MOTOR EFFICIENCY

Calculating Efficiency of Electric Motors

(Example Motor)

Volts = 14.2
Amps = 28.0
Io = 1.1A (no-load amps at the operating speed)
Rm = 0.055 Ohm (internal resistance of motor)

Input Watt = V x A = 14.2 x 28 = 397.6 Watt

Copper Loss = Amps ² x Rm = 28 x 28 x 0.055 = 43.12 Watt

No-load Losses = Volts x Io = 14 x 1.1 = 15.62 Watt

Total Losses = 43.12 + 15.62 = 58.74 Watt

Output Watt = Input Watt – Total Losses = 397.6 – 58.74 = 338.86 Watt

Efficiency = Output Watt / Input Watt = 338.86 / 397.6 x 100 = 85.23%

Please note that we calculated the efficiency of the motor with a given prop. After calculating the efficiencies with a few different sized props (on the same motor), it will be evident how copper loss is mainly responsible for heat buildup and consequently lower efficiencies