The back electromotive force (BEMF) of a brushless DC motor (BLDCM) is the induced electromotive force generated when the windings cut the magnetic field of the permanent magnet as the motor rotates. The back EMF parameter directly affects the motor's operating efficiency, control performance, and the reliability of sensorless control systems.

Below is a clear and practical guide to understanding and testing the Back-EMF of BLDC motors.

Ⅰ.Principle of Back EMF Testing for Brushless DC Motors 

Back EMF testing of brushless motors needs to be based on their physical characteristics. According to the principle of electromagnetic induction, the back EMF is generated by the rotor rotating and cutting the magnetic field. Its magnitude is closely related to the rotor angular velocity, magnetic field strength, number of winding turns, and air gap. After the motor design is finalized, the rotational speed becomes the core variable affecting the back EMF.

Key to Testing: 

The key to testing the back electromotive force of a BLDC motor lies in capturing the induced voltage signal of the non-conducting phase winding, especially at the zero-crossing position—a three-phase, six-state motor always has one phase suspended at any given time, and the voltage of that phase can directly reflect the back electromotive force characteristics. 

Ⅱ. How to Test Back-EMF in Brushless DC Motors (BLDC)?

Using a brushless motor testing system to test the back EMF of a brushless motor is more accurate and efficient.

1. Hardware-Level Advantages:

The brushless motor testing system employs a high-precision voltage acquisition module, directly connected to the three-phase winding terminals of the motor, eliminating the need for an additional neutral point circuit and avoiding signal attenuation and phase distortion. For different scenarios such as air conditioner fans and washing machine DD motors, the system can be customized with a dual-station parallel detection unit to simultaneously complete tests of multiple parameters, including back EMF, Hall effect signals, and phase difference.

2. Automated Testing Workflow

The brushless motor testing system achieves automated operation: after the operator pneumatically clamps and secures the motor, they can start the test program with a single button. The system first controls the motor to enter a preset speed range, then uses synchronous sampling technology to capture the back EMF signal at the PWM turn-off moment, effectively avoiding high-frequency interference.

After digital filtering and phase correction, the DC brushless motor test data automatically generate reports on parameters such as back EMF waveform and zero-crossing delay, and upload them to the MES system in real time for traceable management.

3. Test Core:

The core of back EMF testing for brushless DC motors lies in accurately capturing effective signals and avoiding interference. Through the deep integration of customized hardware and intelligent software, the brushless motor testing system achieves both highly efficient automation of the testing process and ensures accurate and reliable test results, providing strong technical support for motor production and R&D.

Ⅲ.About AIP

AIP specializes in global motor testing, offering reliable, customized motor test solutions.

If you’re looking for a professional Back-EMF testing solution or a trusted BLDC motor tester manufacturer, AIP is ready to support your production and R&D needs.

Contact us today to get customized BLDC motor test solutions!