Need solar power solution for my 2011 MacBook Air.

Discussion in 'MacBook Air' started by Hummer, Sep 12, 2011.

  1. Hummer macrumors 65816

    Hummer

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    #1
    I'm camping out for at least 3 days for the next iPhone and I'm looking for something that can power my MacBook Air. I've found a charger that is supposed to work, but the reviews are terrible so I'm looking for possibly a DC option.
     
  2. blueroom macrumors 603

    blueroom

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    #2
    They'll be enormous and are not practical for camping or laptops. Get a HyperMac battery pack or an iPad with battery pack e.g. Energizer XP18000
     
  3. Chipg macrumors regular

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    #3
  4. Hummer thread starter macrumors 65816

    Hummer

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    #4
    Is there any way a car battery could last longer than this? Or could I plug a car battery into this? It claims I can only get 3 hours charging on DC.
     
  5. deeddawg macrumors 604

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    #5
    A small car battery might be double this (compare amp-hour ratings).
    No need to buy this AND a car battery; you should be able to just hook up a 100watt inverter directly to a car battery (assuming the inverter has a fuse).

    Very rough calculation suggests this gadget may be plenty -- Macbook Air power adapter is 45W. That's just under 0.4 amps at 120V. Since this thing is 28 amp hours, it should give you at least 70 hours of run time since you likely won't be pulling a full 45W out of the power adapter all the time.
     
  6. billy12 macrumors member

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    #6
    Not quite - 45W is the output rating. The power supply isn't 100% efficient, so it'll draw more than that.
     
  7. deeddawg macrumors 604

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    #7
    Good point. The specs written on it show the input as 100-240V 1A and output as 14.5V 3.1A , so assuming 120V and 1A would be 120W (though I suspect max 1A would be at 100V). So perhaps 30hrs runtime if you're pulling the max power through the adapter and not counting inefficiencies in the 12V to 120V conversion on the powerpack side.

    In reality though, it's unlikely that typical usage would require 100% utilization of that capacity (the adapter would get REALLY toasty dissipating 65W!) and thus typical potential runtime would likely be significantly longer than 30hr.
     
  8. Chipg macrumors regular

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    #8
    One thing not to be forgotten is the power loss used by the inverter.

    The 28 amps per hour would probably power the AIR for 50ish hours after you take into account the loss from powering the inverter. It's a 600w inverter so not as efficient as a 100w inverter but it would be a good item to have in the future to leave in your car trunk for a safety jump start device, camping power etc. 4 or 5 people could all work at the beach all day on their laptops from this.

    The OP might want to google other makes of jumper boxes with built in inverters, I know there are 5-10 other makes and models, maybe he can find one with a 40amp hour battery or higher.
     
  9. Chipg macrumors regular

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    #9
    Sure, if you go that route tell the salesperson you need a car battery with storage capacity NOT cold cranking amps (big difference) then go buy a $49 60w power inverter, the thing is power inverters take juice to run so the larger one you get the more battery power it'll rob, the trick is to get one a little over the size you need to be the most efficient.

    It's my understanding the AIR when not charging it's internal battery and not rendering video or doing intensive CPU tasks uses very LITTLE power.
     
  10. Hummer thread starter macrumors 65816

    Hummer

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    #10
    Thanks guys, I'm going with the car battery and inverter. Any idea of the largest capacity battery I should get for under $150?
     
  11. alecgold, Sep 14, 2011
    Last edited: Sep 14, 2011

    alecgold macrumors 65816

    alecgold

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    #11
    Why don't you get a car battery and a Hypermac car-charger? That should be cheaper than getting an inverter and also an inverter (12V DC --> 220V/110V AC -->18VDC) is much less efficient. If you have the car-charger, you can directly couple it to the car-battery and have just 12V DC-->18V DC which is much more efficient. A good expensive inverter gets 80% efficiency, the hypermac is said to get 92%. For $50 you get an inverter with an efficiency that can be well below 60%.
    Car-Charger from Hypermac

    so a quick calculation, the air has 60W and lasts about 5 hours on that. that takes around 12Wh.
    a 12V 28 amp car battery has 336Wh. Without losses that gives you 28 hours. With an inverter it could get as bad as just 17 hours. A DC-DC would get your 27 hours.
    One other thing, a big bad-ass car battery, 12V, 100A costs around 150. So that would get you a theoretical life of around 100 hours... With a DC-DC converter it would get you around 92 hours, with an inverter it would get you around 60 hours.

    And you have the added safety of not messing with 110/220V outside, it's just 18V max. Although it wouldn't hurt to keep everything dry :D

    Oh, no affil with Hypermac-things, I just am a happy user of the car-charger myself.
    One more thing, I have no idea of the weight of a 100Ah battery, but i would advice to bring a trolley or something. It might be a tad heavy.
    One last more thing, these batteries need to be charged before use, they are not charged to maximum capacity when you buy them. so find a car-battery-charger and have it charged right up until the moment you need it.
     
  12. alecgold macrumors 65816

    alecgold

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    #12
    Oh, and I found this on the Hypermac site:

    Most power invertors available in the market (even the one sold at Apple Store) are not pure-sine wave inverters. The MacBook power adapter is not designed to work with such modified-sine wave inverters and continual usage may damage the power adapter and MacBook. Square-wave inverters also do not offer good voltage regulation or frequency stability which will degrade EM noise sensitive functions like audio,video,graphic playback and editing, communications, scientific measurements and calibrations. HyperMac Car Charger is a pure DC device with low electromagnetic interferance, producing a clean power signal, important for high fidelity work. It is a must use for professionals and non-professionals alike.

    I have no idea how fast it would get damaged, but that it's something to consider.... :(
     
  13. billy12 macrumors member

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    #13
    What do you mean by this?

    ----------

    As far as I know, switch mode power supplies work fine with modified sine waves.
     
  14. alecgold macrumors 65816

    alecgold

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    #14
    Oh, just a simple calculation, IIRC the macbook air has a 60Wh battery, lasts about 5 hours under outdoor use (maximum brightness, wifi on, perhaps a MiFi or iPhone on the USB to charge it and have internet), so it would consume around 12W per hour of use.


    I have no idea what kind of power supply Apple uses, I just repeats what was on the website of Hypermac.
    A bit more searching on the Good Old Google reveals that it might not be that harmful, so it seems a bit of b#ll*cks from Hypermac. Shame on them:)
     
  15. billy12 macrumors member

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    #15
    The Apple supply is a switch mode supply.

    W (watts) is a measure of the rate of energy consumption (1W=1J/s). Wh (watt-hours) is a measure of energy capacity (1Wh=1W for 1h=3600J).

    The 2011 13" Macbook Air (MBA) has a 50Wh battery (per Apple's specs). If we assume 5h battery life as in your example, the MBA consumes an average of 10W over those 5h (50Wh/5h=10W). If the car battery is rated at 336Wh, ignoring any inefficiencies in the conversion (which is unrealistic, of course), we get 33.6h (336Wh/10W=33.6h).
     
  16. alecgold macrumors 65816

    alecgold

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    #16

    With all this in mind, what whould you choose inverter or car-charger?
     
  17. billy12 macrumors member

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    #17
    The more efficient and safer (no 120/220VAC) solution is the DC-DC car charger, but it only works with the Macbook (or anything else that takes 18VDC).

    The more versatile solution is the inverter, since you can plug almost anything that runs off 120/220VAC into it.
     

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