Micro VFDs

[itsmoked]

I have to run a 1/4hp 3ph motor with a VFD as quietly as possible.

I'm told that one of the biggest tools in this noise level reduction effort is the ability to reduce the "excitation" current.

What is the name for this in VFD land?
Field weakening?
V/Hz?

Is the needed parameter available in most micro VFDs? Or only on some? Name names?

Are there any VFDs that are known to provide exceptionally quiet results right out of the starting gate?

Since this is such a small motor I'm hoping I can do this with a voltage doubling 120VAC input model.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Skogsgurra]

Keith, you are welcome over here to listen to a variable speed motor you have to watch to see it running. You can't hear it.

I'll send you a short video - with sound.

Gunnar Englund

http://www.gke.org

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[Skogsgurra]

It's on its way to San Diego now. 50 MB of sheer poetry and delight!!

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[itsmoked]

I wait with baited breath!

Keith Cress
kcress -

http://www.flaminsystems.com

 

[dpc]

I would suggest a change order to provide for field investigation in Sweden! And perhaps a sub-consultant..

 

[Skogsgurra]

Good idea! But I finally got it out of mys house. Hope it got to your place, Keith!

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[ScumPunk]

Hi, Keith,
The most likely way that you can reduce the audible noise from a VFD is to increase the switching frequency (sometimes called Pulse or carrier frequency). Once this gets above 10-12kHz it should become much quieter. Without wishing to promote my own company, Siemens Micromaster 410 is available as 110V 1 phase input / 230V 3 phase output, with a maximum pulse frequency of 16kHz. The default is 8kHz, and there is a derating if it is increased, but if you used a higher rated unit you could still get full power continuously.
The trade-off between noise and power is the main thing you would have to check on, I expect. At this size of drive, there's unlikely to be a fan fitted. I've not heard of any other way of reducing the acoustic noise from a VFD, but uthers may know different.
Cheers,
Mort

 

[itsmoked]

Gunnar... I think you blew up AT&T. That mail server has gone down in the last 20 minutes.

I have not received it. It is probably being bounced in it's totality back to your inbox. LOL

I sent you an email(edm) of a link you can send it to, that won't choke to death.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[sreid]

Look at a Delta Electronics VFD-S which comes in a 1/4 HP 120 VAC version. The max switching frequency is, however 10 kHz but my experience is that most motor noise comes from the bearings. Magnetostrictive noise should not be a problem in a small motor. Delta has good pricing.

 

[jraef]

I'm told that one of the biggest tools in this noise level reduction effort is the ability to reduce the "excitation" current.

Keith,
This sounds to me like some of the marketing rhetoric I hear spewing from people selling "energy savers" that use the Nola circuit to reduce the voltage to unloaded motors. The noise reduction is often touted as a side benefit, some even going so far as to claim that the sound energy represents wasted energy and therefore additional savings. The drawback to this is that it only applies if the motor is unloaded, typically by at least 50%. A loaded motor will get full voltage, therefore no side benefits.

VFD noise reduction is based on the ADDITIONAL noise that VFDs usually cause the motor to produce, meaning that there are ways, as described above, to mitigate it up to the point of there being no noticeable noise GAIN. But I have never heard of using a VFD to reduce normal noise in a motor, other than the wind noise reduction on fan cooled motors because of running them slower. At full speed, I would hazard to guess that a VFD driven motor will be, at best, no more noisy than one without a VFD.

I am open to learning, but I am skeptical.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[DickDV]

I basically agree with jraef's comments above. There is one little game that might be played other than using the maximum carrier frequency available on the drive.

First, if this is a centrifugal load(fan or pump), be sure the V/Hz ratio is set to squared, not to linear. That at least will minimize the motor magnitization in the midrange of speed.

Second,if your motor is not fully loaded at full speed, you might experiment with entering a lower motor nameplate voltage. You could keep lowering it until the motor amps at full speed reach nameplate FLA. This further reduces motor magnitization current and might (that's MIGHT) cut noise a bit further.

Finally, a TENV motor will likely run the quietest, all other things being equal since there is no exposed fan.

 

[itsmoked]

Thanks gentlemen. I suspect the guy who suggested this to me was using it in a pump application and at less than full speed.

Your argument/description certainly makes sense Jeff(as usual).

Thanks for that squared/linear tip DickDV.

sreid, I am looking at your Delta recommendation. Thanks.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[LionelHutz]

Some of the larger drives use carrier frequency modulation or spread spectrum type of control to spread out the carrier noise and eliminate the characteristic VFD whine. I'm doubtful though that any really small VFD's will come with that feature.

 

[Skogsgurra]

Spread spectrum is even worse than the whining. Siemens used to have it. Even gave that parameter a name "Simosound". Sounded like you got gravel in the bearings and your head felt "empty" after being exposed to the Simosound for only a few minutes.

Gunnar Englund

http://www.gke.org

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