Rockwell Automation 1336_S_F_T Allen-Bradley Dynamic Braking - Manual (Page 6)

Heavy Duty Dynamic Braking 6
1336-5.64 — July, 2005
How to Select a Dynamic Brake
Module Gather the following information:
• Power rating from motor nameplate in watts, kilowatts, or horsepower
• Speed rating from motor nameplate in rpm or rps (radians per second)
• Motor inertia and load inertia in kg-m 2 or lb-ft 2
• Gear ratio (GR) if a gear is present between the motor and load
• Motor shaft speed, torque, and power profile of the drive application
Figure 2 shows the speed, torque, and power profiles of the drive as a
function of time for a particular cyclic application that is periodic over t
4
seconds. The desired time to decelerate is known or calculable and is within
the drive performance limits. In Figure 2, the following variables are
defined:
ω
(t) = Motor shaft speed in radians per second (rps)
N(t) = Motor shaft speed in Revolutions Per Minute (RPM)
T(t) = Motor shaft torque in Newton-meters
1.0 lb-ft = 1.355818 N-m
P(t) = Motor shaft power in watts
1.0 HP = 746 watts
ω
b = Rated angular rotational speed
Rad/s
ω
o = Angular rotational speed less than
ω
b
(can equal 0)
Rad/s
-Pb = Motor shaft peak regenerative power in watts
ω
=
2
πN
60