What I wanted to know is if the terminal voltage you read on a battery in a charger is representative of it's actually capacity?
In other words, if I pull batteries out of a charger as soon as they read 1.40V is that indicative of the battery being 95% charged - given the fact that they usually will read "full" if taken out and replaced in a charger when at ~1.42- 1.43V?
I thought the right way to get a real indication of charge requires putting a load on the battery while reading a terminal voltage. And I also thought that a 10watt, 1ohm resistor ought to suffice.
Hey Burpee,
Unless I misunderstand you, the fundamental problem is that the voltage of the cell on the charger is the charging voltage, whereas the voltage of the cell under a 1 ohm resistor load is a discharging voltage. So they are not going to be even close to being the same.
But the bottom line is that it is extremely difficult to determine the state-of-charge of a NiMH cell based only on voltage, even if you take the trouble of measuring voltage under load. The only way to do this is to make a calibration curve for a specific cell type by charging (or discharging) to a known state-of-charge, then measuring the OCV and CCV under a given load. There is simply no other way to do this for a NiMH, at least not without some pretty expensive testing equipment.
Quite frankly, the only time you know the state-of-charge of your NiMH cells is when they come off your charger at 100%.
Sorry that I am not more help.
Cheers,
BG
