Permanent magnet DC motor...

Discussion in 'General Electronics Chat' started by Externet, Sep 7, 2008.

  1. Externet

    Thread Starter AAC Fanatic!

    Nov 29, 2005
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    57
    Hi.
    A plain ferrite permanent magnet motor running voltage is 11.2 Volts and current is 34.7 Amperes while lifting a bucket of water from a well, takes exactly 30 seconds.

    Replacing its magnets with rare earth-neodymium fancy and much stronger ones, performing the exact same bucket lifting work, will its performance improve with lower current consumption or less lifting time ?
     
  2. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Its current will remain the same because the coils are the same.
    Its efficiency will improve so its heating will be less and its output power will increase which will cause it to lift quicker.
     
  3. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    The current the motor draws depents on the load on its axis. Now, if you use stronger magnets but still have the same load on the motor axis then your reduce the current consumption but the speed the motor will reduce too. In this way, you save money on electricity but you will need more time to lift the bucket.
    However, you can use a bigger bucket to lift more water in about the same time as the small bucked. If you use a bigger bucket then the motor will draw more current and its speed will be almost the same as with the small bucket.
    Be careful not to put a big load (bucket) as the motor will exceed its current rating and will be destroyed.
    As you have understand, you cant increase the output power of the motor by changing only the magnets. You will increase the torque but the speed will reduce thus the power is the same.
     
  4. Externet

    Thread Starter AAC Fanatic!

    Nov 29, 2005
    759
    57
    Thanks gentlemen.

    Now scratching my head, and scratching again...
    Yes, the same bucket, yes the same motor, yes the same voltage, yes the same height. Stonger magnets.
    -Do not consider any different working conditions-

    Audioguru : 'Same current; faster lift'

    Mik3 : 'Reduced current, slower lift' ...
    I do not understand how electricity money is saved if less current takes more time to do the same work. Wattshour would remain the same, wouldn't ?

    :confused:

    King: It is a starter motor, the bucket is no thimble ;)
     
  5. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    oh, yes you are right you dont save money, i missed that!
     
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