For the unstable speed of fire smoke exhaust fans, 3C smoke exhaust fan manufacturers have proposed solutions, hoping to be of great help to everyone.  
The fire-fighting exhaust pipe high-temperature smoke exhaust fan is a DC-type speed-controlled motor. The speed of the circular fire damper is adjusted by a variable resistor, which changes the angle of the SCR (Silicon Controlled Rectifier). Then, the SCR controls the rectifier to adjust the working voltage across the motor, so as to achieve the purpose of speed control. If the motor speed is unstable, from the perspective of analyzing the basic principle, the following four situations are possible:  
1. One of the four rectifier diodes has a problem.  
2. The bidirectional thyristor has many issues. For 70℃ fire dampers, common problems usually include breakdown short circuit, open circuit, failure to turn on, or poor internal contact.  
3. Variable resistor issue. Since the vertical high-temperature smoke exhaust fan is installed on a panel with adjustable resistance, it is used frequently and for a long time, so poor contact is very common.