Table of Contents
Advertisement
Indoor Blower Motor
Power Choke
(4 and 5 Ton Only)
Figure 7.
WARNING
During blower operation, the ECM motor emits
energy that may interfere with pacemaker operation.
Interference is reduced by both the sheet metal cabinet
and distance.
The NF97UM line uses three different motor sizes; 1/2 hp,
3/4 hp and 1hp. The motor communicates with the integrated
control via a 2-way serial connection. The motor receives
all necessary functional parameters from the integrated
control and does not rely on a factory program like traditional
variable speed motors. NF97UM units use a three-phase,
electronically controlled D.C. brushless motor (controller
converts single phase a.c. to three phase D.C.), with a
permanentmagnet-type rotor (Figure 8). Because this motor
has a permanent magnet rotor it does not need brushes like
conventional D.C. motors.
Internal components are shown in Figure 8. The stator
windings are split into three poles which are electrically
connected to the controller. This arrangement allows motor
windings to turn on and off in sequence by the controller.
IMPORTANT
Earlier ECM motors used on other GE Appliances
furnace models are not interchangeable with motors
used on the NF97UM furnace line.
Blower Motor
(B3)
A solid-state controller is permanently attached to the
motor. The controller is primarily an A.C. to D.C. converter.
Converted D.C. power is used to drive the motor. The
controller contains a microprocessor which monitors varying
conditions inside the motor (such as motor workload).
STATOR
(WINDINGS)
BEARING
Figure 8. Blower Motor Components
The controller uses sensing devices to sense what position
the rotor is in at any given time. By sensing the position of
the rotor and then switching the motor windings on and off in
sequence, the rotor shaft turns the blower.
All NF97UM blower motors use single phase power.
An external run capacitor is not used. The motor uses
permanently lubricated ball-type bearings.
Internal Operation
The motor is controlled via serial communication between the
integrated control on the furnace and the controller attached
to the motor shell. The messages sent back and forth
between the two controls serve to communicate rotational
direction, demand, motor size, current draw, torque, and
rpm, among other variables.
Motor rpm is continually adjusted internally to maintain
constant static pressure against the blower wheel. The
controller monitors the static work load on the motor
and motor amp-draw to determine the amount of rpm
adjustment. Blower rpm may be adjusted any amount in
order to maintain a constant cfm as shown in Blower Ratings
Tables. The cfm remains relatively stable over a broad range
of static pressure. Since the blower constantly adjusts rpm
to maintain a specified cfm, motor rpm is not rated. Hence,
the terms "cool speed", "heat speed" or "speed tap" in this
manual, on the unit wiring diagram and on blower B3, refer
to blower cfm regardless of motor rpm.
Initial Power Up
When line voltage is applied to B3, there will be a large
inrush of power lasting less than 1/4 second. This inrush
charges a bank of DC filter capacitors inside the controller.
If the disconnect switch is bounced when the disconnect is
closed, the disconnect contacts may become welded. Try
not to bounce the disconnect switch when applying power
to the unit.
Page 24
ROTOR
31-5000723 Rev. 0
Advertisement
Table of Contents
