Wiring Methods for Brushless DC (BLDC) Motors and Controllers

Connection of Brushless DC (BLDC) Motors

There is no established standard for wiring brushless DC (BLDC) motors and controllers, so the Hall sensor and phase leads may be labeled ABC, UVW, or even not labeled at all. Rather than trying to analyze the motor to understand its phasing, it is often easier to determine the correct connections through trial and error.

Since the three Hall sensors can be connected in any order, there are six possible ways to connect the motor phase leads (see Table 1).

Table 1: Motor Phase Lead Configuration

Of the six phase connection combinations, only one is correct; at the same time, three connections will completely prevent the motor from rotating; the remaining two incorrect connections also require special attention. If the motor is connected in these two incorrect methods, the motor will rotate, but its performance will be severely degraded.

Three key factors in determining if a motor is improperly wired are: torque, torque ripple, and direction. In both poorly performing configurations, the torque is significantly lower than that of a properly wired motor, and the torque ripple is also noticeable as the motor turns. Finally, the direction of the motor's rotation may also be different depending on how it is connected.

The easiest way to determine if the motor is wired correctly is to find the three wiring configurations that make the motor turn. We can compare how the motor runs in each configuration, and the correct configuration will have the highest torque and lowest current draw. Here are the steps:

Assign arbitrary numbers to the three Hall output lines of the motor and connect them to the three Hall sensor inputs on the evaluation board.

Connect the supply voltage and ground of the Hall sensor to the power supply.

Arbitrarily assign letters (such as A, B, and C) to the phase wires of the motor and then connect them to the three phase outputs of the evaluation board.

Power up the evaluation board and start the motor. If the motor turns, follow these steps to find the best phase wiring configuration:

Shift each phase line by one position (for example A, B, and C, then C, A, and B), and compare the torque and torque ripple for each configuration.

Move each phase line one more position (C, A, and B, then B, C, and A) and compare the torque and torque ripple.

Use the wiring configuration that provides the highest torque and lowest torque ripple.

If the motor does not rotate, swap any two phase wires until the motor rotates.

Go back to step 3 and compare the three wiring configurations that will turn the motor, and choose the one that gives the highest torque and lowest current consumption.

If the motor is turning in the opposite direction to what is required, swap the two Hall input lines and repeat steps 3 and 4.

In addition, once the motor is spinning, you can use an oscilloscope to observe the phase voltage (or phase current) to check if the connection is correct. If the connection is correct, the phase voltage waveform will be approximately symmetrical (see Figure 1).

Figure 1: Phase voltage waveform with correct wiring configuration

If the phases are not connected correctly, the shoulders of the waveform where the phases are in the high impedance, zero current state will look very different.