> > It's worth noting that the quoted and calculate lifetimes apply to
> > electrolytics with full rated voltage applied. Aluminium
> > electrolytics die far quicker at extended temperatures when no
> > voltage is applied (which may be the opposite to what is expected
> > intuitively)
>
> Do you have some figures to support that?

Not off the cuff - but it's true :-)

> Does it apply when low voltages
> are applied or only very close to 0V?  Is there an 'optimum derating' of
> voltage?

Worst with no voltage AFAIK.
But aluminium wet electrolytics (which is what are most commonly dealt
with). should ideally be run at a voltage approaching their rated value. Low
voltages wrt rated leads to earlier death. Again, no references.

With no voltage applied the electrolyte dries out rapidly afaik. I suspect
that Philiups will have tutorial material on all this if you look hard
enough.

OK - Googling using
        capacitor failure philips electrolytic

produced this most interesting paper


http://www.ec-central.org/magazine/nov_dec_02/tech_paper_lifetesting.pdf

They note that for a capacitor which is usuallynot in use, most
deterioration occurs in this stae and is caused by dielectric thinning.
The paper discusses many of the questions raised on this thread.


        Russell McMahon

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