Issues with Rectifier Diodes
A fault in one of the four rectifier diodes can cause speed instability.
Carbon Powder or Defective Carbon Brushes
Carbon powder accumulation between the rotor and the motor’s commutator, or defects in the motor’s carbon brushes, can lead to unstable operation. Adhering to a targeted troubleshooting approach, begin by measuring the variable resistor. If the resistance value changes periodically with adjustments, the resistor is functioning properly. Further inspection of the thyristor might show no issues. However, upon dismantling the large-current metal-sealed diode from the circuit board—where one end is screwed into the board and the other end is soldered—it may be found that the positive and negative connections are loose. This can be verified by measuring while shaking the diode, confirming intermittent contact issues.
Thyristor Problems
Thyristors can encounter various issues such as short circuits, open circuits, inability to switch on, or internal contact faults.
Loose Variable Resistor
In vertical centrifugal fans, the variable resistor is often mounted on the control panel and subjected to frequent use. Over time, it is common for the resistor to become loose, contributing to speed instability.
