Re: Tiny DRSSTC completed

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Sue Gaeta <sgsparky@xxxxxxxxxxx>

Hi Steve,

I wound a coil with 36 awg wire, and I know that that is quite an 
accomplishment all by itself, congratulations!

Could it be that your driver chips really don't like operating at that 
frequency? I swept mine (H bridge supply off), starting around 100KHz, and 
as I got higher in frequency, the driver supply current would increase and 
the ICs would run hot. When I got to around 400 KHz, I saw the current rise 
above an amp and I quickly shut it off! I was afraid that Chernobyl would 
happen before I had time to crank the pot the other way again!

I notice that people tend to worry about whether the IGBTs can handle the 
high frequencies, but don't think about the frequency limitations of the 
driver.

Sue

Tesla list <tesla@xxxxxxxxxx> wrote:
Original poster: Steve Ward

Hey everyone,

I built this super cool little coil over the past few days, its a very
small DRSSTC. You can read all about it here:

http://www.stevehv.4hv.org/drsstc.5.htm

Thats my new site by the way... though its not close to being done yet.

http://www.stevehv.4hv.org/

Anyway, this little guy is running at 350khz, and thats due to the use
of 36awg!! You know, the stuff that is impossible to see with the
naked eye unless you are within 6" of it. Even this tiny coil has a
DC resistance of 200+ohms.

So far ive blown a few things. First to go were some gate drivers,
not sure what i did wrong but they werent happy and got really hot
(this was during the prototype stage). The spec sheet says they arent
supposed to latch up, but i think that is exactly what happen s, and it
seems to be a rare event that i cant explain. Secondly i welded my
power switch shut. I guess it didnt like the inrush current from
charging the voltage doulber caps instantaneously ;-), i now have a
soft start setup... no more problems. Finally, i blew my bank of
little 1600V PP caps i was using for a MMC. Not sure if it was the
current or the voltage that did them in, but i noticed the performance
dropped off considerably, and these caps were super hot. Now they
read 20% lower than they did just earlier today! That is, they were
at 51nF, now its down to 42nF... that certainly is not good. Replaced
them with the good old CDE 942C series caps, 3 x .15uf in series...
shouldnt have any problems there :-). And im happy to report that NO
IGBTs have been sent to the trash can as of yet :-), then again i
think i can squeeze 18" sparks out of this setup, so we will see what
happens as i try to reach that goal. I can smell the burning silicon
already...

Seeya,

Steve