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Registered Member #2405
Joined: Fri Oct 02 2009, 12:59AM
Location: Wisconsin
Posts: 140
Filter or snubber how ever you wish to call it the end result is the same it removes the ripple, so I guess you could call it a filter cap. They are placed across the HVDC+ and HVDC-. I tried using only one at first but then added the second one and then it cleaned up the signal really well.
The ringing is usually 10mHZ or higher and this ringing measured right at 10MHZ. you could actually calculate the value needed based on ripple percent but I just winged this one.
Edit: If you look at the H Bridge photo the caps are the two white ones that are stretched across from one side of the PCB to the other attaching to the HVDC supply on both positive and negative rails.
Registered Member #1643
Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039
Daniel Kramnik wrote ...
Killa-X wrote ...
I use voltage Quadrupler on mine with a variac, I run my mini sstc at 400-450v on 500v mosfets, never once had to change out fete and I've had the coil for over a year of use...it's a lovely easy schematic that works for just about any size coil...I use it on a 4.5 x 24 inch, kicking 24-36 inch sparks depending what mode
Amazing! Is this with a full bridge? Minibricks, or TO247?
Do you use laminated busses, TVS? I'm surprised you've been able to get away with running the bus voltage so close to the transistors' ratings. I suppose it's less of a problem with SSTCs than DRSSTCs; I was only ever able to get 9" - 10" out of my mini SSTC, although it was definitely limited by primary-secondary flashovers. What sort of coupling/insulation do you use?
Really old video on the old half bridge...I haven't recorded a video of my full bridge sstc, and I run 500v 50A hiperfete, which are the 2x1.5 x 0.3 or so cm mosfets...
The last picture is an older full bridge but I kept the same secondary and primary. No lamination
I use a 4" sphere as my topload. You most certainly can use spherical toploads!
A salad bowl is not a good topload though because of the edge at the lip. It will be very lossy as the voltage gradient at the edge will allow corona and breakout. Some stores sell metal spheres called "gazing globes" which are sold as decorations for gardens, which work well.
One of the things I need to save up for is a nice toroid though, practicality aside... spheres kind of detract from the visual effect, especially when it makes a really well made coil look tacky.
Heating is a difficult subject to predict but one that is very important to deal with.
I have my MUR860s on 1"x1.5"x.75" finned extruded black anodized TO-220 heatsinks but I honestly question if it is neccessary. Unless you are experiencing massive inductive kick with high currents I doubt the freewheeling diodes would be dissipating much heat. Just my experience though. Some people get tons of fet heating and others almost none, all at the same power levels. It is hard to predict sometimes what will or will not get hot. I know of someone who keeps blowing to-220 freewheeling diodes from heat but their fets run cool to the touch. Mine is the opposite of that, I can only run my 500kVA sstc CW for about 5 minutes before I deem the fet heatsinks too warm even with a small fan blowing on them, but the diodes are ice cold. Primary coil heating is also a thermally limiting factor with my sstc, but I have massively high coupling as it is built like a bi-polar TC with one end tied to RF ground (primary in the center of secondary winding and on a form only 1" dia larger than the secondary). Also, as I've said before, my coil is very high fres as well, at around 1MHz.
Registered Member #4104
Joined: Fri Sept 23 2011, 06:54PM
Location: Uk .
Posts: 122
I isolated my mosfet body diodes with 2 ultrafast diodes 20 A rated , one is in series with the mosfet ( should be a schottky but they are to expensive :( ) to isolate the internal diode then the othere ultra fast diode is the freewheeling diode . I get heating in them at 1kw supply 4ish amps @ 230v In , mosfets seem the coolest but i can only do short runs till the heating becomes worse
after many many fets going dead between all pins i hope to fix it , the ultrafast diodes seem to be working , havent killed them yet , just the mosfets :P
I isolated my mosfet body diodes with 2 ultrafast diodes 20 A rated , one is in series with the mosfet ( should be a schottky but they are to expensive :( ) to isolate the internal diode then the othere ultra fast diode is the freewheeling diode . I get heating in them at 1kw supply 4ish amps @ 230v In , mosfets seem the coolest but i can only do short runs till the heating becomes worse
after many many fets going dead between all pins i hope to fix it , the ultrafast diodes seem to be working , havent killed them yet , just the mosfets :P
I have a similar setup using superfast diodes and sckottky's with my full bridge of 460's both are only 3A and I have no problem keeping them cool the only problem I have is when one of the fets dye (i think due to bad gate drive ) which also kills the schottky dut it only fails when I set the power to 11
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Mini SSTC Inquiry - 220v?
