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Jeff Liebermann Jeff Liebermann is offline
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Default Why do some manufacturers wrap the electrolytic capacitor that gets the hottest in a switching power supply in shrink wrap?

On Tue, 30 Aug 2011 15:47:21 -0500, Chuck wrote:

Extron has been doing this for years and of course it is the first
part to fail in their units. Smart Technologies Sympodium power
supplies, that they have contract built in China, fail in a year or so
for the same reason. Technicians and electronic engineers at my work
place can't think of a rational reason why these manufacturers do
this. This is pro gear where reliability is a great concern so it
doesn't seem to be planned failure mode. Thanks. Chuck

Probably to keep you from touching the can, which is probably
electrically hot. The life you save may be your own.

Electrolytic caps do not normally get hot. There is a temperature
rise equal to the ripple current times the square of the ESR
(equivlent series resistance). If the ESR is too high, usually due to
underspecifying the voltage rating or capacitor type, it will get
warm. There are derating curves for capacitors at various
temperatures. There are also lifetime prediction calculators which
include the operating temperature.

If you're shopping for a conspiracy theory, I guess the capacitors are
badly specified or picking up heat from adjacent heat dissipating
devices. A nearby resistor or heat sunk xsistor will heat up a cap
quite nicely. The shrink tube will have little effect on the cap
temperature. Black absorbs more heat, so it might be slightly warmer
from nearby radiation. At best, maybe a degree or two.

Pro audio is the same as consumer audio, except for the price tag and
the hype.

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