David Another important factor when considering power supply caps is ripple current rating. It is generally the ripple current that makes them get warm.
I think the "usual" thumbnail calculation still work for caps if you can reduce the temperature by 20 degrees they will last at least 4 times as long. That is an activation energy (Arrhenius eqn) of about 1ev. I also believe though I cant quote that they are best run at about 75% of their specified working voltage. I have always wonderd about this but it would seem to be a mistake to have too low a voltage on electrolytics ...maybe something to do with the strength of the instulating layer formed. Alan G3NYK ----- Original Message ----- From: "Dr. David Kirkby" <[email protected]> To: "Discussion of precise time and frequency measurement" <[email protected]> Sent: Tuesday, June 21, 2011 12:40 AM Subject: Re: [time-nuts] Replacing electrolytics - any disadvantages of high temp ones? > On 06/20/11 10:44 PM, Poul-Henning Kamp wrote: > > In message<[email protected]>, "Dr. David Kirkby" writes: > > > >> 1) Higher temperature devices (like 105 deg C) will be more relieable than low > >> temperature ones like the standard 85 deg C cap. I'm sure at high temperatures, > > > > You should check both temperature and lifetime rating of the capactors. > > I have, but I would assume one rated at 6000 hours at 125 deg C would be at > least as good as one rated at 7000 hours at 105 deg C. > > > There are many capacitors on the market these days with 5000h or > > even 2000h rated life. > > > > That is 7 or 3 months respectively. > > Even 1000 hours I've seen. But these are of course at the maximum temperature, > which few would use them at. Otherwise failure rates would be a lot higher than > they are. > > I've not seen any electrolytics rated more than 10,000 hours (14 months), but > they last a lot longer if the temperature is lower. > > My PC is already more than 14 months old, and has been on 24/7. Hopefully it is > not dying on me. > > > And yes, it should be criminal to manufacture and sell those. > > Well, I think the MTBF will be a lot more than that in practical use, as few > would design equipment to run at 85 deg C, which is the lowest maximum > temperature rating I've seen on any cap. > > -- > A: Because it messes up the order in which people normally read text. > Q: Why is top-posting such a bad thing? > A: Top-posting. > Q: What is the most annoying thing in e-mail? > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
