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Keeping NMH Batteries Charged

Discussion in 'Electronic Repair' started by Brad, Dec 14, 2004.

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  1. Brad

    Brad Guest

    Hi,

    NMH batteries have a poor shelf life after charging them. I
    would like to build a "trickle" charger to keep them (1.5V AA) charged
    until I need them. They will always be in the charger. I thought about an 8
    cell holder. Cells will not be charged in series. Each cell will have a
    resistor in series with it. What is a safe trickle current (always present)
    for a AA NMH battery?

    Thanks in advance, Brad

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  2. Jerry G.

    Jerry G. Guest

    The AA type battery needs about 120 to 150 ma of current minimum to properly
    charge. This would be the threshold charge current for the battery. To
    maintain the charge, about 15 to 30 ma of charge current should be adequate.
    This is for the average. The exact specs should be enquired about from the
    manufacture of the battery you want to deal with, if you want to have peak
    efficiency.

    NiCads are best stored in the discharged mode at about 60 F, to 70 F deg.
    When new, NiCads store best if never charged. It is the opposite for lead
    acid type batteries, including lead acid gel cells when it comes to storage.
    Lead acid batteries have the best shelf life if kept properly charged up.

    Concerning any of these batteries, they will usually not last more than
    about 3 years whether they are used or not used. The chemical makeup inside
    these batteries breaks down with age. Most of these batteries are good for
    about 600 to 1000 charge cycles over their lifespan. After about 350 to 400
    charge cycles, they start to very slowly go down from their peak performance
    after each charge, regardless of their age. This is for most chargeable
    NiCad batteries.

    The above in relation to NiCads, can also apply to most Lithium based
    batteries as well. One exception is that Lithium based batteries charge best
    if pulse charged, rather than pure DC charged. DC charging Lithium cells
    lessens their average lifespan in relation to what their best lifespan would
    be.

    --

    Jerry G.
    ======


    Hi,

    NMH batteries have a poor shelf life after charging them. I
    would like to build a "trickle" charger to keep them (1.5V AA) charged
    until I need them. They will always be in the charger. I thought about an
    8
    cell holder. Cells will not be charged in series. Each cell will have a
    resistor in series with it. What is a safe trickle current (always present)
    for a AA NMH battery?

    Thanks in advance, Brad

    Before you type your password, credit card number, etc.,
    be sure there is no active key logger (spyware) in your PC.
     
  3. mike

    mike Guest

    Jerry G. wrote:
    snipped discussion of every rechargeable technology EXCEPT the one
    asked about.

    I can't give you a reference, but I remember reading that there was
    evidence that battery deterioration was highly dependent on how
    long they were charged. That convinced me to switch to a timer based
    system that delivers the same charge, but at higher current for short
    intervals each day. So, short charge at C with 0deltaV termination
    just in case.

    I also read that early NiMH cells did NOT like trickle charging, but
    that newer cells were more tolerant. But I've never seen any
    information that would let you determine what to do with the
    cell that you happen to be holding in your hand.

    I've collected a lot of cells over the years. I charge 'em once a month
    at C with 0deltaV termination. But I stagger the groups so there's
    always a set that's been sitting only a few days at most.

    --
    Return address is VALID.
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  4. jakdedert

    jakdedert Guest

    I was under the impression that NiMH stored best at half charge...always
    made me wonder--upon reading that recommendation--how to determine 'half
    charge.' I usually charge mine up, let them sit until I need them and top
    off before use.

    jak
     
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