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NiMH battery compatibility with NiCd chargers

Discussion in 'Electronic Repair' started by Wild Bill, Jun 29, 2004.

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  1. Wild Bill

    Wild Bill Guest

    Hi.. I don't have any experience with NiMH batteries, and I never much cared
    for the problems associated with NiCd cells, so I'd like to know if using
    NiMH will be less problematic than NiCd.

    Will NiMH cells charge and last perfectly well in NiCd chargers, or will
    NiMH chargers be required for best results?
    When I use the term NiCd charger, I mean the more sophisticated commercial
    chargers, not just the transformer & diode types.

    Ideally, I'd like to find a trouble-free, rechargeable battery (if possible)
    for a few applications.
    I'd like to avoid any type of battery that will short if it's not being
    charged or used.. which always seems to happen with any of the NiCd types
    I've had.

  2. Yes.
    Tho', there are what claim to be NiCad/NiMH combo-chargers. Not many
    folks in (see below) speak well about them.
    Mox-Nix. NiMH have different charging characteristics/curves
    than NiCad's. You want to get a "smart" NiMH charger, versus
    a "timed" NiMH charger.

    Using Google Groups, look back in just the last 6 months or
    so for "NiMH". The digital camera folks are *anal* about
    battery performance: charging, storage, use, capacity, etc. -- and
    they all, in general, swear by NiMH's.
    (I say "6 months" because these are all FAQ's that come
    up every few days or so. You won't live long enough to
    read _all_ of them. :)

  3. Andy Cuffe

    Andy Cuffe Guest

    For best results, you need a charger designed for Ni-MH, but they seem
    to be more tolerant than many people would have you believe. I
    rebuilt the Ni-Cd battery pack in my cordless phone using some Ni-MH
    cells I had on hand and it still works well after 3 or 4 years of
    almost constant charging. I would think you would have more trouble
    with a 'smart' Ni-Cd charger than a simple charger because it's hard
    to say how the smart charger will handle the wrong type of battery. I
    have no seen any shorted Ni-HM cells yet. What I have seen is a very
    high self discharge rate in old Ni-MH laptop batteries. It's not
    unusual to see a laptop battery that will run for 2 hours when freshly
    charged, but if it's left sitting for even a few hours it becomes
    mostly discharged.
    Andy Cuffe
  4. Wild Bill

    Wild Bill Guest

    Thanks, since most digital cameras are just about the hardest service for
    batteries in consumer gear (maybe second to RC vehicles), they are probably
    a major improvement over NiCd, which is what I've been hearing rumors of.

  5. Wild Bill

    Wild Bill Guest

    Thanks for the additional info Andy. While the phone example you mentioned
    isn't a highly scientific analysis, it's just the sort of example I was
    hoping to see. I'm confident from reading your posts for years, that you're
    prone to practical solutions, and don't think too much of half-assed

    I've got some handheld test gear that use sub-C cells and they have too
    little space to install full-sized C cells (even alkaline would be fine for
    them, though). These instruments use the simple rectifier, filter, resistor
    components for charging from a wall wart.

    I haven't bought much rechargeable stuff like most consumers do because of
    the poor characteristic experiences I've had with NiCd cells. I'm sure I
    never got enough use out of any NiCds to say that they were worn out..
    instead, they just failed before any useful life was gotten from them.

    I'm drawn to the extra capacity of NiMh, and hope they can provide a much
    better service life for some equipment that will primarily be used in remote

  6. Jeff

    Jeff Guest

    Slow chargers YES, (just extend the charge time to cope with the,
    probably, larger capacity of the NiMH cell), fast 'intelligent' chargers

    NiMH cell have different end point voltage characteristics, so
    chargers do not detect full charge correctly, with the possibility of

    NiMH cell do not suffer as badly as NiCs's with memory effect and are
    higher capacity, the only downside is that their self-discharge rate is
    quite high. This means that they must be recharge frequently, and are
    very good in equipment that is not used very often.

