Dynamometer and Instrumentation for Determining Electric Motor Power, Efficiency, and Power Factor

Abstract

Alternating current (AC) electric motors are widely used in the agricultural industry,
yet many students do not understand their basic operating characteristics. Welldesigned
laboratory activities can provide an excellent method for students to observe
and actively study motor operation. However, commercially available electric motor
dynamometers are prohibitively expensive for many agricultural systems technology
programs at both the secondary and university levels. This article describes the
construction and evaluation of an inexpensive “spring-and-string” electric motor
dynamometer that allows students to actively study the power output, efficiency, and
power factor of small, fractional horsepower AC electric motors. The necessary
instrumentation is also described. The dynamometer and instrumentation produced
consistent results when used to test a 1/20-hp electric motor.