Motor Mouth: Brushless or Brushed Motors: Examining Options

We’re discussing the benefits of choosing a brushless motor (BLDC) over traditional brushed motors and how one versus the other works in the HVAC industry. Talk with our team about the solution that’s right for your application.

Advantages of BLDC motors (vs brush dc motors)

• Higher power density
• Better heat dissipation
• Longer life, only wear items are bearings
• Better suited to speed and position control applications
• High efficiency

Disadvantages

• Higher cost
• Must be electronically commutated

Outer vs Inner Rotor

Outer rotor motors are more cost effective to produce, as they can be wound and assembled with the same equipment used for brush dc motors.

Inner rotor motors offer better heat dissipation as the windings are thermally in contact with the outside case through the core laminations.

Application Example

Fail safe modulating commercial valve and damper HVAC actuators require a long service life and require speed and positional accuracy. In addition, they incorporate a spring that is wound when the actuator opens. On power fail, this spring drives the actuator to the closed position to cut off air or water flow. As such, the motor must have low resistance to rotation when powered off.

Typically, brush dc motors will not provide the cycle life required. In addition, the sliding friction of the brushes on the commutator produce a relatively high resistance to rotation in a power off condition.

A BLDC motor has the long life, high efficiency and low rotational friction needed for this application. Speed and position feedback are provided by the built in rotor position hall effect sensors.

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