HT204360: Using the USB-C port and adapters on your MacBook (Retina, 12-inch, Early 2015) and later

Learn about Using the USB-C port and adapters on your MacBook (Retina, 12-inch, Early 2015) and later
StuBlack
Level 1 (0 points)

Q: USB-A to USB-C Adapter

I wondered what the technical reasons were for the statement "USB hubs and other USB devices that supply power won't charge your MacBook. Use the supplied USB-C Charge Cable and 29W USB-C Power Adapter to charge your MacBook" ?

MacBook, Mac OS X (10.5.6)

Posted on Jun 24, 2015 8:18 AM

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StuBlack

Q: USB-A to USB-C Adapter

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  • by Phil0124,

    Phil0124 Phil0124 Jun 24, 2015 8:26 AM in response to StuBlack
    Level 7 (27,002 points)
    iPhone
    Jun 24, 2015 8:26 AM in response to StuBlack

    Because the powered USB hubs only supply power to their ports, but not up the USB cable that connects them to the MacBook. Even if they did, it would likely not be enough power to charge the Mac any way. 

  • by StuBlack,

    StuBlack StuBlack Jun 24, 2015 10:28 AM in response to Phil0124
    Level 1 (0 points)
    Jun 24, 2015 10:28 AM in response to Phil0124

    I doubt it's that simple - I don't understand why a powered USB hub port couldn't supply power to the USB-C via a USB-A to USB-C adapter cable in principal.

     

    I think the real answer lies in the fact that USB can deliver different power profiles, not just the 5V that we commonly associate with USB.

     

    I suspect the MacBook uses one of the 12V or 20V power profiles - see here https://en.wikipedia.org/wiki/USB#USB_Power_Delivery.

     

    The Apple USB-C Power Adapter is rated at 29 Watts, if it were working at 5 Volts this would imply 29 Watts/5V = 6 Amps current, in excess of the 2.0Amp rating for 5V, from the page above.

     

    This is my only explanation but I'd be grateful for a more informed view.

  • by StuBlack,

    StuBlack StuBlack Jun 24, 2015 12:20 PM in response to StuBlack
    Level 1 (0 points)
    Jun 24, 2015 12:20 PM in response to StuBlack

    I think my theory may not be correct.

     

    All 62 reviews of this productsay it works, albiet charging slower than with the 29W adapter supplied.

     

    So I conclude there is no technical reason for Apple to state "USB hubs and other USB devices that supply power won't charge your MacBook".

  • by Knotsure,

    Knotsure Knotsure Jun 24, 2015 6:29 PM in response to StuBlack
    Level 1 (0 points)
    Jun 24, 2015 6:29 PM in response to StuBlack

    I Will be very disappointed if I cannot charge my MacBook from my anker 13000 pack. was a reason I liked this laptop.