Comparing the Maximum Voltage of Brush DC and BLDC Motors

The maximum voltage capabilities of brush DC and brushless DC (BLDC) motors are fundamentally different, which is primarily due to each motor technology’s specific design and operating principles. In brush DC motors, physical brushes conduct the electrical current, which limits their maximum voltage. However, the electronic commutation of brushless motors empowers them to handle higher voltages more effectively and efficiently. We explore these differences more in-depth below.

Exploring the Voltage of Brush DC Motors

In most cases, the different winding options of brush DC motors are designed to run close to the maximum recommended speed of 10,000 RPM at nominal voltage and without load. The 16DCT brush DC motor datasheet in Figure 1 paints a clear picture of this, as it illustrates a typical brush DC motor’s recommended maximum supply voltage.

Image 1 - A Portescap 16DCT Brush DC motor datasheet. The different coil options are designed to run close to the max continuous speed of 10,000 RPM at nominal voltage and no load.

This limitation of the maximum continuous speed ensures a reasonable lifetime of the motor, as the wear in the mechanical commutation system increases with the number of revolutions and therefore with the motor speed. Supplying a much higher voltage than the nominal voltage is not recommended in applications where a reasonable lifetime is expected from the motor. Exceptions include disposable applications that require high speed at a very short lifetime of only a few hours, as well as industrial power tools, which can require high peak speed at no load for very short durations depending on the tool.

Exploring the Voltage of Brushless DC Motors

As its name implies, the commutation of a BLDC motor is performed electronically and is not subject to mechanical wear; this means that the limiting factor for the maximum speed is typically not its commutation, but the rotor assembly and bearings. BLDC motors therefore allow a much higher maximum motor speed compared to brush DC motors (Figure 2).

Figure 2: 16ECP36 datasheet showing it can run up to 63,000 RPM

The balancing of the rotor assembly itself is critical in avoiding excessive vibration at higher speeds. The bearings supporting the rotor assembly will limit the maximum speed depending on factors like the bearing size and type, lubricant and sealings used, and mounting distance. A third limiting factor can be found in motors with integrated electronics, where the maximum supply voltage is limited by the PCB integrated into the motor.

One thing to keep in mind is that at nominal voltage, BLDC motors often run at a much lower speed than the maximum recommended speed. The motor speed can therefore safely be increased up to the maximum recommended motor speed by increasing the supply voltage of the motor (Figure 2). However, due to the increasing iron losses in the motor at higher speeds, the reduced maximum continuous torque should be considered to avoid overheating of the motor.

Figure 3 - A 16ECP36 8B 245 motor running at 24V and 48V supply voltage

Conclusion

Are you unsure about how to safely operate your motor, or which motor fits your application’s needs? engineers can support you in determining the right boundaries, including speed, torque, temperature, and lifetime, for your application. Reach out to us here to discuss!