DC Motor and Drive

[singapore11singapore]

Hi All,
I have a two DC motor application; the motors are mechanically coupled. They are driven by 2 DC drives; one each. One of the motors has had its armature rewound. Now when I run this motor up with the DC drive I get to around 50% load and begin to hear loud humming...it doesn't trip as yet...just the humming sound becomes more apparent. Running no-load seemed fine.
Question: what is causing this humming?

I have asked the plant to re-autotune the DC drive of the "humming" motor as obviously I suspect the resistance and inductance to have changed. I have asked them to also check the mounting of the encoder and ensure it is ok.

I have asked them to run the motors singularly. That is motor A/drive A measuring the speed/voltage/currents field/armature) etc....
then run motor B/drive B doing/measuring the same and see if the resultant data obtained are very similar.

Anything else I could suggest?

Regards

 

[Skogsgurra]

A detailed diagram showing all connections and what kind of drives and motors is a good start.
Make sure that windings have the right polarity (commutation windings or compensation windings are sometimes a problem). DC drives are not very common these days, so you may have a problem finding someone that can make it OK again.

The best strategy is to decouple both motors and run them under identical conditions. They then should behave almost identically. So your approach is right. I have done the same thing using a car battery. That sometimes makes any difference more pronounced and also makes measurements less dangerous.

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[Compositepro]

Are your drives capable of making the motors share load equally, or do they assume that the motors are identical and therefore should share load equally? This is not a good assumption on DC motors. If the same voltage is applied to two different motors they will turn at slightly different speeds. The drives can correct for speed differences, but if the motors are mechanically coupled there will be no speed difference. So one motor will end-up carrying most of the load and there can be oscillations in the motor currents as the drives fight each other for control. Common practice for DC motors that are mechanically linked and have to share load is to connect the armature coils in series so that the same current passes through both motors. But this requires double the drive voltage or changing motor connections on a 180 VDC motor to 90 VDC.

 

[lukin1977]

What type of DC motors are? Series, Shunt, Compound?