, from a tiny
bump to a large spike, and the spark length didn't change.
Again with feedback SSTCs you don't have to worry about all that stuff. The
inverter tracks any frequency changes due to streamer loading and just keeps
the power coming.
*** an aside
Personally I quite like the fixed bang energy of the OLTC. It makes the
system a bit tamer and easier to build/get working.
The OLTC does have an electrolytic filter bank that stores a lot of energy,
but it's connected to the IGBTs through a choke and a fuse, unlike in a big
pulsed SSTC where you tend to have several thousand uF of low ESR caps
bolted directly to your IGBT terminals.
With all that stored energy in a low impedance circuit, a failure of a
pulsed SSTC can be pretty spectacular, the transistors tend to blow apart
and scatter shrapnel and gorilla snot all over the place. (safety goggles
are a good idea here)
But then when a pulsed SSTC works, it's even more spectacular 8-9