Allen-Bradley 20G - Page 15

Rockwell Automation Publication PFLEX-AT001L-EN-P - September 2017 15
Determining Dynamic Brake Requirements Chapter 2
Step 2 – Peak Braking Power
P
b
= Peak braking power (watts)
1.0 Hp = 746 watts
J
T
= Total inertia reflected to the motor shaft (kg•m
2
)

b
= Rated angular rotational speed

o
=Angular rotational speed,
less than rated speed down to zero
N
b
= Rated motor speed (rpm)
t
3
– t
2
= Deceleration time from 
b
to 
o
(seconds)
Calculate Peak Braking Power:
Record Peak Braking Power:
Compare the peak braking power (
P
b
) to the drive rated regenerative power (P
rg
).
If the peak braking power is greater than the drive rated regenerative power, the
decel time will have to be increased so that the drive does not enter current limit.
Drive rated regenerative power (
P
rg
) is determined by:
P
rg
= Drive rated regenerative power
V = DC bus regulation voltage from
Appendix A
R = Minimum brake resistance from
Appendix A
P
b
=
P
b
J
T

b

b

o
–
t
3
t
2
–
-------------------------------------------
=
Rad
s
----------
2N
b
60
-------------=
Rad
s
----------
P
b
ooooooooooooooooooooooooooo ooooooooo–
ooooooooo ooooooooo–
--------------------------------------------------------------------------------------------------------------------------------------------------------=
P
rg
V
2
R
------
=
P
rg
ooooooooo
2
ooooooooo
------------------------------------
=