Graphic illustration of three-phase motor changing to single-phase operation


There are two wiring methods for changing three-phase m […]

There are two wiring methods for changing three-phase motor to single-phase operation. Today we will briefly analyze them.

First, when the three-phase motor is star connected:

Second, when the three-phase motor is triangular connection:

The key point of positive and negative inversion is to change the connection of capacitor terminal.



1. Calculating Method of Capacitance Capacity


Starting capacitance and running capacitance calculation formula, running capacitance formula: C=1950I/Ucos phi, C for running capacitance capacity (uf- micro method) I is the motor rated current value (A) U is rated voltage, since we here is to change the single-phase operation, so the rated voltage value is 220 volts.Cos phi is a power factor, many motors are labeled, starting capacitance is generally running capacitance 1--4 times.


2. Empirical Formula of Capacitance Capacity


100W power corresponds to the capacity of 7 microfarad, that is to say, about 70 microfarad capacitance of 1KW motor is ok.This value is only an approximate number, can be adjusted according to their own load.It is only recommended to change the motor below 1.5kw. After modification, the power will attenuate, and heavy load cannot be carried. If the power is slightly greater than 1.5kw, another starting capacitor needs to be added.