Miniature a. c. Motors

Abstract

Small electric prime movers find so many applications in nearly every field of human activity that they are manufactured in a great variety of designs, and in very large numbers. To achieve economic production, interchangeability, and basic performance standards, a range of electric motors generally known as fractional horsepower motors has been defined. This group, which comprises motors with outputs.up to 746 watts (1 hp) at 1000 rev/min, as well as miniature motors which have outputs expressed in milliwatts are dealt with here. The types range from three-phase induction motors (which are scaled-down versions of their larger counterparts) and special versions suitable for single-phase running, to series wound types and synchronous motors which, because they are small, permit the use of other electromotive principles.