[time-nuts] Replacing electrolytics - any disadvantages of high temp ones?

Alan Melia alan.melia at btinternet.com
Mon Jun 20 23:59:38 UTC 2011

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.


----- Original Message ----- 
From: "Dr. David Kirkby" <david.kirkby at onetel.net>
To: "Discussion of precise time and frequency measurement"
<time-nuts at febo.com>
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<4DFFBAF4.4070004 at onetel.net>, "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
> >
> > 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
> 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
> which few would use them at. Otherwise failure rates would be a lot higher
> they are.
> I've not seen any electrolytics rated more than 10,000 hours (14 months),
> 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
> would design equipment to run at 85 deg C, which is the lowest maximum
> temperature rating I've seen on any cap.
> -- 
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> Q: Why is top-posting such a bad thing?
> A: Top-posting.
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