nbritton

Q: MacBook Retina vs Air Power Consumption, Off-grid Applications

What is the average and maximum power consumption of the MacBook Retina 12" and MacBook Air 13"? I'm trying to compare these two models for off-grid use and having trouble finding any details. In the real world, which device has the longest battery runtime?

 

Which would be better for operation off of 12 volt batteries? I need a solution that doesn't involve using an inverter because those waste energy in the conversion process.

 

Also is the Apple 29 watt and 45 watt power adaptors full range power supplies, can they accept an AC or DC voltage anywhere from 100 to 240 volts? I'm assuming these switch mode power supplies will work on DC input voltage, since AC is presumably bridge rectified to DC anyways. So a battery bank of ten 12 volt batteries wired in series to provide 120 volts DC would work to power the standard Apple power adaptor?

Posted on Jul 19, 2016 7:33 AM

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Q: MacBook Retina vs Air Power Consumption, Off-grid Applications

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  • by Csound1,

    Csound1 Csound1 Jul 19, 2016 7:38 AM in response to nbritton
    Level 9 (50,202 points)
    Desktops
    Jul 19, 2016 7:38 AM in response to nbritton

    They will run on any AC voltage from 100 to 240, they will not run on DC of any voltage.

  • by nbritton,

    nbritton nbritton Jul 19, 2016 9:08 AM in response to Csound1
    Level 1 (8 points)
    Desktops
    Jul 19, 2016 9:08 AM in response to Csound1

    Csound1 wrote:

     

    They will run on any AC voltage from 100 to 240, they will not run on DC of any voltage.

     

    How do you know they won't run on high voltage DC? Did you read this somewhere in Apple's literature? Typically Switch Mode Power Supplies have a primary full wave bridge rectifier stage that converts AC to high voltage DC and then a secondary DC-DC converter stage that drops the high voltage DC down to low voltage DC. If you understand how a bridge rectifier works then you will know that it can pass DC just as well as AC, so inputting a high voltage DC will in essence just bypass the primary rectifier stage and go straight to the DC-DC converter. I'm willing to bet that it will work.

     

    http://power-topics.blogspot.com/2007/09/using-ac-dc-input-power-supply-with.htm l

  • by Csound1,

    Csound1 Csound1 Jul 19, 2016 9:38 AM in response to nbritton
    Level 9 (50,202 points)
    Desktops
    Jul 19, 2016 9:38 AM in response to nbritton

    The MagSafe power supply requires AC voltage between 100 and 240 at 50 or 60 cps, it has NO provision for DC at all.

  • by Lanny,

    Lanny Lanny Jul 19, 2016 9:57 AM in response to nbritton
    Level 5 (7,895 points)
    Desktops
    Jul 19, 2016 9:57 AM in response to nbritton

    The requirements are printed right on the side of the power supply.

     

    Excerpt from the link that your provided:

     

    Always check your power supply’s Operations Manual or spec sheet to confirm that it is designed to operate from either an AC or DC input.
  • by Csound1,

    Csound1 Csound1 Jul 19, 2016 9:58 AM in response to Lanny
    Level 9 (50,202 points)
    Desktops
    Jul 19, 2016 9:58 AM in response to Lanny

    I think he is wondering if you can bypass the psu and power the Mac directly from a DC source, so he is on his own with this.

     

    Easiest way to go off grid would be to use an inverter to get 100 to 240v AC and use the MagSafe as intended.

  • by marinerblue,

    marinerblue marinerblue Jul 19, 2016 12:41 PM in response to nbritton
    Level 1 (12 points)
    Notebooks
    Jul 19, 2016 12:41 PM in response to nbritton

    One way to look at the problem is battery capacity / hours of life: the MacBook's battery is 41.4 Wh, the 13" MacBook Air's battery is 54Wh.  The MacBook is supposed to last ten hours on battery, so it uses about 4.14W on average; the MacBook Air claims to go 12 hours on the 54Wh battery, so it uses about 4.5W on average.  The MacBook's display probably uses more power which is traded off against a lower-power processor.

     

    The MacBook can be charged over USB-C from battery packs like the Anker PowerCore+ that have USB-C ports, meaning other USB-C charging options may be more easily adapted to 12VDC/off-grid battery use.  There are existing auto-oriented USB-C adapters, though they really only supply enough current for overnight charging, not "charge-and-use" scenarios.  I haven't seen any auto USB-C adapters that support the USB-C Power Delivery spec that would make real "charge-and-use" work.

     

    Apple used to sell a MagSafe airplane adapter (MA598Z/A) that worked with EmPower jacks on planes about ten years ago - you could possibly use one of those, plus a MagSafe-MagSafe2 adapter, to run a MacBook Air if you were interested in building a solution yourself.