View Full Version : Me and capacitors
Bushfiva
16th Jun 2010, 13:12
A propos nothing in particular, I just resurrected my third computer with bad capacitors. This time, they hadn't blown, but just looked a little chubby. All three machines made in 2007, all different brands but from the same OEM. When I went to the capacitor shop under the tracks, the lady mentioned she's selling about 10 times as many 6.3V 500 - 1500uF caps as any other right now.
Hmmm. I just replaced 6 x 1000uF 16v in the PVR. That cured the problems the memsahib had been having. All the old ones measured "OK" when tested afterwards, but the device didn't work with them in. I suspect heat effects. I fitted a cooling fan in there (there was just room for it).
Bushfiva
16th Jun 2010, 16:08
They're just ****ty caps. The new ones will be good forever, if you chose a reputable brand.
Loose rivets
16th Jun 2010, 19:17
On the UK Vintage radio forum, the chaps sometimes revive old capacitors by under-running them for a period, so that they regain their electrolytic surfaces.
Anyone remember Hunt's condensers?
All good stuff, but I'm about to find out if a tuner/amp that has been sitting in storage for 7 years, still works. It was a good amp - should be, I can hardly lift it, presumably cos of the transformer. Real amps come out of kit like that.:}
Environment could be a factor: some types of capacitors don't like excessive humidity or vibration.
Old electrolytics will usually respond well to being "reformed" - start them at relatively low voltage, and gradually (like over several days) run them up to full rated.
If they go BANG, well, you did put something around to catch the gunk, right? There was a brown line right round the wall of a former shack of mine where a 32uF 500vw let go. Happily, I was in the next room at the time, but it lifted the PSU off the bench to spray the stuff round the room.
jimtherev
16th Jun 2010, 22:38
... and as I've mentioned before somewhere, we had a bank of 500 uF 500V in series / parallel; a couple of occasions when one let go, causing a chain reaction involving another score or so, that was
(a) fun - to a 20 y-o jtnotyetrev
(b) noisy
(c) expensive
and gave the cleaners lots of overtime picking bits of silvered wax paper out of all sorts of interesting crannies.
Interesting smell, too.
Never liked electrolytics in series. Lots of reasons why.
I've got this lovely big 5kV block paper - weighs about half a hundredweight. No idea of capacity, but I'd guess at least 32uF and possibly a lot more. It was the reservoir C for the HV supply for my HF linear. All the bits are still extant in the shack, but I doubt it will all get reassembled.
seanbean
17th Jun 2010, 01:01
Interesting article (http://newenergyandfuel.com/http:/newenergyandfuel/com/2009/12/24/understanding-digital-quantum-capacitors/) here. Essentially a sort of flash drive that acts as a capacitor.