motor parameters determination

Discussion in 'General Electronics Chat' started by h.d, Jan 5, 2008.

  1. h.d

    Thread Starter Active Member

    Oct 22, 2007
    150
    0
    hi all
    right,,if we have a dc-motor and we dont know any if the parameters
    only the terminal voltage
    so how to determine the motor parameters????
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    My first effort would be to try to take the information marked on the body of the motor and attempt to track down the datasheet from the manufacturer.

    Failing that, I would measure the DC resistance. I would then apply the know voltage and measure the current it consumed. I would then stall the motor and measure the stall current it consumed. I would get a tachometer and measure the speed of the motor in RPM.

    There are other parameters that would be nice to know but these will do for a starter.

    hgmjr
     
  3. h.d

    Thread Starter Active Member

    Oct 22, 2007
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    i should determine the maximum and nominal torque and current
     
  4. hgmjr

    Moderator

    Jan 28, 2005
    9,030
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    Yes, that would be good information to obtain. Calibrated Torque meters are not that easy to come by unfortunately.

    hgmjr
     
  5. h.d

    Thread Starter Active Member

    Oct 22, 2007
    150
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    yes , for that i ask
    the problem that the i havent the nameplate and the kit number
     
  6. hgmjr

    Moderator

    Jan 28, 2005
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    214
    It is almost cheaper in the long run to put the unknown motor aside and then purchase a motor for which you can obtain a datasheet.

    hgmjr
     
  7. h.d

    Thread Starter Active Member

    Oct 22, 2007
    150
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    the motor cost is 120 $
    u think that purchase a new one is more cheaper than test it ??????????????
     
  8. hgmjr

    Moderator

    Jan 28, 2005
    9,030
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    $120 does up the ante in favor of testing over replacement.

    If you need to know the torque and you know anybody that can provide access to a torque-meter then maybe you can borrow one.

    hgmjr
     
  9. h.d

    Thread Starter Active Member

    Oct 22, 2007
    150
    0
    yes, i will test the motor in the drive laboratory in my university
    there we have the needed equipment
     
  10. h.d

    Thread Starter Active Member

    Oct 22, 2007
    150
    0
    i test the motor in noload mode
    220 Vdc
    0.5 A
    4750 rpm
    Ra=35.5 ohm
    but i kmow that the motor is 2hp ?????
     
  11. h.d

    Thread Starter Active Member

    Oct 22, 2007
    150
    0
    is their answer?????
    from the last values can i involve the power of the motor?
     
  12. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
    1
    Power and Voltage will give you operating current.. One horsepower is just over 700W, so you can do the math on that one. It's hard to figure out things like rotor inertia, friction, and torque without the proper equipment.

    Steve
     
  13. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    746 Watts to the horsepower. (Actually, they were mining ponies, not horses at all...)

    Torque (in foot-pounds) = horsepower * 5252 / RPM

    I leave it to the reader to convert to SI units if needed.
     
  14. h.d

    Thread Starter Active Member

    Oct 22, 2007
    150
    0
    ok am dont ask about the units
    i ask about if i can calculate the power of the motor from the measured valuse tha i get it (noload curren,noload speed,Ra, & the nominal operating voltage)
    i need the torque an dthe power.
     
  15. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
    1
    Power cannot be determined via no-load conditions. I'm not a motor expert, but I believe the power rating has a lot to do with the ambient temperature rise acceptable.

    Steve
     
  16. h.d

    Thread Starter Active Member

    Oct 22, 2007
    150
    0
    i think that too
    i should load the motor to determine the torque and power
    but the deficcult is how to load it and measure the load..
    that what i will search about it.
     
  17. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
    1
    I guess acceptable temperature level has a lot to do with motor construction. Things like maximum wire temperature, PM demagnetizing temperature, epoxy temperature rating, etc. Sometimes you can gauge the motor power by knowing it's type and size, since that is a pretty consistent thing. Sorry I cannot help anymore than this, I actually still have yet to take my motors course :p

    Steve
     
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