Re: Geek .15uF caps Was: "plate" capacitors

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>

Hi David,

I don't know of any "minimum" temperature.  You can run super high RMS for
a short time as long as they never have a chance to heat up.  Cooling them
with a fan "may" help but the center of the cap is what needs cooling and
it is very well insulted buy 200 layers of poly...  Cool air folw on the
outside just isn't going to make much difference.

I suppose you could freeze them in liquid nitrogen but the epoxy may crack
and other damage may start.  Easiest to just use more caps rather than
getting too carried away.

For very short term currents.  The dV/dT rating is then the limit.
Basically the current that will instantly (or over repeated hits) blow the
internal connections from pure giant current pulses rather than heating.

Cheers,

	Terry

At 05:34 PM 4/20/2001 -0500, you wrote:
>From: "Tesla list" <tesla-at-pupman-dot-com>
>> Polypropylene is a soft low temperature plastic that does not like heat at
>> all.  85C is the limit although they play a few games to get that as high
>> as 105C.  One should not run them with the outside temperature getting
>much
>> over 10C above the air temperature.  Even thought the cap is say 40C on
>the
>> outside, the poly film is a very good insulator so the heat generated in
>> the center gets traps and the middle may be cooking at 110C where it melts
>> and fails.
>
>What is the minimum operating temperature for a polypropylene cap?
>
>If cooled to its minimum operating temp, could the cap be made to
>process significantly more power without damage?
>
>That is, could the power limit be shifted from the thermal limitation
>of the dielectric to the current capacity of the lead-plate bond?
>
>DK
>