Re: gEDA-user: electrolytic capacitors

[gene <carzrgr8@xxxxxxxxxxxxx>]

Peter Clifton wrote:
> It will still have had its life-time shortened.
> 
> The spec you quote above, AIUI, means that after somewhere between 1000
> and 5000 hours of operation at 105 degrees centigrade, the cap (as
> measured at 20 degrees) will be outside of its quoted specifications.
> 
> I can't remember the exact numbers, but derating to lower temperatures
> has a stupid factor of lifetime increase. It might even be as much as
> double the life-time for every 10 degrees drop in working temperature.
> 
> I guess that merely being at elevated temperature is also lifetime
> degrading. You circuit wouldn't need to be on for the electrolyte to be
> degrading.
> 
Looking at the data sheet, they claim after being exposed for the test, 
the device will return to to within +/-20% original value, and the 
tan-delta will be within 200% original.  So the thing gets lossy, I suppose.

Is the endurance a cumulative thing?  I've got a requirement of around 
3.5 A ripple current (although I really need to double check this in 
simulation), which is a lot of ripple.  I planned to use 2 caps in 
parallel, each with about 1.8A max ripple.  But I'm worried that 
eventually, the things won't do their job.


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