Finding Horsepower

Electrical power is rated in horsepower or watts. A horsepower is a unit of power equal to 746 watts or 33,0000 lb-ft per minute (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. It is 1/746 of 1 horsepower. The watt is the base unit of electrical power. Motor power is rated in horsepower and watts.

Horsepower is used to measure the energy produced by an electric motor while doing work.

To calculate the horsepower of a motor when current, efficiency, and voltage are known:

HP =( V x I x Eff ) / 746


HP = horsepower
V = voltage
I = current (amps)
Eff = efficiency

• Example: What is the horsepower of a 230v motor drawing 4 amps with 82% efficiency?

HP =( V x I x Eff ) / 746

HP = (230 x 4 x .82)746/

HP = 754.4/746

HP = 1 Hp

Eff = efficiency / HP = horsepower / V = volts / A = amps / PF = power factor

To calculate the horsepower of a motor when speed and torque are known:

HP =( rpm x T(torque))/ 5252(constant)


• Example: What is the horsepower of a 1725 rpm motor with a FLT 3.1 lb-ft?

HP =( rpm x T ) / 5252

HP = (1725 x 3.1) / 5252

HP = 5347.5 /
5252
HP = 1 h