In the past
we've kept to simply using a standard computer and 19" monitor to
evaluate how long an Uninterruptable Power Supply will last under total
power failure conditions. Comparing the amount of time the UPS can sustain a PC
and monitor vs. the manufacturers listed specs gives everyone a rough idea of
what to expect in real world situations.
However, Volt-Amp (VA) ratings tend to be a little
obtuse for most of us, and for this review we're also going
to measure the UPS' output voltage levels with the unit in a
utility over-voltage, and utility under-voltage situation.
For that we'll be making use of a Sencore PR57
Variable Isolation Transformer, Digital Multimeter and a few other apparatuses.
During these tests, we'll be looking to see if the UPS output voltage drops
below acceptable levels to cause computer instability.
This may seem a little overly elaborate, since most
of us trust that a UPS will supply pure sinusoidal 120V AC, but that isn't quite
the reality. A UPS' output voltage can vary.
The point of this test is simply to simulate
different degrees of a utility power failure. As we have seen first hand in
our own office, the utilities can fluctuate by a wide degree, and in
the country where "brown-outs" are a common affair, it should be
interesting to see how a UPS holds up to a range of AC voltage
senario's, while supporting a running PC.
With a standardly equipped Pentium 4 2GHz Computer
and 19" CRT monitor plugged into the Belkin Universal 1000VA UPS, we pulled the
plug and recorded how long the battery lasted.
Not surprisingly, the 1000VA Belkin Universal UPS lasted
essentially as long as another 1000VA reference UPS, the Powerware 5125. That time was, about 23 minutes before the
Belkin UPS lost power and the computer shut down. For comparisons sake, we also
tested the 500VA Belkin Home Office UPS, which managed just over 4
minutes with the same computer configuration before its battery ran dry.
* Using a Sencore PR57 Variable
Isolation Transformer we were able to measure the current load of the
connected test system which was comprised of a 19" CRT monitor, and
typically outfitted Pentium 4 2.0 GHz computer. By using the formula V (x)
A = VA we were able to calculate the total system power load, which in
this case was approximately 300VA.
Tests - approx. 300VA load*
||Belkin Home Office
The key point to take away is that VA ratings and time are not a 1:1
relationship. Just because a 1000VA UPS kept the test system running for 23
minutes does not mean a 500VA UPS should keep that same system running for half