In an off-list conversation with someone who really seems to know
power supplies I was told that running a UPS or any other
"inverter" to supply an SMPS (switching mode power supply like in
most newer computers) is a risky thing.
I can't find a copy.. but if I remember correctly it is a result
of the power curve. If I get it right (and I'm not at ALL sure I
did) - because the SMPS is sampling the input voltage very fast -
and the input from the typical non-sine wave UPS is not a true
sine wave, there is the possibility for some MAJOR overshoot on
the SMPS ouput for short periods. Short, but long enough to fry
something in the power supply. This can account for not too
common but seemingly unexplainable death of the SMPS in a
computer. It seems to be something of a matter of probability and
timing.
I know one organization that has replaced three brand-new power
supplies in less than 3 months. Running on a UPS. I wonder if
this may be their problem.
The solution is to place some substantial inductance - like an
isolation transformer - in the line to act as a low-pass filter of
sorts.
It makes sense to me. Comments from the original informant would
be preferred. Or maybe there are others who know of this problem
as well.
Bob
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