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Re: IGBT SSTC finally possible?

Original poster: "Steven Ward" <srward16-at-hotmail-dot-com> 

>So you're saying the sparks look just like the sparks of a normal SGTC?
>(except they have more energy and thickness).  That is a major
>advancement.  The OLTC of course also produces normal SG type
>sparks, but it uses cap discharge and ringdown.

Yeah, if you saw it in person you might scratch your head and ask "where is 
the spark gap?".

>I think Ken H said he needed to run his durations at about 350uS
>before breakout because he used a large toroid.  So maybe if you
>had such a large toroid, you'd need similar durations to break out?

Yes, thats very much possible.  My setup ( being a rather extreme spark 
length to coil length ratio) doesnt work without at least some sort of 
breakout.  Due to the high coupling it just arcs down the secondary... i 
need to fix this.

>It seems to me that if the primary is resonantly building up energy
>in your coil design, then this energy would also be transfering to the
>secondary at the same time.

Yes, exactly.

  So the coil may follow CW type
>energy transfer rules rather than disruptive coil rules, for the primary
>to secondary energy transfer,even though your coil is pulsed.
>Of course this depends on how one defines *CW*.   In any
>case the energy builds.  By using a filtered DC
>supply, this gives the storehouse of energy that is needed for
>large peak voltages and currents.

Yep.  Low ESR caps help a lot.  I also have some 10uf PP caps right on the 
IGBT half-bridges.

  This is something like my
>pulsed DC tube coil work that used filter caps to store large
>amounts of peak energy despite a low peak energy draw from the
>mains.  The difference was that my system still had the very
>long 8mS duration.

Yeah, 8ms is a long time!  i would really like to see some more info on 
this John.  What were the resulting spark lengths?

>What sort of coupling do you use?  Does the system require a
>tight coupling?

Yeah, rather tight at about .22 now i think.  I recently (today) tried a 
new primary with lower coupling and the results were pretty sad.

My current downfall is that the 1/4" cu tube gets HOT!!!  My MMCs get a 
little bit warm too, but not enough to bother me.

>>No wonder you're getting long sparks !   Who needs NST's right?

Like Steve Conner said: "Pigs? Where we're going, we don't need pigs!"

And now that i look at my large SGTC in the garage, thoughts of selling off 
all its parts for money for new IGBTs and MMCs comes to mind.  Really... 
the high voltage power supply is phased out of it and yet the results are 
just as awesome if not better.

>I think the relatively short duration pulses also contribute to the
>spark appearance.  It seems that long durations tend to produce
>more flamelike, thick sparks.

Yep, seems that once you get the leader formed, the rest of the power just 
goes into forming corona ON that leader making it look thicker.

>Well it's all very interesting.  I hope to find time soon to work on
>such things.

It sure is fun!