Constant Torque ECM Motor Evolution

January 8, 2024

Motor Minute™ Technical Tip – Constant Torque ECM Motor Evolution

Hi, Chris from Regal Rexnord here with your Motor Minute technical tip. Helping you become an HVAC motor pro one minute at a time.

Today’s Motor Minute™ topic is the evolution of constant torque ECM motors.

In the last two months I made reference to constant torque ECM motors with PWM communicating capability. While this is not new technology, it may be new to you, so I thought I would explain what that means.

From the introduction of constant torque ECM motors in 2006 until around 2013, the predominant programming of constant torque ECM has been to operate with simple 24 VAC speed taps. These motors are typically connected to “Heat”, “Cool”, and “Fan” terminals on the HVAC system circuit board as seen here.

However, around 2013 we started offering pulse width modulation (PWM) communication in our constant torque ECM motor platform.

Notice how the low voltage motor connections are no longer connected to heat, cool and fan terminals at the OEM circuit board. They are now connected with a plug. And at the motor it is simply one connection to terminal 1. The motor looks exactly the same, because physically it is.

The plug at the HVAC circuit board and at the motor is an important indication that this motor does not have speed taps that can be adjusted at the motor.

With PWM communication, airflow is typically selected or adjusted by the use of DIP switches, jumper pins or menu-driven display. This information is located in the HVAC unit installation/service manual.

For diagnostic purposes, the PWM signal on terminal 1 can be measured with a voltmeter set to DCV. The DCV value(s), per demand (heat, cool, fan), can be found in the HVAC unit installation/service manual.

While 24 VAC speed taps are still the most widely used type of constant torque ECM in HVAC equipment today, the use of PWM communication in these motors is growing. And this is not the last technology change in store for constant torque ECM motors.

Keep your friends close, keep your manuals closer.

And that’s a wrap on this segment of Motor Minute technical tips. Remember that we provide motor training and product information in multiple formats including videos, literature, podcasts, articles, of course Motor Minute technical tips and classroom education both online and face to face. All of this industry leading training is available at no charge to HVAC professionals at regalmmu.com. Thank you for taking the time to build your motor knowledge.