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DC motor speed

  1. Jun 14, 2015 #1
    After bearing failure of 24V, 15A dc motor. We change the bearing of the dc motor. But after changing it the motor is running forward/ reverse but there is no control over the speed.

    Where is the problem? Is that in the techo or drive card?
    Any body please help.

    Helping in highly appreciated...........
  2. jcsd
  3. Jun 14, 2015 #2


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    1) The stator and rotor have scratched each other, and some of the windings have been damaged.

    2) The tacho-generator or encoder has been damaged, due to a skew shaft.
  4. Jun 15, 2015 #3
    Thnx Hesch for your suggestion, but there is no screech between rotor and stator.
    In case of winding failure it won't run, isn't it?
  5. Jun 15, 2015 #4


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    I don't know how your motor is made up, but I think that electronic commutation of the motor is used. In this case I'm sure that the drive will report an error in a coil.

    In case of a mechanical commutation, there is a lot of coils in the motor, and if one of these are damaged, the motor will be unstable. The drive, which then is a simple dc-drive, will not detect/report an error.

    But what about the tacho-generator/encoder? Connect an oscilloscop and see if they are running stable.

    ( I've seen so many times in case of an error, that the mechanical connection from motor shaft to e.g. encoder shaft is not correctly fastened. )
  6. Jun 15, 2015 #5
    Here is a good troubleshooting guide that may be of some help.

    To expand on what Hesch is saying about multiple commutator coils: when you check the brushes, if there are more than one pair, you can remove some of them so there is only one pair left, (that is two brushes on directly opposite sides). Now when you rotate the armature and read the ohmmeter you can check each of the commutator windings separately, as you slowly turn the rotor by hand (with all power disconnected!) Be sure to replace all the other brushes when done. Don’t forget to check the tachometer (if equipped) for output signal.
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