NiMH longevity versus mAh rating?

Discussion in 'Digital Photography' started by Bill Tuthill, Dec 28, 2004.

  1. Bill Tuthill

    Bill Tuthill Guest

    Do you think the high-capacity (> 2000 mAH) NiMH batteries
    take fewer recharge cycles than lower capacity NiMH batteries?

    We have some old 750 mAH GP batteries that are still working
    but have already had to discard several 2100 mAh Energizers.
    Are some brands just better for longevity than others?
     
    Bill Tuthill, Dec 28, 2004
    #1
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  2. Bill Tuthill

    Bob Salomon Guest

    No. Depends on the brand perhaps.

    The latest Ansmann 2500 mAh have the same life cycle rating as the older
    1650 mAh cells from Ansmann. But that rating is in an Ansmann smart
    charger. In a different type of charger that overheats the cells you
    would lose rated performance of the cells.
     
    Bob Salomon, Dec 28, 2004
    #2
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  3. Do you, by any chance, use a fast recharger?
     
    Darin Kaloyanov, Dec 28, 2004
    #3
  4. Bill Tuthill

    Paul Rubin Guest

    You have to be careful about charge termination and temperature control.
    A lot of consumer chargers are just the pits.
     
    Paul Rubin, Dec 28, 2004
    #4
  5. Bill Tuthill

    Harvey Guest

    Perhaps your applications are different as well. Not many people today are
    using 750 mAh batteries for digital cameras. I am going to be testing some
    "defective" 2100 Energizers next week in the lab to see how many mAh I can
    get out of them. But they were charged in a 1/2 hour charger which may be
    too much for them. I do not like to see charge times below 4 hours
    personally due to the heat build-up.
     
    Harvey, Dec 28, 2004
    #5
  6. Bill Tuthill

    MarkH Guest

    Personally, I am not worried about using my 1 hour charger. Sure the cells
    get quite hot, sure their lifetime will be shortened. Will replacing these
    cells make me poor? They are already over a year old and still working
    well, I have already had decent value from them. If they last another
    year, that will be a bonus.

    Time is short, batteries are cheap.
     
    MarkH, Dec 28, 2004
    #6
  7. Bill Tuthill

    Harvey Guest

    My sister says the same thing to me. But time is long for me and batteries
    are expensive. And if people are replacing the batteries more often then
    necessary, that is all the more chemicals going into landfills and leaching
    into the ground water.
     
    Harvey, Dec 28, 2004
    #7
  8. Bill Tuthill

    SleeperMan Guest


    Latest charging technique lays on temperature - newest discovery is that if
    you monitor temp instead of voltage drop comes out much more precise. It can
    happen that voltage drop happens too late, when batteries are already
    overcharged and too hot, however if you monitor temp, charger will shut down
    in just right time. My GP charger has individual temp sensor for each
    battery and it charges each cell separately. Biggest mistake in many fast
    chargers is charging in groups - two or even four connected in series. So,
    when first one (with minimum capacity) is full, it keeps charging because
    other 3 are still not full, while charger monitors the sum of 2 (or 4)
    cells, so drop in one cell is so minimal that it doesn't cut off....result
    is that cell dies way sooner.
    Still, it's reccomended that every now and then to charge cells with slow,
    14 hour cycle
     
    SleeperMan, Dec 28, 2004
    #8
  9. Bill Tuthill

    Ken Weitzel Guest

    Hi...

    In a perfect world temperature monitoring might be
    worthwhile monitoring for state of charge...

    Unfortunately in real life ambient varies widely enough
    to make it useless. Hot day at the cottage the temperature
    may be in the upper eighties. Batteries will be charged
    before they start. Winter day at home, a nice sleeping
    temperature might be 65 degrees... batteries will never
    be fully charged.

