I have a Powercom PCM Black Knight UPS (600AP model). It seems to work
perfectly as a UPS, but the computer monitoring is a little off.

For example :-

1) The battery is reported as "92%" full, and no more. The terminal voltage
is fine, but it never charges more than 92%.

2) The mains voltage readout claims that the incoming mains is 216.4v at
the moment, but really it's 238v. It's always about 91% of the actual
value as confirmed by a DMM, a plug in power meter, and another UPS.

3) When it's on battery, the outgoing mains voltage shows as 216.4v, when
the inverter is actually producing a perfectly good 238-240v.

Now, I'm hoping that the fact that these figures are off by very similar
amounts means that somewhere, an A-D conversion circuit is a bit off, and
can be tweaked. Does anyone have a schematic to indicate which of the
various adjustment pots would do this? Or is it a "fixed at design" thing?

Also, it measures "power loading" as 17%. When placed onto battery, the
power loading initially was around 15%, descending to 3% over 20 mins.
When returned to mains operation, loading stays at 3%, and rises back to 15-17%
over the next few hours. Huh? That's harder to understand, as the load on it
is pretty constant 85VA/51W (as measured), which would be about 14%. It's
almost as if the power loading measurement depended on the 12v battery
voltage for accuracy. Which would be bonkers ...

Mike.
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Mike Brown: mjb[at]pootle.demon.co.uk | http://www.pootle.demon.co.uk/