Rockwell Automation 1336_S_F_T Allen-Bradley Dynamic Braking User Manual
Page 10
Heavy Duty Dynamic Braking
10
1336-5.64 — July, 2005
The average power in watts regenerated over the period t
4
is:
The Dynamic Brake Resistor power rating of the Dynamic Brake Module
(singly or two in parallel) that will be chosen must be greater than the value
calculated in Step 5. If it is not, then a Brake Chopper Module with the
suitable Dynamic Brake Resistor must be specified for the application.
Step 6 — Calculate the Percent Average Load of the Dynamic Brake Resistor
The calculation of AL is the Dynamic Brake Resistor load expressed as a
percent. P
db
is the sum of the Dynamic Brake Module dissipation capacity
and is obtained from Table 1a, 2a, or 3a. This will give a data point for a
line to be drawn on the curve in Figure 3. The number calculated for AL
must be less than 100%. If AL is greater than 100%, an error was made in
a calculation or the wrong Dynamic Brake Module was selected.
P
av
=
P
av
= Average dynamic brake resister dissipation (watts)
t
3
- t
2
= Deceleration time from
ω
b
to
ω
o
(seconds)
t
4
= Total cycle time or period of process (seconds)
P
b
= Peak braking power (watts)
ω
b
= Rated motor speed (Rad / s)
ω
o
= A lower motor speed (Rad / s)
[t
3
- t
2
]
t
4
✕
P
av
=
[
–
]
[
]
✕
[
]
2
P
av
= _________ watts
P
b
2
ω
b
+
ω
o
ω
b
(
)
✕
+
(
)
AL =
AL
= Average load in percent of Dynamic Brake Resistor
P
av
= Average dynamic brake resistor dissipation calculated in
Step 5 (watts)
P
db
= Steady state power dissipation capacity of dynamic brake
resistors obtained from Table 1a, 2a, or 3a (watts)
P
av
P
db
✕
100
AL =
[
]
[
]
✕
100
AL = _________ %