EMI Comparison between AC, Brushed, and Brushless Motors

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om_tech_support_JT
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EMI Comparison between AC, Brushed, and Brushless Motors

Postby om_tech_support_JT » Tue Mar 06, 2012 11:24 am

Q: Which motor exhibits the most electrical magnetic interference/noise between AC motors, brushed DC motors, and brushless motors?

A: If we look at the 3 motor's design, construction, and characteristics, the brushless motor would likely exhibit the least amount of EMI. The bearings of both an AC motor and a brushless motor are the only rotating parts. The brushed motor also has rotating brushes to commutate its windings. The brushes of a brushed motor generate some EMI. The current losses resulting from the inefficiency of an AC motor also generates EMI. The brushless motor is more efficient than AC motors so its current losses are lower, which means less EMI.

In addition, we also need to look at EMI generated by the respective controllers or drivers of these motors as well to make a complete comparison. AC inverters which generate sine waves, like our FE series inverters, will output cleaner noise. Some say some brushless motor system generate more erratic noise since it generates square wave pulses. However, components we have in today's driver designs as well as measures to reduce EMI makes this comparison very difficult. Testing is the best method to find out.

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