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Morning !Hay Professor! How do these evap motors "know"what to do and when to do it.? ? What kind of "sensors" do they have to make the motor run to keep up the duct static pressure ? Thanks and Enjoy your day!!!!!


  • D lux_2
    D lux_2 Member Posts: 230

    mostley programed at factory have to use oem motors
  • Jim M
    Jim M Member Posts: 29

    I'll take a stab at it but would really like to here from a motor expert on this one. As I understand it the microprocessor on the motor head monitors the back emf on the winding and uses that info with the programmed CFM to increase or decrease motor RPM.

  • Jim Bergmann_2
    Jim Bergmann_2 Member Posts: 79
    ECM Motors

    Sometimes it not knowing everything as much as knowing where to find it. I pulled some notes from a power point from at the instructors workshop in Arlington VA last year. The presentation was done by the owner of HVAC DYNAMICS, Christopher A. Mohalley Owner / Instructor Chris does instruction for GE on the ECM motor and additionally does training for hire across the country.

    The ECM motor is a brushless DC, Three - phase motor with a permanent magnet rotor. Motor phases are sequentially energized by the electronic control, powered from a single-phase supply. The input power supply is 120/240vac with the proper jumper connection. The motor control converts AC power to DC power, the microprocessor uses sensor less technology allowing the motor control to determine speed (frequency) and torque (current) to maintain airflow to an OEM specification. The motor then control converts DC power back to AC three-phase power for motor operation.

    In a series of tests by the OEM, (i.e. the air handler manufacturer) the motor is “taught” the relationship between speed, torque, airflow and external static pressure. In these tests, or airflow characterization process, a development engineer will adjust the ECM torque and chamber static pressure, and measure the resulting ECM speed and airflow. These values over a wide range of static pressures and airflows are used in a GE supplied development program to create a set of blower constants that are specific to each air mover (furnace / air handler). “Airflow” is programmed by the OEM and is specific and unique to the motor and air mover combination. So each motor knows the specific airflow the OEM is looking for over a wide range of external static pressure, specific to each unit, for each demand (heat, cool, continuous fan). At the time of installation, all that is required of the installer is to set the required CFM (Cubic Feet per Minute) for each demand to the size of the equipment the motor is used in and/or with.
    •We are no longer setting speeds; we are selecting the exact CFM designed by the OEM for the demand.
  • Techman
    Techman Member Posts: 2,144

    Hi Jim !WOW. Thank You Sir!Enjoy Your Day!
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