"Larry Jaques" wrote in message
...
Which reminds me to fix that old laptop I bought the battery for
but
never fixed... I wonder if DSL would stay up here if the power
went
out. I could add the little 400W inverter and run the PK5000 with
the
laptop for inet access. The ammeter would help me track power for
the
12v toys I have, too, wouldn't it? Back to Futurlec...


I bought the 50ADC meter for that. It's good for an inverter of up to
600W. 400W has been plenty for what I need between generator runs
during an outage. An inverter makes a good load for battery capacity
testing because it shuts off before discharging the battery low enough
to damage it. I plugged in a 100W crock pot as a safe representative
load.

A cheap Harbor Freight multimeter reads up to 10 Amps which is 120W to
or from a 12V battery. I use a digital multimeter for testing, an
analog meter for continuous monitoring.

HWiNFO32 shows laptop battery charge or drain power in the Sensors
window.
http://www.hwinfo.com/download32.html
If the laptop is part of the inverter test load the battery power log
entry captures the time when the inverter's low battery shutoff trips.
The .csv log file loads neatly into a spreadsheet but you may have to
adjust the checklist of field separators.

What I've found is that if I am using the laptop efficiently the power
drain varies widely, from 20W to 35W on this one. The only way to get
a stable and repeatable measurement is to run it at idle or on a task
that continuously writes to the hard drive, like logging data or
recording HDTV, both of which capture the time when the battery ran
out. It's also in the Event Log if the computer successfully entered
Sleep mode. I can compare the run times of batteries or UPSs but not
predict it for normal use.
jsw