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Capacities of C size NIMH batteries compared to AA.

Discussion in 'Hobby Electronics' started by Mauried, Oct 9, 2008.

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  1. Mauried

    Mauried Guest

    You now seem able to buy AA NIMH batteries with 2500 mAH capacities
    but similar branded C size Nimh batteries have only 4500 mAH.
    Given that the C battery is 4 times the volume of the AA something
    seems wrong here.
    Anyone seen NIMH C batterys with much more than 4500 mAH capacity.
  2. Interestingly, the best Energizer NiMH C cells are only 2500mAh rated,
    same as their AA cells (@ 500mA CC discharge to 1V).
    Compare the data sheets of both and the discharge curves are identical
    up to and including 2C.
    The only spec difference is internal resistance and impedance, which
    are both lower in the C cell of course.
    Claim of 6000 here:
    but no data sheet to back it up.

  3. Phil Allison

    Phil Allison Guest


    ** Firstly - the volume ratio from AA to C is close to 3:1.

    It would be rare to find a C cell with 3 times the capacity of the BEST
    available AA of the same chemistry class.

    So there is nothing " wrong ".

    The explanation lies in market forces:

    AA cells would have to be easily the highest selling size by FAR - as a
    result it is also the part of the market where there is the fiercest
    competition for top performance ( Eg - Duracell have been fighting
    Energizer over it for decades with saturation TV marketing ).

    No similar thing exists with C or D sizes - so cell makers have much less
    motive to go to the same efforts with them.

    Another example is with "sub C" size Ni-Cd cells that way outperform similar
    C size cells - cos "sub C " is what the RC hobbies use.

    ...... Phil
  4. Phil Allison

    Phil Allison Guest

    "Phil Allison"

    ** Correction:

    ....... Phil
  5. Ooober

    Ooober Guest

    Is the SA of the electrode(s) more important than the volume - which is the
    limiting or critical factor the electrolyte volume or the electrode(s) SA?
  6. Mauried

    Mauried Guest

    The dimensions of the NIMH batteries that Jaycar sell which are the
    ones Ive been comparing capacities of are

    AA 13.5 mm by 50 mm
    C 26 mm by 50 mm
    Thats pretty close to 4:1 , not 3:1
  7. Mik DaDik

    Mik DaDik Guest

    Gday All,
    Ok Volume of a cylinder = Pi*r*r*l

    So if L and Pi are the same the difference is r*r (of C size) / r*r (AA)

    Therefore 13x13 / 6.75x6.75 = ratio of 3.71:1 or just under 4:1 ratio..

    Sorry for the school stuff but it was 35 years ago since I did that so I
    was interested if I still had it in me.


  8. Phil Allison

    Phil Allison Guest

    "Phil Allison"

    ** Several AAs I have here are 14mm x 48mm

    Several C cells I have are 25mm x 47mm

    Makes the ratio 1 : 3.1

    Get a vernier gauge.

    Then read the rest of my post - wanker.

    ...... Phil
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