Lexicon DIY-Knowledge

Single-phase AC motor


Motor de corriente alterna monofásica

Moteur à courant alternatif monophasé

The universal motor or series-wound motor is probably the most common single-phase alternating current motor. A rotary current asynchronous motor can also be operated as a single-phase motor by means of a special circuitry. Since any rotary current motor can be run on two different voltages ? the most common type is the 220/380 V version ? we have shown here the star connected circuit for 3 x 400 V (Fig. A) and the delta connection for 3 x 230 V (Fig. B). If a three-phase 230/400 V motor is switched to single-phase operation, the delta circuit of Fig. B has to be chosen: on the terminal board, the terminals have to be connected vertically.

The mains feeder wire R is connected to terminal U, the neutral conductor M to terminal V. A running capacitor has to be placed between terminals V and W for clockwise rotation. If, however, the capacitor is placed between terminals U and W, counterclockwise rotation is obtained. See Fig. C and D.

Rule of thumb for the calculation of the running capacitor:

100 watt output power × 8 µF
The output power drops in this circuit by 1/3 of the power as rotary-current motor, the starting torque even to 1/3. These machines are hard or impossible to start on their own which means that a starting condenser would have to be used for the initial start-up phase.

Other types of single-phase AC motors such as the repulsion or Deri motor are rarely used today.