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Question about cordless telephone

Discussion in 'General Electronics' started by [email protected], Dec 11, 2004.

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  1. Guest

    I have a cordless telephone with NiCd rechargeable battery.

    I am wondering what the best strategy for prolonging the life of the
    battery.

    Should I always leave the phone in the cradle to recharge or will that
    cause a memory effect. I seem to recall one manufacturer's
    instructions recommending always having it in the cradle.

    I would think being a NiCd (as opposed to NiMh) that I should run the
    battery down before putting it back in cradle. Of course if I do that
    then I am without a phone during recharging.

    Thanx in advance for suggestions.



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  2. Aplin17

    Aplin17 Guest

    Be careful not to reverse charge the batteries if you do leave it off charging.
     
  3. Lou

    Lou Guest

    Hi

    Contrary to a popular belief, the "memory effect" doesn't affect the
    life of a NiCd, quite the opposite in fact. What it does affect is
    the useful charge, that is the charge effectively recoverable after a
    full recharge. The memory effect results in a drop in the terminal
    voltage after a fraction of the stored charge has been recovered,
    making the remainder unusable by the electronic circuit it feeds. The
    fact that some charge always remains in the elements protects them
    against dendrite formation and element inversion, the two main
    killers of batteries.
    The small amplitude charge/discharge cycles are also influence
    favourably the life expectancy. Also note that the memory is not a
    permanent condition, and can be erased after some ch/dsch cycles.

    If you want to use the full capacity of your battery, you must only
    work in a regime of complete ch/dsch to avoid memory. It will however
    affect the life because large amounts of electrode material is
    transformed/displaced each cycle, and this material does not
    necessarily land back where it originated, resulting in a progressive
    deformation of the electrodes. There is also the danger of unequal
    capacities among elements, with the risk of the weakest element being
    reversed at the end of the discharge.

    Thus, leaving your phone on its cradle might look like the safe
    option, but it is not necessarily the case: some simplified chargers
    continue supplying a much too large current after the battery has
    been charged, resulting in a continued electrolysis exceeding the H2
    recombination capacity of the cell, eventually causing its failure by
    a lack of electrolyte (the cell "goes dry"). A symptom of this problem
    is the battery pack getting warm after 12 h. charge.

    Lou

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  4. On 14 Dec 2004 08:26:36 -0600,
    Thanx for such a detailed explanation. If the battery pack does not
    get warm after twelve hour charge would this suggest that there is not
    overcharging happening? Is there any other way to determine
    overcharging??

    It is interesting that one of my phones instructions say to leave
    phone in cradle and the other says to let it discharge completely.
    Both are NiCd btw.

    If leaving the phone in the cradle too long is bad then when I go away
    on vacation for a week or two, the best strategy would let the phone
    just discharge.


    -----------------------------------------------------
    -----------------------------------------------------

    A: Because it messes up the order in which people normally read text.
    Q: Why is top-posting such a bad thing?
    A: Top-posting.
    Q: What is the most annoying thing on usenet and in e-mail?
     
  5. Lou

    Lou Guest

    You can measure the residual current supplied by the cradle after a
    full recharge: if it exceeds the capacity/20, it's probably unsafe.
    Ideally, it ought to be in the region of C/40. It is not a good idea
    to let the phone discharge completely: you risk element inversion;
    the best solution in this case is to disconnect or remove the battery
    from the phone.
    Lou

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