Pfeifer Industries :: Power Transmission Applications
 
Power Transmission Fundamentals
Horsepower / Kilowatt

Horsepower / Kilowatt

Horsepower (HP):
Quantity one (1) HP is the rate of work required to raise 33,000 pounds one (1) foot in one (1) minute

Kilowatt (KW):
Quantity one (1) KW is the rate of work required to raise 11,163 kilograms 0.305 meter in one (1) minute


Note:  It is important to realize that when you increase or decrease speed (RPM), horsepower also increases or decreases proportionately.  HOWEVER, torque always remains constant.

Conversions:  

HP =

4KW x 1.31

KW =

HP x 0.7457

ft-lb =

Nm x 0.737562

in-lb =

Nm x 8.85

Nm =

ft-lb x 1.356

Nm =

in-lb x 0.113

ft-lb/sec =

HP x 550


Torque
Torque

Torque:
The twisting or turning effort around a shaft tending to cause rotation. Torque is determined by multiplying the applied force by the distance from the point where force is applied to the shaft center. It is measured in terms of pounds, or ounces; acting on a lever arm, measured in terms of feet or inches (Metric = Newton Meters (Nm). This lever arm is connected to a shaft that can rotate.

Torque (ft-lb) = Force x Distance

Note: Torque can be present at zero (0) rpm, in which case the horsepower would be zero (0).

Full-Load Torque:
Full-load torque is the torque to produce the rated power at full speed of the motor.


Note: Ratios, whether by gears, belts, chain and sprockets or anything else, are usually thought of as speed reducers, or less often, as speed increasers. They should be thought of more in terms of what they do to torque. A speed reducer is a torque increaser and vice versa. The laws of physics dictate that a change of speed via a ratio, proportionally changes the torque, as a factor of the ratio. Disregarding the friction in the system, the torque is multiplied or divided as a factor of the ratio. Thus a 5:1 speed reduction ratio, multiplies the input torque five (5) times (a MECHANICAL ADVANTAGE) and 1:5 speed increasing ratio would reduce the torque 5 times (a MECHANICAL DISADVANTAGE).

Conversions:  

HP =

KW x 1.341

KW =

HP x 0.7457

ft-lb =

Nm x 0.737562

in-lb =

Nm x 8.85

Nm =

ft-lb x 1.356

Nm =

in-lb x 0.113

ft-lb/sec =

HP x 550


Horsepower / RPM / Torque Relationship

Horsepower