1. Single Phase AC Motors

2. Operation
A 3 phase motor self starts due to a rotating magnetic field in the windings
If a single phase was applied to one winding, it would simply pulse and produce no torque
If we could simply ‘push’ the rotor, it would begin to spin for the same reasons in a 3 phase motor

3. Operation To make the spin happen, we add a start winding to the motor
A start winding usually has the same number of turns as the run winding but a smaller diameter wire
This creates an inductive reactance causing the current to lag

4. Split Phase Motor A split phase motor has 2 windings: Run winding
Start winding

6. Split Phase Motor
The two windings cause the current to lag depending on the inductive reactance of each
This mimics the effect of a changing magnetic field
Once started, the switch cuts out to stop burning out

8. Split Phase Motor
Can be reversed by changing connections to any one winding
Has a high starting current
Used in simple domestic machines

9. Capacitor Start Motor Similar in effect to the split phase motor
Capacitor causes current in start winding to lead voltage
Start and Run windings are approximately 90° out of phase

10. Capacitor Start Motor High torque
Used in compressors, refrigerators and when high torque starting is needed

11. Capacitor Start – Capacitor Run Motor
2 capacitors are connected in parallel with the start winding
Once started, the first capacitor cuts out and leaves the second to continue to maintain an out of balance magnetic field

12. Capacitor Start – Capacitor Run Motor
This type is similar to the last but has:
Better torque
Improved power factor