w_tom wrote:
Learn what plug-in UPSes do before recommending them. The
typical UPS connects AC power directly to computer when not in
battery backup mode. Directly as in AC mains noise goes
directly to computer. The noisiest power is delivered by UPS
when in battery backup mode. Of course, greatest noise from
UPS is not a computer problem. Computer power supply contains
functions that make irrelevant this large UPS noise as well as
smaller noise from AC mains.


Where in my post did I say I was talking about a "typical" UPS? The
post you first responded to was about an On-line UPS, that is, one that
only uses line power to recharge the batteries, and then uses the
batteries to power the converters that provide the power to the
equipment. The only noise output from one of these is in the conversion
of the DC power to a sine wave type output, in other words, nothing
compared to the noise you can get from regular mains power.


The 'junk' power is worst when a computer grade UPS is in
battery backup mode. 'Junk' made totally irrelevant by how
power supply is designed. 'Junk' power was irrelevant to
power supply operation even 30 years ago. One should have
known this, an industry standard, that old and that well
understood.


What??? A computer grade UPS output is far cleaner than the output from
the main power lines. You don't have the ups and downs of the power
along with the various ripples induced by turning on and off large
pieces of equipment or faulty lines. Nor do you have to worry about the
power going off, then on, then off, then ... This will kill almost any
equipment, including computer power supplies. Yes, a good, that is
expensive, power supply may filter out most of the "junk" that comes
into it, but that junk also stresses the components, lowering their life
expectancy. It is much better to start with "clean" power from a good
on-line UPS.


"Michael W. Ryder" wrote:

Your statement about UPS systems is totally wrong. They can make a huge
difference. If the power coming into the building is noisy or marginal
and the UPS uses this "junk" power to recharge a group of batteries that
then provide the power to the computer it can be the difference between
a working system and a costly paperweight. And this is not conjecture,
but experience.