# Motor "singing" (high frequency noise) using VFD



## itsme_Bernie (Apr 12, 2013)

First, I am mad I EVER sold the old, quiet motor I had a few years ago.
I'll save the story of why I ever sold it.

My issue is I have this new, lightly used Baldor 3PH, 1/2 HP motor from a reputable seller on EBay.

I DOES work.  It is just not nearly as QUIET as my lovely old motor.  It makes an electronic "singing" noise at normal speed and at lower rpm when dialed down with the VFD.

It is an a vertical head right in front of me, or I wouldn't really care.

Do I have phases swapped around?  Or is this motor just loud??  ACK
I was hoping to run this past you guys just incase there was something I could possibly do so I can enjoy using it.  

I appreciate any advice or experience.


Bernie


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## itsme_Bernie (Apr 12, 2013)

Btw, the noise pretty much goes away, or is drowned out at 2000+ rpm


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## CluelessNewB (Apr 12, 2013)

You may want to try changing the carrier frequency of your VFD.  This helped significantly on a sander I have with a "Huanyang" VFD I purchased on Ebay.  The same motor did not make the noise when hooked to a Teco VFD.


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## 8ntsane (Apr 12, 2013)

Bernie

I have heard a few motor/VFD combo,s that wine or sing as yours does.
One thing that comes to mind, is the use of shielded wiring. I know most guys don't bother with it, and have no issues, Just a thought.

I have a few VFDs in my shop, and the motors don't wine at all. You might want to give the maker of the VFD a call, they probably have a tech line, they may shed some light on your problem.


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## itsme_Bernie (Apr 12, 2013)

Thanks Guys

I will certainly try the carrier frequency CluelessNewB...  I would be lucky if it was that easy!! 

Thanks 8ntsane.  I am using crazily insulated 10 guage industrial wire, but didn't even think of shielding!   Hah, if I get desperate, I'll rewire, or find a way to shield these outside?  I'll see if it gets to that.

 I'll let you know later tonight!


Bernie


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## DMS (Apr 12, 2013)

Mine still does it, but I purchased a line reactor, and ran through the "auto tune" mode on the VFD. Better now.


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## itsme_Bernie (Apr 12, 2013)

Can't call you clueless anymore Clueless!  Hah hah

For now, adjusting the Carrier frequency (didn't even know that existed before) did most of it.

I am HAPPY, whew.  At least I can work with it like this- I was pretty much kickin my-damn-self with this new motor.  

This is a Teco FM100 201 (1HP) 220V phase converter.  I really have to go through these settings and fine tune this thing.  

But there are 100 custom functions!! Hah hah!  Any advice on other important ones?  


Bernie


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## Ray C (Apr 13, 2013)

The squealing sound is definitely from the carrier frequency.  There's a sweet spot with at least two considerations.  The higher the frequency, the motor runs more efficiently but, the VFD runs hotter.  I'd suggest bumping up the carrier just until the noise stops bugging you and don't go much higher (at least in the warmer months when the unit will have a harder time cooling off).  Also, as carrier frequency increases, conducted and radiated emissions increase -meaning, it's more likely to cause interference with radios and TVs.  Shielding the wire between the motor and the VFD will help the radiated emissions.  The shielding must be grounded to have any effect at all.  Chokes are available to filter the input line feeding the VFD.  There are two kinds, one is a passive inductor that just snaps over the input cord with a plastic case.  Another is an active inductor/capacitor in series with the line.  You can only use one type at a time and either will cut down on the conducted emissions.

To a much smaller extent, there are radiated emissions coming from the unit itself.  Enclosing the VFD in a proper panel box will help a little but not too much because panel boxes are rated for fire/explosion containment -not electro-magnetic containment.  -But it will help a little if the box is grounded.

Ray


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## Rbeckett (Apr 13, 2013)

You could enclose the VFD in a Faraday Cage to reduce radiated noise, but it is sort of expensive and time consuming to build one that may or may not eliminate you particular radiated signal.  Just a thought anyway..
Bob


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## itsme_Bernie (Apr 13, 2013)

Thanks guys- 

The sound is actually coming straight out of the motor itself! The VFD is silent, that I can tell.  I will double check again later.

I could try shielding the wire, which sounds like a good idea anyway.  The setting options go 1-15, and the factory setting was 14.  I now have it on 11.  (Funny "Spinal Tap" movie connection there hah hah)

When I muffle the actual motor vent with my hands, it muffles the sound.  Let me see of I have a pic somewhere...


Bernie


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## olduhfguy (Apr 13, 2013)

Bernie -

I don't know for sure why the engineers decided to use audible frequencies for their pulse rate on motor drives but the low-end DC PM machines like Sieg sure do - It's right around 1000 Hz. I don't think the technology of the day allowed for higher PWM frequencies, because it would require much faster switching times for the Mosfets and fast recovery diodes. A lot of the newer ones seem to be 25-30khz so are out of the range of human hearing. Now, the SCR controllers run at 60 Hz so they just 'hum'.....

-Pete


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## DMS (Apr 13, 2013)

You're right, the sound is coming from the motor, but it's caused by the way the VFD is generating the 3 phase. Basicically the VFD is turning the power on and off very fast. This can cause the mechanical portions of the motor to vibrate slightly, and if the frequency of the switching is below 20kHz, that vibration will be audible. A line reactor will smooth that out a bit too.

I may try playing with the switching frequency of mine, I saw it listed as a parameter, but I figured the auto tune would deal with that.


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## Ray C (Apr 13, 2013)

To a large extent, it's because of the hysterisis properties of the rotor and stator materials...  What's optimal for a motor is not optimal for the power source so it's a tradeoff.  And yes, much if it is in the audible/perceptable range and unless you use some very expensive materials for the cores, it shall remain that way.

Ray



olduhfguy said:


> Bernie -
> 
> I don't know for sure why the engineers decided to use audible frequencies for their pulse rate on motor drives but the low-end DC PM machines like Sieg sure do - It's right around 1000 Hz. I don't think the technology of the day allowed for higher PWM frequencies, because it would require much faster switching times for the Mosfets and fast recovery diodes. A lot of the newer ones seem to be 25-30khz so are out of the range of human hearing. Now, the SCR controllers run at 60 Hz so they just 'hum'.....
> 
> -Pete


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## stevec (Apr 15, 2013)

A possible cause could be that the windings in the motor are loose and vibrating at the switching frequency. if this is the case then dunking the windings in transformer varnish is about the only cure.
Talk to a motor rewinder if this appears to be the case.

Steve


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## Ray C (Apr 15, 2013)

That's about the size of it.  If anyone still re-winds motors, it would probably help but, there's also a thermal component.  There's a miniscule amount (but it's additive over surface area) of temperature change which, believe it or not, makes sound as the  surrounding air changes density.  I've got all kinds of oscillators soldered to boards and you can hear them.  Also, some of the noise is coming from the capacitors and inductors inside the VFD unit itself...



stevec said:


> A possible cause could be that the windings in the motor are loose and vibrating at the switching frequency. if this is the case then dunking the windings in transformer varnish is about the only cure.
> Talk to a motor rewinder if this appears to be the case.
> 
> Steve


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## itsme_Bernie (Apr 17, 2013)

Thanks guys- 

What the heck would that cost? 

Dangit- I thought i would get a Baldor motor and be "set"!!  It is much louder than the lovely old ones.


Bernie


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