An887, ac induction Motor Fundamentals

FIGURE 5:
TYPICAL CAPACITOR 
START INDUCTION MOTOR
They are used in a wide range of belt-drive applications
like small conveyors, large blowers and pumps, as well
as many direct-drive or geared applications.
Permanent Split Capacitor (Capacitor 
Run) AC Induction Motor
A permanent split capacitor (PSC) motor has a run type
capacitor permanently connected in series with the
start winding. This makes the start winding an auxiliary
winding once the motor reaches the running speed.
Since the run capacitor must be designed for continu-
ous use, it cannot provide the starting boost of a start-
ing capacitor. The typical starting torque of the PSC
motor is low, from 30% to 150% of the rated torque.
PSC motors have low starting current, usually less than
200% of the rated current, making them excellent for
applications with high on/off cycle rates. Refer to
Figure 9 for torque-speed curve.
The PSC motors have several advantages. The motor
design can easily be altered for use with speed control-
lers. They can also be designed for optimum efficiency
and High-Power Factor (PF) at the rated load. They’re
considered to be the most reliable of the single-phase
motors, mainly because no centrifugal starting switch is
required.
FIGURE 6:
TYPICAL PSC MOTOR
Permanent split-capacitor motors have a wide variety
of applications depending on the design. These include
fans, blowers with low starting torque needs and inter-
mittent cycling uses, such as adjusting mechanisms,
gate operators and garage door openers.
Rotor
Main
Winding
Input
Power
Centrifugal Switch
Start Winding
Rotor
Main
Winding
Input
Power
Capacitor
Centrifugal Switch
Start Winding
Rotor
Main
Winding
Input
Power
Capacitor
Start Winding

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2003 Microchip Technology Inc.
DS00887A-page 5