Causes and Solutions for Brushless Motors Running in Only One Direction

When a brushless motor runs smoothly in one direction but exhibits jerking, weakness, or fails to run in the opposite direction, troubleshooting can typically be focused on the following three common causes. Please check them in order.

1. Check the Hall Signals (For Hall Sensor Motors)

1.1. Symptom: Normal forward rotation, but severe jerking, abnormal noise, or complete locking during reverse rotation.

1.2. Possible Cause:** A damaged Hall sensor inside the motor or poor contact in one of the signal wires, preventing the controller from identifying the correct commutation position.

1.3. Solution:**

• Observation Method: Slowly rotate the motor shaft manually. Use a multimeter to measure the voltage between each of the three Hall signal wires (not the red/black power wires) and ground. Under normal conditions, the voltage on each signal line should fluctuate regularly between 0V and 5V (or 3.3V). If one line's voltage remains constant, the corresponding Hall sensor is likely faulty.
• Replacement Method: If possible, test with a motor of the same model. If the problem disappears, the Hall sensor assembly in the original motor is likely faulty and requires repair or replacement.

2. Check the Speed Control Signal

2.1. Symptom:** The motor consistently rotates in a single direction regardless of the forward/reverse command.

2.2. Possible Cause:** If using an analog voltage (e.g., 0-5V) for speed control, the signal wire may be subject to interference, or the "zero point" may have shifted (meaning 0V no longer corresponds to zero speed).

2.3. Solution:**

• Measure Zero Point: When the controller sends a "stop" command, use a multimeter to measure the voltage between the speed control signal wire and ground. The ideal value is 0V. If a small voltage (e.g., above 0.1V) is detected, a zero-point shift exists.
• Check Wiring: Ensure signal wires are properly shielded, routed away from power cables, and that all terminals are tight and secure.

3. Adjust Hall Wire Sequence

3.1. Symptom:** Unidirectional rotation occurs.

3.2. Root Cause:** The factory-installed angular relationship (phase sequence) between the Hall sensors and the three-phase windings inside the motor does not match, causing the controller to receive incorrect commutation signals.

3.3. Solution:**

• Fix Power Wires: Securely connect the three main power wires (U/V/W) to the motor and leave them unchanged throughout the test.
• Label Hall Wires: Label the motor's three Hall signal wires (typically yellow, green, blue, etc.) as A, B, and C.
• Six Tests: Connect these 3 wires to the drive's Hall signal ports in all 6 possible sequence combinations. After each connection, power on and test the motor at low speed in both forward and reverse directions.
• Find the "Best Combination": Compare the 6 tests to identify the single wiring sequence that results in equally smooth, quiet, and powerful operation in both directions. This is the correct Hall wire sequence for the current power wire configuration. Permanently secure this wiring.

Important note: Perform all wiring operations only with the power completely off. During testing, ensure the motor shaft is unloaded to prevent unintended startup.

Updated on: 29/12/2025