rMB 12 Rechargeable on any USB 2.4a outlet?

Discussion in 'MacBook' started by bibyfok, Apr 6, 2015.

  1. bibyfok, Apr 6, 2015
    Last edited: Apr 6, 2015

    bibyfok macrumors 6502

    bibyfok

    Joined:
    Jun 14, 2012
    Location:
    France
    #1
    Is there any things that would prevent the rMB 12 to be recharged on any 5V 2.4a USB port? Does anyone know the tension that will deliver the 29W adapter?
    I would love to see this computer be able to be recharged with external batteries or with something like this!
     
  2. Theophil1971 macrumors 6502

    Theophil1971

    Joined:
    Mar 20, 2015
    Location:
    USA
    #2
    5V @ 2.4amps is only 12 watts... So, nope. Any charger will need to be a full 29 watts (5.8amps)
     
  3. bibyfok thread starter macrumors 6502

    bibyfok

    Joined:
    Jun 14, 2012
    Location:
    France
    #3
    I can recharge my 85W rMBP on a 45W charger without any issue except longer recharge time.
     
  4. MyopicPaideia, Apr 6, 2015
    Last edited: Apr 6, 2015

    MyopicPaideia macrumors 68000

    MyopicPaideia

    Joined:
    Mar 19, 2011
    Location:
    San Diego, CA
    #4
    Can this be true, physically? Because I've been told that apparently USB 3.1 only can handle 3.0amps? The speculation is that Apple's charger is running higher voltage, and thus standard USB as well as iPhone and iPad chargers may not be able to charge the MB because of too low voltage rather than too low amps. The battery interface circuitry on the MB may not activate at 5V, it may be something like 9-10V instead.

    Nothing to stop you charging all your iDevices with the MB charger though, assuming a USB-C/Lightning cable is released by Apple.
     
  5. newellj macrumors 603

    Joined:
    Oct 15, 2014
    Location:
    Boston, MA, US
    #6
    Assuming that something is smart enough to step down the voltage from the rMB adapter (assuming it's more than 5v nominal). I don't know if the adapter is smart enough to do that. I'm doubtful that iPhones and iPads are able to do that. I could be wrong...
     
  6. MyopicPaideia macrumors 68000

    MyopicPaideia

    Joined:
    Mar 19, 2011
    Location:
    San Diego, CA
    #7
    Apparently USB 3.0 and up has a mandatory 5V compatibility requirement, but that is according to forum member Rigby, I haven't verified that. So if he/she is right, the iPhone and iPad don't have to do it, the cable will "know" to deliver 5V when connected...apparently.
     
  7. Rigby macrumors 601

    Joined:
    Aug 5, 2008
    Location:
    San Jose, CA
    #8
    The way it works is that a USB power supply must default to 5V so legacy USB devices cannot be damaged. Higher voltages and currents are only enabled after a negotiation between the device and the power supply.

    You can download the specs if you are interested in the technical details:

    http://www.usb.org/developers/docs/usb_31_040315.zip
     
  8. newellj macrumors 603

    Joined:
    Oct 15, 2014
    Location:
    Boston, MA, US
    #9
    Thank you - so plugging an iPhone into the rMB adapter (assuming correct cables/adapters) shouldn't hurt the iPhone? I think that's the bottom line, please correct if not.
     
  9. MyopicPaideia macrumors 68000

    MyopicPaideia

    Joined:
    Mar 19, 2011
    Location:
    San Diego, CA
    #10
    Excellent, thanks for this, and sorry for quoting you without quoting you, appreciate the follow up! :)
     
  10. Lucifer666 macrumors 6502a

    Joined:
    Sep 20, 2014
    #11
    We shall see.

    I'm liking this spec though. Should be fun :)
     

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