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135
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AIRAH Industry Nights 2021
EC MOTORS
FOR HVAC&R FANS EC motors, also known as BLDC motors (brushless DC), BLPM motors (brushless permanent magnet), are electronically commutated permanent magnet brushless DC motors and are from the external
Skills summary
rotor motor family.
■ What?
newly manufactured equipment and for retrofit into existing plant
They are now used extensively in various applications, both for
A close look at EC motors, including what they are, how they work, controls, benefits, and safety precautions.
such as computer room AC units, refrigeration condensers and
■ Who?
This Skills Workshop explains how they work and the benefits they offer.
Relevant for anyone involved in the design, selection, installation, operation and maintenance of fans and fan systems.
What is an EC motor? You can think of an EC motor as an electric motor with a built-in variable frequency drive (VFD). These are very efficient motors with on-board electronics to allow for synchronous speed control with complete motor protection. This eliminates the need for contactors and overloads on the mains supply to the motors, and for shielded mains cable from the VFD to the motor. EC motors tend to be more common in the smaller motor sizes, where the AC equivalents are far less efficient. AC motor or internal rotor motor efficiencies increase as the motors increase in power sizes. As with all things, there are high-quality motors built to comply with the highest global standards with full R&D backup. There are also low-cost, reverse-engineered or copycat products that may seem similar at first glance, but often have little or no engineering support.
general HVAC systems.
It also covers details of their operation, and relevant safety precautions you should take when working with this equipment. Shortcomings in quality, performance, electrical compliance, and product support should be understood and considered carefully.
Evolution of the EC motor
Different brands also have different inclusions and capabilities. Some can only do the basics, while others go “all out” with many programable and communication options.
As energy efficiency became important, manufacturers started running close to the limits of the ERM AC motor, and began looking for other ways to improve motor efficiencies.
What is an external rotor motor?
By taking a VFD, changing the AC rotor to one with permanent magnets and combining them, the EC motor was born. At the time, electronics were large and expensive compared with today, and due to the size, they had to be mounted in a separate box like a VFD and wired into the motor. In the mid-1990s, as electronics became smaller and less expensive, they were merged into the motor housing to create the more compact and user-friendly EC motor we see today.
External rotor motors, known as ERM motors, are motors where the stator or stationary component of the motor is inside the rotor. These motors were originally designed for gyroscopes but became popular for fans because they are more compact than traditional internal rotor motors. From these original motors, blades were added to create the most common style of refrigeration fan seen for the last half a decade. In the chase for energy efficiency, the EC motor was developed.
Today the EC motor manufacturers are on the third and fourth evolutions of these motors. As the EC motor benefits became more understood and used in various industries, EC motors kept improving. Manufacturers also received feedback from the market and made changes for specific applications.
How does an EC motor work? For the most common variety for use in HVAC&R, you supply standard AC voltage into the electronics, where it is converted to DC voltage through a rectifier and filtered with the help of capacitors to form a DC link. The inverter, using electronic switches called IGBTs, switches the voltage in a controlled manner to the motor windings to create the rotating magnetic field. The advantage of having electronic switches is that it can control the magnetic field, making it stronger or weaker, faster, or slower, by changing the frequency and amplitude of this voltage to the
Figure 1 – Typical AC external rotor motor Summer 2020
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