split phase what does it mean? Also why use a capacitor. purpose
I have motor 1/4 hp. 1725 rpm 115 V for a cone roof exhaust fan .
The split phase motor is a single phase motor that has two windings, a start and a run winding. The start winding is made with smaller gage wire and fewer turns relative to the run winding to create more resistance, thus putting the start winding's field at a different angle than that of the run winding, and causing the motor to rotate. The run winding, of heavier wire, keeps the motor running the rest of the time.
A split-phase motor uses a switching mechanism that disconnects the start winding from the run winding when the motor comes up to about 75% of rated speed. In most cases, it is a centrifugal switch on the motor shaft.
The split-phase motor's simple design makes it typically less expensive than other single-phase motor types made for industrial use. However, it also limits performance. Starting torques are low, typically 100% to 175% of rated load. Also, the motor develops high starting currents, approximately 700 to 1,000% of rated. Consequently, prolonged starting times cause the start winding to overheat and fail; so don't use this motor if you need high starting torques.
Other split-phase motor characteristics: Maximum running torques range from 250 to 350% of normal. Plus, thermal protection is difficult because the high locked-rotor current relative to running current makes it tricky to find a protector with trip time fast enough to prevent start-winding burnout. And, these motors usually are designed for single voltage, limiting application flexibility.
Good applications for split-phase motors include small grinders, small fans and blowers, and other low starting torque applications with power needs from 1/20 to 1/3 HP. Avoid any applications requiring high cycle rates or high torques.
Split phase motors do not use capacitors.
Capacitors are used on capacitor start, capacitor start/run, and Permanent split capacitor motors. Start capacitors help increase the torque in the start windings and run capacitors help with the efficiency of the run windings.