Magsafe power adapter query

Discussion in 'Misc' started by Warren Oates, Dec 8, 2011.

  1. Warren Oates

    Warren Oates Guest

    What problems might arise using a 45 watt power adapter on a MacBook
    that's supposed to use a 60 watt supply?

    I've looked around, and it seems that a _higher_ wattage won't hurt your
    computer, but a lower-wattage adapter might cause "operational problems"
    and these are unspecified.

    My sister in law isn't too bright. Her adapter "broke" so she bought a
    new one from "a guy" and apparently it's not the right wattage. I told
    her when it happened "Go to FutureShop, they sell them there." Of
    course, now they only sell the new-style ones. This is one of the older
    ones with the little flat white plug that has an amber or green light.

    She needs a new battery too, but that's easier to find.

    Sorry, I don't have the exact model/year of the MacBook, and it would
    pointless asking her. She'll have to bring it over (just so I know what
    battery to get). I know she's still on 10.5.8.
    Warren Oates, Dec 8, 2011
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  2. Warren Oates

    D Finnigan Guest

    Remember that Watts = Amps * Volts.

    Watts is total power used, which is current (amps) times "pressure"

    Now, if the MacBook in question is drawing more amps than the power supply
    is rated to deliver, that's a problem. On the other hand, if the power
    supply is beefier than the MacBook requires, that is not a problem. The
    MacBook takes what it needs, and nothing more.
    D Finnigan, Dec 8, 2011
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  3. Warren Oates

    Warren Oates Guest

    I sort of understood that. I was wondering what the symptoms of drawing
    more power might be.

    On another note, are the newer Magsafes compatible with the older ones
    in the way they connect to the computer? Is it just a newer plug going
    into the same socket ("port" if you like)?

    Thanks for the feply.
    Warren Oates, Dec 8, 2011
  4. Warren Oates

    nospam Guest

    none. magsafe adapters have a chip that tells the computer what the
    power capacity of the adapter is, which means the macbook will not draw
    more than the adapter can supply because it knows how much is

    the net effect will be that the battery will charge slower than it
    otherwise would, or possibly not at all in some cases.
    nospam, Dec 8, 2011
  5. Warren Oates

    Warren Oates Guest

    Thanks again! That's what I was looking for. She should get a new power
    supply before changing the battery then, I reckon (because the battery
    might not be dead at all). And before her house burns down too.
    Warren Oates, Dec 8, 2011
  6. Warren Oates

    nospam Guest

    it will only fit if the macbook does not have a protective case. if it
    does, the case will preclude the new style connector from making good
    what he wrote will not happen. you *can't* overload a magsafe adapter.
    nospam, Dec 8, 2011
  7. Warren Oates

    Warren Oates Guest

    Fair enough. It probably won't burn her house down then. But what about
    the "performance issues" that I read about on an Apple site? I'm
    guessing it might not drive an external monitor. Or maybe it won't
    recharge the battery properly. Or run the fan? I'm not totally familiar
    with MacBook stuff. It's moot, because she and the oul' Woman just
    called and they've bought her a brand new 85 watt power supply that
    matches the output of the one that "broke."

    I think she needs a new battery though. I did all that PMU stuff.
    Warren Oates, Dec 8, 2011
  8. Warren Oates

    nospam Guest

    Fair enough. It probably won't burn her house down then. But what about
    the "performance issues" that I read about on an Apple site?[/QUOTE]

    the only performance issue is if you run the macbook without a battery
    at all, it will go into a power-save mode which is slower.
    it will work fine, but the 85w is for macbook pros, not macbooks.

    the worst that can happen with an underpowered adapter is that the
    battery won't charge and may possibly discharge slowly if the she's
    doing something intensive on the macbook. more than likely the battery
    will charge, but just slower than it would have if there was more power
    available. it really isn't a problem because as i said, the magsafe
    tells the mac how much power it has (that's why there's a brief delay
    until the green/orange led comes on - it's querying).

    apple's own airline adapter is unable to supply enough power to run a
    macbook pro and why the battery discharges even when plugged into seat
    option-click the battery icon in the menubar and it will say if it's
    normal or needs service. if the battery is just old, it will have
    diminished capacity, which is to be expected.
    nospam, Dec 8, 2011
  9. Warren Oates

    David Empson Guest

    The battery will charge slower than it should, or not charge at all
    while the computer is running, only while it is asleep or shut down.

    If the operating power used by the computer when working hard exceeds
    the rating of the power adapter, the computer may need to draw power
    from the battery as well as the adapter, so the battery might go flat
    even though the computer is plugged in. I expect that if the battery got
    low enough in this situation, the computer would warn then force a
    shutdown or hibernation, in the same manner as running from battery
    without a power adapter.

    As others have noted, there are no safety/overload concerns because the
    computer knows how much power the adapter can supply.
    MagSafe adapters with the old and new style plugs are interchangeable.
    I'm using the one which came with my 2007 MacBook Pro (white plastic
    plug) as a spare for my 2010 MacBook Pro (which came with an adapter
    with a metallic right angle plug).
    David Empson, Dec 8, 2011
  10. Warren Oates

    Warren Oates Guest

    What happens is that the battery (with no external power) gets down to
    about 70% and then the computer just shuts down. I managed to keep it
    going one time until it got down to about 40%. From 100% to 40% took
    less than an hour.

    As it happens, it's a MacBook Pro 15" (1,1 the System Profiler says).
    Anyway, she's got a new properly-rated power lump and I'll order her a
    new battery from my Hongkong supplier. Might even arrive in time for

    Thanks, David, and to everyone who replied.
    Warren Oates, Dec 9, 2011
  11. Warren Oates

    nospam Guest

    sudden shutdown is usually due to an internal cell failing. it's time
    to replace the battery.
    nospam, Dec 9, 2011
  12. Warren Oates

    David Empson Guest

    If the computer shuts down abruptly while the battery is at a percentage
    that high, either the battery is badly out of calibration, or it has a
    faulty cell and needs to be replaced.

    The computer is supposed to warn that you are running on reserve power
    when the battery gets to about 5%, then it will force shutdown somewhat
    after that.
    That's the first generation from February to October 2006. If it is
    still on its original battery I would not be surprised if the battery
    had failed.
    The MacBook Pro is supposed to use an 85 W adapter, so 45 W would be
    seriously underpowered. It may not be enough to operate the MacBook Pro
    at reasonable load, so the battery would be used more heavily. Otherwise
    what I wrote previously still applies (assuming a reliable battery).
    David Empson, Dec 11, 2011
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