Battery pack creation

Discussion in 'General Electronics Chat' started by svdsniper, Apr 11, 2011.

  1. svdsniper

    Thread Starter New Member

    Feb 28, 2010
    9
    0
    Hi

    Simple question, i need to make a battery pack to fit a small potting box, it needs to be 4.5v and have more that 1.x Ah. My plan is this.............i can fit a total of 5 rechargable NiMh aaa batteries inside so i was thinking i need to solder the batteries together with wire, 3 x aaa in series to get 4.5v easy..............now with the other two i wish to increase the capacity so can i still solder these with wire in parralel to the aa cells that would supply the positive and negative terminals of my pack?
    I know this is ok with 6 cells as i have done it before with a total of 24 cells but was wondering if using an uneven number of parralel cells would cause any problems?
    Your thoughts please?

    svdsniper
     
  2. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The single battery cell without another in parallel with it will become completely discharged first. The remaining paralleled cells are stronger and will charge the single cell in reverse while powering the load through it. Then the single cell might be destroyed.
     
  3. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,699
    907
    NiMH are 1.2V nominal. Try four in series, connected with braid or tabs. I would not pot them, as they get warm during charging and discharging. Heat will decrease their life. If you are not really good at soldering, get someone else to do it for you.

    John
     
  4. svdsniper

    Thread Starter New Member

    Feb 28, 2010
    9
    0
    Hi all

    Heres a question for you. I created a battery pack from 4 nimh cells that gave a fully charged voltage of 5.6v and i created another from 3 cells with a fully charged voltage of 4.56v. The device to be powered has a draw of 0.2-0.3a. the 4 cell pack ran down after less than 1.5 hours but the 3 cll pack ran for 2.5 hours.............can someone please explain why????
    To my thinking the 4 cell pack should have lasted longer due to its larger usable voltage spread (device runs from 3.0v up to a max of 5.6v) but this 4 cell pack was rubbish compared to the 3 cell pack! any ideas as to why???

    thanks

    svdsniper
     
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