    Ken
     
    Ken Weitzel, Dec 28, 2004
    #9
  10. Bill Tuthill

    Steve Wolfe Guest

    Latest charging technique lays on temperature - newest discovery is that
    if
    You can always use a constant-voltage charger, which will take the cell
    to exactly the rated voltage, and no more. As an added bonus, as the
    voltage of the cell approaches that of the charger, the voltage differential
    lessens, and the rate of charge drops - preventing a lot of the heat
    buildup.

    steve
     
    Steve Wolfe, Dec 28, 2004
    #10
  11. Bill Tuthill

    SleeperMan Guest

    That's the whole point of overheating...it's not important how hot is
    ambient...Only important thing is the temperature of CELLS. IF it's hot, you
    just have misfortune that cells will be charged less than in cold winter
    day. Plain fact. But, if it's cold, don't worry...cells will get hot. In any
    case, fast charging NEVER fully charges batteries - no matter which type
    they are. 1 hour charging only charge batteries to appr. 60-70%. The rest of
    the charge must be gained my trickle charging. That's why it's always a good
    idea - if it's possible - that you charge batteries overnight even in a fast
    charger.
     
    SleeperMan, Dec 28, 2004
    #11
  12. Bill Tuthill

    SleeperMan Guest

    Wrong.
    NiMH (and NiCd also) can never be charged with constant voltage system (
    This system is for lead acid akkus). Only with constant current. However, if
    that current is low enough ( like C/10 or C/20), cells can be connected for
    weeks...without any harm, as with such low currents they won't get warm. You
    should note that these cells do have pretty big self-discharge - appr. 1 %
    per day, so if yours lie in a drawer for a month, they loose about 30% of a
    charge.
     
    SleeperMan, Dec 28, 2004
    #12
  13. So then what happens when, for example, I put three sets of Lenmar NoMem Pro
    AA NiMH batteries in the Lenmar Pro88 charger that came with them, and after
    they are charged for about 8 to 10 hours (red lights out), a multimeter
    reading shows they have all been charged to 1.4xx volts instead of 1.2
    volts?

    The charge ratings for the Lenmar Pro88 charger are as follows:

    AA - 4 x (2.8V DC 200ma)
    AAA - 4 x (2.bV DC 80ma)

    Obviously the batteries have been overcharged--since their label shows
    1.2V--but have they been permanently damaged or is there a way to rapid
    discharge them and use another (better) charger to recharge those batteries?
    Or do the batteries and charger all go in the trash at this point?
     
    Daniel W. Rouse Jr., Dec 28, 2004
    #13
  14. Bill Tuthill

    MarkH Guest

    At the risk of answering a troll - are you serious?

    Sorry if you really don't understand: The 1.2V is the voltage under a load,
    while charging the voltage may exceed 1.6V, while under no load the voltage
    might be 1.4xx. The is nothing unusual about this.
     
    MarkH, Dec 28, 2004
    #14
  15. Bill Tuthill

    SteveB Guest

    I've taken a lot of voltage readings on NiMH cells over the last few years
    and I would say that on average NiMH batteries are fully charged in between
    1.33v to 1.45v when just removed from a charger, they settle around 1.25v to
    1.30v for quite a long period during discharge, and they have about 25% or
    less charge left in them at 1.20v.
     
    SteveB, Dec 28, 2004
    #15
  16. Hmm... okay, then there's nothing apparently wrong with the batteries of the
    charger. I guess there has to be another factor as to why I get "battery
    exhausted" after less than 100 photos taken. After all, they are 2000 mAh AA
    batteries.
     
    Daniel W. Rouse Jr., Dec 28, 2004
    #16
  17. Yes I was serious. Why would I be trolling?

    So I guess there is nothing wrong with the batteries or the charger, yet I
    still keep getting "battery exhausted" after less than 100 photos with 2000
    mAh AA batteries.
     
    Daniel W. Rouse Jr., Dec 28, 2004
    #17
  18. Bill Tuthill

    Pete D Guest

    "Fast" chargers are perfectly fine as long as they cutout before damaging
    (overheating) the batteries.
     
    Pete D, Dec 28, 2004
    #18
  19. Bill Tuthill

    Pete D Guest

    NiMh are perfectly fine in landfil, NiCad are horrendous in landfil and
    should be set in concrete.
     
    Pete D, Dec 28, 2004
    #19
  20. Bill Tuthill

    Pete D Guest

    And this information was dreamt in which dream???
     
    Pete D, Dec 28, 2004
    #20
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