Re: Help! My Coil Blew Up

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

Original poster: "S.Gaeta" <sgtporky-at-prodigy-dot-net> 

I guess in spite of the age of the individuals involved, this SSTC crowd is
just another "old boys" club.

I will get it working myself anyway. I have always gotten my projects to
work no matter what, and this will be no exception.


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Tuesday, February 03, 2004 7:41 AM
Subject: Help! My Coil Blew Up


 > Original poster: "S.Gaeta" <sgtporky-at-prodigy-dot-net>
 >
 > I built Justin and Arons Quasi Self resonant coil, and it blew up Friday
 > night.
 > Two mosfets failed. One was shorted and the other blew to bits. Even
before
 > it blew up I was only getting 8" stremers out of it with 130 volt input,
and
 > the fets ran hot. I checked the phasing of all the driver coils and
 > everything looked right. The thing that was really disturbing was that I
was
 > getting ringing on the output of the H bridge even with a light bulb as a
 > load, and 12 volts pure DC on the rails. Some pics of the coil, and
 > waveforms can be seen at
http://community.webshots-dot-com/album/113763981zJBnik
 >
 > Well anyway, the two mosfets that shorted were not supposed to be on at
the
 > same time. The two that were bad would have placed a short right across
the
 > DC buss. The other two tested good. It appears that the driver survived
all
 > this mayhem. It puts out a good waveform with only the good fets connected
 > to it. So at 8:15 PM, the cause of death was determined to be shoot
 > through. Now I had 10 ohm resistors in series with each gate with the
 > schottky across each one. It did improve the waveform, so the only thing
to
 > do now is try and improve the layout of the GDT and MOSFETs.
 >
 > I re-read the HV Guys instructions, and realised that I messed up big time
 > with the antenna. They say to put it no closer than 20" from the
secondary,
 > and I had mine maybe 6" away, so maybe having it too close may have
 > introduced parasitics, or some other bad noise into the system. I also
used
 > 13 turns on my GDT instead of 10 like they suggested. With my resonant
 > frequency being around 236 KHz, which is a little on the high side, I
could
 > probably do better with less turns on the GDT. I also noticed that they
 > don't have a toroid in their photos. I used one because Dan's SSTC had
one,
 > but his circuit is also completely different than this one. Are Toroids
bad
 > with this design?
 >
 > Has anyone else had problems with shoot through or cross conduction?
 >
 > If anyone can offer me any further insight, or suggestions, I would really
 > appreciate it!
 >
 > Thanks,
 > Sue
 >
 >