Re: Took the cells out of a DeWalt Cordless Drill
Thinking logically, you have 10 sub C all in series to produce 12V. You have a charger which should output a bit over 12V (probably 13.8V) to charge the cells. The charger says it pumps 1.9A and will charge the cells in 1 hour. The 1.9A will pass through all the cells in series, so expect the capacity of those cells to be close to 1.9Ah. Probably 1.7Ah, the little bit of extra time is probably just to round it to something easily remembered and to ensure the cells are topped off, without excessive time on the charger to cause overcharging problems.
BTW, they could be 2.0Ah cells if DeWalt decides to play it safe and give a little more capacity to prevent overcharging problems. A highly possible scenario from an industry leader eager to ensure that its products don't fail prematurely.
Knowing that the upper limit would be 2.0Ah and the more likely capacity would be 1.7Ah, you could then do a first charge assuming it is 2.0Ah (That would be about 8hr 20min on that 240mA charger you have. 8hr 30min should be fine to ensure complete charge.) Allow it to cool to room temperature after charging.
Next, we can try and perform the standard Energizer battery test to check its capacity. This test will discharge the cell at the rate of 1/5C until the voltage of the cell drops below 1.0V. We assume it is 2.0Ah capacity, so 1/5C is 0.4Ah. We need to discharge at a rate of 0.4A. This can be achieved with a 3R resistor. Use a resistor that can handle at least 1.2W.
If it takes closer to 5hrs, you have a 2.0Ah cell. If it takes less than 4hr 15min you have a 1.7Ah cell. You should probably perform this test a couple of times and with a few different cells to average the results.
Or to make it simpler on yourself, just go out and buy a smart charger that works on delta V.
