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

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

"Steve Smith" wrote in message
...
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

On Sun, 10 Apr 2005 11:16:30 -0500, "R. O'Brian"
wrote:

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

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


"Steve Smith" wrote in message
...
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



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

Strider

R. O'Brian wrote:
The motor is the problem. ...

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

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:

On Sun, 10 Apr 2005 11:16:30 -0500, "R. O'Brian"
wrote:



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



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



"Steve Smith" wrote in message
...


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




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

Strider

So I need to try a couple more things to know where the problem lies.

Thanks people,
Steve

Bob Engelhardt wrote:

R. O'Brian wrote:

The motor is the problem. ...


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

On Sun, 10 Apr 2005 17:12:48 -0400, Bob Engelhardt
wrote:

R. O'Brian wrote:
The motor is the problem. ...

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

The Mitsubishi drives I have at home allow modification of the PWM
frequency. Allen-Bradley drives I use at work do as well. Changing
this frequency may reduce the noise generation, particularly if it
moves away from a mechanical harmonic frequency.

Pete Keillor

Steve Smith wrote:
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).
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

The second vfd is running at a pwm freq. that your motor does no respond to.
Motor susceptibility to "singing" varies all over the place depending on
motor size, insulation system, enclosure, mass, air gap, etc. There are
many variables.

Virtually all small vfd's generate very similar waveforms. The main
variable is the pwm freq. This is user adjustable on most vfd's and is
provided by the manuf. to help eliminate or suppress "singing", as many
users think the noise is detrimental or annoying. The only other way is to
install a reactor between the vfd and the motor. However, this is
expensive, inefficient, and takes up space.

Randy


"Bob Engelhardt" wrote in message
...
R. O'Brian wrote:
The motor is the problem. ...

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

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 bone tired from limping around
after falling on the stairs

Jon Elson wrote:

Steve Smith wrote:

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).

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

Jon Elson suggested a reactor as well (thanks guys). I thought about
this, but was worried about creating excessive voltages at the VFD. Has
anyone actually used a reactor to filter a VFD output?

Steve

R. O'Brian wrote:

The second vfd is running at a pwm freq. that your motor does no respond to.
Motor susceptibility to "singing" varies all over the place depending on
motor size, insulation system, enclosure, mass, air gap, etc. There are
many variables.

Virtually all small vfd's generate very similar waveforms. The main
variable is the pwm freq. This is user adjustable on most vfd's and is
provided by the manuf. to help eliminate or suppress "singing", as many
users think the noise is detrimental or annoying. The only other way is to
install a reactor between the vfd and the motor. However, this is
expensive, inefficient, and takes up space.

Randy


"Bob Engelhardt" wrote in message
...


R. O'Brian wrote:


The motor is the problem. ...


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

Peter T. Keillor III wrote:

On Sun, 10 Apr 2005 17:12:48 -0400, Bob Engelhardt
wrote:



R. O'Brian wrote:


The motor is the problem. ...


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



The Mitsubishi drives I have at home allow modification of the PWM
frequency. Allen-Bradley drives I use at work do as well. Changing
this frequency may reduce the noise generation, particularly if it
moves away from a mechanical harmonic frequency.

Pete Keillor


I've tried a number of frequencies with no effect. I should continue and
try the rest.

Thanks,
Steve

On Mon, 11 Apr 2005 20:03:48 -0400, Steve Smith
wrote:

Jon Elson suggested a reactor as well (thanks guys). I thought about
this, but was worried about creating excessive voltages at the VFD. Has
anyone actually used a reactor to filter a VFD output?

Steve



Allen-Bradley sells line reactors for both the load and line sides of
a vfd. Apparently they are useful with noisy power or long leads.
I've never used them, but most of my motor leads are under 10'. The
link below is their tech bulletin for line reactors.

http://literature.rockwellautomation.com/idc/groups/literature/documents/td/1321-td001_-en-p.pdf

Pete Keillor

R. O'Brian wrote:

The second vfd is running at a pwm freq. that your motor does no respond to.
Motor susceptibility to "singing" varies all over the place depending on
motor size, insulation system, enclosure, mass, air gap, etc. There are
many variables.

Virtually all small vfd's generate very similar waveforms. The main
variable is the pwm freq. This is user adjustable on most vfd's and is
provided by the manuf. to help eliminate or suppress "singing", as many
users think the noise is detrimental or annoying. The only other way is to
install a reactor between the vfd and the motor. However, this is
expensive, inefficient, and takes up space.

Randy


"Bob Engelhardt" wrote in message
...


R. O'Brian wrote:


The motor is the problem. ...


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

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.

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

Thanks! If the final motor makes too much noise, I'll pursue a reactor
(probably at the scrap yard..)

Steve

Peter T. Keillor III wrote:

On Mon, 11 Apr 2005 20:03:48 -0400, Steve Smith
wrote:



Jon Elson suggested a reactor as well (thanks guys). I thought about
this, but was worried about creating excessive voltages at the VFD. Has
anyone actually used a reactor to filter a VFD output?

Steve





Allen-Bradley sells line reactors for both the load and line sides of
a vfd. Apparently they are useful with noisy power or long leads.
I've never used them, but most of my motor leads are under 10'. The
link below is their tech bulletin for line reactors.

http://literature.rockwellautomation.com/idc/groups/literature/documents/td/1321-td001_-en-p.pdf

Pete Keillor



R. O'Brian wrote:



The second vfd is running at a pwm freq. that your motor does no respond to.
Motor susceptibility to "singing" varies all over the place depending on
motor size, insulation system, enclosure, mass, air gap, etc. There are
many variables.

Virtually all small vfd's generate very similar waveforms. The main
variable is the pwm freq. This is user adjustable on most vfd's and is
provided by the manuf. to help eliminate or suppress "singing", as many
users think the noise is detrimental or annoying. The only other way is to
install a reactor between the vfd and the motor. However, this is
expensive, inefficient, and takes up space.

Randy


"Bob Engelhardt" wrote in message
...




R. O'Brian wrote:




The motor is the problem. ...




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