Re: IGBT SSTC finally possible?

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

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

Hi John,

Comments within:


>Steve,
>
>The ISSTC work that you and others have been doing is very impressive.

Thanks, i think so too ;)

>I've been busy and haven't been following the solid state TC scene
>very closely.  It looks like the sparks are becoming more bolt-like
>and less bushy in these newer designs.

Yep. my new coil completely resembles a medium sized SGTC except one 
difference.  The sparks seem to have more energy and thickness.  When they 
strike something they stick to it, and ground strikes are very cool.  But 
basically they look JUST like a normal SGTC.

  Is that the case?
>What type of pulse-rates and durations are you using, and how
>is the pulsing controlled?

For my coil, the pulse duration is about 150uS at anywhere from 30 to 300bps.

  Have you compared various pulse-rates,
>and firing pulse durations, etc.

Yes, and basically, longer pulses give longer sparks until a point where 
they dont get longer, but thicker.  The problem is, the voltage and current 
build up with my coil, so the longer its on, the higher the peak currents 
and voltages reach (my setup will hit 600A peak and about 9kv in the tank 
circuit even though im supplying only 350VDC... sorta like resonant charging).

  I don't think I've seen any
>schematics
>for these newer coils, are any available?

Yes, there are schematics on my site.

the controller:

http://www.hot-streamer-dot-com/srward16/ISSTC/ISSTC_sch1.JPG

The power electronics:

http://www.hot-streamer-dot-com/srward16/ISSTC/ISSTC_sch1.JPG

  I don't think I've seen
>any
>descriptions of the how the coils operate.

Here is how it works (assuming you know how an H-bridge type SSTC works).
Its pretty much the same as a normal SSTC but we have now added a tank 
capacitor that will resonate with the primary (2 resonant circuits like a 
SGTC).  Now, rather than charge up the tank cap and then discharge it all 
at once, we charge up the tank capacitor over many RF cycles (maybe 8-40 
cycles).  Now each RF cycle will build more and more voltage and current in 
the tank circuit, and the secondary eventually sucks it all out and makes a 
spark.  So the reason it makes more SGTC like sparks is the very high peak 
powers, rather than a normal SSTC that has lots of RMS power.  People may 
ask, why use IGBTs??  IGBTs can handle the extreme peak currents (several 
hundred amps) much better than mosfets.  This is the only reason 
why.  IGBTs have been tested to i think 10X their rated currents.  Just 
keep the durations short enough to keep them from exploding ;).  Also, 
overdriving the gates to 25-30V will lower the Vce drop, thus allowing 
these massive currents at the increased risk of perhaps gate punch through.

Hopefully this is insightful.

Steve


>Thanks,
>John