Singing VFD

I have two different VFD's. Both turn a motor (different motors) just fine. One is completely silent (TECO), the other one makes a noticeable and irritating whine (actually the motor makes the noise). The noise is coming from the PWM in the drive.

I haven't tried every PWM frequency, but I have tried about a dozen. They all whine until I get up to 16kHz, where I don't hear it. This would be fine except that above 12kHz the drive is only rated at 80% (2.4HP); I intended to run a 3HP motor with it.

The noisy VFD is a 3HP Cutler Hammer that I just bought. I have it set up for test with 4' of Romex connecting between the VFD and a 3HP motor. The motor is grounded to the VFD and has no load.

I would appreciate suggestions on how to quiet the drive but keep the PWM frequency at 12kHz or below. Will a load change things? Will a different motor change things?

Thanks, Steve Smith

Reply to
Steve Smith
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The motor is the problem. Chances are it is not a high quality motor and this means the windings and laminations are not supported by resin impregnation as well as they could be. Even a high quality motor will make some noise, but it will be more of a hiss than a whine depending on the enclosure type and pwm freq.

Randy

Reply to
R. O'Brian

A quick check would be to pick up a used $5 motor and wire it up while its sitting on the floor and fire the sucker up.

Gunner

Leftwingers are like pond scum. They are green, slimy, show up where they are not wanted, and interfere with the fishing.

Strider

Reply to
Gunner

I'm certainly no expert, but I have a little direct experience with this. I have a 3 ph motor and VFD on my drill press. It is the 2nd VFD. The first one sang, this one does not. Same motor, same wiring.

Bob

Reply to
Bob Engelhardt

It isn't the motor I'll be using the VFD on. I suppose what I should do is get some hydraulic oil and fire up the forging press with it (intended 3HP use).

Gunner, I think your idea is how I got to where I'm at...except it was more than $5.

Steve

Gunner wrote:

Reply to
Steve Smith

Oh, heck, if you're going to be running a hydraulic pump with it, you most likely won't hear the whine. I don't know of ANY hydraulic pump that could possibly be called quiet.

But, if it still is a problem, an output reactor has a chance of helping. It filters the very square output waveform of the VFD to be much more rounded off. This should reduce the magnetic effects that are causing the windings to sing.

Jon

Reply to
Jon Elson

You know Jon, that finally occurred to me. It is getting pretty close to solving the whole thing, except I was planning on also running a (2HP) lathe off of it (NOT hot switching them!). This may be sufficient; the lathe motor is enclosed, so I bet it will be pretty hard to hear 12kHz.

Thanks, Steve whose head would be clearer if he wasn't b> Steve Smith wrote:

Reply to
Steve Smith

I believe that high switching frequencies are hard on the motor. Particulary if the motor is not designed to be used on VFDs.

Reply to
Chuck Sherwood

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