2-2 Determining Dynamic Brake Requirements
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)
• Required decel time (per Figure 2.1
, t
3
– t
2
). This time is a process
requirement and must be within the capabilities of the drive
programming.
• Motor inertia and load inertia in kg-m
2
or WK
2
in 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 2.1 shows typical application profiles for speed, torque and
power. The examples are for cyclical application that is periodic over t
4
seconds. The following variables are defined for Figure 2.1:
ω(t) = Motor shaft speed in radians per second (rps)
N = 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
ω
o
= Angular rotational speed less than ω
b
(can equal 0)
-P
b
= Motor shaft peak regenerative power in watts
ω
2πN
60
----------=
Rad
s
---------
Rad
s
---------
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