  7. snip
    Unless you made any modifications to the charging current I
    suspect the NiMhs, being about double the original NiCad's
    capacity, are gently warming themselves at a continous C/20-C/10

    Good qualty recent manufacture NiMh cells can handle that
    overcharge for short periods but nevertheless gradually
    deterioate. That may not have been noticed since their
    original capacity was about double the NICads.

    They will last about 4-5 years in a low load like the phone but
    far less with high loads due to their internal resistance buildup
    as a result of the continous overcharge. .

    For maximum life Nimh must not be overcharged, nor trickle charged
    and maintenance charged with care. They also die quickly with
    heat yet are exothermic during charging especially so towards the
    end of charge. Tricky buggers..

    The NiCads are more rugged and handle overcharging better but were
    also most likely being slowly cooked at about a C/10-C/5 rate in
    the phone. Continous C/20-C/10 is generally fine for them (but
    not for NiMh).
  8. Trickle charging NiCads and not using them after is what causes
    them to short out. Continous charging at too high a rate (>C/10
    as in many phones etc) ) also causes them to deterioate quickly.
    But they do handle sloppy recharging well -- if used soon
    after.. They are rugged.

    NiCads thrive on regular use and thus can't be beat for high
    charge-discharge current applications like power tools.

    NiMh should not be trickle charged -- they deterioate. New
    quality maker NiMhs only weakness is the somewhat higher self
    discharge rate and need for careful charging because they are
    exothermic and,perversely, their life, very heat sensitive...
    They very rarely short out.

    Qualty cells and made for NIMh quality chargers will give
    excellent results The key points are keeping them cool during
    charge and no overcharging (which heats them up more)..
  9. Peter Duck

    Peter Duck Guest

    In message <>
    I understand that this 'downside' was true only (mostly?) of early NiMHs.

    I've had a mobile phone ('cellphone' to USians) with the same batteries
    for three or four years: it's only for occsional/emergency use, i.e.
    mostly in glove-compartment or coat-pocket without being switched on for
    incoming calls.

    The need for recharge (when battery-state reaches a notch or two above
    'empty') still only arises two or three times a year ...

    That seems to be a common experience, and much better than nicads were (are?).
  10. Eric R Snow

    Eric R Snow Guest

    Greetings Bill,
    This must be the day for batteries. When shopping for my first digital
    camera last year I did tons of research on-line. The upshot of the
    battery question was to use NiMH batteries. For reasons like lasting a
    long time between charges, no "memory effect", price, etc.. Powerex
    batteries made by Maha got the best overall reviews. Thomas
    Distributing sell them and has good package deals on batteries and
    chargers. I love being able to recharge batteries when they are not
    nearly dead and not having to worry about degrading the battery
    performance. I use the 1800 mAh AA size. Last year these were the best
    value. These batteries last three times longer in my Pentax digital
    camera than Duracell batteries. I have no connection with anybody
    selling batteries but I am a great advocate for NiMH rechargables and
    Thomas Distributing. The batteries work great and Thomas has great
    prices and service.
    Eric R Snow,
    E T Precision Machine
  11. Engineer

    Engineer Guest

    ( snip)
    Can you explain why NiMH's do not like being trickle charged?

    Tks and cheers,

  12. Wild Bill

    Wild Bill Guest

    Thanks for the additional info and your experience with actual usage.

  13. Wild Bill

    Wild Bill Guest

  14. NiMH degrade (any cell chemistry does since at the very least
    reactants are being used up) when over charged and are more
    sensitive than NiCad to that. Some kind of end of charge
    mechanism is needed such as the common timer for 1/10C range
    charge rates or a delta voltage or temperature sense method for
    faster rates.

    Timed trickle charging is inaccurate and nearly an oxymoron.
    It's very close to maintenance level (compensating self discharge
    which is high for NiMh) charging. That makes charge state
    unpredictable so not used. On the otherhand continuous trickle
    charging overcharges eventually
    Being so close to maintenance charging levels the sense methods
    e.g. the last two, are inaccurate. And anyway if one is using
    such methods simple trickle charging is cost incongrous.
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