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Li-ion charger

Discussion in 'Electronic Design' started by ian field, Sep 8, 2006.

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  1. ian field

    ian field Guest

    Before I blow myself up - what is the simplest safe charger design for
    Li-ion cells?!!!

  2. Mr. Wizard

    Mr. Wizard Guest

    Texas Instruments has Benchmarks line of gas guage and charger I.C.'s
    for Li+ batteries. They are fairly simple to use and should save you
    the trouble of blowing things up.
  3. ian field

    ian field Guest

    Not having accounts with any trade suppliers unfortunately limits me to the
    rather meagre range of semiconductors stocked by Maplin - and whatever I can
    skip raid!
  4. A plethory of stuff at Linear

    BTW dont put a Sony label on it

  5. ian field

    ian field Guest

    I wasn't going to put any label on it - why particularly not Sony?!

    Besides - I thought it was Dell laptops leading the way in using Li-ion
    batteries as incendiary devices!!!
  6. Mark Fortune

    Mark Fortune Guest

    Sony make the batteries for Dell and Apple laptops which have recently
    been in the media recently for removing eyebrows.
  7. Get a RS or farnell account, fake some letter heads, as long as you
    pay by credit/debit card no probs.

    BTW where are you based?


  8. They were made by Sony, for Dell, but they have no indication that
    they are made by Sony, unless you enter the code numbers on Dell's non
    working battery recall website and it spits out a recall notice. All I
    ever get is "Server not found", but I have at least one battery involved
    in the recall. Sony also made the battery packs for Apple that are
    being recalled. I've pulled the batteries out of all my newer laptops,
    just in case.

    BTW, on the TV news out of Orlando a couple days ago they reported on
    a Dell laptop that caught on fire in the cab of a big pickup truck. The
    moron threw it into the back of the cab where it set the truck on fire.
    His excuse was that he just wanted to get it away from his daughter. I
    would have either thrown it out the window, or pulled off to the side of
    the road and set it off in the dirt to burn. Tourists!

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  9. Chris Jones

    Chris Jones Guest

    Go to the website of the battery cell manufacturer and get the datasheet.
    If you don't put several cells in series but rather just use one cell, then
    you should be able to get away with just a current-limited constant voltage
    power supply, but some kind of redundant circuitry to disconnect the
    battery if the charger develops a fault might be needed depending on where
    the thing is being used. You must make sure that you don't charge the
    battery above a certain voltage (about 4.2V but read the datasheet) nor
    discharge it below another certain voltage (again see datasheet). If you
    want to float-charge a lithium cell then the voltage is supposed to be a
    bit lower than the value used for cyclic charging and discharging. You
    should consider the likelihood and consequences of any component failing,
    and I would choose to put the battery in a substantial diecast metal box in
    case it catches fire anyway.

  10. RS (in UK, not Radio Shack) will take credit card orders on the Web. So
    will Rapid. Farnell will, but only for orders over a value which I've
    temporarily forgotten. There are other suppliers, too. Get a copy of
    'Television' magazine.
  11. Either £20 or £30 for mail order, or £5 if you're going down to the trade
    counter to pick it up. That £5 limit applies to cash-at-the-trade-counter
    orders too, IIRC.
  12. dt

    dt Guest

    How many cells, of what capacity/charge current and from what power
    source (240v or 12v)?
  13. The Maxim MAX1811 - it's a single-chip 500mA lithium-ion battery charger. Feed
    it +5V, add some decoupling capacitors and wire it up to a lithium battery.
  14. PeteS

    PeteS Guest

    If you don't want to use a pre-made charge controller, then here's the
    standard charge method for _standard_ Li+ (but check the battery
    datasheet from the mfr carefully)

    Constant current (at up to the 1C rate) until the battery terminal
    potential reaches 4.2V per cell. It's usually ok to charge Li+ in
    series, but due to imbalance (especially in older batteries), it's best
    to measure each individual cell for the 4.2V (The line of T.I. gas
    gauges and chargers mentioned earlier do, in fact, do this).

    Switch to constant voltage mode until the charge current drops below
    some threshold (usually CCrate/10)
    Stop charging.

    Do not trickle charge Li+ (this can have spectacular side effects).


  15. ian field

    ian field Guest

  16. ian field

    ian field Guest

    Recently I heard RS had waived the requirement to be an account holder, so I
    emailed them and they sent me the CD cat. As I wanted some LEDs I logged on
    to view the data sheets before deciding which ones to buy and their system
    refused me access! They ignored my email asking about this so I didn't
    bother with them anymore!!!
  17. ian field

    ian field Guest

    Allegedly someone in Aus' described it as a "flamethrower"! - and going by
    the photo of an unusually well illuminated conference room shown on the news
    that's a fair comment!!!
  18. ian field

    ian field Guest

    The Sony connection is something I should have guessed! From my monitor
    repair days quite a lot of Dell monitors were Sony's in disguise. Quality
    was either very good or very bad _ one model in particular had a tall steel
    heatsink in the middle of the board which hit the CRT bowl if the base
    flexed, Sony decided that the best cure was to glue a rubber block to the
    CRT, this trapped the heatsink between the PCB and block so the PCB warped
    and cracked!!!
  19. ian field

    ian field Guest

    Thanks - all good advice, the question was more general as pertaining to
    whatever cells I might happen to come by, but one Toshiba pack contained an
    array of Panasonic cells which have what might be part numbers stamped on
    them, this might be a good starting point.
  20. Tim Auton

    Tim Auton Guest

    By 'refused me access' do you mean it wouldn't let you have the
    datasheets without logging in? That always was annoying, but I noticed
    recently that you don't need to be logged in to see datashets any more.
    Even before that, creating the required account was pretty
    straightforward, even if it was a pointless inconvenience.

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