Power supplies with solid polymer caps
in [Repair]
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From: Man-wai Chang to The Door (28800bps) on 21 Nov 2009 02:26 William Sommerwerck wrote: > If I interpret your question correctly, it's meaningless. > > Polymer capacitors (ie, plastic-dielectric caps, such as polystryrene, > Mylar, and Teflon) simply cannot produce the huge capacitances in small > spaces that electrolytics can. They cannot easily replace electrolytics. > > How about ceramic caps? -- @~@ Might, Courage, Vision, SINCERITY. / v \ Simplicity is Beauty! May the Force and Farce be with you! /( _ )\ (x86_64 Ubuntu 9.10) Linux 2.6.31.6 ^ ^ 15:26:01 up 8 days 4:31 1 user load average: 1.00 1.01 1.03 不借貸! 不詐騙! 不援交! 不打交! 不打劫! 不自殺! 請考慮綜援 (CSSA): http://www.swd.gov.hk/tc/index/site_pubsvc/page_socsecu/sub_addressesa
From: Arfa Daily on 21 Nov 2009 04:43 "William Sommerwerck" <grizzledgeezer(a)comcast.net> wrote in message news:he7m0i$tjl$1(a)news.eternal-september.org... >> Depending on how stressful the position that they are used in - and many >> such positions these days *are* - I would have to beg to differ. They > really >> are /that/ unreliable ... > > If that's the case... then why have I had such good luck? > > I just remembered another failure -- bypass caps in the video driver board > of my NAD. > > Just that, I suspect - good luck, coupled maybe, with the fact that you buy equipment from the 'better' end of the market which has, at least in the past, tended to be designed to a better spec with a few cents more spent on components. These days, however, even that may not continue your run of good luck. I see equipment on a daily basis coming from what you would normally call 'reputable' manufacturers, that are just badged items of Chinese design / manufacture. Even some of their *better* stuff now borders on a 'con-trick' in terms of design quality and quality of components used. To some extent, I don't think it is all the capacitors' fault, to be honest. The places that electrolytics are found in today's equipments, tend to be very stressful to them, and when you couple in other factors such as the international law on pain of death that requires designers to place electros as close as is physically possible to anything that runs hot, and then to mount the power supply or whatever board they're on, upside down in the corner of the equipment with the least airflow, it's actually not that surprising that these devices exhibit such *apparent* unreliability. I also suspect that the eco-fanaticism that has given us lead-free solder doesn't help either, as the elevated process temperatures required to get this hateful stuff to stick to anything other than itself, is known to not do some components a lot of good, and I'm sure that, no matter how comparitively brief these additional early-life heat stresses on the electros are, they have to be at least another potentially destructive factor to consider in terms of long life and reliability ... Arfa
From: larry moe 'n curly on 21 Nov 2009 05:07 Jeff Liebermann wrote: > > The caps in the photo really are solid polymer caps. > <http://www.dslreports.com/forum/r19863881-Solid-Polymer-Capacitor-Failure> The caps in the photo really are NOT solid polymer caps. They're regular Sacon brand conventional wet electrolytics, only housed in the same kind of packaging normally used for polymer caps. Even some of the replies in the message thread where that photo is from mention this. Real polymer caps, except Fujitsu hybrids, don't have explosion rupture cutouts, unlike the caps in the photo -- notice the "K" rupture cutout on top of each cap.
From: William Sommerwerck on 21 Nov 2009 07:22 > I also suspect that the eco-fanaticism that has given us lead-free > solder doesn't help either, as the elevated process temperatures > required to get this hateful stuff to stick to anything other than > itself, is known to not do some components a lot of good, and I'm > sure that, no matter how comparitively brief these additional > early-life heat stresses on the electros are, they have to be at > least another potentially destructive factor to consider in terms > of long life and reliability ... I wonder what's going to happen when these lead-free joints start failing en masse... I can just see a class-action suit against the European Economic Community.
From: William Sommerwerck on 21 Nov 2009 07:28
I just remembered another "failure"... Several years ago I bought a KLH Audio (sadly, now out of business) powered woofer, which I tossed in the garage. A week ago I finally got around to pulling it out and connecting to the LFE output of my BD player. (This was intended mostly to keep the main speakers from being overdriven.) When I turned it on and up its gain (that's "syllepsis"), it made "pumping" noises, all on its own. After a few minutes of "charging up", this went away. It would seem that after a few years of non-use, one or more bypass caps had deformed, allowing instability. I used to own several KLH Model Eight radios, and though they were 45 years old, none needed a capacitor replacement. |