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Registered Member #93
Joined: Thu Feb 09 2006, 04:11PM
Location: Houston, Texas
Posts: 64
Well, it'd be difficult to call it a MMC with these caps, more like an MC.
Anyway, I was looking at some Eurofarad capacitors available on eBay. These appear to be very beefy caps that, properly hooked together, *might* be useful for a DRSSTC tank. They weigh in at 3.75 uF, 580V(rms), 152 Amps (I'm assuming at their rated voltage).
Others here have referred to these as snubbers, and they certainly look like they might be, but I'm worried that they might just be some exotic type of filter cap with poor pulse characteristics.
Does anybody have any additional information about these caps? I've tried Google to no avail.
I'd be interested in anyone's opinion about using these as tank caps for a medium-large DRSSTC.
Registered Member #2919
Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
RickR wrote ...
Well, it'd be difficult to call it a MMC with these caps, more like an MC.
Anyway, I was looking at some Eurofarad capacitors available on eBay. These appear to be very beefy caps that, properly hooked together, *might* be useful for a DRSSTC tank. They weigh in at 3.75 uF, 580V(rms), 152 Amps (I'm assuming at their rated voltage).
Others here have referred to these as snubbers, and they certainly look like they might be, but I'm worried that they might just be some exotic type of filter cap with poor pulse characteristics.
Does anybody have any additional information about these caps? I've tried Google to no avail.
I'd be interested in anyone's opinion about using these as tank caps for a medium-large DRSSTC.
Thanks,
Rick
I've run them to 4KVA (apparent input, not reactive, power) in my induction heater with only mild heating. I think in their former life, these were GTO snubbers. Should be fine for a DRSSTC...judging from Eurofarad's GTO snubber ratings, this thing should have a ~2KVDC rating. They only make sense for a large DRSSTC, though. Even with ten in series (which should be enough), you still have a 375 nF MMC.
Registered Member #599
Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624
I murdered one of these capacitos in the name of science.
Firt thing was overvoltage stress test. Since only RMS voltage was given, i wanted to test how high DC voltage these could stand. Guestimation from other snubber capacitor datasheets gave me values from 900VDC to 1300VDC
So i hooked up simple test setup: variac, rectified NST and HV meter:
500V... 1000V... 1500V.. SNAP.. 1600V... 2000V... 2200V SNAP SNAP POP ok :)
Judging from that i would say absolute maximum DC voltage is 1kV
Now lets pop it open. Hacksaw cuts easily through fibre glass.
Outer shell was very well glued. Couple teespoons of odorless mineral oil came out
Terminal plate was soldered on sprayed metal. It required quite a bit of hammering.
They see me unrollin', they hatin
Foil separated from metallized film. Construction is identical compared to CDE942 series capacitors.
I unrolled maybe 15 meters of this stuff and found couple self healing spots like one in picture. All at the edge of the foil as usual. Rest of the film looked really good
I made a mess
So, what did we learn from this? Well, these eurofarad capacitors are Metallized film-foil hybrids just like CDE942 series. They are oil impregnated. Foil edges are bonded together with spray metal and terminals to spray metal with heavy soldering.
Just respect the voltage ratings and there is no reason what so ever why these would not work in any kind of tesla coil! :)
Registered Member #93
Joined: Thu Feb 09 2006, 04:11PM
Location: Houston, Texas
Posts: 64
Hey Kizmo,
Thanks for actually jumping in there and doing the experimental research! That's really useful information. I ended up buying 20 of these on the speculation that they'd be useful in a large DRSSTC. I haven't gotten to the point of using them yet, but your research indicates that they ought to perform well.
Registered Member #599
Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624
Thanks :)
I have pile of these too and was wondering same thing.
Maybe next step of my more or less destructive testing is to put another cap in drsstc circuit and crank it up untill it starts popping (self healed flashover from peak voltage)
I have done this before with dry resin film caps, its very easy to hear and shouldnt hurt the capacitor too badly since its self healing type
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Eurofarad caps for MMC?
