Re: Help! My Coil Blew Up

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

Original poster: "Robert Jones" <alwynj48-at-earthlink-dot-net> 

Hi,

I think you may need to give people a little more time to respond.

I don't have any direct experience on SSTC.  Your failure sounds like it
could be caused by a lot of things.

I would expect the bigger the toroid the better to get your frequency down.
Your frequency does seems high that maybe causing the unexpected heating.
In any case if the fets are getting unexpectedly hot it indicates you have a
problem. I think you need clamping zeners too. Stick to 12v in till you have
every thing looking right unless you have a bucket of new fets.  I also
suggest you run it of an external oscilator untill you have it all checked
out and check the signal from your pick up.

Your link down loads a file with an unknow extension??

Bob

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Wednesday, February 04, 2004 7:48 PM
Subject: Re: Help! My Coil Blew Up


 > 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
 >  >
 >  >
 >
 >