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

Dr. David Kirkby david.kirkby at onetel.net
Tue Jun 21 11:54:37 UTC 2011


On 06/21/11 12:59 AM, Alan Melia wrote:
> David Another important factor when considering power supply caps is ripple
> current rating. It is generally the ripple current that makes them get warm.

Yes. I must admit I did not give that any thought, which was rather stupid of 
me. But I did not buy cheap caps. I will check the ripple ratings, but its hard 
to know exactly what is needed.

> 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.

Yes, I have heard this before about not using them at too low a voltage. I don't 
know whether its an old-wives tale, or if there is any truth to it.


> Alan
> G3NYK

Thanks for your comments Alan,

Dave G8WRB.



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