OK to use 85W to charge new 13" MBP?

Discussion in 'MacBook Pro' started by jja1, Jul 8, 2009.

  1. jja1 macrumors newbie

    Joined:
    Jul 2, 2008
    #1
    We just added a new 13" MBP to the family which already includes a late 2007 15" MBP for which I have several 85W Magsafe power adapters. I'd like to consolidate to one adapter around the house.

    Is it ok to use the 85W with the 13" MBP? I know the 13" ships with a 60W adapter...can't seem to find any info that says using an 85W is a bad thing..
     
  2. thegoldenmackid macrumors 604

    thegoldenmackid

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    #2
    My BlackBook gets charged via an 85 watt all the time, three years later and no problems.
     
  3. wmf macrumors newbie

    wmf

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    May 26, 2009
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    #3
    I've found info says OK

    I cannot answer from personal experience, but if it is helpful, in the Apple Store there are reviews for both power adapters. Some reviews say the 85W can be used in place of the 65W (but not vice versa).

    (As I need to purchase a new 65W, I am wondering if there is any benefit in getting an 85W instead. Does it recharge faster or anything. And if there is and problem, as you have asked. They are the same price.)
     
  4. ashjamben macrumors 6502a

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    #4
    you can charge a macbook with a macbook pro charger, but not charge a macbook pro with a macbook charger. the macbook pro with try and take too much power and eventually burn the cable.

    theres also no benefit from using a macbook pro charger with a macbook.
     
  5. Freyqq macrumors 68040

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    Dec 13, 2004
    #5
    I've used a macbook charger for my mbp with no ill effects. That seems like it would have even less of a chance of working, but it works fine. It just charges slower. I assume in your situation the charger would just downclock itself to 60w if it needed to.
     
  6. thegoldenmackid macrumors 604

    thegoldenmackid

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    #6
    I would not say that a MacBook charger really "charges" a computer to much extent, sure it does, but it takes so much longer to do so. It makes me wonder whether the processor underclocks itself similar to taking the battery out of the computer.
     
  7. Snowbound macrumors regular

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    May 19, 2008
    #7
    In my experience you will be fine going with the 85. It will simply draw less power to charge the 13"
     
  8. NewMacbookPlz macrumors 68040

    NewMacbookPlz

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    Sep 28, 2008
    #8
    The computer will only take what power it needs.

    The only issue in mismatching chargers is using one too low in rating for the computer, like a MB or MBA charger with a Pro or an MBA charger with an MB as the brick won't be able to send enough power to the computer.
     
  9. jbrenn macrumors 6502a

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    Aug 27, 2008
    #9
    I purchased a 85 watt magsafe and on the box it said for macbook and macbook pros. so it will work fine.
     
  10. tempusfugit macrumors 65816

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    May 21, 2009
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    Chicago
    #10
    ive charged my 13" (45 watt) on my mother's charger for a 17"mbp (at least 65 im guessing) and it worked fine. never tried it the other way around though...
     
  11. steve31 macrumors 6502a

    steve31

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    #11
    I charge mine with my 24 apple cinema display which is 85w but was made for any Macbook so I would think that it would be fine to charge with a 85w power block.
     
  12. TheHoff macrumors 6502

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    Oct 22, 2008
    #12
    At your own risk...

    I have a 15" MBP, my wife has a 13" MB (both recent unibodies) so we have an 85w and a 65w. It wasn't until recently that I realized they were different; we have been swapping them back and forth like they were interchangeable.

    2 months after purchase, the 13" MB battery would no longer take a charge. It was replaced at the Apple store without a hassle but we didn't realize we were doing anything wrong.

    Did we cause it? Dunno... but now we keep our chargers separate.
     
  13. miles01110 macrumors Core

    miles01110

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    #13
    Wow, lots of hot air in this thread.

    Everyone with an 85W adapter please take a look on the bottom of the brick.

    With some simple multiplication (P = VI, Power = Voltage * Current) you can see that the adapter is capable of outputting 85W **or** 60W, thus making it perfectly acceptable to use with either the Macbook, the low-end Macbook Pro, or the high-end Macbook Pros. There is no risk in doing so outside of the normal risk you incur every time you plug in any piece of electronics.

    In addition, the 60W adapter can be used to power and charge **any** Macbook Pro. The only difference will be that it will take longer to charge, and might not charge if you're powering it through the 60W adapter whilst doing processor-intensive work.

    Power is power- using one adapter instead of the other does not affect the machine.
     
  14. w00t951 macrumors 68000

    w00t951

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    #14
    What are talking about? The wattage rating on the side does not tell you that the PSU will start pouring electricity into the computer. It means the total number of watts that it can supply, total. Just like desktop PSUs are compatible (a computer meant for a 200W will take a 1000W) the MBP will charge more slowly and underclock the processor. The MB will have no problems, maybe even a boost in performance.
     
