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NiMH battery charging with a phone charger

Discussion in 'Power Electronics' started by Armqus, Nov 2, 2016.

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  1. Armqus


    Nov 2, 2016

    I have 8 NiHM batteries in series. A single one has the stats "1.2 volts" and "1400 mAh".
    Can I charge them with a Nokia phone charger that outputs 5 volts and 750 mA?
    And how long would it take to charge them?

    I thought of ripping the mini-USB connector apart and charging the batteries because I lost their original charger.
    Last edited: Nov 2, 2016
  2. Armqus


    Nov 2, 2016
    I was impatient so I cut the mini-USB away, tested out which one of the black and white wire was positive and negative, even though I had the idea white was positive, but yet I had an urge to test it with my multimeter. Now the AC/DC charger seems to be charging the batteries.. I can feel some minor heat on the batteries so I guess it's charging up properly.

    Will be posting an update later.
  3. Alec_t


    Jul 7, 2015
    If you are trying to charge the batteries in series (not a good idea, unless you can be sure they remain balanced) the charger voltage will need to be at least 9.6V, so the 5V charger couldn't cope on its own. If the 5V charger is heating the batteries then either the batteries are dead or the charger polarity is incorrect.
  4. Armqus


    Nov 2, 2016
    Well, it's kinda 4x4.
    The batteries were at 0 volts when I started charging them. After about 30 minutes they were at 3,6 volts. The heat wasn't really so much of heat that I let you imagine. I'd say it was like about the same my body heat. Or lesser.
    Last edited: Nov 2, 2016
  5. Audioguru


    Sep 24, 2016
    Your photo is not a schematic and it does not show what is connected to what.
    I assume that you have two groups of 4 battery cells in series? Then you are feeding the 5V to both groups in parallel? Then if the cells are good they will never reach a full charge because each cell should be 1.4V to 1.5V when fully charged that needs a charger voltage of 5.6V to 6.0V.

    Energizer battery company's website has a Ni-MH Applications Manual here:
    This is their second manual and it has an error on the graph showing charging voltage, pressure and temperature. It describes that as it charges the temperature rises which is correct but the graph does not show the temperature rising. Here is the correct graph from the 1st manual:

    Attached Files:

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