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Drake, The spreadsheet name was Peukert.xls and all it computed was the Peukert effect - greater discharge current <-> smaller battery capacity. Peukert's equation is based on a constant discharge current from fully charged to fully discharged (10.5 volts at the current in question). The misunderstanding (almost urban myth) comes when considering what happens when a battery is subject to partial (or even complete) discharge at a high current. The amphours accrued at a high discharge rate actually have little effect on the total amphours that can be delivered at a low discharge rate. Example: Brand XYZ L-16 battery battery has a capacity of 400 Ah @ C/20 or 300 Ah @ C/6. There's a 25% difference between these two capacities. >From a full battery, discharge at 50 amps until the voltage is 10.5 volts, that takes 300 Ah. The battery is functionally dead, 100% DOD, if we need 50 amps at more than 10.5 volts. But at 20 amps the battery is not dead. The battery will still deliver another 80 Ah for a total of 380 Ah (5% less than 400 Ah @ C20) before the voltage gets down to 10.5 volts. The 380 Ah and 5% numbers here are just for example purposes; if you did this test to a L-16 the total would probably be higher than 380 Ah, but you certainly would get less than 400 Ah. Kent Osterberg Blue Mountain Solar, Inc Drake Chamberlin wrote: Kent, |
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