Power and Horsepower in Electrical Motors
Electrical power is rated in Horsepower or Watts
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Electrical power is in general rated in Watts or Horsepower. A horsepower is a unit of power equal to 746 watts or 33,000 lb.ft per minute (or 550 lb.ft per second).
A watt is a unit of measure equal to the power produced by a current of 1 amp across the potential difference of 1 volt. A watt is 1/746 of 1 horsepower.
Even if the watt is the base unit of electrical power, its common to rate motor power in either horsepower or watts.
Power in Watts
Electric power of a motor can be expressed as:
Pw = ηm U I (1)
where
Pw = power (W, watt)
ηm = motor efficiency
U = voltage (V)
I = current (A, amps)
Power in Horsepower
Horse power of a motor can be expressed as:
Php = Pw / 746 (2)
or
Php = ηm U I / 746 (2b)
where
Php = horsepower (hp)
Example - The Horsepower of an Electrical Motor
The horse power of an 230 V electrical motor with 85% efficiency pulling 10 amps can be calculated as:
Php = 0.85 (230 V) (10 amps) / 746
= 2.62 hp
Standard Horsepower Ratings
Standard horsepower ratings of electrical motors - 1 to 4000 hp are indicated below:
- 1, 1 1/2, 2, 3, 5, 7 1/2, 10, 15, 20, 25, 30, 40, 50, 60, 75, 100, 125, 150, 200, 250, 300, 350, 400, 450, 500, 600, 700, 800, 900, 1000, 1250, 1500, 1750, 2000, 2250, 2500, 3000, 3500, 4000
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Related Topics
- Electrical - Amps and electrical wiring, AWG - wire gauge, electrical formulas, motors and units
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