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Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
It is possible to use glass encapsulated paper-in-oil or poly film caps, but there is one problem with these capacitors, they get hot, and when they get hot they break the glass tube.
I used to use several 5 KV Dearborn glass caps in series for a Tesla coil, and I could operate for about 5 to 10 minutes before one would burst. After that time I would have to replace it or a couple of caps that were significantly heating, and then I could resume after the whole string cooled down.
I was exceeding the voltage rating and really pushing the capacitors hard. They were only filter caps, they were never ment to be used as a pulse discharge capacitor.
If you do plan on using them, don't run your capacitors for more then 5 minutes or you may loose one due to bursting, that is if they are in glass, its hard to see from the picture.
Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
Mica's are only good for up to maybe 300W with a Tesla coil in pulsed duty. I know because I have worked with Sprague caps in this situation and they short out badly at higher power levels. A friend of mine, Bill who sold me my Sprague Mica caps, actually killed his NST recently while trying to run his small demonstration Tesla coil.
Mica's are only intended for decoupling a load from the HV DC to the AC output, so consider how much you load a Mica cap.
I think these caps would probably be better suited for a Marx generator, but I want to see what other's suggest.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I have one of those "Cathodray" caps here, a 50nF 10kV version. I think they were meant for smoothing EHT supplies to picture tubes, and would spew their guts almost instantly in Tesla coil service.
I think they are paper in oil inside some kind of bakelite plastic case. The "Visconol" is a trade name for the dielectric oil used by that company (and it is non-PCB as far as I know)
The big white jar object that teravolt noticed in the background seems to be a transmitting-type mica capacitor, I think you would have much better luck with that
Registered Member #118
Joined: Fri Feb 10 2006, 05:35AM
Location: Woodridge, Illinois, USA
Posts: 72
Hmm... these caps may contain PCB's. A similar Cathodray cap is listed as containing PCB's in "Identification of PCB-Containing Capacitors". They apparently use a paper dielectric and will most likely not work (for very long) in a TC. They'd look great in a Frankenstein-looking small Marx Generator though...
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Are these capacitors suitable??
