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Demystifying Electric Motors: AC, DC, and EC
Reading time: 8 minutes
Safety
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EC (Electronically Commutated) motors, DC (Direct Current) motors, and AC (Alternating Current) motors are all types of electric motors, but they differ in how they operate and how they are used. Both AC and DC motors serve the same function: converting electrical energy into mechanical energy. Yet, they differ in many ways. These motors are used to power elevators and cranes, to pump the water we drink, and even to cool nuclear power stations.
When used to power ventilation products, there are important distinctions between each type of motor that can affect the benefits a homeowner would recognize. For example, AC motored fans are much more durable than DC or EC motored fans and are ideal for non-conditioned areas that frequently experience high levels of moisture. While an EC motored fan will give the current or future homeowner increased energy savings, especially at partial load.
At Fantech, we use all three of these motors to power our fans. For your convenience, we have detailed below how these three types of electric motors operate, their advantages and disadvantages, and typical applications for each type of motor. Use the guide below as a resource to educate your customers on the different benefits of each.
AC Motors
C motors are powered by AC input voltage. They rely on an outside stator (the stationary part of the motor) with coils that produce a rotating magnetic field. The internal rotor creates another magnetic field that interacts with the other magnetic field to induce rotation of the motor.
Because they must create their own magnetic field, AC motors are less efficient than DC motors. This may not matter too much in a small application, like a blender. Yet, it would be much more noticeable in a commercial bath fan that would need higher amounts of power to reach the next level of airflow.
AC motors are known for their use in many household appliances such as computers, fans, and air conditioners. They are also commonly used in compressor drives and systems, irrigation and hydraulic pumps, and more. Essentially, AC motors are better for high-speed applications that require less maintenance.
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When Used in Small Fans
When AC motors are used in small fans, it creates a durable, cost-effective ventilation solution (when compared to fans with DC or EC motors) that will not need a lot of support.
Fans like the FG 4 assist multi-family or large-scale building designers when designing HVAC systems; as they can use these products to move conditioned air to areas that normally wouldn’t benefit. Additionally, these AC motored fans are designed to supply or extract (depending on the installation method) to move air throughout or from the building at a low CFM/W.
Other products, like the RAHU (Residential Air Handling Unit) FIT® 120 fresh air appliance, use AC motored fans to bring in fresh air and to exhaust out stale air. This product is ideal for multi-family solutions due to its small square design with efficient and powerful airflow distribution.
Benefitting from Fans with AC Motors
Aside from multi-family and/or large-scale building designers, building owners and maintenance personnel alike also will appreciate these fans. For building owners, tenants and customers will enjoy a comfortable living/working/entertainment space. For maintenance personnel, they will have one less product within the building that needs regular motor maintenance. When installing, you as well will additionally enjoy the lack of programming (if the fan does not use an external speed control).
| Electric Motor Type | AC Motors | DC Motors | EC Motors |
| Topic: Fit | ✗ | ✗ | ✔ |
Reason: AC, DC, and EC motors all use AC power supply. AC motors are typically single speed and are only controllable through an external speed control. DC motors have a range of speeds they can be set at, but also need an external device to adjust their speed. EC motors are speed-controllable and have this capability built-in.
| Electric Motor Type | AC Motors | DC Motors | EC Motors |
| Topic: Fit | ✔ | ✔ | ✔ |
Reason: AC, DC, and EC motors can be used within similar sized housing as they are relatively within the same size as one another.
DC Motors
DC motors are highly efficient, and do not create as much heat as AC motors. One of their main calling cards is their high startup torque; ideal for machines that are hard to start. Additionally, this type of motor initiates a “soft start”. This allows the motor to start quietly, and they respond much quicker to inputs that relay commands to stop, to start, or to accelerate.
One major drawback of DC motors is that they are constructed with brushes and a commutator. This adds to the maintenance, limits the speed capability, and reduces the life expectancy of brushed DC motors.
DC motors are best suited for applications that require high torque at low speeds while maintaining the set airflow even at higher levels of static pressure.
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When Used in Small Fans
Small fans that use DC motors are more efficient than fans with AC motors while being slightly more expensive. Like fans with AC motors, DC motored fans allow maintenance personnel or homeowners to simply remove the collection of dust from the impeller once a year.
Small fans that use DC motors at Fantech include the bathfan SELECT FIT and SELECT Series, and the bathfan COMMERCIAL exhaust system. These bathroom ventilation exhaust fans can hold their designed airflow all the way up to 0.4 in. w.g., which is better than the leading competitors.
Another advantage of using these fans is the ability to set the airflow. DC motored fans like these allow building designers the versatility to move moist and stale air out for inhabitants at a high speed, while also giving designers the ability to achieve ASHRAE 62.2 guidelines by running the fan at a continuous low speed.
Benefiting from Fans with DC Motors
Like with AC motors, fans with DC motors are easy to specify. They help the designer reach indoor air quality guidelines set forth by organizations like ASHRAE. These fans also overcome high airflow restrictions in ductwork; further allowing the designer more leeway when constructing the plan for their application. Plus, it gives you some room to operate if adjustments need to be made on the fly; such as adding more turns or elbows in the duct or increasing the length of the duct run.
