Resolved MBA charger sizes

Discussion in 'MacBook Air' started by ShrubbySoup, May 6, 2012.

  1. ShrubbySoup, May 6, 2012
    Last edited: May 12, 2012

    macrumors regular

    ShrubbySoup

    Joined:
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    UK
    #1
    Hey guys I just had a thought,
    Can you use a larger Watt charger for the mac line than what they need?
    Say the MBA takes a 15W I think, then can I go to the apple store, buy a 45W for the pro (confirm?) and use it, therefore charge it faster?
    Thanks
     
  2. macrumors 6502a

    Joined:
    Oct 21, 2011
    #2
    You can use it but it definitely won't charge faster. It will still only charge at a 15 watt rate. Basically the electrons in the 45 watt charger are too big to fit into the MBA. So although they are larger it is harder for them to fit thus making it charge at the same rate.
     
  3. thread starter macrumors regular

    ShrubbySoup

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    #3
    Ahhhh thanks, better to ask than not know at all ;D
     
  4. macrumors Core

    miles01110

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    #4
    Wow. Just... wow.
     
  5. keantan, May 6, 2012
    Last edited: May 6, 2012

    macrumors regular

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    #5
    I would like to point out it has nothing to do with the size of the electrons. It is to do with the voltage and current ratings of the circuits in the MacBook Air. The charger is RATED at 45W, this implied that it can supply (assuming like most computers) it supplies a voltage of approx 12-15V at approximately 3 amps. (Equation is P = IV) this is the maximum amount of current it can supply. The macbook air would have a reduced current tollerance of 1A. (Since we know MBA charges are approx 15W). If you plug a 45W charger into a 15W rated MBA it will charge at 15W rate (confirming what the previous poster mentioned). Just because a charger CAN supply 45W doesn't mean it has to. Protection circuits are in place so you dont blow your computer (this is standard practice so consumers don't whine about broken electronics). Current can destroy electronic components very quickly. Much more quickly than voltage as it provides a greater heating effect (Ever wonder why heaters etc have such a high wattage from 240V? (110V in the US) that's why).

    //end rant

    Source: Am an Electronics Engineer
     
  6. macrumors member

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    Munich
    #6
    Thanks guys for beating me to it. Very good explanation by keantan!

    Even on a Sunday I was compelled by this:

    There is nothing wrong about leaving out techno-babble, but this is really a bit beyond the point. :eek:

    The first thing that came to my mind would be, how do those gigantic electrons generated in a 1.6GW power plant get into the power line? ;)

    -Drsoong

    ["Dr." only in the nick, but a M.Sc. in Experimental Physics]
     
  7. macrumors 6502a

    Joined:
    Oct 21, 2011
    #7
    That's what a transformer is for. It resizes the electrons thus changing their voltage.
     
  8. macrumors regular

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    #8
    [​IMG]

    Transformers do NOT resize electrons. Transformers are basically two coils that generate and respond to changes in electromagnetic fields. Electrons flow through 1 coil that generates a magnetic field which induces electron flow in the other coil. The number of winds in each coil determine the RATIO of flowing electrons between the two coils, hence the voltage ratio between the two coils.
     
  9. macrumors 6502a

    rbrian

    Joined:
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    #9
    Actually, Keantan, I think you'll find that Transformers are robots in disguise. The tiny electron all-spark grows into a giant blue shiny thing and brings inanimate objects to life. Putting 45W electrons into a 15w Air will cause it to grow legs and attack you!

    [/dead pan mode]

    i'm sorry, I couldn't help it. :eek:
     
  10. macrumors regular

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    #10
    I see what you did there ;) ahaha,

    What did the electron say to the transformer coil? You have me so many high frequency waves you raise me to another level

    [​IMG]
     
  11. drsoong, May 6, 2012
    Last edited: May 6, 2012

    macrumors member

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    #11
    what radius?

    Now, I really have to take out the big guns: :)

    Any classical view, and therefore a classical radius of an electron, is an indequate description, and therefore moot.

