On 09/02/2020 20:59, Paul wrote:

And while one biased company claims electrolytics
dry out after 3 years (a made up number), another
company (likely using field statistics for their
own capacitors) finds the time constant is 17 years.
And I would have to conclude that the 17 year number
is likely to be closer to the truth (based on old computers
still in a running state, like my first computer from
1998-1999 or so which still operates just fine).


Temperature, both rated and operating, is a factor. As I understand it a
rating of,say, 7000 hours at 105C means for every 10C lower actual
operating temperature it doubles the lifetime. Operating them at 65C
will give approx 12 years of continuous use.

In a old computer the power supply always had it's own fan keeping the
unit relatively cool. In modern TVs, set top boxes etc the room for a
noisy fan giving a decent air flow is somewhat limited and temperatures
within many boxes are 60C+. Many capacitors in switched mode supplies
also seem to be fitted very close to hot heat-sinks! In my experience
it's usually the power supply capacitors that have an early failure.

Some manufactures will fit capacitors rated at 7,000 hours at 85C so
when operating at 65C the life expectancy is closer to 28,000 hours (3
years continuous use).

There is also a problem with life expectancy from self heating due to
the Equivalent Series Resistance (ESR). For a switched mode supply a
capacitor with a low ESR is required. A decade or so ago I read a
technical report from one of the more respected capacitor manufacturers
(Rubicon I think) where they claimed that they used physically larger
cans/packaging than some of their Korean competitors to ensure lower ESR
figures. I always found that when changing duff electrolytic with Korean
brand names such as SamYoung etc. that the replacements from a variety
of reputable brands were physically larger - usually the same diameter
can but the height of the can was maybe 5mm more.

I've had capacitors fail in a couple of PVRs after a couple of years but
carefully selected replacements lasted close to 10 years.


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