Re: SSTC idea

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "jimmy hynes by way of Terry Fritz <teslalist-at-qwest-dot-net>" <chunkyboy86-at-yahoo-dot-com>


This is the most interesting part of coiling to me. It's is not easy to 
understand, and you can't look up the answer in a book.  I have been having 
trouble getting the drsstc running, mostly stupid stuff like bad 
connections and shorts to the heatsink. I was trying to run the gates with 
no dead time but there was enough stray inductance that the  shoot through 
caused a big enough spike to blast the freewheeling diodes. This week I'm 
adding separate gate drivers, because the turnoff is 1usec slower than turn 
on. I hope I'm almost there, but lately it has been a case of two steps 
forward two steps back. There are wounded parts all over the table, but the 
IGBT body count is still 0 :-)

For most sstcs and vaccuum tube coils, you want higher peak power/average 
power. With spark gap coils, the pk/avg is so high that it doesn't matter. 
If it did, we would run coils in the megahertz range. I think I remember 
Ken Herrick talking about the topvolts on his coil rising linearly then 
dropping quickly at breakout to a near constant value for the rest of the 
burst (the cw wave region). I think that the peak/average ratio is 
important until you reach the point where most of the energy of the burst 
is stored in the topload, as opposed to just pumping through it. I hope to 
be operating in that sudden release area, so it will act like a normal 
tesla coil.

Another reason I think of the drsstc as closer to oltc and spark gap coils 
than to staccato SSTCs and VTTCs is that each bang is a fixed length, 
determined by coupling and fres, so running it cw would be like  firing the 
gap right after quenching. if I drove the gates continuously, it would be 
operating in a different mode, and would indeed vaporize (or at least 
everything surrounding my precious IGBTs would)

  Tesla list <tesla-at-pupman-dot-com> wrote:
Original poster: "Stephen Conner by way of Terry Fritz "

At 20:42 15/03/03 -0700, you wrote:
 >Original poster: "Jim Lux by way of Terry Fritz "
 >
 >
 >
 >
 >Herein lies the fundamental difference between CW (tube and SSTC) coils and
 >disruptive coils. A huge tube coil (even a 100 kW one) doesn't have the
 >peak powers that a disruptive coil does. And that's why the spark
 >characteristics are so different. The power levels when the spark is
 >growing are radically different.
 >
 >
 >By lowering the fres to something lower, you can get the peak currents down
 >(L gets big) for the same bang energy, but that effectively increases the
 >time over which the energy is transferred, reducing peak power to something
&gt!
;reasonable.. Go far enough, and the peak to average ratio starts to get
 >close to 1 and you have a CW coil.
 >
 >Staccato operation of a tube coil is sort of in between..

I think this is pretty interesting, I can see the disruptive and CW camps
kind of converging nowadays. If Jimmy Hynes ever gets his DRSSTC to work
then the confusion will be complete. As far as I understand it, the DRSSTC
is a kind of ultra-staccato SSTC with a resonant primary that builds up
hundreds of amps. It operates in short bursts of ~100uS and if you ever
tried to run it CW it would vaporise.

Steve C.





Jimmy