Re: Increasing the speed on Southbend 10-16” Models. Late 1930s-late 1940s.

Milan Trcka
 

Glenn,
My understanding of the problem lies in the damage to the motor bearings. The high frequency components of the drive currents in the stator generate currents in the rotor. Some of these RF currents flow through the balls of the bearings and erode them through discharge machining. This occurs as the balls roll on the surfaces and some spots generate small arc. As the spark damage progresses, more and more of the sparking is concentrated at the site of the original damage until the bearing fails. Newer motors have brushes that ground the rotor to eliminate this problem. I would expect this problem be less severe in low power motors. But the bearings would be smaller so perhaps not.

One of the articles: https://est-aegis.info/2017/10/how-do-vfds-cause-bearing-damage/

Milan

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