Brushless DC Motor Controller Troubleshooting

Correctly judge functions of various outgoing lines of the BLDC motor controller

Fig.1 BLDC controller outgoing line

The BLDC motor controller is usually equipped with the following outgoing lines:

Electric motor line (Figure 1 in A line): The BLDC motor controller has three lines, namely A, B and C phase line. The yellow line represents A-phase, the blue line represents B-phase, the green line represents C-phase. Of course, there is exception. Thus, the maintenance staff should try to change the sequence of the three lines until the electric motor can operate normally.
Power source line (Figure 1 in B line): The electric line of the BLDC motor usually has three wires. The thinner one is the locking line, which can provide 14V and 5V power source for the BLDC motor controller. The other two thick lines (red and black) is responsible for power supply for the power tube.
Speed-limiting line (Figure 1 in C line): The national standards stipulate that the upper speed limit of the electric vehicle is 20km/h. Therefore, the controller turned out by manufacturers of controllers with the BLDC motor are left with the speed-limiting line when leaving the factor. When it is plugged on, the upper speed limit of the electric motor is 20km/h, which is in line with the national standards. If it is disconnected, the speed of the electric vehicle will be higher than 20km/h for the convenience of users’ selection.
Brake cable (Figure 1 in D line): The brake cable is connected to the handle switch of the BLDC motor. During braking, the braking signal will be sent into the SCM to implement the brake disconnection or the brake locking.
Speed line (Figure 1 in E line): The speed line is connected with the speed meter of the electric vehicle’s meter disk. In the BLDC motor, it is connected with the phase line of the BLDC motor via a current-limiting current. Changes of the motor’s speed are reflected as current changes of the BLDC motor’s phase line. In the speed line, the current also changes and is reflected as the speed changes of the instrument panel.
Throttle line (Figure 1 in F line): The throttle line is connected to the Hall within the throttle of the brushless DC motor. There are three throttle lines, the anode throttle line, cathode throttle line and signal line. Generally, the red line is the anode throttle line, the black line is the cathode throttle line, the signal line is the blue one. When the throttle rotates, the magnet moves within the throttle with the Hall as the reference, and the induced voltage signals ranging from low lows to high ones are generated. The signals are then sent into the SCM to implement the speed-regulating instructions.
BLDC motor’s Hall lines (Figure 1 in G line): BLDC motor’s Hall lines are connected with the Hall within the electric motor to decide the phase shift moment of the electric motor. There are five Hall lines. The red one is the anode; the black is the cathode; and the remaining three are Hall signal lines. The three signal lines should be connected with the electric motor in the correct sequence. Otherwise, the electric motor cannot operate normally. Sometimes, the connection sequence of these three wires with the electric motor should be repeatedly changed until the electric motor can operate normally.

Visual inspection of the BLDC motor controller

The defects are observed via visual inspection. The inspection focuses on whether the wire is well welded, and whether the power MOS tube, 14V voltage-regulator tube, large electrolytic capacitor, SCM, and oscillator are well welded. As what is marked in A, B, C, D and E in Fig. 2, the non-performing points should be eliminated.

Fig.2 BLDC Motor Controller

Use the multimeter for inspection when there is no connection:

Use the multimeter to measure whether the earth impedance of the external power end is normal, which should be usually larger than 2k Ω.
Test whether there is short circuit existing between pins of the six MOS tubes. This is very important. If the controller with the BLDC motor (such as MOS tube) is poor, the overcurrent protection is weak or the heat dissipation is unreliable, the MOS tube might be penetrated through. See Part A of Fig. 2.
Check whether there is short circuit between pins of the power source voltage-regulator tube.
Measure whether resistance between 78L05 and ground is normal, which should be usually larger than 1.5kΩ.

Measure the DC working points under the electrification

Test LM317 output (which should be 14V), 78L05 output (which should be 5V), throttle line and Hall line, resistance line, and power between the red line and the black line (which should be 5V).

Try power-on operation

Just connect the brushless DC motor line, Hall line and throttle line. After ensuring correct connection, connect it with the power and try to rotate the throttle. First slowly rotate for a small distance (at a slow speed) to see whether the motor’s operation state is normal. If not, the machine should be stopped immediately for reinspection. Only when the BLDC motor is normal when operating at a slow speed can the speed be accelerated. Otherwise the devices might be damaged.
When the electric motor is operating normally, check whether the functions of braking, resistance, speed meter, under-voltage and current-limiting are normal.

How to find where to sold the speed limit line. Figure 1 C line. Want to add it for 2 of my electrical scooters. Single motor 600w (zero9 scooter)

- - - -> by: Staffan Söderberg