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



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.