magsafe to USB2 adaptor?

Discussion in 'MacBook Air' started by wfriedwald, May 15, 2019.

  1. wfriedwald macrumors regular

    wfriedwald

    Joined:
    Jan 1, 2017
    #1
    here's the deal: just got back from traveling abroad - and all over the world, it's impossible to recharge my macbook. the USB2 charging ports, normally used for phones, are EVERYWHERE, but standard AC outlets (or ANY AC outlets) are NOWHERE. Impossible to find, even though I have an adaptor for the European power outlets.

    So, what I need to find is an adaptor that will let me power my MacBook air (with a magsafe power port and cable) via a standard USB2 charging port. does such an adaptor or cable exist? Need to know!

    thanks!

    w
     
  2. Audit13 macrumors 601

    Audit13

    Joined:
    Apr 19, 2017
    Location:
    Toronto, Ontario, Canada
    #2
    Usb chargers/ports won't provide enough power to charge or power an air.
     
  3. wfriedwald thread starter macrumors regular

    wfriedwald

    Joined:
    Jan 1, 2017
    #3
    Nuts! Rats! there's no possible workaround? I was in a hotel room that had no AC outlets whatsoever - not even the European or the middle eastern system.
     
  4. Audit13 macrumors 601

    Audit13

    Joined:
    Apr 19, 2017
    Location:
    Toronto, Ontario, Canada
    #4
    Usb ports can't supply much more than 5 volts and 2.5 amps.
     
  5. wfriedwald thread starter macrumors regular

    wfriedwald

    Joined:
    Jan 1, 2017
    #5
    I have a power supply doodad used for phones, is there any way to use that to power a macbook? (it outputs to USB, yes, alas!)

    Failing that, does anyone have any other suggestions?
     
  6. chrfr macrumors 604

    Joined:
    Jul 11, 2009
    #6
    No, as the other posts have said, there's no way to power your computer by USB. There's no adapter that could work.
     
  7. wfriedwald thread starter macrumors regular

    wfriedwald

    Joined:
    Jan 1, 2017
    #7
    so there's just no way to power a laptop without AC? I know I'm a little dense, but I just spent a night in a hotel room with no AC outlets and then went to an airport with no AC outlets. I can't be the only one. I guess we're all just S-O-L! oh well.
     
  8. Mr_Brightside_@ macrumors 68030

    Mr_Brightside_@

    Joined:
    Sep 23, 2005
    Location:
    Toronto
    #8
    There's no way, no. If you bought a USB-C MacBook it might trickle charge via the USB port in the wall, but that's it. I find it a little surprising that you say there were no outlets though, was this a hotel chain?
     
  9. wfriedwald thread starter macrumors regular

    wfriedwald

    Joined:
    Jan 1, 2017
    #9
    right - the Atlantis Palm in Dubai - admittedly I don't go there very often (this was the first time) but absolutely no AC outlets of any kind! all the lights etc were wired directly to the walls.
     
  10. oneMadRssn, May 16, 2019
    Last edited: May 16, 2019

    oneMadRssn macrumors 601

    oneMadRssn

    Joined:
    Sep 8, 2011
    Location:
    New England
    #10
    The 45W Magsafe2 charger for the Macbook Air outputs 14.85V at 3.05A; so 45W of power.
    USB power adapters output 5V at 2.4A max, but most are 1A or 1.2A; so 5W-12W of power.

    As you can see, that is a huge difference. There's just not much power in USB chargers.

    In theory, the Macbook doesn't need all 3.05A to charge - I bet it would trickle charge from a lot less. I don't know what the minimum is though. I'm sure someone online has measured how many watts the charger draws over time. However much it is drawing at the very end of charging a battery (going from 95% charge to 100% charge) is probably close to the minimum.

    It is possible to make an adapter with a DC-DC step-up converter to boost 5V to 14.85V; obviously reducing the current.

    Assuming the USB charger is putting out the maximum 12W and perfect efficiency (boost converters are very efficient, so this is safe to assume), you would get 14.85V at 0.8A. If 0.8A is enough, it would charge the Macbook, but probably super super slowly and only if the Macbook is off.

    If you could plug in to two 12W USB chargers at simultaneously, you could get 14.85V at 1.6A. I bet it would charge decently well at 1.6A, maybe even full charge overnight, but still much slower than with a real adapter.

    Such an adapter would be fairly easy to make for anyone that has taken an undergraduate circuits class. But it would require destroying a Magsafe2 charger to get that Magsafe2 connector. Also, as I said above, if the Macbook/Magsafe needs a minimum current to charge, it won't work if that minimum is higher than you can get.
     

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9 May 15, 2019