Motor Fault Analysis: Diagnosing and Repairing Non-Operational Electric Motors

Electric motors are crucial to the functionality of many devices, but diagnosing faults can sometimes be complex. Here’s a comprehensive guide to identifying and repairing issues when the motor won’t operate:

1️⃣ Inspect the Power Supply and Key Components:

Turn on the key switch and check the battery display.

Measure the input voltage to the controller (36V) and the output voltage (5V for brushed motors; 10-20V for brushless motor sensors).

If the voltage is low, inspect the fuse, key switch, battery box contacts, and wiring connections for loose or faulty parts. Look for signs of swelling or leakage in the battery and ensure internal wiring is reliable.

Fix issues by polishing corroded contacts, securing power cables, or replacing defective components like the battery or switch.

2️⃣ Verify Controller Output:

Ensure the controller provides proper 5V output (or 10-20V for brushless sensor systems).

If 5V output is abnormal even after disconnecting the throttle, the controller may be faulty.

If output is normal, test the throttle voltage (should range between 1-4.2V). Replace the throttle if faulty.

3️⃣ Test the Brake Handles:

Mechanical Brake Handles: Measure the resistance between two leads. Resistance should alternate between ∞ and 0 during normal and braking states. Faulty components require replacement.

Electronic Brake Handles: Check the power supply voltage (5-15V). Test if signal voltage alternates between 0V and 5V (or 15V). Consistent braking indicates a fault requiring replacement. Disconnecting the brake handle can also confirm issues.

4️⃣ Inspect Brushed Motors:

Disconnect motor wires and measure the resistance. A functioning motor shows low, stable resistance when rotated.

Address common issues like broken wires, worn brushes, or oxidized commutators by replacing parts, sanding commutators, and cleaning insulator gaps.

For geared brushed motors, if the motor operates but the hub doesn’t turn, replace worn reduction gears.

5️⃣ Examine Brushless Motors and Sensors:

Check sensor power supply voltage (5V, 10V, or 15V depending on the controller).

Ensure sensor signal voltage alternates between 0V and the supply voltage during motor rotation. Faulty sensors should be replaced.

Inspect motor wiring for damage, particularly from improper anti-rotation mechanisms. Reattach or replace damaged wires as needed.

6️⃣ Troubleshooting Brushless Motors:

Begin by inspecting the sensor. Connect the key switch and measure the voltage between the red (+) and black (-) wires of the controller’s sensor output. The voltage should be 5V (or 10V/15V depending on the controller). An abnormal reading indicates a controller fault.

If the sensor power is normal, rotate the brushless motor and measure the signal output from the three sensor wires. Each output should show a regular fluctuation between 0V and the sensor power voltage. Irregularities suggest sensor damage.

7️⃣ Understanding Brushless Motor Sensors:

Brushless motor sensors consist of three switch-type Hall elements. These detect the rotor magnet’s position, allowing the controller to regulate the stator coil current flow systematically and drive motor rotation.

Inspect the three motor power wires for damage. Excess torque or insufficient anti-rotation measures can cause the shaft to twist and sever motor wires. Repair damaged wiring or replace it entirely. Ensure a proper anti-rotation plate is installed to secure the shaft against twisting.

8️⃣ Examining Brushed Motor Controllers:

Brushed controllers typically utilize PWM circuits, commonly with TL494 as the core. They control motor speed by managing the pulse width modulation of power through field-effect transistors.

Popular transistors include IRFZ44N, IRFZ48N, IRF2807, and IRF3710, which are compact (TO-220 package) and offer high current capabilities, making them ideal for motor control.

9️⃣ Common Controller Faults:

Controller issues often stem from field-effect transistor breakdowns, diode failures, output power faults, or protection circuit malfunctions. After ruling out power supply, throttle, and motor faults, the controller is identified as the faulty component.

🔟 Controller Replacement Tips:

Ensure compatibility between the controller and output device types (e.g., throttles and brake handles):

Throttles: Verify if it’s forward control (1–4.2V) or reverse control (4.2–1V).

Brake handles: Identify whether they are electric or mechanical switches, open or closed types, or whether electronic switches are high-level or low-level.

Improper matching can lead to new faults. Carefully align replacements to fit the new controller setup.

By following this structured approach, you can effectively diagnose and repair electric motor issues, ensuring optimal performance and reliability.

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