    From a phycisist's point an electron is a point-like particle, where the only best approximation to describe it is its probability density, determined by ψ∗ψ ́ = |ψ|^2 (Schrödinger equation).

    Since, we know that there is never any chance to clearly say to absolute accuracy where the electron is (see "Heisenberg uncertainty principle"), the electron might be in the MBA or might still be in the in the charger. It is therefore entirely to the electron to decide where it wants to be.

    Obviously, the more obedient electrons are highly-priced (ever looked at your energy bill? The more electricity you consume, i.e. electrons that volunteer to work in your appliances, the higher it is.), and Apple can market a 85W "capable" charger, but it would be prohibitively expensive, even for :apple:'s price-tags on their chargers, to afford enough willing electrons.

    :D:D

    -Drsoong
     
  12. macrumors Core

    miles01110

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    #12
    Through a larger pipe, obviously.
     
  13. drsoong, May 6, 2012
    Last edited: May 6, 2012

    macrumors member

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    #13
    attack of the electron

    Now, that you mention it, I vaguely recall such an encounter with electrons from an undergrad physics lab experiment...

    http://www.tu-ilmenau.de/fileadmin/media/exphys1/Physikpraktikum/Bilder/A4_2.jpg

    :eek:
     
  14. macrumors 68000

    maril1111

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    #14
    I feel like PUEVLO was trolling you guys or i hope thats the case... :D but thanx for the explanations everybody
     
  15. macrumors 6502

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    Kansas
    #15
    I'm pretty sure the air uses a 45w 13' mbp uses 60w and the 15 and 17 use 85w.
     
  16. thread starter macrumors regular

    ShrubbySoup

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    #16
    Thanks
     
  17. macrumors 6502a

    rbrian

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    #17
    I just checked, and sure enough my 11" Air has a 45w charger. For some reason I thought it was 30w. Either way, it's much less than the 120w my work Toughbook needs to do everything much slower than my Air, if it all!

    ----------

    I studied that picture, and cool though it is, I can't work out what it is I'm looking at. It certainly doesn't look like an Air with legs! :D
     
  18. macrumors member

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    #18
    It is a close-up picture of electrons forced into circular motion through Helmholtz coils in a so-called Teltron Tube (http://en.wikipedia.org/wiki/Teltron_Tube).

    Filled with Hydrogen gas, one can observe the electron beam in beautiful blue colour.

    Part of most undergraduate physics labs.

    -Drsoong
     
  19. macrumors 6502a

    rbrian

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    #19
    I see, very cool! Almost makes me wish I didn't drop out of college...
     
  20. macrumors regular

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    #20
    Digressing, remember seeing one in second year of A levels, don't see em in engineering though. Very cool kit
     
  21. macrumors 6502

    Joined:
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    Kansas
    #21
    Yea. I mean you can use the higher watt on the lower ones. It wonb't charge any faster however if you decide to upgrade it's good. You can't however use a lower watt to charge a higher one.
     
  22. macrumors regular

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    #22
    This has definitely made my day! How on earth can you make up stuff like this?
     
  23. macrumors regular

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    #23
    I'm not gonna lie. I voted UP your post.
     
  24. macrumors 68000

    Confuzzzed

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    #24
    This has become my favourite thread of all time. Thank you all for the entertainment x
     
  25. macrumors Core

    alphaod

    Joined:
    Feb 9, 2008
    Location:
    上海 (Shanghai)
    #25
    The MacBook Air normally comes with a 45W adapter.

    Apple makes two more capacities, the first one at 60W used on the 13" MacBook and MacBook Pro; the second charger is at 85W and is used on the 15" and 17" MacBook Pro.

    You can certainly use the 60W and 85W adapters on your MacBook Air; it will not charge the computer any faster; it auto senses the computer that it's connected to and will adjust the output current automatically. The drawback to using the other two adapters are noticeably larger [and heavier] than the 45W adapter if you do travel.

    If you're looking for another adapter, I would consider buying the 85W to keep at home. It is larger and heavier, but will charge any MacBook, MacBook Pro, or MacBook Air as needed. When charging the MacBook Air, the 85W will run cooler.
     

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