Manual automatic air compressor control circuit

This circuit realizes the manual and automatic conversion function through a conversion switch SA. When the compressor needs to be operated manually, SA is placed in the manual position. When it needs to be operated automatically, SA can be placed in the automatic position. The specific control circuit principle is shown in the figure below.

How it works

1. Manual control

When the compressor needs to be operated manually, the conversion switch SA is placed in the manual position, and the start button SB2 is pressed. The AC contactor KM coil is energized and attracted, and its auxiliary contact KM1 is closed and self-locked, and its main contact KM2 is closed, connecting the three-phase power supply of the compressor motor M, and the motor starts to operate. The motor shaft drives the compressor piston to operate, so that the compressor is put into normal operation. When the compressor needs to be stopped, just press the stop button SB1.

2. Automatic control

When the compressor needs automatic control, the switch SA can be pulled to the automatic control position. At this time, if the controlled pressure is lower than the lower limit, the contact KP (12) of the electric contact pressure gauge is connected, causing the transistor VT to be turned on, and the relay KA line is energized and attracted to operate. At the same time, its normally open contact KA1 is closed, and the relay KA1 is self-locked. The other contact KA2 of KA is closed, connecting the power supply of the AC contactor KM coil, KM is energized and attracted, and the main contact KM2 is closed to connect the three-phase power supply, and the compressor operates normally. As the air pressure increases, the pointer of KP leaves the lower limit contact. Since the contact KA1 of KA is closed and self-locked, when the pressure is greater than the lower limit but less than the upper limit, even if the upper and lower contacts of KP are not connected, the transistor VT can still be turned on and the relay KA is attracted, and the contact KA2 remains closed, and the compressor still keeps running.

When the air pressure reaches the upper limit, the contact KP (13) of KP is closed, the lower limit contact shorts the base of transistor VT, making VT cut off, the relay KA loses power and releases, its contacts KA1 and KA2 are disconnected and reset, KM loses power and releases, the compressor motor M stops running, and the compressed air supply is stopped. This reciprocating cycle controls the air pressure in the gas tank between the upper and lower limit pressures.