On Sat, 10 Nov 2012 08:51:39 -0500, "Jim Wilkins"
wrote:

wrote in message
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...
The small standby UPS does no wave shaping when allowing the load to
run on "line " voltage - and most are, at best, modified sine wave
output.

A UPS "modified sine wave" is a sequence of positive and negative
square pulses at 160 to 170V, with enough off time between them to
reduce the average (RMS?) voltage to 120V. I've seen the pulse width
increase at higher loads that pulled down the peak voltage.

An APC Smart-Ups has a pure sine output on battery.
https://www.apc.com/products/family/index.cfm?id=165

But a SmartUPS is not a standby - a Back-UPS is.

Some of them can run off large external batteries without overheating.
Check the surplus stores for used ones. The downloadable manual shows
the simple but not obvious way to remove the old batteries.

That is not a "small standby UPS" by anyone's definition. It is an
online UPS - AKA dual conversion.

I just discovered that the sensor-logging feature of HWiNFO32 v4.06
freeware can record the run time of an unattended laptop on its
battery, It captures the battery voltage, the power drain and the
estimated percent of remaining capacity, which will show a sudden drop
to empty if the battery's microcontroller IC needs to recalibrate
itself with a full discharge cycle.
http://www.hwinfo.com/

I use recording TV and displaying Internet weather radar as
representative high and moderate power applications to check UPS run
time. During an outage I wouldn't let it run idle on precious battery
power though that's the easiest measurement to make. The Event Log
will capture shutdown time.

I haven't tried yet, but it should also show when the UPS or inverter
powering the laptop plus your test load shuts off and the laptop
switches to internal battery.