Re: Terry's DRSSTC

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Sue Gaeta" <sgsparky@xxxxxxxxxxx>

Me Too!

I am glad to see that there is someone else is still working on these things.
Someone commented that there has been a lul in the solid state work, but I 
have been  quietly working here in my lab too. I finally put the finishing 
touches on my Plamasonic I PCB that I started two years ago, and also 
finished stuffing the two resonant driver boards that I got from Dan. I 
found two nice beefy 24 volt center tapped transformers on Monday that will 
work well to power both the driver circuit and two muffin fans!

I drilled out some holes in the chassis for the Plasmasonic, but the drill 
walked a little in spite of my making divots first. The problem is that I 
have a hand drill with no press, so I will have to move a few holes today :-p.

I built the high voltage rectifier PCB, but I changed my mind and want two 
fuses instead of just one. I want one ahead of the bridge rectifier and 
bulk caps in case something shorts there, but I also imagined another 
scenario. What if a MOSFET shorts? - All the energy that is stored in the 
big bulk caps will discharge across that short and KABOOOOOOOOM!!! (Dave 
Sharpe says it so much better than me!). So now I want another fuse between 
the bulk caps and the MOSFETs. Your line filter sounds like it's really top 
notch, lots of good protection and all too! I don't have anything between 
my line cord and HV supply except a fuse :-o. Maybe I need to re-think 
things a little better. At least I have a commercial line filter on my 
built from scratch SSTC. That's a great idea you have there - using the 
same psu/filter assembly to power each coil. That would save on parts and 
space consumption.

I have also been playing with the driver a bit and swapping out different 
MOSFETs and IGBTs. I had these discontinued 47 amp devices from ST that I 
thought would be perfect for my coil, but the gate capacitance is 
tremendously high, and the waveform was awful, and the driver supply 
current was above an amp!
I swapped to the IXYS 48 amp ones and they were much better. I dropped the 
gate resistors to 4 ohm and added schottkys, and the results were better 
still. Beautiful waveforms, and the supply current was only 0.6A. People 
who complain about their driver chips getting hot should experiment like 
this. Even different brands of devices with close to the same ratings can 
be considerably different.

I think you are right on the Poly filter caps at the IGBT bridge. I think 
Dan himself had one on his DRSSTC that he demo'ed at the Teslathon, but it 
isn't in the schematic.

I should have the Plasmasonic one up and running by tonight.
My DRSSTC progect is going to start out as a SSTC for now until I can find 
those capacitors at a reasonable price, or in someones garbage :-). I still 
have a ways to go yet on that project. I still have to wind the 1:2 GDTs, 
and wind the much lower Fres secondary. No more cheating and using my 
medium sized SGTC secondary for all my solid state excursions any more!

Good luck on yours Terry!
Sue


Tesla list <tesla@xxxxxxxxxx> wrote:
Original poster: Terry Fritz


Hi All,


I have been working on ?my? DRSSTC :-) I have Dan's Resonant Driver Board
put together without too many left over parts ;-) Real nice stuff Dan has
figured out!


Today I worked on the input section design. I went with a voltage doubler
so I can run fully off 120VAC. I also added a bunch of heavy
filtering/protection for the AC line.


http://www.hot-streamer.com/TeslaCoils/MyCoils/DRSSTC/DRSSTCinput.gif


It runs off my 15 amp variac box so there is no soft start. The MOVs and
hydraulic breaker protect the line from the usual over voltage and shorting
events. The filter is a dual stage type to cut RFI and all that. The two
diodes are ?slightly? over rated sinc e I hate blowing stupid diodes ;-) The
220uF caps and 1 ohm resistors form a low pass filter (might need poly MF
bypass too?). Right now it is a rather low Fc frequency since I suspect
that the resistance will have to be smaller in the long run. The resistors
also happily control fault currents ?if? things go nukies. The main caps
are four 4700uF 200V caps and two 1000 ohm 100W resistors to drain them.
Hmmm... Maybe those should have been 10K/25W... :o) No wonder I have so
many extra parts laying around :D


I think there should be some big poly caps right ?at? the IGBTs. I note
some of Dan's coil pictures show these. I worry that the big electrolytics
may not like 300 amp 200kHz stuff and may wimp out. I have some 4.7uF 600V
500Ap polys that I can mount right on the IGBTs This may also relieve the
need for such heavy copper buss work to the IGBTs. Electrolytics just are
not ?RF? things. Note the fancy stereo amps that have electrolytics for LF,
film for MF, and mica for HF all in parallel for wide band frequency
bypassing. This same input power system may have uses for OLTC stuff too,
noting Steve's successes in heavy DC power for OLTCs ;-))


I hope to run my existing coils off it. My big coil can play tuning tricks
toward reducing primary current which helps the IGBTs. I could also make
new coils, but later when I know what needs to be optimized.


So I am ?trying? to get a DRSSTC going here too ;-)) If all else fails,
Gerry just got a pole pig :-))


Cheers,


Terry


BTW ? Details of my tube coil are at:

http://www.hot-streamer.com/TeslaCoils/MyCoils/TubeCoil/