What Is an ECM Motor? Everything You Need to Know

In recent years, there have been many advances in HVAC technology.

One of those advances is the use of ECM motors.

But what are ECM motors anyway? And how do they affect your furnace or AC unit?

An ECM motor is a brushless DC motor that is capable of adjusting its speed and torque. By using a controller, an ECM is programmable and maintains energy efficiency across a wide range of speeds.

In this article, I’ll go over what an ECM motor is and how it works. I’ll also discuss the different types of ECM motors and what they are used for.

How does an ECM motor work?

An ECM (Electronically Commutated Motor) is a brushless DC motor that is controlled by a microprocessor.

An ECM motor has two main parts:

  1. A brushless DC motor
  2. A controller

The ECM motor works by energizing a series of electromagnets inside of the motor’s stator. The electromagnets are activated in a circular fashion to rotate the motor’s rotor.

The ECM’s controller is the part that’s responsible for sending power to the motor’s electromagnets.

The controller can be programmed for different types of operations. Each manufacturer will program the ECM depending on what the motor will be used for.

For example, an ECM could be programmed to maintain constant airflow for a furnace blower. Or an ECM could be programmed to maintain a constant speed for an AC condenser fan.

Below is a video from Lesics that provides an animation of a brushless DC motor in action.

I’ll talk about the different types of ECMs below.

ECM motor types

The brushless DC motor inside of an ECM allows for a variety of control methods.

In HVAC applications, there are three main types of ECM motors:

  1. Constant torque
  2. Constant airflow
  3. Constant speed

Constant torque ECM

A constant torque ECM is programmed to maintain the same amount of torque regardless of static pressure.

For example, if the pressure increases in the HVAC system, then a constant torque ECM will increase its power to maintain the same torque.

How does a constant torque ECM differ from a PSC motor?

A constant torque ECM will maintain more airflow than a PSC when there is air restriction in an HVAC system.

However, a constant torque ECM will still lose some airflow due to air restriction—just not as much as a PSC.

Where is a constant torque ECM used?

Constant torque ECMs are commonly used as blowers in air handlers. They can be used as replacements for PSC motors since they are more efficient and cost less than other types of ECM motors.

Constant airflow ECM

Constant airflow ECMs are also known as constant CFM or variable speed.

A constant airflow ECM is programmed to maintain the same amount of airflow regardless of static pressure.

For example, if the pressure increases in the HVAC system, then a constant airflow ECM will increase its torque and speed to maintain the same airflow.

How does a constant airflow ECM differ from a constant torque ECM?

A constant airflow ECM will maintain the same airflow regardless of air restrictions in the HVAC system. Whereas a constant torque ECM will lose some airflow due to air restriction.

Where is a constant airflow ECM used?

Constant airflow ECMs are used in high-efficiency furnaces and ACs.

Unlike constant torque and constant speed ECMs, constant airflow ECMs are true variable speed motors. This allows a constant airflow ECM to deliver precise amounts of airflow. 

For example, if the filter in the air handler gets dirty, the heating or cooling capacity of the HVAC unit will remain unaffected.

Constant speed ECM

Constant speed ECMs are also known as constant RPM.

A constant speed ECM is programmed to maintain the same speed regardless of static pressure.

For example, if air restriction is introduced into a system, a constant speed ECM will increase its torque to maintain the same speed.

How does a constant speed ECM differ from a constant torque ECM?

A constant speed ECM will maintain the same speed regardless of air restrictions in the HVAC system.

Whereas a constant torque ECM will lose some speed due to air restriction.

Where is a constant speed ECM used?

Constant speed ECMs are typically used for AC condenser fans. Constant speed ECMs are used in AC condensers because they allow the equipment manufacturer to tweak the fan blade shape to maintain sufficient airflows at low speeds.

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