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 stored charge.
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 capacitor.
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 hand tools.
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 motor's start winding consists of a copper band across one tip of
Figure 7-35. - Universal motor schematic.Continue Reading