At 09:22 AM 3/4/99 -0800, you wrote:
>>? However, comparing a ripple-current rating for 105 deg C with a ripple
>current rating for 85 degrees C is hardly valid. My guess is that 105
>deg C capacitors are going to last longer in a typical anode supply.
>
I think John's point is that higher max. operating temperature rating seems
to automatically imply some other performance enhancements over an 85 C
rated cap, and I can't see that it does. Choosing the cap with the 105
deg.C rating, mainly because of that rating, may be false economy if the
max ripple current rating is only marginal for the application. Mallory
and Phillips still provide the ripple current rating at 85 C, even for
their 105 C caps. This implies that the max ripple current rating drops
(substantially ?) as the temp rises from 85 to 105 deg. C (even though the
'C' and ESR remain stable). The temp rating only assures that the 'C' and
ESR will remain within specs up to those temps, without a permanent change
in either occurring. There's no mention of what happens to ripple current
rating.
There's no indication from either supplier's catalogs that running a cap at
well below the max design temp will result in longer life, even though it
does seem reasonable to expect that it might. 85 deg.C is pretty damned
hot (185 F). I suspect that if you select the right rip. current rating
and the lowest ESR you can afford, 85 C rating is plenty.
Phil
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