dkuhajda wrote:

Sounds like a weak/bad battery.
You did not post that you performed the proper test on the battery.


No, I didn't. However, from the fact that the AC output dropped
to 85 volts but the battery still held at around 12.5-12.75
without really sagging led me to believe it was probably ok.


Find out the MAXIMUM current output available under UPS mode of operation.
Place a suitable load on the output, calculate that your computer is not
overloading the unit. Most UPS units will NOT handle both the computer and
the monitor for very long. Then pull the plug while monitoring BOTH the AC
output voltage AND the battery voltage at the SAME time.


This is what I did (i.e., monitoring both the AC output and the
battery level) although not with a computer for a load. This is
only a 280 VA unit not intended for really large loads. I was
planning on using it for my wife's CPAP machine since we
occasionally have power outages at night. The 40 watt lamp I used
was just convenient.


FYI it is normal for the meter reading voltage to drop to below 90 volts
when the UPS detects a no load condition. 40 watt light bulb is simply not
large enough to test the output, since most computers alone have 300 watt
power supplies.


So there not only is a maximum load but also a minimum load for a
given UPS? I could understand there being a voltage foldback for
a no load condition depending on the design of the unit, but a 40
watt bulb pulls 1/3 amp. That isn't totally trivial as the UPS is
only rated for a bit over 2 amps max (depending on application of
course). Seems like an extremely narrow operating range.

So you're saying that if I put a 150 volt bulb on this (over half
the maximum rated load), the output voltage should increase?
(assuming the battery was good)


UPS sealed lead acid batteries last ALMOST 2 years before they should be
replaced. Occasionally one will last a bit longer, but for full back up
performance, replace them every two years.


Yes, I have no idea how long it was in there (I got the unit from
a friend) so it could be that old. However, I still would expect
a bad battery to not be able to hold a voltage of over 12.3 volts
under load even if that load is 1/7 of the maximum load rated for
that UPS. This is a fairly lightweight unit and using it as a UPS
for a 40 watt load did seem plausible.

- Jeff