Charging MBA with iMac

acousticbiker

macrumors 6502
Original poster
Jun 28, 2008
458
6
I have a 1st generation Retina iMac (late 2015). I would like to charge my Retina MacBook Air by using a USB A to USB C cable (iMac USB A to MBA USB C). I tried a version of this kind of cable from Amazon which supports USB 3.1 Gen 2 but my MBA says ‘Not charging’ in System Report.

Will any cable allow this or is the power output from the iMac USB just not sufficient?
 

chrfr

macrumors G3
Jul 11, 2009
8,172
2,507
I have a 1st generation Retina iMac (late 2015). I would like to charge my Retina MacBook Air by using a USB A to USB C cable (iMac USB A to MBA USB C). I tried a version of this kind of cable from Amazon which supports USB 3.1 Gen 2 but my MBA says ‘Not charging’ in System Report.

Will any cable allow this or is the power output from the iMac USB just not sufficient?
The power output from the iMac is nowhere near enough to charge the Air.
 
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chrfr

macrumors G3
Jul 11, 2009
8,172
2,507
How about through the Thunderbolt 2 port via a Thunderbolt 2 to USB C adapter?
The Thunderbolt 2 to Thunderbolt 3 adapter does not pass power, and with what that costs, a proper USB-C charger would be less expensive. There is absolutely no way to charge your Air with that iMac.
 

CWallace

macrumors 604
Aug 17, 2007
6,558
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Seattle, WA
On the MacBook Pros, each USB-C port supports 4.5 watts of power delivery to a single connected device. The four TB3 ports provide a combined 45 watts with all connected to devices (two at up to 15 watts each and two at up to 7.5 watts each).

Extrapolating from that, I expect that the iMac's two TB3 ports can each provide 15 watts which would be insufficient for an MBA even if you found a TB3 to TB2 adapter that passed power.
 

acousticbiker

macrumors 6502
Original poster
Jun 28, 2008
458
6
On the MacBook Pros, each USB-C port supports 4.5 watts of power delivery to a single connected device. The four TB3 ports provide a combined 45 watts with all connected to devices (two at up to 15 watts each and two at up to 7.5 watts each).

Extrapolating from that, I expect that the iMac's two TB3 ports can each provide 15 watts which would be insufficient for an MBA even if you found a TB3 to TB2 adapter that passed power.
It’s conceivable that an iMac could provide more power than a MacBook Pro. Anyone know of one that passes power?
 

chrfr

macrumors G3
Jul 11, 2009
8,172
2,507
It’s conceivable that an iMac could provide more power than a MacBook Pro. Anyone know of one that passes power?
The 2017 and newer iMacs provide 15W of power from the USB-C ports, same as a MacBook Pro: https://support.apple.com/en-us/HT204392
This should be able to charge an Air that’s asleep or off. I do have to wonder why you’re looking to do this rather than spending $20-30 on a charger that meets the intended specifications and use.