ISSTC Development
Updated June 13,2004
Personal correspondence with Dan (removed from public page 6-13-4)
Q. 6-6-4. Howdy Dan: A couple Q's, on your site you mention a crowbar circuit on the new schematics, I like that idea and have tried to identify it on the new Full Bridge Power Section and don't see it. Is it on one of the revised pages I don't have yet? Wouldn't there would be fuses and maybe signal diodes in a crowbar? On your Self-Resonant Driver schematic, regarding parts UH:A thru UH:F, SN74HS14N. I can find nothing on this part, the 'HS' should indicate 'High Speed', but I can find nothing in any broker's stock or even data sheets. The '74HC14' is the closest that I've located and is a hex Schmidt trigger. Any ideas?
A. John, Yeah, I haven't incorporated it yet in my schematics. But the crowbar is basically for the input power rail. I have a shorting switch for the big capacitors (to discharge through a resistor), and another relay for input power. During crowbar fault, both these relays activate turning off input power and also discharging capacitor.
Crowbar faults:
Duty Cycle exceeds some limit
Voltage Input exceeds some limit
+15V Drive rail drops below specified voltage (usually 14V)
As for the SN74HS chip, the HS I believe is obsolete now being replaced by the
HC ? Its really not critical at all - any of the logic series should work.
In fact, now I'm using a tri-state hex buffer with an ENABLE. This also gets
connected to the crowbar circuit so that during a failure condition, the
full-bridge stops switching altogether. Dan.
Tesla List Discussion
6-5-4. Increasing the coupling also helps in theory, but I think it's a dead end, as it encourages flashovers. In the long run you may need to LOOSEN the coupling, to get the primary out the way and stop it getting incinerated. More voltage helps too- going to 240V should double your spark length. And using heavier wire for your primary will be a must, and a bank of electrolytic caps on your H-bridge DC supply. You'll probably need to shorten the on-time too as you get beyond the IGBT ratings :)))) Steve C.
I agree. I think the ISSTC may benefit from increased primary voltage (up to 480VAC mains input) and using a standard pancake type primary coil. I am presently in the process of trying this out. Also, the comment by Steve regarding using heavier wire for your primary may help, but I don't think its "too" critical. I have so far gotten 80" maximum arc and I still have my temporary 12 AWG stranded wire in my primary tank circuit connecting EVERYTHING! Eventually, I'll upgrade to 4 AWG welding wire (which may increase performance), but it must be said, that small primary wire won't limit performance too much. Dan.
July 14, 2004. Check out this link to some great info on IGBT's, gate drives, etc. From thedatastream. http://thedatastream.4hv.org/gdt_quick.html