Figure 7-37.Capacitor motor used for a wall fan.
Figure 7-38.Three-phase motor.
tapped for different speeds and is connected in series
with the main winding.
The starting winding is
connected across the transformer secondary.
Acapacitor motor for a wall fan (fig. 7-37) contains
a capacitor of approximately 1 microfarad (µf) in the
To increase the effective
capacity and consequently the starting torque of this
motor, connect the capacitor. across an autotransformer.
The taps on the transformer permit a choice of various
Figure 7-39.Three-phase stator.
SPEED CONTROL OF UNIVERSAL FAN
The universal fan motor has a resistance unit in the
base to vary the speed. A lever that extends outside the
base is used to insert the resistance in the circuit.
CONSTRUCTION OF THREE-PHASE
Construction of a three-phase motor consists of
three main parts: stator, rotor, and end bells. Its
construction is similar to a split-phase motor, but the
three-phase motor has no centrifugal switch (fig. 7-38).
The stator, as shown in figure 7-39, consists of a
frame and a laminated steel core, like that used in split-
phase and repulsion motors, and a winding formed of
individual coils, placed in slots.
The rotor may be a die-cast aluminum squirrel-cage
type or a wound type. Both types contain a laminated
core pressed onto a shaft. The squirrel-cage rotor (fig.
7-40) is like the rotor of a split-phase motor. The wound
Figure 7-40.Squirrel-cage rotor.