The 220V motor reverses because a single-phase capacitor motor has two windings, the start winding and the run winding. The two windings are 90 degrees apart in space. A capacitor of larger capacity is connected in series with the start winding. When single-phase alternating current is passed through the run winding and the start winding, the current in the start winding reaches its maximum value first due to the capacitor's action, which makes the current in the start winding overrun the current in the run winding by an angle of 90 degrees in time.
The formation of two identical pulsed magnetic fields in time and space, so that the air gap between the stator and rotor produced a rotating magnetic field, under the action of the rotating magnetic field, the motor rotor to produce induced currents, currents and rotating magnetic field interact with each other to produce electromagnetic field torque, so that the motor rotates.
Initially, people needed some kind of equipment to reverse the need to remove and replace the motor wires, but this method is cumbersome in practice. Later, a clever person installed two gates to change the motor forward and reverse by switching the gates. After a while the reverse switch appeared, this wiring is simpler and reduced in size. Due to the limitations of the contacts, they were only widely used on small motors.
With the birth of the contactor, the motor forward and reverse circuits have been further developed. Can be more flexible and convenient to control the motor forward and reverse, and in the circuit to increase the protection circuit - interlock and double interlock. Low voltage and long distance frequent control can be realized.
Expanded InformationSingle-phase motor uses and models:
Since single-phase asynchronous motors require only single-phase power supply, they are widely used in production, life and other small equipment. But because of its various economic performance indicators are poor, so only made into small power.
China's production of poor horsepower single-phase asynchronous motor, there are several models as follows.
1. BO2 series? Single-phase resistance starting asynchronous motor. Power between 60 to 370W. Characterized by, without any external split-phase components, the use of the secondary winding of its own resistance and start, and the use of centrifugal switch, the end of the start will be removed from the secondary winding. The structure is relatively simple. It has a medium starting torque and overload capacity, so it is suitable for small machine tools, blowers, and medical machinery.
2. CO2 series? Single-phase capacitor starting asynchronous motor. Power between 120 ~ 750W. It is a single-phase motor which is started by increasing the starting torque with the use of external capacitor.
An external capacitor is connected in series in the secondary winding, and at the end of starting, the secondary winding and the capacitor are removed from the power supply together with a centrifugal switch, which, like the BO2 type, turns the motor into one in which only the main winding is running and the secondary winding is idle. Capacitor start motors have a high starting torque but a medium level of overload capacity. It is suitable for air compressors, refrigerators, washing machines, mills, threshing machines, and water pumps.
3. DO2?Single-phase capacitor motor. It is a single-phase motor that utilizes one capacitor to participate in starting and running, and the secondary winding participates in running together with the capacitor and the main winding. Therefore, no centrifugal switch is required. After proper design, the motor runs with an ideal rotating magnetic field, so the motor has good running performance, high efficiency and power factor' and low noise. Its power range of 4 ~ 250W.
Because of the use of a capacitor to take into account the starting and running, weighing the disadvantages of the brake due to the starting time is very short, can only be in the selection of capacitance value, try to meet the need for a longer period of time to run, then select the cheap small value of the capacitor, so the starting torque of this motor is lower, can only be used in the no-load or light-load starting machinery, such as the electric wind helicopter, ventilating fans, tape recorders, etc..
4. double value capacitor motor? This motor is currently no official model, but also in production. Motor power up to 750W, or about 1kW. In foreign countries there are higher power. Due to the larger power, the required capacitor is much more expensive. The starting performance and running performance of this motor are better. Words used in household appliances, small machine tools.
Baidu Encyclopedia - Motor Forward and Reverse
Baidu Encyclopedia - Single-Phase Motor