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Using a lower-current adaptor with my laptop

Discussion in 'General Electronics' started by eug k, Jun 7, 2004.

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  1. eug k

    eug k Guest


    I'm after a smaller/lighter adaptor for my thinkpad. The
    laptop is rated at 16V, 3.36A. There's one that I'm
    looking at that is rated at 16V, 2.2A. It also looks
    a fair bit smaller. What I'm wondering is, can I safely
    use it with my laptop?

    I get about three hours use on a 3.1AH battery, so the
    actual current consumption is nowhere near 3.36A I'm
    assuming. It also takes quite a long time to recharge,
    so the charging current can't be too high either.
    Apart from the coax power plug which may be different, is
    there anything i'm missing out?

    it's a thinkpad 240x, the adaptor's for another thinkpad.


  2. Quaoar

    Quaoar Guest

    The average power requirement is, with certainty, less than the peak
    power requirement. For example, if you are doing something as simple as
    defragmenting the HD, the power required during the defrag can be
    several multiples of the average power. Burning CDs is another heavy
    power consuming process. Only you can determine what the peak power
    requirement might be. Operating with an AC adapter that is rated too
    close to the average power requirment leaves little surplus for
    supplying the peak power. If the AC adapter is operated in excess of
    its capacity, the voltage drops and all manner of potential problems can
    be proposed: HD write failure, memory read/write failures, CPU
    auto-shutdown, overheating from reduced fan speed, adapter overheat/auto
    shutdown, etc. OTOH, depending on your computing habits, none of the
    above might apply.

  3. EM

    EM Guest

    In a word, nope. NEVER use an adapter whose 1) output voltage(s) isn't
    the same as the one your component requires, AND 2) whose output current
    capability is LESS than the MAX. current rating of your component.

    It's okay if your adapter is capable of MORE current, though.

    "Ampere-Hours" has little to do with how much current ("Amperes," or
    "Amps") your laptop uses at any given time. AH and A are two different

    Even though the battery is rated @ 3.1AH, it's no doubt quite capable of
    providing the 3.36A *continuous* that your laptop MAY demand of it...
    only, if you do the math, the battery will last under an hour at such a
    high, constant load:
    (3.1AH / 3.36A = ~ 55 min.).
  4. eug k

    eug k Guest

    What I was hoping is, during those peak power periods, is that
    the battery would kick in. I assume if i can pull the plug
    out while the laptop is running without affecting anything, that
    the battery is connected car-style - always inline, with the
    charger behaving like an alternator.

    Being a small laptop, it doesn't have a burner or even a
    cdrom drive.

  5. eug k

    eug k Guest

    The original adaptor is actually rated at 4.5A but my friend
    who has the same laptop got a 3.36A adaptor with his. The rating
    on the laptop is the same. Dunno why they gave me a bigger one.

    Yes, but since I get about three hours before getting a low
    battery warning, the average current draw would be quite a bit
    less. It also puts out only 11.1V, so the draw at 16V should be

    I'm not sure at what discharge rate the 3.1Ah is for, but
    if the laptop actually took 3.36A, the batt life should be much
    less than 55min.

    There would no doubt be peaks like when the hdd spins up after
    sleeping or something. I'm hoping that the battery would kick
    in during those peaks.

    Does anyone know if that is the case?


  6. Nirodac

    Nirodac Guest

    Are you aware that on some laptops, the CPU speed is slowed down when the
    system is running on batteries, and the LCD screen is dimmed, in order to
    conserve power, and that the speed doesn't increase when the adapter is
    plugged in (screen does get brighter), unless you reboot.

    Stick with the plate ratings, even though what the other posters said is
    correct. Try finding a smaller physical adapter with the same or great
    power rating.
  7. Re: "If the AC adapter is operated in excess of its capacity, the
    voltage drops and all manner of potential problems can be proposed"

    More likely, however, are two different scenarios:

    1. The adapter supplies the increased power, but it overheats, perhaps
    to the point of failure or damage [and, in rare cases that should not
    happen, even if the adapter is overloaded, fire].

    2. The adapter senses that too much power is being drawn and "crowbars
    itself" -- shuts down, totally, completely, instantly. Note, this is
    non-destructive, and if you then shut down, the adapter will be fine and
    will work again, but, of course, if overloaded again, it will shut down

    To the original poster's question, if he never tries to run the computer
    AND charge a significantly discharged battery at the same time, he would
    likely [but not definitely] be ok.
  8. Papa

    Papa Guest

    You are putting your laptop at risk if you use a power adapter that was not
    specified by the laptop manufacturer.
  9. jerrykrinock

    jerrykrinock Guest

    Well, on my laptop (an Apple Powerbook G4), a prior-generation
    lower-power AC adapter works OK, it just charges slower.

    But you need replies from some other thinkpad users who have tried
    this with theirs. Try and find a thinkpad users' forum.
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