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Thread: Exactly how much does this drain the battery?

  1. #11
    Clover Grayscale's Avatar
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    10 amps is a lot... and thats more than 90 watts at 12v
    CarPC install is starting to come along again...

  2. #12
    Nic
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    Quote Originally Posted by NorthGaVigor
    Not true! The alternator produces the same amount of drag on the engine no matter how much current is required by electronics. It is electrical and not mechanical. There is no physical connection inside the alternator itself to produce electricity.

    The only thing that will happen if you go over the output of your alternator/battery combo is you'll lose power or fry your alternator because it will try to produce more current when it can't.

    Air conditioning, power steering pumps are both mechanical and use more gas. Alternators do not!
    this is incorrect, the alternator will produce more strain on the engine if you are drawing more current, if there is more current being produced it is harder to turn the coil inside the alternator, i cant remember who's law this relates to, the air conditioning will however use more power because when it is not in use it is not attatched to the engine.

  3. #13
    See me in my wet t-shirt. stevieg's Avatar
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    Quote Originally Posted by Nic
    this is incorrect, the alternator will produce more strain on the engine if you are drawing more current, if there is more current being produced it is harder to turn the coil inside the alternator, i cant remember who's law this relates to, the air conditioning will however use more power because when it is not in use it is not attatched to the engine.
    And it's harder to turn the coil becuase of an electromagnet? I think, however my searches on google and making me more enlightned. I know when the cars idling and I turn my lights on the RPM goes up which must mean there is more load on it. It must do something with the load, because the one time the car almost stalled when I switched on all the electrics when it was cold!
    Ford Focus MP3 : www.stevieg.org/carpc Blog Updated 29 January 2009!
    Car PC Status: Complete - Undergoing Software Redevelopment

  4. #14
    Constant Bitrate StationRocket's Avatar
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    Quote Originally Posted by NorthGaVigor
    Not true! The alternator produces the same amount of drag on the engine no matter how much current is required by electronics. It is electrical and not mechanical. There is no physical connection inside the alternator itself to produce electricity.

    The only thing that will happen if you go over the output of your alternator/battery combo is you'll lose power or fry your alternator because it will try to produce more current when it can't.

    Air conditioning, power steering pumps are both mechanical and use more gas. Alternators do not!

    I'll also go on record saying that this post is incorrect. I don't have time to explain motor/generator theory right now but i'll say that the forces felt are a due to magnetic fields which are generated by flowing current. More current, more magnetic field density, more resistance to rotation.

    If anyone really wants hear the whole drawn out explination bug me later and if i've got time i'll pull out some of my notes and do it right.

  5. #15
    See me in my wet t-shirt. stevieg's Avatar
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    Just asked my old man about it (He knows things like this and suitably dumbed it down for me) and apparently the reason it increases load is because the more current it needs to generate, the more charge is set on the electromagnets inside the alternator, thus acting as a brake. The more charge in the electromagnet the more current generated.

    But from what I can gather my little car pc on it's 5A fuse isn't losing me much MPG!
    Ford Focus MP3 : www.stevieg.org/carpc Blog Updated 29 January 2009!
    Car PC Status: Complete - Undergoing Software Redevelopment

  6. #16
    Nic
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    yep, sounds about right, i really should be able to pull out a full explination on this sort of thing, i had an exam on it 2 weeks ago :S

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