Shaft power produced from a direct current (DC) electrical motor:
P shaft_kW = η m U I / 1000 (1)
P shaft_kW = shaft power (kW)
η m = motor efficiency
U = voltage (V)
I = current (A, amps)
Shaft power produced from an alternating current (AC) electrical motor:
P shaft_kW = η m U I PF / 1000 (1b)
PF = Power Factor
P shaft_kW = η m 2 U I PF / 1000 (1c)
P shaft_kW = η m 1.73 U I PF / 1000 (1d)
Shaft power as horse power :
P shaft_hp = P shaft_kW / 0.746 (2)
or for a DC motor
P shaft_hp = (η m U I / 1000) / 0.746
= η m U I / 746 (2b)
P shaft_hp = shaft power (hp)
The shaft power produced by an electric direct current motor with 36 V, 85% efficiency and 5 amps - can be calculated in watts as
P shaft_kW = 0.85 (36 V) (5 amps) / 1000
= 0.153 kW
= 153 W
The shaft power as hp
P shaft_hp = (0.153 kW) / 0.746
= 0.21 hp
Standard horsepower ratings for electrical motors - 1 to 4000 hp are indicated below:
Nominal voltage of not more than 600 V AC and nominal frequency 50 or 60 Hz .
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