Determining the source of noise in an electric motor is often more challenging than correcting it. A methodical investigative approach, however, can narrow the possibilities and make it easier to resolve the issue—with one caveat. If the noise is due to something in the motor design (e.g., a manufacturing defect or anomaly), a solution may be impossible or impractical. With that in mind, let’s review the primary sources of noise in electric motors—magnetic, mechanical, and windage—as well as their causes and ways to reduce or eliminate them.
Magnetic Noise
(Note: All noise originates with mechanical forces that transmit waves of pressure through air, liquids, or solid materials. Noise frequency components within the range of human hearing generally fall between 20 Hz and 20 kHz.) Magnetic noise in a motor (a.k.a. “electromagnetic” or “electrical” noise) results from mechanical forces (e.g., pressure) generated by the attraction and repulsion of magnetized parts in its alternating magnetic field. The alternating magnetic field excites vibration and noise at twice line frequency (e.g., hum) but only while the motor is energized. (Tip: If the noise immediately stops when the power is removed, its source is magnetic.)
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