Allen-Bradley PowerFlex 70 Reference Manual

Determining Dynamic Brake Requirements 2-9
A 10 HP, 4 Pole, 480 Volt motor and drive is accelerating and
decelerating as depicted in Figure 2.1
.
• Cycle period t
4
is 40 seconds
• Rated speed is 1785 RPM and is to be decelerated to 0 speed in 15.0
seconds
• Motor load can be considered purely as inertia, and all power
expended or absorbed by the motor is absorbed by the motor and
load inertia
• Load inertia is 4.0 lb.-ft.
2
and is directly coupled to the motor
• Motor rotor inertia is 2.2 lb.-ft.
2
• A PowerFlex 70, 10 HP 480V Normal Duty rating is chosen.
Calculate the necessary values to choose an acceptable Dynamic Brake.
This information was given and must be known before the calculation
process begins. This can be given in HP, but must be converted to watts
before it can be used in the equations.
This information was given and must be known before the calculation
process begins. This can be given in RPM, but must be converted to
radians per second before it can be used in the equations.
This value can be in lb.-ft.
2
or Wk
2
, but must be converted into kg-m
2
before it can be used in the equations.
Example Calculation
Rated Power 10 HP= 746 watts 7.46 kW=×
Rated Speed ω
b
1785= RPM 2π==
1785
60
----------
×
186.98 Rad
s
-------------------------=
Lower Speed ω
o
0= RPM 2π
0
60
-----
×
0 Rad
s
-------------===
Total Inertia J
T
6.2= lb.-ft.
2
0.261 kg-m
2
==
Deceleration Time t
3
t
2
–()15 seconds==
Period of Cycle t
4
40 seconds==

Allen-Bradley PowerFlex 70 Specifications

General

Brand	Allen-Bradley
Model	PowerFlex 70
Category	Controller
Language	English