It should be understood that there is a limit to the amount of static pressure the motor can handle. In order to make PSC motors more flexible for a variety of applications, they include speed taps that allow the mechanical contractor (or manufacturer) to manipulate the motor’s speed to ensure that the correct amount of airflow is delivered for both optimal performance and safety within a range of external static pressures. For example, an equipment manufacturer may utilize a ½ hp motor in a 3-ton drive furnace in order to deliver an average airflow of 1,200 CFM within a range of external static pressures (ESP) often found in assorted applications.īut what if the duct system layout in a specific application has an increased static pressure because the mechanical contractor added a very restrictive media filter? PSC motors are considered single-speed (speed refers to the rate of rotational motion) because they do not have any internal controls that can be programmed to automatically vary the rotation of the motor over an operating range. However, since there are few mechanical components, this design has proven to be very simple and reliable, and can be manufactured at a relatively low cost.
This operational characteristic, which also generates excessive heat, greatly contributes to the degraded operational efficiency of PSC motors (which are at best only 60 percent efficient). In this operation, the rotor constantly lags behind the magnetic field in the stator, resulting in what is known as asynchronous (i.e., not synchronized) operation.
Therefore, as the magnetic field rotates in the stator, the rotor also rotates to maintain its alignment with the stator’s magnetic field. PSC motors, often referred to as induction motors, typically use alternating current (AC) and include two key components in their design - a stator (the stationary section of the motor) and a rotor (the rotating section of the motor).Ī magnetic field is induced in the rotor opposite in polarity of the magnetic field in the stator. The popularity of the PSC motor can be attributed to its simplicity, reliability, low cost and flexibility. PSC motors are typically positioned by most manufacturers as a standard product offering and are used in furnaces, air handlers, condensing units and packaged products. PSC single-speed motor technology has been the standard in the industry for many years and represents the highest installed base. What is this newer motor, and how does it compare to PSC single-speed and ECM variable-speed motor technologies? Why is it popular? Referred to as its X13 motor, this new technology has significantly gained in popularity among all heating and air conditioning equipment manufacturers. In 2006, Regal-Beloit (formerly known as General Electric, now known as Genteq) introduced a third motor technology to the industry. Most HVAC professionals understand the key differences between these two motor types and are comfortable discussing the benefits of one technology over another. Historically, the two predominant motor types have been permanent split capacitor (PSC) single-speed motors and 2.3 electronically commutated motors (ECMs) with variable-speed capability. The type specified in any product design depends upon several criteria, including the product’s performance goals, positioning, cost and potential application. The heating, ventilation and air conditioning (HVAC) industry currently uses a variety of motor technologies in its equipment.