  15. miles01110 macrumors Core

    miles01110

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    #15
    Yes, what's your point?

    Not if the MBP is programmed to draw 60W instead of 85W.

    Still, I fail to see the point of your reply. You basically said that wattage ratings are the maximum amount of power that can be drawn from the adapter, which should be obvious.
     
  16. Mactagonist macrumors 65816

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    #16
    Good post! :cool:
     
  17. TheHoff macrumors 6502

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    Oct 22, 2008
    #17
    Hot air or anecdotal data point? I thought the OP might be interested in someone with the exact same situation who has had an issue with swapping power bricks. I can't be sure our brick swapping is what killed the 13" MB battery but if not it was some coincidence.

    Theoretically, sure, but it seemed to matter to us unless we just chalk up the dead battery to a fluke.
     
  18. ..Ryan.. macrumors member

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    Jun 29, 2009
    Location:
    Melbourne, Australia
    #18
    i can assure you that charging a macbook pro with a macbook charger is not a good thing. the seller i bought my old MBP classic off unknowingly provided me with a macbook charger, 6 months later, i woke to a burning smell, the brick was ridiculously hot, and the wires had burnt, melted away the plastic coating, and singed my carpet, which was smoking up as if about to ignite.

    however, in the OP's case, i am not sure whether it's OK to charge a 13" with an 85W charger, i would just play it safe and use the charger provided with your computer.

    cheers,
    Ryan
     
  19. belvdr macrumors 603

    Joined:
    Aug 15, 2005
    #19
    Ryan is spot on. There's a reason they make the 85W adapter for the MBP. If the draw of the machine is too much, you can risk catching your power brick on fire.

    Case in point, we had a user plug in a HP regular laptop power brick into the dock and it melted it and started smoldering. If you use a 60W adapter on a larger MBP that requires the 85W, you will notice the brick heats up significantly, and can cause a fire.

    Vice versa is okay (i.e. using an 85W adapter for a machine requiring 60W is fine). The wattage is the capacity of the charger, which is not necessarily what it will deliver to the device. Since the capacity of the MBP charger is greater than what the MBP 13" requires, it will work without issue.

    Is there an Apple document that details the machine will not attempt to charge if the power supply is not sufficient enough? If not, I'm guessing the machine is not intelligent and will attempt to draw whatever it needs and thus, potentially the destroying the brick/home/apartment.

    EDIT: I just found this:

    http://support.apple.com/kb/TS1414

    I guess we are left to our own devices to determine what "potential operating issues" means. To be safe, I wouldn't use a 60W in a device that came with an 85W adapter. I like my house and my family. :)
     
  20. miles01110 macrumors Core

    miles01110

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    #20
    This is hardly sufficient evidence to claim that it was the MBP that caused the adapter to burn up. There's been several recent threads about Magsafe adapters that burn up seemingly due to faulty construction, not overloading the adapter. Not to mention in that 6 months the adapter was probably worked over pretty well causing all manner of wiring problems. Whether or not the magsafe is durable is a totally different issue.
     
  21. Fizzoid macrumors 68020

    Fizzoid

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    UK
    #21
    Yes, because the 60w adaptor isn't sufficient to charge it up in a reasonable time when doing CPU intensive work.

    People seem to be implying that the MBP can suck more juice from the PSU than it's capable of delivering, thus causing problems, where as I seem to believe it will just supply 60w and that's it?
     
  22. belvdr macrumors 603

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    Aug 15, 2005
    #22
    The power bricks are designed to deliver a certain amount of power without overheating. The 60W could potentially supply it, but it will heat up even more.

    The "CPU intensive work" term can be deceiving. Anything can cause the CPU to crank up, and since the machine sees power applied, it may very well do it. I just tend to play the safe side since the equipment is fairly expensive and there's no justifiable reason to take the risk.
     
  23. miles01110 macrumors Core

    miles01110

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    #23
    That doesn't make any sense at all. Power draw is power draw- there's no such thing as "too much" for a well constructed power adapter. If the parts in a particular magsafe are faulty or improperly assembled resulting in a meltdown or a fire, that's not the computer's fault.

    Sure, but by saying this you seem to imply that 85W magsafes being used with MBPs can't start fires either, which isn't true at all.

    Magsafe fires are not the product of the computer, they are the result of poorly constructed adapters.
     
  24. magbarn macrumors 68000

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    Oct 25, 2008
    #24
    Will using a 85w on a 13" MBP charge it faster than a 60w?
     
  25. NewMacbookPlz macrumors 68040

    NewMacbookPlz

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    Sep 28, 2008
    #25
    No.
     

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