60W MagSafe with a 15in MBP designed for 85W

Discussion in 'MacBook Pro' started by dukebound85, May 13, 2015.

  1. dukebound85 macrumors P6

    dukebound85

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    #1
    Is it ok to use a 60W magsafe with a 15in mbp that shipped with a 85W?

    If so, is the only difference the rate of charging?
     
  2. yjchua95 macrumors 604

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    #2
    It's safe, it'll just charge slower.
     
  3. dukebound85 thread starter macrumors P6

    dukebound85

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    #3
    is there a risk of a brownout so to speak if the battery is at 0%?
     
  4. chabig macrumors 68040

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    #4
    This question is nonsensical. There is no risk of anything.
     
  5. dukebound85 thread starter macrumors P6

    dukebound85

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    #5
    The point of my question was would the power demands of the mbp ever exceed that that the 60W adapter would be able to provide?

    If the power demands can be met and the ONLY drawback is a longer charge time, then that is good and not an issue. If the adapter is not able to charge the battery while being used, then that is not good.
     
  6. christarp macrumors 6502

    christarp

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    #6
    If you're doing intensive work on a 15" with a 60 watt charger then you'll most likely slowly drain your battery. Not as slowly as if there was no charger, but you will still.
     
  7. chabig macrumors 68040

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    Sep 6, 2002
    #7
    The adapter is capable of delivering a maximum of 60 watts. The MBP will draw whatever it needs, 5 watts...25 watts...until it reaches the limit of the adapter. Then it'll make do with that. That's why battery charging is slower than with an 85 watt adapter. Most likely, you will be able to charge the machine while using it. It'll simply charge slower than with the more powerful adapter.
     
  8. mcarling macrumors 65816

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    Oct 22, 2009
    #8
    Whenever I travel, I use a 45W adaptor (for a MacBook Air) with my 15" rMBP rather than drag around an 85W adaptor. I works just fine. When plug in with a low battery and actively use the machine while it's charging, then charging is slow. Otherwise it's perfectly fine. If I plug in with a full battery, nothing I do has ever drawn down the battery at all. It stays fully charged.
     
  9. Patrick-Photo macrumors regular

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    Mar 22, 2012
    #9
    Yup, and if it uses let's say 70W of power 60W will be via the adapter and the remainder off the battery in the MBP.

    I use a 60W adapter for travel, as long as I don't need to do heavy work (some browsing, text, watching a movie, etc.)
     
  10. snaky69 macrumors 603

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    Mar 14, 2008
    #10
    Yup, pretty much.
     
  11. jsagurton macrumors member

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    Pennsylvania
    #11
    I leave a 60W adapter in my lab and keep my 85W adapter at home for my 17" (spec for an 85W). Like everyone else said, it does charge slower. A few times when I was doing REALLY intensive stuff (Like having Visual Studio open in my Windows 7 VM, doing Hadoop stuff in my Linux VM, running XCode and debugging code, etc. all at the same time, it'll actually use more power than the 60W can deliver and I'll see the charge slowly deplete, like around 5% per hour, but I never run anything that intensive for long).

    So, having done it myself for 2 years now, every day, no, it won't harm your laptop, nor would using an 85W charger with a machine designed for a 60W charger. The computer controls the power draw.
     
  12. Brian Y macrumors 68040

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    Oct 21, 2012
    #12
    It won't kill the magsafe adapter, but it can leave the machine without enough power for full performance.

    Under max load, the MBP is designed to use 85w of power from the adapter AND some juice from the battery before throttling. If you're giving it 60w, then it's going to throttle performance much sooner, because the juice simply isn't there.

    tldr: it won't kill it, but it won't be performing at it's best.
     
  13. joe-h2o macrumors 6502a

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    Jun 24, 2012
    #13
    The computer will simply enter sleep mode if the power demands are unable to be met - there's no harm in this, merely inconvenience.

    Even with the 85W charger that comes with the 15" it's possible to exceed the power capabilities of the 85W unit and have the machine supplement from the battery when it's under extreme load (e.g., playing a game with high GPU and CPU demand) resulting in slowly discharging the battery.

    Using the 60W charger will just result in slower charging of the battery and a higher liklihood of the battery discharging under high load if you choose to use it during this time.
     
  14. snaky69 macrumors 603

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    Mar 14, 2008
    #14
    Not quite. It'll start draining the battery as well as using the power supply. Eventually the battery'll be empty and it'll just go to sleep. But it'll have used the whole power while it was awake.
     

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