Figure 7-34.Capacitor start motor winding circuit.
The procedure for troubleshooting and repair for
the capacitor motor is the same as for the split-phase
motor except for the capacitor. Capacitors are rated in
microfarads and are made in various ratings, according
to the size and type. Acapacitor may be defective due to
moisture, overheating or other conditions. In such a
case it must be replaced with another one of the same
value of capacity. To test a capacitor, remove the motor
leads from the capacitor and connect the capacitor in
series with a 10-amp fuse across a 110- volt line. If the
fuse burns out, the capacitor is short-circuited and must
be replaced. If the fuse does not burn out, leave the
capacitor connected to the line for a few seconds to
build up a charge. Do not touch the terminals after the
charging process as serious injury may result from the
Short the terminals with an insulated handle screw
driver. A strong spark should show if the capacitor is
good. If no spark or a weak spark results, the capacitor
must be replaced.
The procedure for rewinding a capacitor motor is
the same as for the split-phase motor except for the
A universal motor is one that operates on either
single-phase ac or dc power. These motors are normally
made in sizes ranging from 1/200 to 1/3 horsepower.
You can get them in larger sizes for special conditions.
The fractional horsepower sizes are used on vacuum
cleaners, sewing machines, food mixers, and power
The salient-pole type is the most popular type of
universal motor. The salient-pole type consists of a
stator with two concentrated field windings, a wound
rotor, a commutator, and brushes. The stator and rotor
windings in this motor are connected in series with the
power source. There are two carbon brushes that
remain on the commutator at all times. These two
brushes are used to connect the rotor windings in series
with the field windings and the power source (fig. 7-35).
The universal motor does not operate at a constant
speed. The motor runs as fast as the load permits; i.e.,
low speed with a heavy load and high speed with a light
load. Universal motors have the highest horsepower-to-
weight ratio of all the types of electric motors.
The operation of a universal motor is much like a
series dc motor. Since the field winding and armature
are connected in series, both the field winding and
armature winding are energized when voltage is applied
to the motor. Both windings produce magnetic fields
which react to each other and cause the armature to
rotate. The reaction between magnetic fields is caused
by either ac or dc power.
The shaded-pole motor is a single-phase induction
motor that uses its own method to produce starting
torque. Instead of a separate winding like the split-
phase and capacitor motors, the shaded-pole motors
start winding consists of a copper band across one tip of
Figure 7-35.Universal motor schematic.