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HELP!CAN anyone explain the difference between an AC and DC motor?

  1. Feb 4, 2006 #1
    i was wondering y there still got some dc motors,coz ac motors more powerful....can anyone tell me y?
     
  2. jcsd
  3. Feb 5, 2006 #2

    rcgldr

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    Homework Helper

    Here's are two links from the same web site:

    http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/motorac.html

    http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/motdc.html#c1

    Those examples are a bit simplified and don't include brushless motors as shown on this web site:

    http://www.oddparts.com/acsi/motortut.htm

    They've also solved the low rpm issue with AC motors, since they are now optionally used in diesel electric locomotives.

    http://www.railway-technical.com/diesel.html

    I fly radio control models, mostly gliders, but have friends that fly electic powered aircraft. All of these use DC motors as far as I know. The cheap motors use brushes, and use pulse width modulation to control voltage which controls motor speed. The better motors are brushless, the coils are on the outside which is better for heat dissapation. The brushless motors need special speed controllers that sense and control the commutation of the motors. The stronger motors spin too fast for the large props they drive so they use gears to drive a prop. One new type of brushless motor has the outer coil as the moving part, and these are usually higher torque lower rpm motors, and don't require gearing.
     
  4. Feb 5, 2006 #3

    Danger

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    Fascinating train site, Jeff. I've added it to my 'favourites'.
    Yujay, remember also that on a smaller scale, inverter technology to convert DC battery current to AC is an unnecessary complication and expense. You wouldn't want it for something like a cordless drill.
     
  5. Feb 5, 2006 #4

    Cliff_J

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    AC motors can be built with more power since they have access to very large sources of power. 480V and 100A of current is already 100 times more power than what would completely drain a car battery in 1/2 hour.

    AC motors do have some drawbacks though for small applications. So for a small hand drill with a cord that plugs into the wall, it has what's called a universal motor. Its actually a DC motor design that also happens to work on AC. It has the advantages of a DC motor with its high startup torque and maybe reversible direction, but also the disadvantage of brushes that wear out, and so on.

    As Danger said, since a battery powered device only has DC to work with, it makes sense to have a motor that works with that source. It wouldn't make much sense to have to add circuitry and expense to convert to AC.
     
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