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

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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:

http://drsstc.com/~terrell/pictures/TestResistors.JPG

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:

http://drsstc.com/~terrell/pictures/OutputTestHookup.JPG

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:

http://drsstc.com/~terrell/pictures/FullSystem-01.gif

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:

http://drsstc.com/~terrell/pictures/OutputVoltageTest.JPG

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"!:

http://drsstc.com/~terrell/pictures/FullSystem-02.gif

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.....

Cheers,

	Terry