Why is the speed of the centrifugal fan fast and slow?

Some centrifugal fans are speed-adjustable like axial fanswholesale AC axial fans factory. The speed of their speed is changed by the adjustable resistance to change the conduction angle of the thyristor, and then the thyristor controls and rectifies the voltage at both ends of the motor to achieve the speed control. Purpose, from various reasons, we analyze the following four situations are possible.
1. Only one of the four rectifier diodes has a problem.
2. There is carbon powder between the motor rotor and the commutator or the carbon brush itself is bad. Based on the principle of easy repair, first measure the adjustable resistance, and the resistance changes regularly with the adjustment, which proves that the potentiometer is good Yes, no problem was found after measuring the SCR. Because the diode is a high-current gold-sealed tube, one end is screwed on the circuit board, and the other end is welded to the circuit board with a wire. When it is removed from the circuit board, It is found that the positive and negative poles are loose, and then shake it while measuring, confirming that the diode is good and bad.
3. There are many problems with SCRs, which are usually short-circuit breakdown, open circuit, failure to trigger or poor internal contact, etc.
4. Adjustable resistance. The cabinet-type centrifugal fan is installed on the control panel due to the adjustable resistance. The frequency of use is very high, the time is long, and the situation of poor contact is common.

220V DC Brushless External Rotor Motor Fan