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Registered Member #139
Joined: Sat Feb 11 2006, 11:01AM
Location: Perth, Western Australia
Posts: 358
Why do you want to go to the trouble of building an HV cap? A few years ago "Roll your own" capacitors where all the rage google for MMC Tesla and see what you get.
Registered Member #354
Joined: Thu Mar 30 2006, 10:12AM
Location:
Posts: 55
Because I do not found high voltage ones at good price with widstand lots of KAmps Do you know any? I found russian ones but they do not respond to emails. Others caps appear to have lots of mH but real capacity are uH.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
mH? uH? What units are capacitors measured in?
High voltage pulse capacitors are always expensive because the market for them is small and they're not mass-produced. If you do a bit of reading up on peak currents, RMS currents, voltage reversal, etc, you'll know whether you can get away with using ordinary capacitors. Plenty of people use kitchen aluminium foil for plates.
The cheapest dielectric I've ever seen is polythene sheeting that comes in rolls from a DIY store.
Registered Member #325
Joined: Fri Mar 17 2006, 12:42AM
Location: Turku, Finland
Posts: 55
Those mylar sheets should do well as a dielectric, depending on what you want to do with your capacitor (for demanding applications such as resonant circuits, e.g. tesla coil primary cap, you want a less lossy material). IMHO, homemade can be quite good, and if you need high capacitance, an MMC will probably be very expensive and require a lot of soldering anyway. Do you mean 1 microFarad or (heaven forbid) 1 milliFarad? The latter won't be feasible, that is certain.
Just be sure to leave ample safety margins between the plates of opposite polarity to avoid arc-over. For 13.5kV, I would use at least 50 mm (2 inches) just to be one the safe side. Also for a rolled cap you want to connect the turns of each plate on both ends to minimize inductance.
Registered Member #256
Joined:
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Posts: 124
i used a rolled cap for my old TC and it worked great, polyethylene plastic(my dad gets it at work all the time! ;) i couldnt get any plate stacked caps to work at all, and i hear is a better one to use because of high inductance of rolled caps, and also my plates werent connected at each end of the foil would this have made it any better?, i calculated .1uF for it btw and paralleled 3
They were crappy anyway and needed a lot of them because the low capacitance, but they keep well at high voltage. hmm...you can use the PVC pipe as a core for a rolled cap.
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Homemade HV big capacitors
