Capacitor Start Motors: Diagram & Explanation of How a In these motors, the necessary phase difference between the Is and Im is obtained by introducing a capacitor in series with the starter winding. The capacitor used in these motors are of electrolytic type and usually visible as it is mounted outside the motor as a separate unit. (click on an image to enlarge it).Author: Sriram Balu What Is an AC Motor Capacitor? | Sciencing Apr 24, 2017A variation of the starter capacitor scheme uses two capacitors: a large one to start the motor, and a smaller one to keep it running. This improves the performance of larger electric motors.