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Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Wow, a great collection of DRSSTCs! They are all great but I like Chris Hooper's coil with the red plexiglass especially.
My DRSSTC is about the same size, the secondary is 5" x 14". Kind of pushing the definition of "small". The biggest spark I ever got from it was 5ft (a bunch of us were trying our best to, err, reliability test it at the Cambridge teslathon) but I had to shove about 3300W of power in to get that. An extra topload was added and the tank capacitance doubled to 0.1uF @ 10kV too.
In normal operation it gives sparks about 3ft long. It uses a full bridge of 40N60 miniblocks running off 320V DC, with 3300uF of smoothing caps, and runs at 220 kHz. It has a couple of cool features like overcurrent protection, a meter to read out the peak primary current, LEDs to tell you if the PLL is out of lock, and a SCR "dimmer" voltage control circuit to allow you to run it without lugging a variac.
Registered Member #55
Joined: Thu Feb 09 2006, 04:56AM
Location:
Posts: 149
Its been awhile since I have posted anything about this little coil. The coil ran great for quite sometime, then one day after a good long 10 minute run I disconnected the interupter remote from is BNC jack while the coil was still powered up (I thought I had turned it off!) The coil spit a gasp of CW looking sparks and went silent. I blew everything, both IGBTs, both diodes, and all 5V logic. It has been a real pain in the ass since. I replaced just about everything twice over. During the extended repair process I bought a few different spun torroids, one small guy for this coil (8"x2"). In order to get it to work properly with the spun torroid I had to reduce the MMC capacitance by 1/3 (primary tapped at 5) Last night I was running the coil for the first time since I re-replaced the IGBTs and it finally seemed like it was happy. After a 30 second run it stopped working again. One of the IGBTs read shorted. Damn I hate this thing. So now its back to the drawing board. I need to drop the Fres, so I am going construct a drier duct torroid. I also am thinking of adding the diode+10 Ohm resistor in serries with the gate to add deadtime. I had done this originally, but removed the components the first time I blew everything. Could my Fres just be too high for the 40N60s to handle? With the spun torroid I am reading approx 220Khz. Now I am going to rebuild the whole thing including the stand. For one thing I need to make it easier to repair! I will have a few boards built by express PCB and I am thinking acrylic for the stand and supports and coil form.(C.Rs coils sure look good that way! )
Registered Member #139
Joined: Sat Feb 11 2006, 11:01AM
Location: Perth, Western Australia
Posts: 358
williamn wrote ...
I will have a few boards built by express PCB and I am thinking acrylic for the stand and supports and coil form.(C.Rs coils sure look good that way! )
Check out the DRSSTC board thread if you're thinking about a new driver board.
Registered Member #55
Joined: Thu Feb 09 2006, 04:56AM
Location:
Posts: 149
Thanks for mentioning it, I already have a driver board designed, tested and prototyped, its based on Steve Wards DRSSTC #3, with a different OCD circuit. I usually just etch the boards myself, but ExpressPCB does such a great job. I already submitted my order today for a couple boards. These boards have everything on them halfbridge and all, the pic below is the prototype I am using in the minime coil. The new ones are based off of it.
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Small DRSSTC
(I thought I had turned it off!) The coil spit a gasp of CW looking sparks and went silent. I blew everything, both IGBTs, both diodes, and all 5V logic. It has been a real pain in the ass since. I replaced just about everything twice over. During the extended repair process I bought a few different spun torroids, one small guy for this coil (8"x2"). In order to get it to work properly with the spun torroid I had to reduce the MMC capacitance by 1/3 (primary tapped at 5) Last night I was running the coil for the first time since I re-replaced the IGBTs and it finally seemed like it was happy. After a 30 second run it stopped working again. One of the IGBTs read shorted. Damn I hate this thing. So now its back to the drawing board. I need to drop the Fres, so I am going construct a drier duct torroid. I also am thinking of adding the diode+10 Ohm resistor in serries with the gate to add deadtime. I had done this originally, but removed the components the first time I blew everything. Could my Fres just be too high for the 40N60s to handle? With the spun torroid I am reading approx 220Khz. Now I am going to rebuild the whole thing including the stand. For one thing I need to make it easier to repair! 
I will have a few boards built by express PCB and I am thinking acrylic for the stand and supports and coil form.(C.Rs coils sure look good that way! 
)
