Re: Solid State Gap

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

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

Hi Terry,

> >BTW - have you tried cutting the gap off at Ip 
> >max (hint - interesting to test one or two old theories out there - 
> 
> :-)))  I will have to try that...  I ran through the cutoff range and
> didn't notice anything "odd" ;-))
> 
> >watch the spikes ;)? 
> 
> IGBT's have lower high-current losses and the fancy reverse diodes cut
> down drastically on the usual spike problems.  The signals look
> perfectly clean so far.  Amazingingly clean in fact.  I never could
> get MOSFETs to work real well but these IGBTs seem to love this stuff.

Actually it has nothing to do with the switching devices as such. I 
read this crazy idea once which suggested that if you cut the gap off 
with all energy in the mag field, it would cohere in the secondary. I 
tried this by cutting the gap off at the end of the first 1/4 cycle 
and was rewarded with soaring drain voltages as the primary-induced 
fields coupled themselves straight back to the primary (primary-
primary k being almost 1 and primary-secondary k being about 0.08. 
      The log response in the primary shows normal resistance being 
present and you can calculate Q using traditional formulae. 

Cheers,
malcolm

> >
> >Regards,
> >Malcolm
> >
> >On 18 Mar 01, at 20:26, Tesla list wrote:
> >
> >> Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>
> >> 
> >> Hi All,
> >> 
> >> I did more testing with my solid state gap tonight.  I actually
> >> have it hooked up to my small coil but was only running with a
> >> primary voltage of 50 volts so I could play with things :-)) 
> >> Pictures of the setup are below.
> >> 
> >> http://hot-streamer-dot-com/TeslaCoils/MyCoils/SolidStateCoil/2001-3-18
> >> /Se tup.jpg
> >> 
> >> http://hot-streamer-dot-com/TeslaCoils/MyCoils/SolidStateCoil/2001-3-18
> >> /SS gap.jpg
> >> 
> >> As this picture shows, it works (no load on top terminal, thus the
> >> very long ringdown time) :-))
> >> 
> >> http://hot-streamer-dot-com/TeslaCoils/MyCoils/SolidStateCoil/2001-3-18
> >> /Te k00007 .gif
> >> 
> >> The IGBT and the reverse diode seem to work perfectly well.  I
> >> looked at no quench and first notch quenching:
> >> 
> >> http://hot-streamer-dot-com/TeslaCoils/MyCoils/SolidStateCoil/2001-3-18
> >> /No Quench .gif
> >> 
> >> http://hot-streamer-dot-com/TeslaCoils/MyCoils/SolidStateCoil/2001-3-18
> >> /Qu ench.gif
> >> 
> >> I was originally thinking of just not worrying with quenching and
> >> shutting the IGBT of after a few hundred microseconds.  However,
> >> unlike regular gaps where getting first notch quenching is really
> >> hard, with this gap I just set the pulse width trim pot :-))  I was
> >> using a 3pF probe (Tek 5100) in series with a 220k Ohm resistor
> >> hooked to the coil's top terminal to simulate a streamer load.  The
> >> RMS output was 78.72Vrms with no quenching vs. 87.03Vrms with first
> >> notch quenching.  So that gives 10.6% more power. That 10% power is
> >> also going into the streamer rather than heating the IGBT which is
> >> a concern.  I was worried the cheap fiber optics may not run at
> >> this high of speed but all seems well.  I was also worried that the
> >> soft turn off of the IGBT would be a problem.  However, it seems
> >> that once the IGBT begins to turn off, it looks like too high of a
> >> resistance for the energy to swing back into the primary, so it's
> >> cutoff is actually quite effective as shown:
> >> 
> >> http://hot-streamer-dot-com/TeslaCoils/MyCoils/SolidStateCoil/2001-3-18
> >> /Te k00004 .gif
> >> 
> >> Even though the IGBT's cutoff is very slow, almost perfect
> >> quenching is still achieved.  That is an unexpected bonus! 
> >> Although, it makes perfect sense once one see what is going on. 
> >> The turn on time is excellent so not problems there.  One can even
> >> easily slow that down to help reduce that nasty initial pulse that
> >> causes RFI if it is still there with this type of gap. 
> >> 
> >> So It looks like the IGBT gap has the ability to transfer the
> >> primary energy into the secondary and quench very easily.  Of
> >> course, this was only about 50 volts with a little over 1 amp peak
> >> in the primary. There is still a little way to go before I get to
> >> 13kV and 400A peak the small coil normally runs at...  Right now
> >> that would run about $650 but perhaps high voltage/current IGBTs
> >> would be cheaper once all the bugs are worked out.
> >> 
> >> Cheers,
> >> 
> >>  Terry
> >> 
> >> 
> >> 
> >> 
> >
> >
> 
> 
>