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When determining the torque
requirements for a electric motor, consideration should be
given to the load and start time demands during the start
duration, operating torque, and peak load torque. The
starting torque is dependant on the number of times an
electric motor will have to start in a given time, as well
as, the duration of the start cycle. The actual start
torque applied should be many times greater than the
actual start torque required by the application. The
greater difference in torque applied by the motor and the
start torque required by the application, the faster the
applied acceleration of the electric motor. The time
duration required to accelerate a application from a dead
stop to operating speed is given by the following:
T = [ N x WR2 ] / [ Ta
x 308 ] Where: T = Time ( seconds )
N = Velocity at load ( rpm )
Ta = Average Torque During start ( ft-lbs )
WR2 = Rotating Inertia (lbs-ft3)
W = Weight (lbs)
R = Radius of Gyration (ft2)
308 = Constant derived converting minutes to seconds, mass
from weight, and radius to circumference
Running or operating torque is determined
by the following equation: To = [ 5250 x HP ] / N Where: To = Operating or running
Torque ( ft-lbs )
HP = Horsepower delivered by electric motor
N = Rotational velocity ( rpm, revolutions per minute )
5250 = Constant converting horsepower to ft-lbs/minute and
work/revolution to torque Use the peak horsepower to determine the
maximum operating torque. © Copyright 2000 - 2006, by
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