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Terry's DRSSTC actually hooked to a coil now >:-))

Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>

Hi All,

Well I actually have it hooked to a coil now ;-)

I still have heavy primary resistance in place since that allows me to really "toy" with things without driving lots of power or big arcs and such:


I "REALLY LIKE" putting these resistors in series with the primary for testing. They knock the primary Q way down and easily limit the coil's power to anything you want. They are just two Ohmite 25 ohm variables in parallel from DigiKey. You still can operate the coil into all kinds of situations but the current and coil power can easily be limited as you please. Once you have the buss up to 300V, these resistors still let you limit primary current even with a full coil connected. Super nice ;-)) Don't run high BPS rates our you might fry them ;-)

Monitoring the output could not be easier either:


Since the output from the box is relatively tame low voltage (+-340V) stuff, you can just slap on a current monitor and Tek5100 100:1 probe without a thought. I connect the ground of the probe to the system ground and to one phase of the output so all the voltages read 1/2 of what they really are. No need for a differential probe. If one knows the system impedance and the primary current, you know all the primary voltages too. I can drive about 50 amps with the resistors (and the box's current limit setting ;-))) and the Zo is 69 ohms so the primary cap voltage is 50 x 69 = 3450V.

This is a really cool scope pic:


Since I drive off primary current rather than secondary current, I get full notching and all that. You can easily see how the switching follows the zero current crossings even though the frequency is shifting between f1 and f2. There is some discussion on other lists about f1 and f2 things... (yes, I do spy on you 8o)) but by following primary current, you just "ride along" with the frequency... Even in this resistive limited primary case, the primary cap voltage is 3500V and the output voltage is probably in the 85,000 volt range!! The big top load does not break out but I can hear that it wants too ;-))

I just had to taste it:


No worries, "I am a trained professional" ;-))  Note the safety glasses ;-))

One super cool thing I have noticed!! The more power you run the cleaner the signals get!! Not sure why... One would think it would be the opposite. It might be because with everything hooked up "normally", the noise is naturally controlled by the design rather than having probes running off everything with test connections all over. I do worry about hooking probes into it and having them just act as antennas to transmit or receive noise. Probably best not to go poking around in there at high power...

Here is a "bonus"!:


The cheap current monitor transformers seem to loose the 400nS delay at higher power!!! :-))) In fact, they get darn fast!! You can see that they switch right at the zero crossing almost perfectly!!! The zero crossing delay is still in there (300nS) and now it REALLY looks stupid ;-) I switch off at almost exactly 0 amps (you can just barely see the logic gate delay now) but the zero crossing delay make the turn on really late at 12 amps on the other side... The improved CT performance at higher current might be why the noise seems so much less now too... This is cool since it might be able to run higher like 250 - 300kHz rang coils!!!

Running TO-247 IGBTs at 500 amps, 340V, 500KHz, low heating.... Why use FETs anymore... I bet you could make the manufacturer's reps speechless :o))) "Ahhh.. yea golly... I got like a 340V H-bridge thingy here running 500 amps at 500kHz... Maybe a little over 150kW peak power with a little muffin fan for cooling. But it seems to run darn cool so can I just take out the fan?..." But IR reps are pretty sharp... "Hey!! Your one of those Tesla coil coo coos aren't you!! All warrantees are void, your on your own there pally!!!" :o))

Interesting too that the output voltage (blue) shows "no" droop, "no glitches".... Almost perfect!! Probably due to not probing it in noisy places and the improved crossing timing. But you can see the voltage transition slowing a little at the tops of the square waves now. So the IGBTs are finally slowing down just a little bit ;-)

So I stopped fro the night to ponder...

Much much to ponder.....