dc sereis motors

Discussion in 'General Electronics Chat' started by ronn, Dec 24, 2007.

  1. ronn

    Thread Starter Member

    Nov 1, 2007
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    why do dc series motor runaway when unloaded? books said there is an accelerating torque but where will it came from since as it speeds up, more CEMF is develop which makes less current in the field windings and the magnetic field becomes weaker that could result to have a less torque?
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    I'm not sure what you mean by runaway.

    Perhaps you are referring to a situation in which you have two DC motors in series that are identical and equally loaded. As long as the motors remain equally loaded, they both would ideally turn at the same rotational speed.

    If you increase the load on one while leaving the other motor's load unchanged, the other motor would speed up.

    This phenomenon owes itself to the fact that as the first motor's load is increased then the current flowing in the loop is increased and thus the other motor receives an increase in power and so it speeds up.

    hgmjr
     
  3. ronn

    Thread Starter Member

    Nov 1, 2007
    16
    0
    the motor that I'm talking is not two motors. its a dc series motor (it is series because the field is in series with the armature) and runaway means it goes to a speed rapidly that sometimes they tear themselves to pieces before reaching final spped)
    thanks again
    ron
     
  4. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Sorry, my bad. I misinterpreted your use of the word series.

    Perhaps one of our members can answer this one from direct experience with dc series motors.

    In the meantime, I will see if I can find anything definitive out on the Web.

    hgmjr
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
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  6. BlueDevry

    Member

    Dec 26, 2007
    22
    0
    If there is a significant varible load in series with this type of motor then destruction of the motor shouldn't occur.
     
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