An electric motor start capacitor is a crucial component used primarily in single - phase induction motors to assist in starting the motor. It is usually an AC electrolytic capacitor or a polypropylene/polyester capacitor2.
Working Principle2
Single - phase motors cannot produce a rotating magnetic field from the single - phase current they carry. A capacitor is used for phase - splitting. The purpose is to create a phase difference of nearly 90° between the currents in the two windings to generate a rotating magnetic field. Capacitor - induction motors have two windings: the starting winding and the running winding, which are 90 degrees apart in space. A capacitor with a relatively large capacitance is connected in series with the starting winding. When the running winding and the starting winding are powered by single - phase alternating current, due to the effect of the capacitor, the current in the starting winding leads the current in the running winding by 90 degrees in time and reaches the maximum value first. Rotating magnetic fields are generated in the air - gap between the stator and the rotor, which makes the motor rotate.
Structure and Connection
The motor generally has a cage - type rotor, and the stator has two windings, the main winding and the auxiliary (starting) winding1. The start capacitor is connected in series with the starting winding, and a centrifugal switch is usually connected to the circuit1. During motor starting, the main and auxiliary windings are connected in parallel1. The start capacitor remains in the circuit until the motor reaches about 70% to 80% of its full - speed, at which point the centrifugal switch disconnects the auxiliary winding from the power supply1.
Characteristics5
- Simple Structure and Low - cost: The start capacitor has a simple structure, is easy to use, and has a low cost, which makes it widely used in single - phase motor starting.
- High Starting Torque and Low Starting Current: It can increase the starting torque of the single - phase motor, enabling the motor to overcome inertia and friction during starting and start stably. At the same time, the starting current is small, which is beneficial to energy conservation.
Application Scenarios5
Electric motor start capacitors are widely used in the starting of single - phase motors, such as household appliances (washing machines, air - conditioners, refrigerators, etc.), small mechanical equipment (power tools, water pumps, fans, etc.), and office equipment (printers, copiers, etc.). They are the standard solution for single - phase motor starting in these fields.
Selection and Rating4
The capacitance of electric motor start capacitors generally ranges from 20 μF to 300 μF, and the voltage rating is usually between 250VAC and 450VAC. When selecting a start capacitor, it is necessary to ensure that its voltage rating is at least equal to the rated voltage of the motor, and the capacitance value should be selected according to the motor's power and other parameters.
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