Causes and Solutions for Unstable Air Velocity in Centrifugal Fans
2026-07-15
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Special Note: This article primarily focuses on electrical speed control system faults in centrifugal fans equipped with speed control circuits — particularly those using DC speed-controlled motors. In practical applications, if the airflow speed remains unstable after ruling out the electrical issues described below, further investigation of mechanical components and external operating conditions is required.
Causes of Unstable Fan Speed
1. SCR (Silicon Controlled Rectifier) Malfunction
If the SCR experiences an open circuit, short circuit due to breakdown, or is of poor quality, it will directly affect the fan's airflow speed.
2. Adjustable Resistor Failure
After prolonged use, the adjustable resistor may develop poor electrical contact, which in turn affects the equipment's speed stability.
3. Carbon Dust and Carbon Brush Issues
Excessive carbon dust accumulation between the motor rotor and commutator, or carbon brushes of poor quality, can also lead to unstable airflow speed.
4. Diode Malfunction
If any one of the four rectifier diodes in the fan is malfunctioning, it will affect the entire unit, preventing it from operating normally and causing unstable airflow.
Solutions for Unstable Fan Speed
Based on the causes outlined above, it is clear that the primary reasons for unstable fan speed are largely related to component failures. Therefore, if unstable airflow is observed during operation, the following troubleshooting directions can be identified:
1. Test the SCR
By testing the SCR, its operational status can be determined. If it is found to be abnormal, it must be repaired or replaced promptly.
2. Test the Adjustable Resistor
Perform a detailed measurement of the adjustable resistor. If the resistance value changes in a regular pattern as the adjustment is made, the potentiometer can be considered functional. If not, the potentiometer is faulty and must be repaired or replaced with a new one.
3. Clean Carbon Dust
If a significant amount of carbon dust is found to have accumulated, it must be thoroughly cleaned without delay.
4. Replace with High-Quality Carbon Brushes
If the carbon brushes are found to be worn or of poor quality, they must be replaced with high-quality carbon brushes that meet the specified requirements.
5. Inspect the Diodes
When inspecting the diodes, it is important to note that they are high-current, metal-sealed tubes. One end is secured to the circuit board with a screw, while the other end is soldered with a wire. When removed from the circuit board, obvious looseness can be observed at the positive and negative terminals. By measuring while gently rocking the component, it can be determined whether the diode is functional or damaged. Any damaged diode must be replaced.
Post-Repair Procedure
Regardless of which component has failed, after any repair or replacement, trial runs and commissioning must be performed. The equipment should only be put into service after confirming that everything is operating normally.
