Universal Motors

The name "universal" is derived from the motor's compatibility with both AC and DC power. Among the applications using these motors are vacuum cleaners, food mixers, portable drills, portable power saws, and sewing machines. These motors seldom exceed one horsepower.

In most cases, universal motors reach little more than a few hundred rpm under heavy loads. If the motor is run with no load, speed may approach up to 15,000 rpm. This can result in serious heat damage to the motor's components.

Universal series motors differ in design from true induction motors. They have series wound rotor circuitry similar to that of DC motors. The rotor of a universal series motor is made of a laminated iron core with coils around it. The ends of the wire coils connect directly to the commutator.

Electric current in the motor flows through a complete circuit formed by the stator winding and rotor winding. Brushes ride on the commutator and conduct current through the rotor from one stator coil to the other. The rotor current interacts with the magnetic field of the stator causing the rotor to turn. As long as an electrical current is present in the rotor coils, the motor continues to run.