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Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
Id say there are 2 issues to think about. 1) as mentioned these caps almost always have an internal bleeder resistor, which may not be happy with even 2X the voltage rating since that 4X the dissipation in the resistor. My test cap got hot because of this resistor. 2) if you are going to parallel a bunch of caps, all the energy of the bank will dump into one little cap, making the failure much more spectacular, no doubt. So consider the total energy stored, and think about what you would like to have contain that energy in a blast. Personally id probably use some plywood box lined with poly-carbonate for a small 1kJ or so bank. Also plan on oil spraying, maybe even hot oil.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Steve Ward wrote ...
Id say there are 2 issues to think about. 1) as mentioned these caps almost always have an internal bleeder resistor, which may not be happy with even 2X the voltage rating since that 4X the dissipation in the resistor. My test cap got hot because of this resistor. 2) if you are going to parallel a bunch of caps, all the energy of the bank will dump into one little cap, making the failure much more spectacular, no doubt. So consider the total energy stored, and think about what you would like to have contain that energy in a blast. Personally id probably use some plywood box lined with poly-carbonate for a small 1kJ or so bank. Also plan on oil spraying, maybe even hot oil.
Thanks, so I think I'll find out myself. I don't mind losing two caps. They will be used on AC, in resonant circuit.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Just letting you know they survived. I think they were charged to 7kV peak (14kVp-p) each @50Hz, and after a minute run one of them was slightly warm. They were 0.85uF and 0.91uF caps made by Matsushita and Daewoo i think, and the Matsushita one was on the small side, the thing you find in most microwaves, the other one was a bit larger.
So whats the conclusion? I think you can charge any MW capacitor to 6kV if you want to be super-safe, or 7kV if you are fine with just being "safe".
Registered Member #1232
Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881
> So whats the conclusion?
The conclusion is that those two caps you chose to test survived 7kV peak for one minute. Other caps from that manufacturer or other manufacturers may vary. Two devices is not a representative sample of all MOC manufacture!
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Okay. I just thought the smaller cap's size and "crappiness" was worse than most and it still survived without any problems. Make out of this what you want
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How much voltage can a microwave cap take?
