Re: SSTC not working as expected

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

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Rob,
         I'm glad you got it working. Just FYI, the expts I mentioned 
yielded the following results with a generator capable of 3VRMS-at-2A:

Direct base feeding yielded a moderate output.

Feeding a coupled primary caused the generator to current limit 
whenever Fr was closely approached and would light fluoro lamps 
several feet away from the coil. The thing was like a black hole to 
the source. I wonder what it might have done had there been no 
current limiting with only 3V of drive? It was clear that it was 
generating thousands of volts but as always, was extremely sensitive 
to capacitive loading (e.g. me moving a probe close to it). As soon 
as the lamp struck, the loading conditions changed and I had to 
retune for max light output with the lamp lit.

More below:

On 6 Jun 2002, at 12:00, Tesla list wrote:

> Original poster: "rob by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<rob-at-pythonemproject-dot-com>
> 
> Tesla list wrote:
> > 
> > Original poster: "Alan Sharp by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <AlanSharp-at-compuserve-dot-com>
> > 
> > Rob,
> > 
> > Your topload maybe too big - have you got a breakout point?
> > 
> > Another possibility (though unlikely from your description) is that
> > you are at a harmonic frequency - not the fundemental.
> > 
> > how do you stop the flyback transformer from saturating with DC?
> > 
> > Is that snubber big enough?
> > 
> > Alan Sharp
> > 
> 
> Hi Alan! Great to see you on the list.  I fixed my problem, it was too
> low gate drive.  What threw me off was that there was still alot of RF
> coming out of  the transformer.   I am definitely at the fundamental,
> got lots of streamers before the FETS and/or IGBT's blew up.  But the
> new IR "Warp Speed" IGBT's do switch at 250khz, and last longer than the
> FETS, probably due to lower dv/dt.  I am impressed.
> 
> The purpose of this coil and setup is to try unusual driver
> configurations.  I'm pretty bored with the usual stuff.  Yes I do need
> to revisit the snubber.  And I will rewind my ferrite transformer today,
> and also try a gapped one.
> 
> I have been thinking alot about the traditional interupter.  An
> excellent question is:  Why do you just get a small flame or streamers
> CW, but giant discharges when using an interupter?  I believe its the
> flyback principal.  With the interupter you give the coil a chance to
> build up a hefty magnetic field, and then suddenly shut it off.  Perhaps
> the result is a big discharge from the collapsing fields.  Or another
> possibility is that when power is on, the driver is too closely coupled
> to the coil, so when the interupter acts, the coil freewheels its stored
> energy.  Just theories.  But probably could be proven/disproven in a
> faraday cage with a dual channel scope.

I think it's more a matter of plasma characteristics. With CW you get 
a continuously ionized path which clamps the output. With interrupted 
operation, the coil has to ring up to some much higher breakout 
voltage every time. 

Regards,
malcolm