A single-phase split-phase induction motor. A single-phase winding only pulsates and gives no starting torque on its own, so an auxiliary start winding is added, displaced 90° in space. It is made more resistive (thin wire, high resistance) so its current leads the main winding's — this creates a rotating field and the motor starts. Once up to speed a centrifugal switch drops the start winding out. The starting torque is moderate. Such motors are used in fans, pumps and household appliances. The model shows the torque M, the speed n and the state of the start winding.
This page is a utility for simulating single-phase split-phase motor (start winding) online with specified initial values.
Using the model. Close the switch to apply the single-phase voltage — the motor starts thanks to the start winding (the caption reads start wdg on), and once up to speed the centrifugal contact drops it out (start wdg off). Use the "supply voltage" slider and the series rheostat to change the supply: this sets the inrush and, within a small range, the speed. The "load torque" slider sets the load. The scopes show the voltage U(motor) and the current I(motor) — note the inrush spike at start.
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