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replacing batteries in Norelco shaver

Discussion in 'Electronic Repair' started by Darmok, Aug 25, 2005.

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  1. Darmok

    Darmok Guest


    I've got an older Norelco electric shaver, which has some kind of
    'fast charge' ni-cads in it (haven't looked, but that's pretty much
    what they had when it was made). Normally, it will recharge in about
    20 minutes or so. Well, after all these years, one or both batteries
    is dying, and I need to replace them. I was thinking of just putting
    in a couple of Ni-MH cells (these are 'AA' size), because I know that
    they can handle a higher charge rate than standard ni-cads. I've got
    some extras of both, but no 'high charge rate' ni-cads (although, I'm
    pretty sure I could get some at Tower Hobbies, or similar R/C model

    Anyone ever replace batteries in a Norelco (or other brand) shaver?
    Anything I should be aware of or watch out for? Seems like it should
    be a pretty straight forward procedure.

  2. Jim Yanik

    Jim Yanik Guest

    NiMH cells have a more complicated charge requirement than NiCd.
    Unless you plan on designing a new charger,you should only replace with
    NiCd cells similar to what you removed.
  3. Ken Weitzel

    Ken Weitzel Guest


    I'm in Canada, where Norelco is called Phillips, and I have
    one (though there are so many models)

    The heads-up I'd offer is to measure the cells carefully
    before you get it too far apart at an inconvenient time...
    mine has one of the sub-C variations, which is physically
    just a little shorter than a AA. Shorter enough that you
    can't get it in and still put it back together :)

    Take care.

  4. Bill Janssen

    Bill Janssen Guest

    I replaced the NiCads with new NicCads. No problems after about a year.
    Don't remember for sure what size they were but I think they were sub-C.

    Bill K7NOM
  5. Tom S

    Tom S Guest

    Jim, could you be more specific? Not to hijack anyone's thread,
    but we recently replaced a 3.6V NiCd cordless phone battery
    pack (600mAh) with 1300mAh NiMH's, and plan to use the
    phone's base (150mV input) to recharge it. If we're careful to
    time the recharges properly, what other complications could
    there be?
  6. Guest

    The main complication would be very short battery life.
  7. Use nicads with solder tabs. Get then at a hobby shop that supports Radio
    Control models.

    Have changed mine several times no problems.

  8. Jim Yanik

    Jim Yanik Guest

    I hope you mean "mA".
    Well,your cells usually still have a partial charge of unknown amount,and
    thus charging for the "standard time" will overcharge the cells.
    A proper charger will monitor the charge voltage and look for the small V
    drop as the cells reach full charge,regardless of the original charge left
    on the cells,maximizing cell life.

    That's why they are "smart" chargers.
    And from what I've read,you can leave the pack on the charger even after it
    is fully charged. No "forgetting" and overcharging.
  9. Ken G.

    Ken G. Guest

    Yes i have . I have an older 3 head shaver and removed the 2 old AA
    batterys and soldered in 2 ordinary Hi-MH AA cells about a year or so
    ago and the thing has worked just fine , it does not overheat or act
    funny in any way .
  10. mike

    mike Guest

    Call up a norelco shaver repair place. I don't remember the number,
    but I do remember being amazed at how low their battery prices were.
    I'd just been thru the hassle of replacing cells and would have just bought
    them from Norelco had I realized they were affordable. YMMV

    Return address is VALID but some sites block emails
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  11. Darmok

    Darmok Guest

    Thanks for all the input .. very helpful indeed!

    Bill, KB8EB
  12. Charging in only 20 minutes is a 3C charge rate ie, three times
    the cell mAh capacity. Shaver NiCads would be in the 500m-1000Ah
    range. NiMh 2000-2600mAh AAs can handle that 1500-2000mA charge
    rate but must not go over full charge or will be destroyed.

    The question is: is that a timed 20 minutes or a "smart" 20
    minutes? If timed and one starts with fully discharged cells
    then all is well. NiMh have no memory effect so can be charged
    and dicharged from-to any level But, if a smart charger is used,
    it may not properly detect the NiMh charge state and keep charging
    past fully charged.

    For say, 1500mAh cells, that would take about one hour however so
    manul timing would suffice. Monitoring the cell temperature is a
    good idea. Some heating while charging is normal for NiMh but
    after full charge is reached it quickly ruins the cells.
  13. Jim Yanik

    Jim Yanik Guest

    According to what I've read here and there,cell temperature is NOT a good
    way to detect full charge for NiMH cells. For NiCd,its OK.
    By the time the temp changes the NiMH cell is overcharged.
  14. gb

    gb Guest

    I have one (Norelco repair facility) here locally -- still repair very old
    models and parts are very inexpensive (sometime cheaper than the department
    store batteries).

  15. A typo, "1500mAh cells" should read "1500mA."
    My post was poorly worded thanks. My "monitoring the cell
    temperature" along with "some heating" was to imply hand sensing
    as a very simple check of what's going on in the cells if they
    have charged for more than 20 minutes or from an unknown charge

    The assumption was the shaver does not use temperature sensing
    except for catastrophic shutoff and if a smart 20 minute charger
    it is of course designed for NiCad characteristics so may not ever
    shut off.

    Unlike NiCads, NiMh are exothermic while charging so will get
    warm, especially at this rather high charge rate.. Once fully
    charged however the temperature (T) rises sharply after the very
    small voltage drop that indicate full charge . The problem is
    this short delay and the electronics and packaging usually getting
    warm along with ambient variations. So, as you say, it's not
    usually used since difficult to detect reliably.

