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

Dr. David Kirkby david.kirkby at onetel.net
Thu Jun 23 16:10:26 UTC 2011


On 06/21/11 08:39 PM, Poul-Henning Kamp wrote:
> In message<4E008A73.50701 at erols.com>, Chuck Harris writes:
>
>> and yet, I find that some electrolytic
>> capacitors that have been run at lower than normal voltage improve markedly
>> when "reformed" by applying  rated voltage through a 10K resistor for a
>> couple of hours.
>
> I noticed in a datasheet at one point, that the capacity only was
> warranted above a certain percentage of rated voltage.  No explanation
> was given.
>

Note on the link posted by Robert LaJeunesse:


http://www.cde.com/catalogs/AEappGUIDE.pdf


it says voltage derating gives better reliability:


======================================
"Aluminum electrolytic capacitors made with formation voltages
at least 35% higher than rated voltage and with rated tempera-
tures of 85 oC or higher, don’t require much voltage derating. In
applications operating at less than 45 oC no derating is needed,
and with up to 75 oC, 10% is sufficient. For higher temperatures
and with high ripple current, 15% or 20% is appropriate. Since
operating life continues to increase for further derating, military
and space applications use 50% voltage derating."
========================================

I've herd stories one should not operating caps well below their rated voltage, 
but that would tend to suggest that is not so.

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