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Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Hi, I got a bunch of these caps which came from a high power induction cooker:
According to this page they are rated at 800VAC and 1200VDC. I tried applying 800VAC 50Hz to them, and they buzz or hiss audibly, almost like corona crackling... They start to buzz even at just 600VAC or so. I tried abusing one for about half an hour, but the capacitance didn't change (which would indicate spark overs and self healing).
Anyone guess what is this? I wanted to use them in a SGTC at just a bit below their max ratings, do you think they will survive?
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
It's a crackling, snapping sound like the corona on very high voltage transmission lines... It really sounds almost like there is a corona inside the capacitor but I doubt it... I tired abusing it on 1kV AC, it survived for half an hour and capacitance stayed the same, but now the cap even noticably heated up.
Registered Member #4074
Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335
I've experienced the same thing with some very cheap and nasty 630V rolled pp/foil audio caps. Those caps would readily fail when pulsed and seemed to be poorly made (they weren't smoothly rolled and had messy epoxy sealing their ends). At the time I thought it was some internal vibrations, because I didn't think any corona would be noticeable at such a low voltage.
Registered Member #133
Joined: Fri Feb 10 2006, 10:27PM
Location: Pensacola, Florida
Posts: 47
I have encountered a few metalized polyester capacitors that made audible noise with 120 VAC, 60 Hz applied to them. Upon dissecting them, air pockets were discovered within the potting. The capacitors were mechanically vibrating, which was causing audible buzzing.
If you are hearing crackling, then that’s another story.
If you know an engineer or technician that has access to a DC hipot tester, you may test one of the capacitors with high voltage DC and observe the leakage current. Excessive leakage current will be noticed if coronal partial discharge is taking place within the capacitor.
Registered Member #187
Joined: Thu Feb 16 2006, 02:54PM
Location: Central Ohio
Posts: 140
Try powering them with the lights off. Maybe wait a few minutes to let your eyes adjust and look for corona leaks. I have some of those and I remember them being noisy as well.
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Weird caps hiss/buzz at rated AC voltage
