AM band noise from motor and/or controller

[Lil_Guppy]

Just wondering if anyone could give me some advice about reducing or eliminating noise from an AC motor and its speed controller.

The place where I work recently got a complaint about a small amount of radio noise (ok, maybe small is not the word when it fills the entire AM radio band for a one block radius ), and we found that it was a pump motor and/or its speed controller. I'm not exactly sure on the specifics of the motor (single phase, three phase etc) but if anyone has any suggestions as to what part of the set up might be causing the interferance, and how I can go about reducing the noise put out.

If anyone needs some more info on the pump motor or the speed controller, just let me know and I will get back to on the specifics. Thanks.

G

 

[gerty]

We had a problem with VFD's (variable frequency drive) causing interference problems.. We made sure the drive enclosure was grounded and switched over to a metallic flexible conduit, from plastic, and that cured the problems..

 

[Nigel Goodwin]

Just wondering if anyone could give me some advice about reducing or eliminating noise from an AC motor and its speed controller.

It depends entirely on the type of motor and speed controller, you say 'AC motor', is it really just an AC motor?, or a universal AC/DC motor?. An AC/DC motor has brushes, which wear out and cause RF interference, also the speed control method is prone to cause RFI as well!.

 

[stevez]

It sounds like the speed control is a VFD, Variable Frequency Drive. I am told they are extremely noisy. A freind of mine sells these - all very reputable brands. They can be had with the bare essentials for speed control or fully equipped including Radio Frequency Interference suppression equipment. The difference in cost is profound. As an example he said he could sell me a 3 hp, 3 phase controller without enclosure, reactors, etc for $150 for use at home (on machine tool) but warned me that my neighbors would hate me because of the interference. The same drive, with enclosure, disconnect and equipped for suppression, was near $600.

You might contact the pump and drive mfrs. I am told that 'line reactors' are what an engineer might mention in a specification to be sure that some kind of RFI suppression is supplied.