electrical noise ? 2

[PaulLag]

Hello All,
hope everybody is fine.
If I have posted in the wrong section, I do apologize, just suggest me the right one.
Please, I would like to share with you following odd experience I am facing.
I have utilized two AC 220V fans.
One of them is from 2015, the other is recently manufactured.
They have got the same label name and, after a visual inspection they seem identical.
Same blade, same condenser.
I have tested them in the same electrical feeding condition, stabilized by a voltage stabilizer.
The same air flow and electrical consumption is absolutely comparable.
Nonetheless, the recent one produces a more grave sound
I tested them on the same application, so that I would exclude phenomena as aeolian sound or similar.
The sound is disappearing once I reduce the voltage.
Following are my questions
- Have ever any of you experienced something similar ?
- could this difference be generated by a different material utilized in rotor in stator ? Unfortunately my knowledge is not deep in this specific subject, so that I would assume that since they utilize copper, It would not affect
In other words, may the copper type have influence on the generated noise ?
- please, have you got any other ideas ?

I thank you in advance for any suggestion

 

[GregLocock]

Please post the spectra you have looked at and the rpm and number of blades of the fan. A photo might be a good idea as well


Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[electricpete]

> - Have ever any of you experienced something similar ?

Noise that varies among motors, yes. Electrical related noise that varies among motors, yes.

> could this difference be generated by a different material utilized in rotor in stator ? Unfortunately my knowledge is not deep in this specific subject, so that I would assume that since they utilize copper, It would not affect. In other words, may the copper type have influence on the generated noise ?

There are a wide variety of causes of noise that varies among motors, electrical or otherwise (and I agree decreasing noise with decreasing voltage suggests electrical origin). A change in type of copper type used during remanufacture would be very far down near the bottom of my list.

I think capturing the frequency content of the noise like Greg suggested is a great starting place to narrow things down. Personally I use a free app spectroid for Android that does a great job of live display of spectrum, and also color-coded spectrogram showing changes over time (you can walk toward and away from source of noise to help narrow down which frequencies come from this equipment in noisy environment).

With all that said, I wouldn't get your hopes up to get a good diagnosis. Vibration tends to be a better diagnostics tool than noise imo (it is studied more, the patterns are more understandable and repeatable). And actual electrical problems on motors tend to be among the more difficult to diagnose from noise/vibration than mechanical problems.... I generally require more data before reaching any conclusion about electrical sources noise/vibration compared to mechanical sources which often are are very distinctive (example rolling bearing defect)

Also it would be useful to know your reason for asking about the noise. Is the noise itself a problem for people nearby, or are you just worried that it might indicate a problem with the motor?

=====================================
(2B)+(2B)' ?

 

[Tmoose]

what's the frequency Kenneth ?

https://danratherjournalist.org/abo...equency-kenneth/video-whats-frequency-kenneth

 

[PaulLag]

Hello all

first of all, I'd like to thank you for your answers.

@electricpete
first and foremost.
Yes, this fan is utilized in an equipment utilized in a closed room where people work.
therefore, this is the main problem.
As I wrote, having the same air flow, we have the same performance.

@GregLocock & @electricpete
I will try to measure the spectra in the next days.
Please note, the fan is an AC fan with fixed speed.
The one from 2015, with same number of blades, doesn't produce the same sound.


Will keep you updated.
Thanks

 

[3DDave]

Is there a model number for the fan? Are the bearings identical? Is there a difference in clearance in the bearings? Are the fan blades shaped the same? Do they have the same tip clearance? Is it possible the newer fan is just junk and made by careless workers? Is the newer fan blade/motor mechanically unbalanced?

 

[matias correa]

-The blades of both fans should be very clean as dirty blades can cause vibrations.
-Make use of a thermal camera or a thermometer to determine the temperature of the bearing support. If the temperature is above 60° (depending on the machine), you may have a faulty bearing.
-The lubrication can also be checked, as poorly lubricated elements can rotate incorrectly.
-Check the vibrations of the equipment; it may be misaligned or you might have bearings that are defective

Bearings that are defective

 

[hydtools]

Could be different tightness of the coil windings or physical bonding.

Ted

 

[PaulLag]

Hello All

I apologize for the delay, but was the time to have delivered a phonometer with spectrum analysis.
Just to confirm that It has been measured a very high noise @ 250Hz and 500Hz - and only at these frequencies - in the new fan with respect of the old one.
The difference was over 16 dB
Now I'll try to hear the supplier of the fan

I'd really like to thank you all for your help
really appreciated