They are rarely operated 24/7, and they aren't usually supervised by
career engineers. Most hams are relatively inexperienced hobbyists who
may not recognize a problem until it is catastrophic. Someone in this
thread already mentioned that nearly all ham shacks have a bad
electrolytic lurking under the bench.
Eric KE6US
On 4/16/2020 7:38 AM, CUTTER DAVID via Elecraft wrote:
Hello Gill
Doing reliability calculations to MIL 217 was very instructive many years ago
and it taught me that operating well under the limits extended MTBF a lot.
Some military customers instructed that specs were 60% or more degraded to
achieve longer service life. What was your experience of that? It amazes me
that amateur psus last so long! Then, again, they are rarely continuously
operated 24/7.
73
David G3UNA/G6CP
On 16 April 2020 at 15:19 Gill via Elecraft <elecraft@mailman.qth.net> wrote:
As Harlan pointed out - I was an engineer for the FAA until retirement -
We changed electrolytics as part of normal PM's on critical systems
usually every 5 years or so. CDE (Cornell Dubilier) indicates expected
life (MTBF) of devices operated within rated voltage & temp specs to be
about 80-100 thousand hours. Most failures occur quickly around the end
of that period. For 24/7 operated systems, that translates to around
8-10 years before rapid EOL failures begin to occur. Electrolytics can
be thought of like incandescent lamps - they have a finite useful life
and the fail quickly around the end of that time. ESR (Equivalent Series
(AC) resistance) increases which reflects in higher ripple currents in
power supplies are a main culprit. Check out:
https://www.cde.com/resources/technical-papers/reliability.pdf
73 Gill W4RYW
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