RE: DRSSTC - I think I heard Cross Conduction...

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Sue Gaeta <sgsparky@xxxxxxxxxxx>

Hmmm,
You know what? I went through the trouble of beefing up the condutors in 
the DC supply line, then I put that @#$%^& fuse in there. I even put it 
after the bulk caps because I was worried about all that energy being 
dumped into a fault. I have had MOSFETs blow the cases off, but no blown 
fuse. This fuse could be causing more problems than it solves with its L & R.

I think I will get rid of that fuse, and just put a smaller fuse in the variac.

The secondary resonates at 140.4 Khz with the big topload. The pulse width 
is 300uS, occurring every 10mS (100hz break rate). The tank capacitor is 
0.186uF. The secondary is 4.5" in diameter, and the primary is 5.5" in 
diameter.
You could be right about the voltage. For my priliminary test I was using 
40 volts DC input from a supply that current limits at 3A. I was probably 
strangling the poor thing! I used that same exact supply for all three tests:

8 x 2" torroid:  primary tapped at 6 turns,  avg input current = 0.3A at 
40V, spark length = 2.5"

13 x 3" torroid: avg input current = 0.5A at 40V, spark length =2"

20 x4" torroid: primary tapped at 7 turns, avg input current = 0.85A at 
40V, spark length = 0.5"

When I plug the H bridge into the variac, and bring it up to 130 volts, I 
get 15" streamers which are much hotter looking and louder than when I was 
running this coil without the primary capacitor. I should be getting more 
than that! (???)
Maybe it's that @#$%^& fuse!

Thanks Steve,

Sue

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

>I am beefing up the traces, but I don't think anything could stop it once
>it lets go. But the breakers and fuses did not trip so the IGBTs blew
>themselves out of the circuit very quickly.

Hi Terry, Sue, all,


Yes I agree, transistor destruction is just a fact of life. There is no
practical way to protect them with fuses or breakers, the best you can hope
for is that a fast blow fuse would stop the transistor case from actually
rupturing once it had shorted. But a fuse in the DC supply line would add
more resistance and inductance which are Bad Things. The usual procedure
seems to be just let them rupture and build the rest of the wiring chunky
enough to survive an "event".

PS- I second Bob's comment about the loop area of power connections. You can
g et all sorts of unwanted ringing this way. If you minimise the loop area
everything should run cooler and more efficiently. I like to use laminated
copper sheets for the DC bus.


>When I build the bigger H bridge, I have to look into why I can't use as
>much top loading as Steve W. uses. I have enough extra turns available to
>get it in tune, but I get smaller sparks, and it draws much more current

That's interesting. What frequency, tank capacitor, DC bus voltage, pulse
width, etc, are you using? I'll try putting it into my simulation program
and see what it says. My gut feeling is that you aren't delivering enough
power to pump the larger topload up to a decent voltage.


Steve C.