I'm thinking about benchmarking some rechargeable batteries, to know which ones I want to order more of, and to be confident when one has degraded enough that I want to throw it away.
I could spend several hundred on a calibrated network connected load bank.
Or I could hack somehting together. I think we all know what's coming....
I have a usb controlled relay board with 8 spdts. I could line up several battery positions with that, to either charge or discharge.
I also don't want to wait around to look at and write with a pencil the voltage every minute. But I'd like to produce discharge curve graphs.
I was thinking I need two meters. one to measure amperage, and one for voltage. but wait a second...
if My load is really dumb, just a resistive element for instance, do I need to measure current at all? of can I infer it by knowing the unchanging resistance of the load, and the voltage at the load? v=i/r so i=rv. right?
if I had one serial dmm. could I measure voltage, connect a known load, and then watch the voltage until it reaches a lower safety boundary, then disconnect load. record voltage every second, calculate amps by multiplying ohms and volts. then multiply amps and volts for that second to know how many watt-seconds were consumed during that one.. earth second?
Or do I really just need two meters? the wiring is going to be very short, just 8 inches maybe 12 at the most and I'm not trying to damage my batteries, so I don't want an extremely heavy load for AAA's, AA's and 9v's (Anyone want to suggest how many ohms I should use?)
I want to compare these two head to head first:
https://www.amazon.com/gp/product/B0BC8P2TS6https://www.ebay.com/itm/204266648120I want to know with confidence, if they're really giving me 1200mah or 1300mah like they say. or how far off they are.
I have a couple of these 50w 25ohm resistors for load..
https://www.amazon.com/gp/product/B07SPC8CKK/ or maybe I'd use an incandescent bulb