Motor Efficiency

Written by Jerry Ratzlaff on . Posted in Rotating Equipment

Motor efficiency, abbreviated as \(\eta_m\) (Greek symbol eta), a dimensionless number, is the ratio of shaft power power out and electric power input of a motor.


 Motor Efficiency formula

\(\large{ \eta_m = \frac{ 0.7457 \; HP \; Load  }{ P_{in} } }\) 
Symbol English Metric
\(\large{ \eta_m }\)  (Greek symbol eta) = motor efficiency   \(\large{dimensionless}\)
\(\large{ P_{in} }\) = input power \(\large{\frac{ft-lbf}{sec}}\)  \(\large{kg\;m^2\;s^{-3}}\) 
\(\large{ HP }\) = horsepower \(\large{\frac{ft-lbf}{sec}}\)  \(\large{kg\;m^2\;s^{-3}}\) 
\(\large{ Load }\) = output power as a % of rated power \(\large{dimensionless}\)


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Tags: Efficiency Equations Motor Equations