No Control Over DC Motor Speed After Bearing Change - Help Needed

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Discussion Overview

The discussion revolves around a 24V, 15A DC motor that is experiencing a lack of speed control after a bearing replacement. Participants are exploring potential causes for this issue, including mechanical and electrical components, and are seeking troubleshooting advice.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant suggests that the stator and rotor may have damaged each other, leading to issues with the windings.
  • Another participant proposes that the tacho-generator or encoder might be damaged due to a skewed shaft.
  • A participant questions the likelihood of winding failure, noting that if there were a failure, the motor would not run at all.
  • There is a discussion about the type of commutation used in the motor, with one participant indicating that electronic commutation would report errors, while mechanical commutation might not.
  • Another participant advises checking the stability of the tacho-generator/encoder using an oscilloscope and mentions the possibility of a loose mechanical connection affecting performance.
  • A troubleshooting guide is referenced, suggesting a method to check the commutator windings by isolating pairs of brushes and measuring resistance while rotating the armature.

Areas of Agreement / Disagreement

Participants express differing views on the potential causes of the speed control issue, with no consensus reached on the exact problem. Multiple competing hypotheses regarding mechanical and electrical failures are presented.

Contextual Notes

Participants acknowledge the complexity of the motor's design and the potential for various types of failures, but specific assumptions about the motor's construction and the nature of the failure remain unresolved.

Who May Find This Useful

Individuals involved in troubleshooting DC motors, particularly those with experience in electrical engineering, mechanical engineering, or motor control systems.

Arifur
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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...
 
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Suggestions:

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.
 
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?
 
Arifur said:
In case of winding failure it won't run, isn't it?
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. )
 
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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