Capacity Testing and 20 HR Rating
I'm thinking about doing a capacity test on my four GC2's. They have a 20hr rating of 215Ah. One thing I'm curious about is how the 20hr rating would have been determined. Being 6v, would they h...
Forum Discussion
jrnymn7 wrote:
Mex,
In the past, I have considered a few things, in trying to establish what constitutes say a 90% SOC...
1) the Trimetrics readout (assuming it's fairly accurate, which I'm discovering is not always the case),
2) OCV, based on comparisons to 50% and 100% readings (which I'm now realizing I need to allow for more voltage drop as SOC decreases thru the 0% to 50% DOD range, when trying to establish an SOC vs. OCV correlation), and,
3) guess-timating, as best I can, looking at amps x time - ?losses.
It's certainly not a perfect science, but I'm trying my best to consider as many things as possible.
And obviously I need to establish an SG to SOC relationship, as well... which will require a few more capacity tests, I think, at various loads.
What I used to do daily is establish state of charge with a temp compensated all-cells dip. Compare that with amp hour reading (Dang I wish you folks would fall in love with kWh values) and thirdly with voltage. I haven't done the following exercise yet, but it sounds interesting.....use a tungsten load, powered by a DC/DC booster for constant load voltage, which is measured by the metering for energy transaction. I would use the 600-watt rated booster with a <50% loading capacity factor to make the booster less subject to idiosyncratic thermal operating loss issues. Don't forget to adjust battery kWh capacity estimation via temperature of the electrolyte. Capacity/temperature variance can be a real eye-popper.
So I used the hydrometer then audited the metering values. Discrepancies always favor specific gravity. Peukert and other factors can also be proofed. On many and I mean a LOT of cruising sailboats I found Cruising Equipment and E meters to be so far in error it was disheartening. I developed a percentage of correction chart with the vessel owners that served to negate metering amp hour error. For a while. Monthly checkups were necessary. Perhaps today's meters are more accurate. I have no idea.
