Swapping 60w & 85w MagSafe Power Adapters

Discussion in 'MacBook Pro' started by sarah3585, Jan 31, 2012.

  1. sarah3585, Jan 31, 2012
    Last edited: Jan 31, 2012

    sarah3585 macrumors regular


    Aug 12, 2007
    Hello all.

    I have a late 2008 MPB with a 85W Power Adapter. My other half has a 2009 Macbook pro with a 60W Adapter. These laptops are about 6 months apart, why the difference in adapter?

    My BFs 60W recently packed up working (the rabbit nibbled it) so he's been using my 85W. Is this safe for his laptop? I've use to use his now and then, as I never noticed they were different. Was that safe?

    Many thanks.

    We both have 15" btw.
  2. GuitarG20 macrumors 65816


    Jun 3, 2011
    1) the different watt adaptors are based off of different TDP usage by the processor. For example, in 2011, the 13" gets a 60, while the 15" and 17" get 85 because the 15" and 17" can use 85 or slightly more watts at full load, while the 13" is closer to 60W.

    2) Yes, thats fine. The general rule is that you can use one with a larger Watt rating without any having problems. The sensors in the MagSafe will regulate wattage and voltage to keep it safe.
    However, using a charger with less watt rating then the one your MBP came with can cause slow charging and may not keep the battery from being drained (yes, even when plugged in) if the computer is under load. For example, if I was running something that made my computer use 80W and I used a 60W charger, 20W would still be coming out of the battery. Something to consider if you're running under load and want to use a smaller watt rated charger.
  3. dusk007 macrumors 68040


    Dec 5, 2009
    The only thing that really is important with charges is that they have the required voltage which is always the case if they are from the same company.
    Everything else is up to a degree unimportant.

    Too powerfull just means, heavy and inefficient at low load.
    Too weak means either the computer crashes if it doesn't get the required current and the V drops or as with notebooks they suck all the missing power out of the battery.
  4. snaky69 macrumors 603

    Mar 14, 2008
    Let me guess, you have a 15", while your other half has a 13".

    I'm good, right?

    That's simply the wattage that comes with the different models, the 15" is more powerful and thus needs more electricity to work, plain and simple. You can use the 60W from the 13" and even the 45W from the MBA on your 15" MBP, but charging will take forever and a half.
  5. sarah3585 thread starter macrumors regular


    Aug 12, 2007
    No we both have 15". Sorry I should have mentioned that in the OP. Seems odd :confused:
  6. GGJstudios macrumors Westmere


    May 16, 2008
    This should answer most, if not all, of your battery questions:
  7. Naimfan Suspended


    Jan 15, 2003
    His 15" 2009 is the base model, then - the base 15" came with a 60 watt adapter, perhaps due to it not having a discrete graphics unit (it came with the nVidia 9400m).

    As snaky69 said, you can safely interchange them.
  8. Xcallibur macrumors 6502a


    Jul 24, 2011
    You throw that thread about like there's no tomorrow haha.
  9. GGJstudios macrumors Westmere


    May 16, 2008
    They throw the same questions around like there's no tomorrow.
  10. alphaod macrumors Core


    Feb 9, 2008
    The problem is that that answers none of the questions posed by the OP.

    In fact, the only answer in this thread is provided by Naimfan in post #7.
  11. chrfr macrumors 604

    Jul 11, 2009
    It is possible however, that if your 2008 computer is working hard, the 60W adapter may not be able to provide enough power to charge the battery and the computer will then run off the battery and the AC Adapter. The 60W adapter may also get quite warm if trying to charge the battery while the computer is running.
  12. GuitarG20 macrumors 65816


    Jun 3, 2011
    i said that in my post...
  13. mac jones macrumors 68040

    Apr 6, 2006
    Yes use it. Totally safe.

    For instance, I'm typing on a Macbook Air 13" that has a 85W adapter (for my Macbook pro) plugged in.

