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Li - ion batteries and charging question.

Discussion in 'Misc Electronics' started by Daneel, Jul 6, 2005.

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  1. Daneel

    Daneel Guest

    Hi, I have a HP HX4700 Pocket PC that is powered by a Li-ion battery.

    I'd like to know what charging cycle would be best to get the longest life
    out of the battery.
    I know that some types of battery suffer from the memory effect but I was
    told that li-ion batteries do not.
    Is this true?

    And if so does that mean it is ok to charge it even if it is half full or
    whatever?

    The reason I ask is that I am using a USB sync and charge cable, so every
    time I sync my ppc with my home computer it starts charging the battery. I
    sync them several times a day so the battery doesn't get a chance to
    discharge fully.

    There is a setting supposedly to switch usb charging on/off on the ppc but
    even when switched off it charges anyway.Will this shorten the life of the
    battery or will it be ok?

    Thanks very much
    Daneel
     
  2. PeteS

    PeteS Guest

    Li+ batteries do suffer after a large number of charge cycles, so for
    the longest battery life, you should keep that in mind. Whether one
    calls it memory effect or not is irrelevant, although it is not the
    same as the classic memory effect found in nickel-Cadmium cells.

    Most of the Li+ batteries I use (with chargers) are rated at >80%
    capacity after 500 charge cycles. My applications are expected to
    charge / discharge these batteries (in one product at least) for over
    1000 cycles.

    You can charge a Li+ battery at any time without affecting it's current
    ability to hold charge in any real way (apart from the total number of
    charge cycle limitation). Li+ batteries do not suffer from the 'memory'
    effect problem common to NiCad.

    Cheers

    PeteS
     
  3. CWatters

    CWatters Guest

    I'm not sure that much work has been done on this.

    Li-ion cells must not be allowed to discharge below about 2.4V per cell.
    Likewise continious trickle charging isn't recommended either, however the
    charger will be designed to ensure neither happens.
     
  4. JANA

    JANA Guest

    NiCad batteries have a limited number of charge cycles, and will have a life
    span of about 3 years average. Sometimes you can have a lucky one that will
    last longer. Usually after about 500 charge cycles, or about 3 years, they
    will start to degrade in their performance. This is actually the same for
    all chargeable batteries.

    The exception is that the newer technology Lithium batteries do not have the
    memory problems of the NiCad batteries. This type of battery can be charged
    at any time without having to be properly discharged. Their life cycle is
    about the same as the older NiCad types.

    The recommended charge rate from the battery manufacture should be the best
    to use. This is depended on the particular battery design.

    If you are using a separately bought chargeable battery, and designing your
    own charging system, you should consult the battery manufacture for the
    proper range of charging specifications. This also applies to knowing the
    maximum safe loading, and discharge rates, when running the devices with the
    battery.

    When you have a commercially manufactured product, they build their charger
    to match the battery type from the battery manufacture. These products are
    designed to meet speciations that are from the UL, CSA, and EC standards for
    safety and performance. Altering these specifications, will put the product
    outside of the recommended application range, and thus may pose a safety,
    and or performance issue.

    If you have a battery that is not charging, and the charging device is in
    specification, this means that the battery must be changed. There is no
    proper way to revive an older battery that has been through its life cycle,
    or has been damaged.

    There are publications about how to so-called, "revive" batteries, but these
    procedures never work for very long, nor are dependable. When these
    batteries
    go defective, it is because their internal chemical composition has gone
    through its life cycle, and or something in the battery has degraded, or has
    been damaged.

    --

    JANA
    _____


    Hi, I have a HP HX4700 Pocket PC that is powered by a Li-ion battery.

    I'd like to know what charging cycle would be best to get the longest life
    out of the battery.
    I know that some types of battery suffer from the memory effect but I was
    told that li-ion batteries do not.
    Is this true?

    And if so does that mean it is ok to charge it even if it is half full or
    whatever?

    The reason I ask is that I am using a USB sync and charge cable, so every
    time I sync my ppc with my home computer it starts charging the battery. I
    sync them several times a day so the battery doesn't get a chance to
    discharge fully.

    There is a setting supposedly to switch usb charging on/off on the ppc but
    even when switched off it charges anyway.Will this shorten the life of the
    battery or will it be ok?

    Thanks very much
    Daneel
     
  5. PeteS

    PeteS Guest

    On the specifics of Li+ charging:

    Although each manufacturer has their own recommendations, Li+ and
    Li-Polymer chargers usually charge at a constant current (details in a
    minute) up to 4.2V per cell, then charge at constant voltage until the
    charge current reaches a cut off threshold.

    The usual numbers are I(cc) <= Capacity rating (i.e. a 1Ahour cell
    would usually be charged in constant current mode at <= 1A)

    I(cutoff) usually about I(cc) / 10

    Note that on USB, there are strict rules on the amount of current a
    device may draw (100mA mostly, 500mA high power), so the charger in
    your application won't be doing very much current. Of course, I don't
    know what the rating is on the battery you are using, either.

    Cheers

    PeteS


    Cheers

    Petes
     
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