Need for Small Motors

Author: E.E. Kimberly

A man can produce about 100 watts of power continuously throughout a working day. In an 8-hour working day his energy output in useful work would be 800 watt-hours. If he were to sell this energy at prevailing rates which are charged for household consumption, or at 30 cents per kilowatt-hour, his day of labor would be valued at 24 cents. His efforts would not be sufficient to operate the family washing machine for a whole day.

Large motors turn the factory wheels, but fractional-horsepower motors in particular save the backs of men. Fractional-horsepower motors are almost altogether direct-current or single-phase alternating-current machines. Because of the greater cost of providing polyphase power, few small polyphase motors are in use. The small direct-current motor is not essentially different from the large one. This chapter will be devoted to the single-phase motor only. Except for railway service, the single-phase motor is built in sizes up to 50 hp only.

The many types of single-phase motors are distinguished by the means by which their starting is achieved, and they will be described in the approximate ascending order of their merits.