While our customers are wholesalers, Packard knows that you, the contractor, have a choice. You are often presented with many buying options, and being well-informed about your purchase can help make your job easier and more successful.
This is why we have dedicated a section of our site for contractors. In this section, you will find helpful product tips, tools and some clips from our training classes. We’ve also provided a distributor locator so you can find the nearest wholesaler who can give you access to Packard products.
What’s the difference between an EC and a constant torque motor?
There seems to be confusion in the terminology used for Electronically Commutated Motors (ECMs). We hear them called ECs, variable speed, constant airflow, constant torque, constant speed, and permanent magnet, among other terms. The electrical design of these motors is quite different from the design of the shaded pole, permanent split capacitor (PSC), and three- phase motors that we are used to working with. The shaded pole, PSC, and three-phase are induction motors. That is, a magnetic field is induced into the rotor of the motor. However, the ECM is designed with a permanent magnet rotor. The magnetic field in the rotor of this motor is not dependent upon induction to become a magnet. It is permanently a magnet.
In HVAC/R applications, air is typically moved using either an axial fan (fan blade) or a centrifugal fan (blower). A blower is used when higher static pressures are to be overcome. Changes in static pressure impact the performance of a blower in just the opposite way that they impact a fan. Because of this difference between fans and blowers, the EC motor driving the fan or blower must be designed with this in mind.
Currently we see ECMs designed as constant speed, constant airflow (true variable speed), and constant torque.
When a fan blade is used, the ECM is generally designed as a constant speed motor. If static conditions change the motor will adjust its performance to maintain its designed speed. These are seen in refrigeration applications as well as HAC condensing units.
Blowers, on the other hand, will utilize either constant airflow or constant torque EC motors.
The constant airflow ECM maintains a pre-programmed amount of air when operating in a specific furnace or air handler. As operating conditions in the unit change, the motor will adjust its speed to maintain its pre-set airflow. These are true variable speed motors.
Some furnace and air handlers utilize a constant torque ECM. They have “speed” taps. That is, leads from the motor that provide various “speeds”. These taps provide different, but specific, operating torques. When the same load is operated on a different tap a speed change results.
Remember, constant speed, constant airflow, and constant torque are all ECMs. The application determines which design is used.
Packard has developed a complete HVACR critical components training program, which has received approval by North American Training Excellence (NATE) - the leading certification program for HVACR technician, and the only test approved by the entire industry. Below are some video excerpts from our instructor led training courses which we hold at Wholesaler locations nationwide.
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