Buzzing noise after VFD conversion

7milesup

7milesup

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After collecting all my electrical parts I was finally able to get my (new to me) Sharp knee mill running today. It was a bit of a process with the wiring and the programming of the VFD, which is a Lapond brand. https://www.amazon.com/dp/B075M8R77M?ref=ppx_yo2ov_dt_b_product_details&th=1

The issue is there is a buzzing noise emanating from the motor. It is about the same frequency as my tinnitus, so I had to have my daughter come and take a listen. Yep, it is there. One of the parameters that I changed in the VFD was the "carrier frequency" from 12kHz to 16khz, which helped ever so slightly, but not enough. If I lower that number below 10kHz the buzzing becomes prominent.

Would anyone have any thoughts on what else could be causing that, or is this just the way it is? The motor on this mill is a 230v, 3ph, 8A, 1720rpm flavor, and the original motor I might add, which I would like for it to stay that way. I am considering purchasing a different VFD but not sure if that would make any difference. Would love to get a Durapulse from Automation Direct but it seems that they are perpetually out of stock. I am considering a Teco or a Hitachi, but maybe that would not make any difference other than I could then say I have a "name brand."
 
Usually changing the carrier frequency fixes the issue. That has worked for me with Teco units. A filter(choke) between the vfd and motor may help if the vfd manufacturer supports such a thing. Others with more experience may have better advice.
 
High frequency pitch is from the carrier frequency, most of use it is not noticeable after 12kHz. Also make sure you auto tune the VFD to the motor, this can tweak the VFD internal parameters and it can make the motor run smoother and quieter. The noise is more prominent the lower the Hz setting.
 
I watched a Clough42 video where James talked about the carrier freq. and how it affected the noise so that is what clued me in on it. I am having issues with the auto-tune function, Mark. For some reason it will not complete the process but rather, it just runs in reverse for about 15 seconds and then that is it. According to the manual, the process should take nearly 2 minutes with it running the motor in both forward and reverse.
Would the Schaffner filter that you sent a link to me help in this, or would that primarily just help with any ancillary systems such as the CNC controls? Schaffner RFI Power Line Filter. The CNC controls are fully shielded BTW.
I am very close to pulling the trigger on a WEG VFD from Automation Direct, more because they have a programming software package that looks amazing. WEG CFW300 VFD. The TECO is also very tempting.
 
A line filter will have no effect, that is on the input side. What Rabler mentioned is called a dV/dT filter between the VFD output and the motor (sometimes called sine filters) but these are more for longer cables to decrease the voltage spikes to the motor, they are also used for older motors to decrease the risk of insulation breakdown. I have had a few people use them, but did not make any changes to the motor performance or noise. The reason for your auto-tune running shorter is because it is running it static as opposed to dynamic. The latter requires the motor to not be connected to a load so the motor can turn. I would live with it for now, all VFD's have some degree of wine which is a high frequency buzz. Set the carrier frequency to the maximum, it will not cause any motor issues with newer motors. You could also try increasing the motor speed to 80 Hz and see if that helps.

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7milesup said:
After collecting all my electrical parts I was finally able to get my (new to me) Sharp knee mill running today. It was a bit of a process with the wiring and the programming of the VFD, which is a Lapond brand. https://www.amazon.com/dp/B075M8R77M?ref=ppx_yo2ov_dt_b_product_details&th=1

The issue is there is a buzzing noise emanating from the motor. It is about the same frequency as my tinnitus, so I had to have my daughter come and take a listen. Yep, it is there. One of the parameters that I changed in the VFD was the "carrier frequency" from 12kHz to 16khz, which helped ever so slightly, but not enough. If I lower that number below 10kHz the buzzing becomes prominent.

Would anyone have any thoughts on what else could be causing that, or is this just the way it is? The motor on this mill is a 230v, 3ph, 8A, 1720rpm flavor, and the original motor I might add, which I would like for it to stay that way. I am considering purchasing a different VFD but not sure if that would make any difference. Would love to get a Durapulse from Automation Direct but it seems that they are perpetually out of stock. I am considering a Teco or a Hitachi, but maybe that would not make any difference other than I could then say I have a "name brand."
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Moving it up to 16khz is getting closer to the uper limits of your hearing so will sound a bit quieter , i personaly dropped my frequency setting down , which made the buzz much less anoying to me.

I might even have gone down to 1khz to 2khz range.

Stu
 
FWIW, I have about eight VFDs in use. I put one on a motor on my apple packing line and could not quiet the whine. Had to remove the VFD. Guess it seved its purpose, because I learned the correct speed for the output shaft and then made pulley changes to have it run correctly.

I then put the same VFD on a Wells mill with no issue.

Clueless as to why it would whine on one install and not on another.
 
I just went out to the shop and changed the carrier frequency to 4. Nope, not good. Changed it back to 16.
Funny thing is that this mill is quiet enough that I can hear this buzz/whine. My previous mill (PM833T) was so noisy with the geared head that had I converted that one to a VFD operation, I would have never been able to hear it.

I guess the question remains in my mind as to whether a different VFD would still have the whine. I a different VFD would cure it, I would go that route.
 
The noise may be from things moving.

Motor a has just wires where motorb may be better supported where wires cannot move, or the way the windings are wound.

Open the end bell and look at the motor windings, many are tied with cord and coated.

Sent from my SM-G781V using Tapatalk
 
Is the whine changing in pitch to match the carrier frequency? Especially with an off brand VFD, I'm just wondering if you have something like a bad output transistor that is causing the VFD to ouput a messier signal than it should. If you are, male, over 50 and have tinnitus, I'd be really surprised if you could hear 16kHz. I guess it may be a lower frequency resonance in the motor.
 
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