Re: GPS - non-rechargeable versus rechargeable

Discussion in 'General Fitness' started by Chris Malcolm, Jan 17, 2005.

  1. John Laird

    John Laird Guest

    On Tue, 18 Jan 2005 13:53:47 +0000, Dominic Sexton
    <{d-sep03}@dscs.demon.co.uk> wrote:

    >A lot depends upon the load / current too. At higher loads alkaline
    >cells can have lower capacity than NiMh and even NiCd. The first digicam
    >I used ate a set of 4 alkalines in 20 pictures whereas the 650mAh NiCd
    >cells I put in it lasted over twice that.


    The alkaline batteries would have been fine for other applications if you'd
    tried them. Their limitation is an inability to deliver a sufficiently high
    current without exhibiting voltage drop, which the camera electronics will
    detect and promptly shut down. Left to recover, they would have been fine -
    they are usually up around the 2000-3000mAh range (iirc) and could not have
    been flattened as such with such short use. (Unless the high current
    actually caused internal damage, but I would think this unlikely.)

    For non-rechargeable (emergency backup) use in digicams, use lithium cells
    instead. They are 3V cells and can often be found in a 2-AA size which
    directly replaces two ordinary AA cells if the battery compartment has the
    right connections, will cope well with the load and have a high capacity and
    very long shelf life. Not too expensive either, if you look in the right
    places.

    --
    Math illiteracy affects eight of every five people.

    Mail john rather than nospam...
     


  2. In article <[email protected]>, John Laird
    <[email protected]> writes
    >On Tue, 18 Jan 2005 13:53:47 +0000, Dominic Sexton
    ><{d-sep03}@dscs.demon.co.uk> wrote:
    >
    >>A lot depends upon the load / current too. At higher loads alkaline
    >>cells can have lower capacity than NiMh and even NiCd. The first digicam
    >>I used ate a set of 4 alkalines in 20 pictures whereas the 650mAh NiCd
    >>cells I put in it lasted over twice that.

    >
    >The alkaline batteries would have been fine for other applications if you'd
    >tried them.


    They weren't dead but they didn't have much left in them.

    > Their limitation is an inability to deliver a sufficiently high
    >current without exhibiting voltage drop, which the camera electronics will
    >detect and promptly shut down. Left to recover, they would have been fine -
    >they are usually up around the 2000-3000mAh range (iirc)


    Good alkalines have a spec of ~2800mAh but that is (a) at a low current
    and (b) to a low voltage. The actual capacity they can deliver is
    dependant upon the load.

    Energizer have their datasheets online. They illustrate the
    characteristics rather well:

    http://data.energizer.com/PDFs/e91.pdf

    > and could not have
    >been flattened as such with such short use. (Unless the high current
    >actually caused internal damage, but I would think this unlikely.)


    Look at the constant current discharge curves in the PDF linked above
    and you will see how badly they cope with high current. At 1A the
    capacity (to 1V cut off) is about 500mAh.


    --

    Dominic Sexton
     
  3. John Laird

    John Laird Guest

    On Tue, 18 Jan 2005 17:34:09 +0000, Dominic Sexton
    <{d-sep03}@dscs.demon.co.uk> wrote:

    >Energizer have their datasheets online. They illustrate the
    >characteristics rather well:
    >
    >http://data.energizer.com/PDFs/e91.pdf


    I sit corrected - I hadn't realised it was possible to "cook" alkaline cells
    quite so much. The log v log graph is a bit tough to read, there's a table
    of sample capacities for alkalines against lithiums at differing discharge
    rates near the bottom of http://www.a1.nl/phomepag/markerink/battery.htm

    Thanks for the heads-up.

    --
    Where the heck is the ANY key?

    Mail john rather than nospam...
     
  4. On Tue, 18 Jan 2005 17:34:09 +0000, Dominic Sexton
    <{d-sep03}@dscs.demon.co.uk> wrote:


    | Good alkalines have a spec of ~2800mAh but that is (a) at a low current
    | and (b) to a low voltage. The actual capacity they can deliver is
    | dependant upon the load.

    But I have never seen this on the packaging. Unless this is on the
    packaging or referenced on the packaging, there is no way you can screw the
    supplier if a battery fails to supply say 2800mAh
    --
    Dave F
     
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