12v supply?

Discussion in 'MacBook Pro' started by oceanjaws, Jan 20, 2007.

  1. oceanjaws macrumors member

    oceanjaws

    Joined:
    Jan 20, 2007
    Location:
    Walsden, West Yorkshire
    #1
    i live on a houseboat.
    as you may know, that means everything i have runs off domestic batteries (12volt).
    is there any way i can power my book off 12v?
    an inverter is the obvious solution, but there is power loss involved, so i'd like to find out if there's a 12v adaptor for my lovely, clean, white (smudged) macbook.
    yar me hearties!
     
  2. bartelby macrumors Core

    Joined:
    Jun 16, 2004
    #2
    Could you not use a power inverter?
     
  3. oceanjaws thread starter macrumors member

    oceanjaws

    Joined:
    Jan 20, 2007
    Location:
    Walsden, West Yorkshire
    #3
    mm

    as i said
    an inverter is the obvious solution
    but there is some power loss involved and i thought that there would be some way of powering it of a cigarette lighter socket in a car, or something, for those keroak types.
     
  4. oceanjaws thread starter macrumors member

    oceanjaws

    Joined:
    Jan 20, 2007
    Location:
    Walsden, West Yorkshire
    #4
    ok so i spelt keroak wrong, but hey, it was a long time ago since i read that.
     
  5. bartelby macrumors Core

    Joined:
    Jun 16, 2004
    #5
    Ooops, I didn't see that bit:eek:


    Trying to do too much at the same time
     
  6. eluk macrumors 6502a

    eluk

    Joined:
    Dec 14, 2006
    Location:
    East London, UK
    #6
    Kesington do a kit at £60. You'll find in the UK store.
     
  7. orangemacapple macrumors 6502

    Joined:
    Sep 1, 2006
    Location:
    Raleigh
    #7
    16.5 volts

    it seems the power brick puts out 16.5v dc
    so i would assume you would need a transformer to convert 12v to 16.5v

    your lead-acid batteries are usually putting out about 12 to 14v, depending on the charge state. you'd have to allow for the fluctuation in voltage there.

    and then there's the dirty power issue also, with interference supplied by numerous other electrical appliances.

    i would say go with a GOOD inverter - modified sine wave will often damage electronics. i don't know how many people i have known that have used modified sine wave inverters and ruined such things as their dewalt drills and lesser appliances because of the dirty power.

    a PURE SINE WAVE inverter is going to cost you $500 or so, but it'll save your appliances, and your notebook.
     
  8. oceanjaws thread starter macrumors member

    oceanjaws

    Joined:
    Jan 20, 2007
    Location:
    Walsden, West Yorkshire
    #8
    knickers

    i just bid on a modified sine wave inverter on ebay
    impetuous fool!
     
  9. orangemacapple macrumors 6502

    Joined:
    Sep 1, 2006
    Location:
    Raleigh
    #9
    i doubt it will hurt your macbook, (the brick will probalbly protect the mb) but i'm pretty sure it will fry your power brick -- one after the other. but it will probably take a few weeks to do the damage each time - it's usually not an instant fry. dirty power is like that.
     
  10. orangemacapple macrumors 6502

    Joined:
    Sep 1, 2006
    Location:
    Raleigh
    #10
    oh, and you may notice that your brick may buzz some of the time, and your mb may act a little strange -- little hang-ups and random strange thinge that will but the heck out of you and you can't figure out what's wrong -- that won't duplicate usually in the apple store when you complain.

    i've seen appliances last several months before dying (and some after only a few hours).

    just plan your budget on buying a new brick every month or so.
     
  11. oceanjaws thread starter macrumors member

    oceanjaws

    Joined:
    Jan 20, 2007
    Location:
    Walsden, West Yorkshire
    #11
    thanks fir the advice

    i reckon i'll just invest in a good inverter.
    don't want to have to replace brick upon brick
    landfills and pockets empty, you know.
    thanks again
    very helpful.
     
  12. orangemacapple macrumors 6502

    Joined:
    Sep 1, 2006
    Location:
    Raleigh
    #12

    you're more than welcome, and i'm sorry i burst your bubble.
    the modified sine wave converters are fine for things like transistor radios, electric shavers?, lights, that little $20 5" b&w emergency tv?, coffee pot, maybe even a mocrowave oven. -- all the cheap stuff you really don't mind throwing away will probably last forever on it. it's the good stuff that seems the most sensitive.

    good luck and have fun on the boat.
     
  13. tarja333 macrumors newbie

    Joined:
    Aug 15, 2008
    #13
    12 volt POWER

    Hi oceanjaws

    did you sort out your 12volt woes?

    I'm in the same boat,

    will an inverter draw a lot off the car battery? to run the power book? say we want to watch a DVD or something? with out the motor running:confused:


    Gt
     
  14. m85476585 macrumors 65816

    Joined:
    Feb 26, 2008
    #14
    The following is some very approximate math. Most car batteries have a rated reserve capacity (RC), which is how long in minutes they can run a 25A load (basically how long the car could keep running if the alternator went out, as far as I can tell). 25 amps for 1 minute is the same energy as 1 amp for 25 minutes or 1 amp for .42 hours. If a typical battery has an RC on the order of 90 minutes, 90*.42 is about 38Ah. MBPs have 85W Magsafe adapters, so I will assume that they draw 85W all the time (worst-case). Since modified sine inverters are about 95% efficient, that means the power draw at the battery will be about 90W or 7.5A@12V. 38Ah/7.5A=5 hours. But reserve capacity is how long you can run your car will run with a dead alternator before the voltage reaches 10.5V (fully dead). If you want to be able to start your car later, you won't want to drain the battery down that low, and I can't say how much time you can run it because battery discharge curves are nonlinear (for example, the battery might have a 100Ah capacity at a discharge rate of 7.5A even though it has a 38Ah capacity at 25A). The time will depend a lot on the specific battery. If you have a truck or something with a large battery, it might last a very long time, but if you have a Honda Civic (known for having weak batteries), you might only get a few hours out of it. It might end up being a lot longer than my estimate since the laptop will probably not be drawing 85A the whole time. I don't have my wattmeter with me, but I would guess that it will be closer to 50W if you are not doing anything too CPU-intensive.

    Car batteries are really not designed to do much other than starting the car. If you frequently need to run things off one, you should get a marine or deep-cycle battery instead of a regular car battery. If the battery's only purpose is to power stuff, you should get a quality AGM battery typically used in solar power setups. Batteries with more capacity will generally be more expensive. Also, don't buy a battery by the CCA number because that is not a measure of capacity.
     

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