Comments on Uninterruptible Power Supplies
My primary recommendation is Powerware (formerly BEST
Technology, now part of the Eaton Group
) UPS's, specifically the Ferrups ferroresonant unit
for difficult or lightning-prone environments. My recommendations
are based on a lot of real-world experience with manufacturing
environments, which tend to pose the greatest difficulties in
providing computer-grade electrical power. Powerware's 9100 series
is also high quality
and fine for installations where heavy electrical loads
attributable to integral horsepower motors are not present in the
One of our installations is at a rubber goods manufacturer (No!
Not that kind of rubber goods.), where some of the shop machinery
is powered by electric motors big enough to sink a small ship.
Starting some of these motors gives new meaning to "power surge."
One of the motors, a 75 horsepower unit, draws nearly 1000 amps
from the line at start-up. Needless to say, power line instability
is the norm there.
To deal with the power line cruft we have their main computer
system (an H-P 9000 RISC server) attached to a Ferrups 1.4 KVA
ferroresonant UPS. Another Ferrups unit, an 850 VA model, supports
their network gear and also protects the telephone system. On
several occasions, I have 'scoped the UPS output and have never
seen so much as a millivolt of junk, despite all the machinery
running and the continuous power line blips.
The smallest Ferrups unit available is a 500 VA device, which is
what powers the UNIX box here in my office. The largest currently
available is rated at 18 KVA, which will run a heck of a lot of
hardware. I don't know how long the run time is on the 500 VA
unit's battery, because the longest power failure we ever
experienced was only 1-1/2 hours, and the UPS was still going
strong. The 1.4 KVA unit installed at the rubber goods plant has
been able to keep their system up for in excess of two hours before
initiating an automatic server shutdown due to low battery charge
(we subsequently added a second battery to extend the run time to
what is probably close to five hours -- it has yet to be
Ferroresonant UPS's, in general, are larger, heavier and more
costly than line interactive or double conversion units. The UPS
gets its name from the special transformer that isolates the input
from output. The load never sees the raw AC line voltage but
instead, sees the output of the transformer.
A ferroresonant transformer is a special type of transformer
that has been tuned to resonate at the power line frequency (60 Hz
in North America, 50 Hz in Europe and many other locations).
Because it has been tuned to pass a narrow frequency range, the
transformer acts like a brick wall to anything outside of that
range, resulting in very effective power line filtering -- and a
nearly impervious firewall to lightning strikes.
Also, because the transformer resonates at the power line
frequency, it acts like an electrical flywheel and stores energy in
its massive iron core. In the event a momentary decrease or
complete loss of voltage occurs the transformer will replace some
of the missing AC cycles -- a momentary boost. This results in a
true "no break" power source. If the line voltage increases for any
reason (e.g., a spike or transient induced by a nearby lightning
strike) the transformer will buck the increase, keeping the output
within a fraction of a volt of where it should be.
Ferroresonant technology is hardly new. The concept was
developed in the 1930's and has been widely available in heavy duty
power conditioners. My first encounter with a ferroresonant device
was in the 1960's aboard a U.S. Navy warship, where power problems
were routine. Much of the electronic gear was protected by
ferroresonant transformers, which given that this was aboard a
military vessel, amounts to a ringing endorsement of the
"Also, has anyone made a claim to APC for any UPS's that have
been hit and got the money?"
I'm not aware of anyone making such a claim and getting a
settlement. Actually, it's fairly easy for APC (or any other UPS
vendor, for that matter) to weasel out of paying off the claim,
simply because irrefutable proof that the UPS was to blame for
damaged equipment is difficult for a non-technical person to
produce. Even most computer hardware geeks are not experts on power
generation and UPS capabilities, which means most will not be able
to conclusively determine that the UPS didn't do its duty. Adding
to the difficulty is that in many cases, the UPS may continue to
function normally following the destruction of the
I find it interesting that APC in particular has long maintained
that there is no benefit to ferroresonant technology and has even
gone so far as to produce "studies" that "prove" that ferroresonant
UPS's are inferior to line interactive and double conversion units
of the type produced by APC. Yet, almost all power-critical
installations run by the military and many government operations
depend on ferroresonant technology for power protection. So, who's
right: APC, who has a sales ax to grind and has never achieved a
high rate of success in large commercial installations, or the
military, whose primary concern is maximum reliability?
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