Rockwell Automation 1336_S_F_T Allen-Bradley Dynamic Braking User Manual
Page 14
Heavy Duty Dynamic Braking
14
1336-5.64 — July, 2005
R
db1
= 0.9V
d
2
/P
b
= 9.05 ohms
This calculation is the result of Step 3 and determines the maximum ohmic
value of the Dynamic Brake Resistor. Note that a choice of V
d
= 750 Volts
DC was made based on the premise that the drive is rated at 460 Volts.
The most cost-effective combination of Dynamic Brake Modules chosen
in Step 4 is one 1336-MOD-KB050 and one 1336-MOD-KB010 operated
in parallel. This results in an equivalent Dynamic Brake Resistance of
8.76 ohms.
By comparison, a KB050 paralleled with a KB005 results in an equivalent
Dynamic Brake Resistance of 9.57 ohms, which is greater than the
maximum allowable value of 9.05 ohms. If two KB050 Dynamic Brake
Modules are paralleled, the equivalent resistance would be 5.25 ohms,
which will satisfy the resistance criteria set by Step 3, but is not cost
effective.
This is the result of calculating the average power dissipation as outlined
in Step 5. Verify that the sum of the power ratings of the Dynamic Brake
Resistors chosen in Step 4 is greater than the value calculated in Step 5.
AL = 100
× P
av
/P
db
= 32%
This is the result of the calculation outlined in Step 6 and is less than 100%.
Draw AL as a dotted line on Figure 4.
PL = 100
× P
b
/P
db
= 617%
This is the result of the calculation outlined in Step 7 and should always be
greater than 100%.
= 2.8 kW
ω
b
+
ω
o
ω
b
P
av
=
(t
3
- t
2
)
t
4
(
×
P
b
2
)