    No sense in having multiple adapters if your using them one a t a time. I just carry the big one, and i'm covered.
  14. GGJstudios macrumors Westmere


    May 16, 2008
    That's not true. The OP asked:
    My quoted excerpt from the Battery FAQ:
  15. iThinkergoiMac macrumors 68030

    Jan 20, 2010
    While your answer is (partially) correct, your reasoning is not. Wattage is "drawn" by the device, not "pushed" by the charger. You could put a 200W charger on your computer with no harm (this doesn't hold for something extreme like, say, 50,000W). Voltage, OTOH, is "pushed" by the charger. So hooking up the incorrect voltage will fry whatever you've hooked up if you're over, or do nothing (or make run slowly) if you're under.

    Apart from the auto-switching capability of the charger to use either 120V or 240V, the charger does absolutely nothing to "regulate" the voltage. I don't know what it would do if you gave it 175V (though I expect it would work fine) and it would certainly fry itself if you gave it 360V.

    So the voltage must be the same, but the wattage, as long as it meets the required minimum, doesn't really matter.

    One benefit of using the 85W charger on a MBP that only needs a 60W charger is that your battery will charge quite a bit faster. I only have an 85W charger for my 13" MBP, and it doesn't take very long to charge the battery at all.
  16. GuitarG20 macrumors 65816


    Jun 3, 2011
    Thank you for correcting me. I didn't know that-it's good information.
  17. GGJstudios macrumors Westmere


    May 16, 2008
    I just have to say that your attitude is worthy of respect. Too many get ticked off and defensive when someone corrects misinformation. Making mistakes and receiving correction is how knowledge is acquired. Good work!
  18. squeakr macrumors 68000


    Apr 22, 2010
    Your answer too is not fully correct. Voltage is a difference of potential created within the supply, and the supply does regulate the voltage since it is a step-down transformer. By this nature, it takes a given input voltage and regulates the voltage from the given input stepped down to the correct output voltage. Although voltage must be correct, so must amperage (the flow of current) within reason, as if more amperage is output by the charger then a serious over current condition occurs which has to be shunted off somehow, in either the form of heat, reflected power resulting in heat, or a short to some other component in the system.
  19. iThinkergoiMac macrumors 68030

    Jan 20, 2010
    I see my days of working at RadioShack have not made me a master of the knowledge of electricity (no surprise there). Thanks! :)
  20. marshallbedsaul macrumors 6502a


    Nov 14, 2007
    gg wins lol :p
  21. Silvrbill macrumors member

    Dec 20, 2013
    The voltage does not need to be spot on. The charger will work correctly within a given range, it doesn't need exactly 120v or 230v. Anywhere in-between will be just fine. As far as amperage (current) goes the charger will not put out any more current than the device draws from it. Without a load there is no current. Current does not flow through the charger at will, it must be "drawn" from it for a specific purpose. There is no threat of over current to the device from using too small or too large of a charger. The charger will ONLY produce what it's capable of, no more. The threat of using too small of a charger is that the device may want more current that the charger can supply. Then you have a case of the charger becoming hot and possibly starting a fire.
  22. cjmillsnun, Feb 8, 2015
    Last edited by a moderator: Feb 8, 2015

    cjmillsnun macrumors 68020

    Aug 28, 2009
    Then your BF was using an underpowered power brick.

    15 and 17" MBPs have always used 85W bricks.
  23. TheIguana macrumors 6502a


    Sep 26, 2004
    Nope, there was one model the 2009 mid MacBook Pro (15-inch, 2.53GHz, Mid 2009) that shipped with a 60 watt adapter. It only had integrated graphics in the form of an Nvidia 9400m, which is part of the reason it didn't need the beefier 85 watt charger. Apple has got a great support doc on all the models and what the minimum charger they need are: http://support.apple.com/en-ca/HT2346

    Getting back to the OPs original question: it is safe to use the 85 watt adapter with either of your Macs. If the Mac only needs 60 watts of power it will reduce the output to meet the computers needs. If it needs 85 watts then it will provide it.

    In my case we have a mixture of 13" and 15" MBP in our house and I have almost exclusively gone with 85 watt MagSafes to simplify things as there is no question of whether the adapter will be able to provide enough power.

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