    NiCads, being endothermic are more reliably temperature end of
    charge detected since the T change is sharper. In either case,
    _hot_ cells indicate overcharging

  16. Darmok

    Darmok Guest

    Well, I did as someone suggested, and "Googled" for "Norelco battery
    replacements". I found a place that carries replacements for almost
    all versions of the Norelco shavers. When I looked up my model number
    (4845XL) it showed them as a pair of AA NiMH batteries! When I looked
    at the actual cells in the shaver, they were a pair of 600mah Ni-Cds.
    So, since I have a lot of NiMH cells around (for digital cameras and
    hobby use), I decided to solder in a couple of them and see what

    The first thing I noticed was that, for the first time in years, the
    RED charge LED came on (for a few minutes) as well as the GREEN LED.
    It then proceeded to charge for about 20 minutes, then the GREEN LED
    began flashing, and I knew charging had stopped. The case of the
    shaver felt warm, but not as warm as when there were Ni-Cds in there.
    I've been using it now for a couple days, and it has plenty of zip,
    and sounds real good (by the pitch of the motor). BTW, I assume that
    there is some kind of "smart charging" going on, as if I were to plug
    it in after only a couple days, it would shut off (green LED blinking)
    after only a few minutes. Maybe its voltage based?

    I guess I'll know how well, this works after some time has expired,
    but for now, it appears to be working well. BTW, I have 2 Norelco
    shavers, and this is the older of the 2. I use one until it runs
    down, then grab the other one, and put the exhausted one on charge.

    Thanks again ..

    Bill, KB8EB
  17. Doug McLaren

    Doug McLaren Guest

    | The main complication would be very short battery life.

    As you hinted at, that depends on the charger.

    Most cheap rechargable appliances have a slow charger that charge the
    battery at around C/10. If you replace 600 mAh AA NiCds with 2400 mAh
    AA NiMH cells, the charger will work just fine, except that it's now
    charging at a C/40 rate -- which is slow enough that the incresaed
    self discharge of the NiMH cells will become an issue, but it'll
    probably work just fine. (It might not ever fully charge the
    batteries though. But it should be OK anyways.)

    You really only have to worry about the charger if it 1) only charges
    for X hours, which would mean that it won't fully charge the new,
    larger battery unless you unplug it and plug it back in after X hours,
    or 2) is a fast peak-detecting charger, as NiMH cells have a similar
    peak to NiCds, but it's smaller.

    In my experience, most cheap devices that have NiCd or NiMH cells have
    slow chargers that will work fine with either. Only the higher
    quality ones have things that actually detect when the battery is
    actually fully charged -- things like better power tools and the like.
    (And of course, anything with LiPo cells. Overcharging them is bad.
    But LiPo cells don't fit within the `NiCd or NiMH' classification I
    mentioned earlier.)
  18. Doug McLaren

    Doug McLaren Guest

    | Most cheap rechargable appliances have a slow charger that charge the
    | battery at around C/10.

    Of course, since the original poster says it charges the batteries in
    20 minutes, obviously it doesn't fall into this category.

    It would be best to replace those batteries with similar batteries.

    Modern NiMH cells will tolerate overcharge almost as well as NiCd
    cells, but they don't like being charged at over 1C rates, except for
    the sub-C cells which can go a bit higher, probably 2C.

    As another poster suggested, if they're sub-C cells, get them at a
    hobby store that sells R/C stuff. You can buy them online too easily
    enough -- is one of my favorite places.

    Places like Batteries Plus probably have what you need too, but their
    prices are generally quite high.
  19. Doug McLaren

    Doug McLaren Guest

    | >> For say, 1500mAh cells
    | A typo, "1500mAh cells" should read "1500mA."

    Are you sure? 1500 mAh seems right to me. You're talking about the
    capacity of the cell itself, not the discharge rate, right?

    Capacity is given in mAh. Charge/Discharge rates in mA.

    | Unlike NiCads, NiMh are exothermic while charging so will get
    | warm, especially at this rather high charge rate..

    NiCds get warm during charging too. Just not as warm, due to their
    generally lower internal resistance.

    | Once fully charged however the temperature (T) rises sharply after
    | the very small voltage drop that indicate full charge.

    Same with NiCd and NiMH cells -- it's just that with NiMH cells, the
    voltage drop is smaller.

    | NiCads, being endothermic are more reliably temperature end of
    | charge detected since the T change is sharper. In either case,
    | _hot_ cells indicate overcharging

    Endothermic? No way.

    Apparantly there is an endothermic component to the chemical charging
    process (and I see references to that in many places) but the current
    going through the internal resistance will generate heat as well, and
    from what I've seen, the overall temperature _increases_ as you
    charge, even for NiCds, during the entire charge cycle, even when
    you're not charging at an extremely high rate. (Of course, if you're
    charging at a low rate, any temperature changes are hard to detect, at
    least until the cell is fully charged, where it becomes much easier as
    all energy is going into heat, not just some.)

    Perhaps at low charge rates the endothermic component is slightly
    stronger than the exothermic heating, but if you're charging a NiCd
    battery in 20 minutes -- at a 3C rate -- no way. It's going to get
  20. The 1500mA was an estimated 3C charge rate for the original
    NiCads, hence the following words "..that would take about one
    hour.." (to begin to fully charge the new high capacity NiMh etc).
    Well, I do believe that strikes a note but thanks for the reminder
    to be more alert. Sigh.
    Yes.and it's significant but I don't claim to understand the
    electrochemical.theory behind it,. Good NiCads stay pretty cool
    even at high rates. By the way, Li-ion are also somewhat
    endothermic until nearly fully charged.
    I'm warming to your point. Regards.

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