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issue: October 2006 APPLIANCE Magazine - Part 2: Motors & Air-Moving Devices

Motors and Air-Moving Devices
Quiet Control

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by Erin Biesen, Associate Editor

Broan-NuTone worked with A.O. Smith on proprietary motor controls that cut down the noise in kitchen ventilation appliances.

The new motor control design has potential to be used on products such as the Best by Broan line.

Homeowners always want quieter kitchens. At the end of summer 2005, Broan-NuTone determined to reduce the sound level from its kitchen fans. Greg Bird, director of engineering for kitchen ventilation at Broan-NuTone, explains that, “Basically people don’t want to hear any kinds of noise other than a quiet air-flow. Our goal was to deliver just that.”
The OEM, assuming the noise issues were simply in the motor, turned to A.O. Smith Electrical Products Company, a longtime supplier of motors to the company. The companies work closely together on such a variety of products that they have monthly meetings.
A.O. Smith immediately began testing, including extensive testing in its Corporate Technology Center in Milwaukee, Wisconsin, U.S. It also turned to its Tipp City, Ohio, U.S. test center for some of the analysis. “We did some of the initial sound analysis and vibration tests in Milwaukee, and then sent that report down to the sound and vibration expert down at Electrical Products in Tipp City,” says Ron Bartos, director of the Advanced Motor and Electronics Department. “They have a Ph.D. engineer that runs the sound lab and she verified our results.”
The detailed sound analysis showed Broan-NuTone that the motor by itself operated at a typical noise level, and was adequately quiet for Broan-NuTone’s application. However, when the motor control was installed and the motor ran at the same speed the noise increased, which was due to the high frequency harmonics being generated on the power line.
“They were using a triac control, which operates very similar to a light dimmer,” says Bartos. “It generates a lot of high frequency electrical noise, which created a noticeable acoustic noise, especially in a final end product like a blower and a range hood where the sheet metal can transmit noise very effectively.”
A.O. Smith suggested using an alternative electronic control, more sophisticated than the triac, to help reduce the noise. Bartos explains that the new electronic control segments the applied sinusoidal voltage into small sections and reduces the voltage by removing small high frequency components of the incoming voltage waveform.
“The peak offending noise frequency was reduced by more than 12 dB,” Bartos notes. “The dB scale is a logarithmic scale, and any time you drop 3 dB you are reducing the power by half.”
Broan-NuTone made the decision to switch to the electronic control. Each company had its role in the project. Broan-NuTone had the initial raw concept of the motor areas that needed to be worked on, and A.O. Smith helped with the identification of the motor control opportunity during the test phase. A.O. Smith then designed the circuitry to address this area. Now, Broan-NuTone is taking the motor control through the final design changes of incorporating it into the end products, and UL certification, production and circuit board layout.
Designing the circuitry took about 1 year, but once the new control was hooked up they saw immediate results. There is still some testing to be performed and then the control will go through implementation at a manufacturing level. The appliance maker has yet to determine the specific product lines that the new motor control will be placed in, but it is currently looking at its Best by Broan® line.
Both companies feel they achieved their goals, and the OEM has come across no problems or issues in the incorporation of the new control. Bird says, “We did a lot of homework up front and A.O. Smith did a lot of homework up front and together we came up with a pretty viable design.”
“Broan-NuTone probably spends more time on sound quality than any other single area of development outside of aesthetics,” says Bird. “From a pure engineering point of view we spend an awful lot of resources at blower wheel design, motor
application, speed control, ducting, and in general how the sound quality can be improved in all of our product lines that move air.”

Suppliers mentioned in this article:
A. O. Smith
Broan-NuTone LLC

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