These fans are not as durable as AC fans but offer higher energy efficiency which can lead to lower energy costs throughout the year. Furthermore, you can rest assured that the fan you install will meet the designed airflow at a typically seen static pressure.
| Electric Motor Type | AC Motors | DC Motors | EC Motors |
| Topic: Function | ✗ | ✗ | ✔ |
Reason: AC motors are not as efficient as DC or EC motors. DC motors are more efficient than AC motors, by about 30% according to Mader Electric. While an EC motor uses up to 75% less power (when ran at half-speed) compared to an equally sized AC motor.
| Electric Motor Type | AC Motors | DC Motors | EC Motors |
| Topic: Maintenance and Durability | ✗ | ✗ | ✔ |
Reason:
AC motors last longer than DC motors because they do not have commutator bars that wear out.
As a result of their design, the windings of the DC motor wear and break. This in turn requires much more maintenance and a shorter life cycle than an equally sized AC motor.
Because EC motors are brushless, permanent magnet motors with built-in electronics they—because of their design—have an IE4 efficiency class. This means they are super-efficient. This design helps them be virtually silent and vibration-free and induces the ability to have a longer lifespan.
EC Motors
A third type of motor, known as an EC (Electronically Commutated) motor, is a modern solution that could eventually replace AC and DC motors. An EC motor is essentially a BLDC (Brushless Direct Current Motor) with onboard electronics to make the motor rotate.
While in a sense EC motors are better in terms of efficiency, maintenance, and life cycle, they are more costly than AC or DC motors.
EC motors are ideal for applications that require precise speed control and high efficiency. Typical applications include small fans, motion-control systems, and within HVAC applications.
Nowadays, states are adopting stronger requirements for electric-motor powered appliances, such as the residential furnace. Adopted in July 2019, the U.S. Department of Energy (DOE) established new rules for motors used in residential furnaces. These new regulations stipulate that residential furnace fans manufactured on and after July 3, 2019 shall have a fan energy rating (FER) value that meets or is more than the values set forth within the regulation.
For homeowners, this means furnaces developed after this time are manufactured with an EC motor. This change can be seen in their annual energy cost bill, which saves the average household about $300-$500 yearly.
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When Used in Small Fans
Small fans with EC motors have a longer lifespan than fans with DC or AC motors. Because of their brushless DC motor design, they are highly efficient and incredibly long-lasting, but they cost the most out of the three types of fans. Using an FG 4XLEC fan, for example, allows tenants, building and homeowners, and maintenance personnel to control the level of ventilation with a speed controller.
Benefiting from Fans with EC Motors
Using an EC driven RAHU, like the HERO® 150H-EC and the 250H-EC, can help homeowners and building owners reap the benefits of highly efficient operations to induce lower energy costs. Additionally, the high-efficiency and durability of fans with EC motors ease maintenance requirements for maintenance personnel and homeowners alike.
| Electric Motor Type | AC Motors | DC Motors | EC Motors |
| Topic: Initial Cost | ✔ | ✗ | ✗ |
| Topic: Operational Cost | ✗ | ✔ | ✔ |
Reason:
AC motors are usually mass produced and use a simpler design than an equally sized DC and EC motor. Both factors enable AC motors to have a low price point.
On the other hand, DC motors generally cost more than AC motors initially due to their higher manufacturing costs. However, they can save on operation costs since they use less power than their AC counterpart.
EC motors cost the most upfront out of the three motors because of their complex design. On the other hand, they can save even more on operation costs over DC motors and can save 10-75% more than an equally sized AC motor.
| Electric Motor Type | AC Motors | DC Motors | EC Motors |
| Topic: Speed Range | 1800-3600 rpm | 1000-5000 rpm | 100-4000 rpm |
Reason:
Most commonly, AC motors are built to run at specific speeds. AC motors are built with either two or four poles. Two pole AC motors operating at 60 Hz run at approximately 3600 rpm while four pole AC motors have speeds around 1800 rpm.
DC motors also are built with poles, but other factors impact the speed range of these motors more so than the poles do. According to groschopp, a small motor manufacturer from Iowa, they say these factors include:
“…the number of wire turns in an armature, the operating voltage of the motor, and the strength of the magnets that all affect motor speed.”
According to their website, the operating voltage equals the maximum voltage that the motor can achieve. Therefore, it will only be able to perform at a speed rated for 12 V, 24 V, and so on. Typically, however, DC motors can operate at speeds from 1000–5000 rpm.
Since EC motors utilize ball bearings within their design, their speed can range from as little as 100 rpm up to 4000 rpm in small motor designs.
In Summary
There is no one "best" motor as it depends on the specific application and requirements. Each type of motor has its own advantages and disadvantages.
When choosing a motor, it's important to consider factors such as power consumption, efficiency, speed range, torque, and cost. The best motor for a particular application is one that meets the specific requirements of that application while also being reliable, durable, and cost-effective. Other ways to distinguish these motors include their fit, form, function, life cycle, speed range, and controllability.
At Fantech, all of our fans use either AC, DC, or EC motors. See the list below for a quick rundown of products that use each type of motor.
| Products Driven by AC Motors | Products Driven by EC Motors | Products Driven by DC Motors |
|---|---|---|
| FG 4 Centrifugal Inline Fan | FG 4XLEC Centrifugal Inline Fan | bathfan Select SC110-130-150LHO |
| DEDPV-705 UL Listed Ventilator | Rn 2EC Inline Radon Fan | bathfan Select Fit SFC50-80-100LHO |
| ATMO 150E Fresh Air Appliance | HERO® 150H-EC Fresh Air Appliance | bathfan Commercial COM200-300-400-500 |
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