Power supplies with solid polymer caps
in [Repair]
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From: david on 21 Nov 2009 07:44 On Sat, 21 Nov 2009 04:22:04 -0800, William Sommerwerck rearranged some electrons to say: >> 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. It not just that... go search for "tin whiskers". We have nothing to fear from the machines taking over, they will all fail a long time before humans do.
From: david on 21 Nov 2009 07:45 On Sat, 21 Nov 2009 15:26:08 +0800, Man-wai Chang to The Door (28800bps) rearranged some electrons to say: > 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? You cannot get large capacitance values in a small package size with a ceramic dielectric.
From: larry moe 'n curly on 21 Nov 2009 10:51 Arfa Daily wrote: > > 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, 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. So why do the good brands tolerate those conditions so well while the same old junk brands don't? And contrary to what you say, most of the caps aren't in hot spots but are running at under 60 Celcius > 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, But the problems with junk capacitors showed up way before the switch to lead-free solder, and only one of my RoHS mobos has so far popped a cap, probably more because it's newer (late 2007), not because it's better, but it has the same OST brand junk caps. The real fault lies with the makers of junk, period.
From: Jeff Liebermann on 21 Nov 2009 12:20 On Sat, 21 Nov 2009 02:07:39 -0800 (PST), "larry moe 'n curly" <larrymoencurly(a)my-deja.com> wrote: >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. Ok, I stand corrected. >They're regular Sacon brand conventional wet electrolytics, only >housed in the same kind of packaging normally used for polymer caps. Groan. So much for my method of using the case style to recognize the difference between electrolytic types. >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. So that's the trick to recognizing the difference. Thanks. -- Jeff Liebermann jeffl(a)cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
From: Baron on 22 Nov 2009 15:57
Arfa Daily wrote: > As far as your contention that most of the caps that fail are running > at under 60 deg and are not in hotspots, that may be true if you are > talking just mobos, which are a bit of a special case in that apart > from all the problems that have been caused in the past with boards > built using caps with fake electrolyte, the caps that fail are all > decouplers on constant DC rails, and are rated voltage wise pretty > close to the continuous voltages that are applied to them. Even > accepting that, many of the decoupling caps that do fail on mobos, are > sited very close (by nature of the job that they have to do) to LSIs > which *do* run very hot. > > The caps that I am talking more about in general, are on switch mode > power supplies, where they are subjected to huge stresses from the > high frequency pulse currents that they have to endure, and the self > heating caused by this in all but the most expensive types, very > specifically specced for use in these positions. Further, the ones > that fail most regularly are, without doubt, the ones positioned close > to heatsinks. I replace hundreds every year in the course of my daily > work. Although the caps positioned on switchers are by far the most > common ones to fail, they are by no means the only ones. I also > replace many in other circuits, for instance audio output stages, > where failed ones are almost invariably close to heatsinks. > Arfa I'm in complete agreement with Arfa. Internal heating caused by the ever increasing switch mode power supply frequencies is the most common cause of failure. High external temperatures don't help one bit since it reduces the components ability to get rid of internally generated heat. A place where I'm finding more and more capacitor failures is in the memory supply voltage regulator circuits, sometimes causing CPU failure in addition to memory damage. -- Best Regards: Baron. |