Rockwell Automation AK DBU - Dynamic Braking Unit 600/690 VAC User Manual
Page 46
C-8
Design Information
Calculate Maximum Dynamic Brake Resistance:
V
d
= DC Bus Regulation Voltage
R
= Minimum Brake Resistance Value
Record the Maximum Dynamic Brake Resistance R
db1
in above table.
The choice of the Dynamic Brake resistance value should be less than
the value calculated in this step.
If the value is greater, the drive can trip
on DC bus overvoltage.
Step 5
Calculate Required Joule Rating
(joules = Watt-Seconds):
Drive Efficiency = 0.975
Step 6
Select a Resistor
Select a resistor bank from the following tables or from your resistor
supplier that has all of the following:
• a resistance value that is less than the value (R
db1
in Ohms)
calculated in
, but as close as possible below this value.
• a resistance value that is greater than the minimum resistance for the
DBU listed in
,
• a power value that is greater than the value calculated in
(P
av
in watts),
• a watt-second value greater than the value calculated in
Line Voltage
V
d
P
max
R
P
max
x R
R
db1
600V AC
950V DC
268,000 W
3.2 Ohms
857375
Ohm
690V AC
1090V DC
305,000 W
3.7 Ohms
1128695
Ohm
R
db1
oooooooo
·
[
]
ooooooooo
[
]
--------------------------------
=
P
b
2
-----
⎝ ⎠
⎛ ⎞
t
3
t
2
–
(
)
×
watt-seconds
=
Watt-second losses
P
b
2
------x t
3
t
2
–
(
) x 1
motor efficiencyxdrive efficiency
(
)
–
[
]
=
Total watt-seconds
watt-seconds
watt-second losses
–
=