To spin a squirrel-cage rotor in single-phase asynchronous motors, it is necessary that the stator windings create a rotating magnetic field, as in three-phase machines. This is achieved due to the phase shift of the current in the additional winding relative to the main winding due to the inclusion of a capacitor in series with it. It is called a worker, since during the operation of the motor it remains constantly connected (unlike the starting one).

Since the axes (magnetic poles) of the windings are perpendicular, the optimal phase shift is also equal to 90 degrees - it is with this that the maximum efficiency, torque on the shaft and the width of the horizontal section of the motor load characteristic are achieved. This angle and the ratio of the current in the windings directly depend on the capacitance of the working capacitor.

Its theoretical calculation is quite complicated and inaccurate even for fans with their relatively stable and predictable load. In practice, a capacitance of 6-7 microfarads is usually chosen for every 100 W of electric motor power consumption.

Due to reactive processes (especially during start-up and shutdown), the voltage on the working capacitor can significantly exceed the phase voltage. Therefore, you should make a margin of at least 1.15 times. For reliable and safe operation in a ~220 network, capacitors with a rated voltage of 450 V are usually chosen.a