Do ECM Motors Have Capacitors? Fact Behind That

The fact that an external run or start capacitor is not necessary is one of the features of the ECM. But the compressor might still require a run capacitor. Start (S) and Run (R) lines from the compressor are connected to the capacitor. Next, the power or line leads are connected.

Do ECM Motors Have Capacitors

Do ECM Motors Have Capacitors?

It is a three-phase, brushless DC motor, the circuit board, electronic control module, and three-phase motor with a permanent magnet rotor are its three main parts. It aids in maintaining adequate airflow throughout the system and reduces the overall electricity consumption of an AC or furnace.

Do ECM Motors Use a Capacitor?

ECMs, or electronically controlled motors, boost functionality while saving energy. Permanent split capacitor motors, sometimes referred to as PSC motors, use non-polarized capacitors and brushes to deliver power to the spinning components. 

These brushes are known for degrading over time. Since ECM motors lack brushes, they require minimal maintenance and have a longer lifespan. It aids in maintaining adequate airflow throughout the system and reduces the overall electricity consumption of an AC or furnace.

How Does an ECM Motor Operate?

Devices that heat or cool an area are known as HVAC (Heating, Ventilation, and Air Conditioning) systems. They are especially important when creating huge office structures or climate-controlled environments.  An ECM engine, commonly referred to as a variable speed motor, represents a substantial improvement for furnaces and air conditioners.

The microcontroller in the ECM motor is a key component in enabling it to work better. Each winding of the stator is progressively energized and de-energized by the microcontroller to produce an electrical current. The rotor inside this ring of magnets can spin thanks to the magnetic field created by the processor-based pulse control. 

To more precisely control the magnetic fields and lessen the eddy currents and losses suffered by traditional mechanically commutated motors, the microprocessor uses a closed-loop feedback mechanism. This permits the use of brushless motors, which have fewer points of physical contact among their moving parts and hence are tougher.

Working Principle

Until the settings are entered into the microprocessor and the control board dip switches are adjusted in the appropriate location, the motor torque and airflow should stay constant. The motor’s rpm will shift. The motor may need to turn faster or slower depending on the machine’s conditions to maintain continuous torque and airflow. 

Higher static pressure is present as the load or demand on the device increases, for instance when it is really hot outside. Condensation on the evaporator coil is brought on by an increase in cooling demand, which lowers airflow. Static pressure is increased by airflow resistance, which can be caused by a blocked filter or filthy coil. 

The torque on the engine increases with increasing load. It basically indicates that it requires more “muscle” to move an engine when the torque is increased. Greater “strength” or torque is required to operate the motor since higher pressure actually creates more resistance on the fan motor’s blades.

What Is the Difference Between a PSC Motor and an ECM Motor?

Both Permanent Split Capacitor(PSC) motor and Electrically Commutated Motor(ECM) are modest sizes and offer affordable, trustworthy power. The use of ECMs in the industry is beginning to take off as a more advantageous option for PSC motors in terms of energy efficiency. 


EC motors are more modern than the more traditional PSC motor because they make use of microprocessing technology. Due to the numerous windings in its stator and the need for precise timing via a control module to move the rotor, their design is architecturally complex. 

However, this complexity has a drawback—while it enables an EC motor to operate more efficiently, quietly, and with better working characteristics than PSC motors, maintenance on an EC motor is more time-consuming and expensive.

Torque Curve

How a motor’s torque varies with RPM is determined by its speed/torque curve. PSC motors show a nonlinear torque-speed curve, thus, the torque fluctuates significantly with speed. 

The proportional relationship between speed and torque offered by EC motors enables operators to predict the torque at any given speed. This enables EC motors to change speeds and torques without much difficulty when coupled with their speed control, which cannot be true for the PSC motor.


Both motors have good reliability, although the ECM still prevails in this regard. PSC motors’ working lifespan is adversely impacted by the capacitors’ propensity to burn out after extended use. EC motors are brushless and have a straightforward design, making them suitable for prolonged use.


Due to their incredible efficiency, EC motors are swiftly taking over as the new industry standard for air handler fans and other applications. Due to the heat generated by their capacitors, PSC motors’ overall efficiency is reduced to about 50%. 

ECMs not only consume less energy by default but their microprocessor controllers also can be tuned to further cut current draw during off-peak hours and maximize energy usage while in operation. This increases the efficiency of ECMs above 90%, and the energy savings can quickly offset the greater initial cost of the motor.

Dynamic Response

A motor’s capacity to respond to changes in operator demands or applied loads is known as its dynamic response. An efficient motor can adjust its speed fast and make up for a sudden change, like an increase or reduction in airflow. ECMs can function at a variety of rates, which enables them to gracefully handle unpredictability. 

On the other hand, PSC motors are sometimes referred to as “on-off” motors since they struggle to change speeds and are intrinsically difficult to manage without losing efficiency. Therefore, PSC motors are unable to react to dynamic situations as quickly or occasionally at all as ECMs can.


Some people may be put off by PSC motors’ loud noise and vibrations, but since fans frequently use them, this is not a major drawback. For frequency-sensitive applications, EC motors are ideal because of their almost silent operation and lack of vibration.


PSC motors are widely accessible and inexpensive since they have long been the industry standard for usage in industrial furnaces, air handlers, condensers, and other packaged goods. 

PSC motors operate well in retrofit and original equipment manufacturer (OEM) applications, where designers may choose a quick and inexpensive PSC motor that is certain to work, while not being as programmable as EC motors. 

ECMs are more expensive per unit, but they pay for themselves in energy savings. In summary, EC motors will save more money over time than PSC motors, so it is up to the consumer to decide which motor is the more affordable option.


When it comes to selecting the best motor, the application is always key. PSC motors have been used effectively time and time again and will offer a low-cost method of providing rotation for a variety of uses, including HVAC applications. 

Although they are more difficult to use, EC motors are a fantastic option because they offer exceptional energy savings, controllability, power density, and reliability. Always explore the most recent motors available with your provider, and utilize the knowledge to locate the perfect machine for your needs. 

Here’s a comparison chart between the two motors given below for a quick conclusion.

CharacteristicsPSC MotorsECM Motors
Speed CurveNonlinear Linear
Dynamic ResponseLow/NoneHigh

What Usually Fails on an ECM Motor?

Electronically Commutated Motors (ECMs) are very dependable and have a long life when used properly. However, when used in applications for which they were not intended, exactly as PSC induction motors, their life cycle will be shortened.

Use of Blower

When a blower is used in an application with static pressure greater than.8″ WG, failure is a common occurrence. This reduces the lifespan of both a PSC and an ECM. It will result in the metal oxide varistor (MOV), a disk in the controller, failing in an ECM. The MOV will often be stained, cracked, or torn apart if it has failed.

Electrical Surges

If the motor has experienced electrical surges or lightning strikes, the MOV may potentially be harmed. The MOV could be harmed if the power source is prone to brownouts or other causes of voltage fluctuations.


Moisture is yet another significant cause of failure. ECMs are used in high-efficiency applications with blowers. Condensation could develop as a result. The connections in the controller are covered with potting material by motor manufacturers as a safeguard against this condensation. 

The electrical connections in the controller are often covered in a black, rubbery substance. This material could be harmed and exposed to moisture if an attempt is made to replace controller components. This can lead to a call-back from the service. 


It can be said that ECMs are moderation of PSC motors in several specifications. The capacitor is not a core element of it as per PSC but the need for a capacitor in ECM can’t be overlooked. The type of motor you need depends on your purpose. So, determine the objective and go for an ECM with proper management. 

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