Re: Terry's DRSSTC - DRSSTC protector

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Steve,

At 09:03 PM 3/17/2005, you wrote:
> Good luck with this Terry.  I must say i am a bit skeptical, but then
> again i havent really analyzed this as much as you have :-).

I think it will be cool!  It just sticks an extra ~60kHz LC between each 
leg of the H-bridge to "calm" things if there is a "boo boo".  This blurb 
explains it:

http://drsstc.com/~terrell/notes/DRSSTCprotec.pdf


> Just curious, have you tried letting your coil arc to grounded targets
> yet?

No.  Just the "air" sparks are real pretty and have "astounded" audiences 
so far ;-)))  In every case, arcs to the primary have taken out 2 of the 
H-bridge IGBTs but nothing else (with the new beefed up trace cards and 
aside from "explosive" damage to some transorbs).  Minimal damage now days, 
but unbolting the card and replacing the two dumb $7 IGBTs is sort of 
getting old every time I hit the primary.  I will go to a bigger top load 
to fix that too, but I want to "ring out" this problem first for sure.

Only running about 8kV in the primary now and getting anxious to go to 21kV 
on the primary on a bigger coil that can really kick out BIG 
arcs >:))))  My short little secondary coil is easy to carry, but too short 
for secondary to primary arcs :-p

> Aside from the primary coil that is...  Im wondering if maybe
> just the fact that the secondary is power arcing is too much for your
> IGBTs to handle?

Modeling of the arcs suggests a bunch of problem this protector should 
fix.  Basically, these arcs are forcing very fast reverse currents back 
into the H-bridge from the secondary terminal's stored energy.  These 
currents force the bridge into conduction modes at "bad times" and are 
cross conducting the mess.  The protector should slow all this down so that 
things are under "control".

So the "theory" goes...

Cheers,

        Terry



> Steve