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Topic: Charging Batteries in Parallel (Read 659 times) previous topic - next topic

JoeTac

May 25, 2012, 08:12 pm Last Edit: May 25, 2012, 08:14 pm by JoeTac Reason: 1
I have a set of NiMH(3000mAH) batteries that I will be using to power my arduino, but I don't get enough time out of them so I wanted to wire up 3 more sets in parallel to them so I can get 12000mAH. Is this a problem or will my batteries explode? I will also have a solar panel to charge them up.

Thanks

EDIT: These batteries are AA and are in a battery box

jackrae

From the text I gather you are enquiring about discharging batteries in parallel, rather than charging.

If you are concerned about "circulating" or back-fed current then place a diode (3 required) in each of the battery positive feed lines, with all negative lines connected as a common ground point.  The three diode cathodes are connected together and then to whatever your positive consumer terminal is.  The output voltage will be around 0.7 volts lower than you currently (excuse the pun) have but the diodes will eliminate of any single battery being back-fed if its state of charge is different from the others.

If you are interested in charging then you're in a whole different ball park since getting the currents to balance for charging purposes is much more difficult (until someone says otherwise)

JoeTac

If you were to charge them in parallel, but added an extra resistor in parallel with the set of batteries would that balance out the charge?

jackrae

See the attached for a mention of the problems trying to charge NiMh in parallel

http://www.powerstream.com/NiMH.htm

JoeTac

If I were to put a Current Regulator(similar to http://www.youtube.com/watch?v=2UDVLeCqZl0) in series with each battery do you think there would be an issue?

jackrae

Yeh, Three such circuits would do your job.

However they would each need isolation diodes in series with the circuit outputs, again to effect isolation between circuits.

Negative of PSU goes to the common ground point.
Each CC regulator circuit positive output is connected via an isolator diode (cathode terminal) to the junction of the battery and its discharge isolator diode (anode terminal).

For the purpose of Rc calculations you can ignore the effect of the diodes since they are merely a virtual resistance in the load circuit so do not affect the constant current feature.

I'd suggest limiting charge current to C/10 (300ma) in each stack, therefore your PSU must be capable of delivering at least 900ma

If you go for must higher currents then you really should have temperature monitoring on each battery stack since NiMh are somewhat prone to getting rather hot at high charge rates.

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