Centrifugal fan is a DC speed regulating motor, its speed is to change the conduction angle of thyristor by adjustable resistance, and then control the voltage to reach both ends of the motor after rectifying by SCR, in order to achieve the purpose of controlling the speed, the speed of the motor is unstable. From the principle analysis, the following four cases are possible.
1One of the four rectifier tubes has problems.
2 In line with the principle of easy first and then difficult repair, the adjustable resistance changes regularly with the adjustment, it is proved that the potentiometer is good, and then the SCR is not found. Because the two tube is a high current gold seal tube, one end screw is fastened to the circuit board, the other end is welded to the circuit board, and when removed from the circuit board, it is found that the positive loosening phenomenon is found.
3 SCR problems are also not small, usually breakdown short circuit, open circuit, can not trigger or poor contact, etc.
4 Adjustable resistance, centrifugal fan due to adjustable resistance installed on the control panel, the use of high frequency, long time, contact bad situation is common.