What are the reasons for the unstable rotating speed of the mine energy saving fan?

What is the cause of mine fan speed instability?

1. There is a fault with one of the four rectifier diodes of the mine fan motor.

2. It may be that the toner of the rotor and commutator of the mine fan is not equal to the carbon brush itself, resulting in unstable rotation speed.

3, there may be a lot of problems on the SCR, such as open circuit, bad contact, short circuit, can not touch, etc.

4. An adjustable resistance to control the speed of the mine fan may be installed on the control panel. If you use too much, you will have poor contact, which will also affect speed control.