Capacitor-start and capacitor-run motors are types of single-phase induction motors designed to provide improved starting performance and efficiency compared to regular split-phase motors. They achieve this through the use of capacitors, which help control the motor's starting torque and running efficiency.
Capacitor-Start Motor:
In a capacitor-start motor, there are two windings – the main winding and an auxiliary winding. The main winding is designed for normal operation, while the auxiliary winding is used only during starting. A start capacitor is connected in series with the auxiliary winding.
Starting Process:
When the motor is powered, the main winding and the auxiliary winding are both energized. However, due to the phase shift introduced by the capacitor in the auxiliary winding, a rotating magnetic field is created that generates a high starting torque. This high torque helps the motor overcome the inertia of the load and start quickly.
Switching Off:
Once the motor reaches a certain speed, a centrifugal switch disconnects the start capacitor and the auxiliary winding from the circuit. This prevents the capacitor from affecting the motor's efficiency during normal operation.
Efficiency:
While capacitor-start motors provide good starting torque, their efficiency during running is not as high as some other motor types. This is because the auxiliary winding is disconnected after startup, and the motor continues to run on the main winding alone, which may not be optimized for efficiency.
Capacitor-Run Motor:
Capacitor-run motors, on the other hand, are designed to maintain a high level of efficiency throughout both starting and running phases.
Design:
Capacitor-run motors have two windings – a main winding and a permanent capacitor, which is connected in parallel with the main winding. Unlike the start capacitor in the capacitor-start motor, the permanent capacitor in the capacitor-run motor remains connected during both startup and operation.
Starting Process:
The permanent capacitor in the capacitor-run motor helps create a phase shift in the current of the main winding, which produces a rotating magnetic field and sufficient starting torque. This means that the motor can provide good starting performance without the need for additional switches or winding disconnections.
Efficiency:
Capacitor-run motors maintain a higher level of efficiency throughout their operation because the permanent capacitor remains connected. The phase shift caused by the capacitor improves the power factor and reduces the motor's current draw, leading to better efficiency.
In summary, capacitor-start motors are designed for improved starting torque but might sacrifice efficiency during normal operation due to the disconnection of the auxiliary winding. Capacitor-run motors, however, are designed to maintain both good starting performance and high efficiency by using a permanent capacitor that remains connected throughout operation. The choice between these types of motors depends on the specific requirements of the application, balancing the need for starting torque and operating efficiency.