Re: Help! My Coil Blew Up

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

Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz> 

Hi Sue,

On 4 Feb 2004, at 20:48, Tesla list wrote:

 > 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.

Some things to check (without checking what you've already checked):

- Deadtime between opposite legs of the bridge conducting. The
ringing in the output waveform is a bad sign

- have you disabled the substrate diodes in the MOSFETs? A circuit
diagram would be helpful (although unless it is posted pronto, I
won't be able to see it before next Monday NZT as we're about to have
a long weekend)

An old boy who hasn't built one yet.


 > ----- 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 > >
 >
 >
 >