using voltage to estimate % charge left in NiMH batteries....

[mpenza]

Is the voltage a good indication? I found that when fully charged, the batteries are about 1.37V. The voltage drops with usage....

 

[ckiang]

Originally posted by mpenza
Is the voltage a good indication? I found that when fully charged, the batteries are about 1.37V. The voltage drops with usage....

Not a very good indicator. The voltage can be 1.3V for e.g, but the battery may not be able to drive anything because either it has not enough current, or the internal resistance is too high. It's never accurate to measure a battery's voltage without a load applied (as in the case when it's in your camera). Commerical batteries apply a known load across the battery terminals before giving you a reading.

Regards
CK

 

[mpenza]

hmm... do you have any idea what sort of load would be useful? I could have a circuit just for measuring "% capacity" left.

 

[ckiang]

Originally posted by mpenza
hmm... do you have any idea what sort of load would be useful? I could have a circuit just for measuring "% capacity" left.

That I am not too sure. If you want to simulate a digital camera, you will need a load with lower resistance (so it will draw more current). If you want to simulate a lower power device, e.g. a clock, you can use a smaller load. Maybe can work out from a typical digital camera's current consumption.

Regards
CK

 

[Flare]

From what I know. Voltage isnot a good indicator as NiMh experience a sudden fall in voltage near the end of its charge, unlike alkalines which falls more gradually.