All rights reserved. This article answers many of the frequently asked questions about electric motors. Universal motors have brushes and commutators and are used for portable tools like routers, skilsaws, and electric drills. Single-phase induction motors have no brushes, run only on AC electrical power, and are usually found on stationary tools such as table saws, drill presses, planers, and jointers. Universal motors do not have a synchronous speed, but have a maximum no-load speed that depends upon the voltage applied to the motor.
Most motors can put out a lot more maximum horsepower than they can sustain continuously.
By forcing more mechanical load on the motor, slowdown is increased and so therefore is the output horsepower. Mechanically, horsepower is torque times rpm, and increasing the mechanical load means that the rpm is slowed slightly and the drag torque is increased to obtain more torque times rpm. Electrically, horsepower is volts times amps, and by conservation of energy, the mechanical output horsepower must be balanced by electrical input horsepower. Since the voltage is relatively constant, this means that as a motor is loaded, the input current increases. But the electrical winding impedance has a resistive component, so that higher current means more power dissipated in the windings.