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Slip rings require regular maintenance and add mechanical complexity.
* More mechanical and acoustic noise, especially during start-up under load.
* Generally lower efficiency than squirrel-cage motors.
* Larger physical size for a given power rating.
* Not fully enclosed, increasing exposure to moisture and dust and limiting use in hazardous or damp environments.
* Often displaced in modern applications by induction motors with variable-frequency drives or permanent-magnet synchronous motors.