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Motors and batteries

  1. Feb 21, 2007 #1
    1) will a 12v 3.5amp/hour battery support a 120v - 4.7 amp motor? if not kind of battery specifications will.

    2) Is an electric motor a DC or AC.

    help is much needed,thank you.
     
  2. jcsd
  3. Feb 21, 2007 #2
    No. It wont. But by voltage conversion, inbetween by transformer, you can.
    better to go for 120V battery with 5 Amp/hr so that atleast for 1 hour u ll get backup supply.
     
  4. Feb 21, 2007 #3

    AlephZero

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    Even with a voltage converter, 4.7 amps at 120V would convert to 47 amp at 12V (ignoring the inefficiency in the converter). The 3.5 amp-hour battery would go flat in less than 60*3.5/47 = 4.5 minutes.

    Of course that might not be a problem, depending on what you want to do.
     
  5. Feb 22, 2007 #4
    It won't even make it 4.5 minutes. A 3.5 amphour battery is simply not designed to handle 47 amperes ever. Think of it like this: I can hold a given weight at arms length for a given amount of time. I can hold a twice that weight at arms length for a shorter amount of time. But it is unlikely that I can ever hold 1000 pounds at arms length no matter how short of a time. I'm simply not built to handle it.
     
  6. Feb 22, 2007 #5

    russ_watters

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    It might - a jump-start battery can handle quite a bit for a few seconds. 3.5Ah would be unusually small for one of those though. For example, this one is 9Ah: http://hitches4less.stores.yahoo.net/stcoeljustsy.html

    Whether or not that would be useful depends on what the OP is trying to do...
     
  7. Feb 22, 2007 #6

    AlephZero

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    You can get sealed lead-acid batteries down to 12V 1.3AH. They would certainly bang out 50 amps or more, but not for long.

    Probably even a 12V NiCd pack would manage 50A if you short circuited it (but don't try that at home!)
     
  8. Feb 22, 2007 #7
    The battery probably won't hold not for any backup time u need like 10 of those batteries to have decent backup.
    An electric motor is usually DC driven cause from the way it works, if u put AC current on it, it will move back and forth thus staying in the same place and we don't want that to happen do we ?!
     
  9. Feb 22, 2007 #8

    russ_watters

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    Actually, most big commercial/industrial motors are syncronous ac. The oscilating induction field drives the motor in sync with it.
     
  10. Feb 22, 2007 #9
    r u sure about that? i mean i know that the engine operates by varying its polarity on 1 side, and keeping it the same on the other. would be difficult to do that using AC, unless you r using a permanent magnet system ? what do u think?
     
  11. Feb 22, 2007 #10

    russ_watters

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  12. Feb 23, 2007 #11

    AlephZero

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    And most small motors in mains powered domestic electrical equipment (fans, vacuum cleaners, etc) are (non synchronous) AC.
     
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