Discharging Ni-MH batteries

Thread Starter

MMH

Joined Feb 8, 2013
143
Hello there everybody!!

I just read that Ni-MH batteries should not be discharged below 1.0 volts. While discharging(a single 1.2v cell) with a DC motor, the voltage across the terminals went down to 0.4 volts. BUT. after leaving it alone for around an hour, the open circuit voltage measured 1.13v. Is this alright, or should I stop discharging it when the "voltage across the terminals(while discharging)" is 1.0v??
 

richard.cs

Joined Mar 3, 2012
162
I would imagine that's 1 volt when under load however deeply discharging a single cell doesn't tend to do that much harm. As soon as you've got several in series you start to get problems where the weakest cell is pushed into reverse by the stronger ones - that's a lot nastier.

On the other hand there's very little usable energy left below 1 Volt so why not stop there?
 

Thread Starter

MMH

Joined Feb 8, 2013
143
Thanks for answering!!

I am aware of the fact of reverse polarity. I did not stop discharging at 1v since I was calibrating it. Can you be sure of that as when I connected the batt to the motor(after discharging it to 0.4v and leaving it for an hour) the voltage Slowly got down to 1.2, then 1.19 and so on.
 

Thread Starter

MMH

Joined Feb 8, 2013
143
Thanks for answering!!

The capacity of the cell is 2700mAh and I don't know the current the load draws . The amperage of the circuit is 20mA.
 
Last edited:

richard.cs

Joined Mar 3, 2012
162
The current drawn by the load is important in answering your question. A cell that size under a 1 mA load really should be stopped at 1 Volt. At a 3 amp load then you can go a lot lower.

As I said there's not much energy left below one volt anyway - Ni-mh cells have quite a flat discharge curve and they've really fallen off the end by that point.
 
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