"bob prohaska" wrote in message news:tbvec1$3d2tb$1...@dont-email.me...
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I've done a lot of measurement like that, initially recording the
Kill-A-Watt values by hand at irregular intervals as you appear to have
done, then I automated the measurements with a pair of TP4000ZC DVMs logging
battery voltage and current to a laptop, a much better arrangement that
graphs the readings and shows trends and events such as when the battery
reached full charge or discharge, and that my UPS inverter trips out on low
voltage a few seconds after the fridge turns on, so Ah capacity and run time
measurements are somewhat random. The minimum sampling interval is 1 second
and it doesn't accurately capture compressor starting surges, I use a
digital storage scope for that. The TP4000ZC can also log temperature with
an included sensor or a K type thermocouple.
Besides the DVMs I bought very flexible silicone-insulated wire to connect
the meters without knocking them over, screw-on banana plugs to make test
leads, and non-gendered Anderson PP45 connectors to join (or bypass)
everything in various configurations. The 30A pins can be soldered, the 45A
ones need a crimp tool. 12AWG Si wire fits the 30A pins and housings without
issues, 10AWG can be forced with difficulty. Gendered pin / socket
connectors are dangerous on batteries where both sides can be live.
Since the output files can be imported into a spreadsheet and manipulated
you can use a lower current, higher voltage shunt for more resolution and
rescale the mV reading to Amps. Each meter writes to its own log file which
I combine by aligning the time stamps, thus they can be different types. One
reading per minute seems a good compromise between resolution and file size.
To go further, the DPS5020 is a digital voltage and current regulator that
can also log its output readings to a computer. It needs a DC power source
such as an old 19V laptop power brick, battery charger or whatever else you
may have, up to 60V.
https://www.electronics-lab.com/ruideng-dps5020-50v-20a-power-supply-module-review/
The designer assured me that it isn't harmed by voltage from the battery
back-feeding into its output, it simply powers up, but the voltage does pass
through to the input so its input supply may need protection such as a large
series Schottky diode.
I built a rectifier supply for it from an old arc welder transformer that
takes it to 20A at up to 30V. A case is available if you don't want to make
one. I made a box for a DPS5015, bought one for the DPS5020. The purchased
case was a tight fit for an added diode on an insulated heatsink.