Rockwell Automation 20G PowerFlex 750-Series AC Drives - Manual (Page 206)

206 Rockwell Automation Publication 750-RM002B-EN-P - September 2013
Chapter 4 Motor Control
t
3
- t
2
= total time of deceleration from rated speed to 0 speed, in seconds
P
b
= peak braking power, watts (1.0 HP = 746 Watts)
Compare the peak braking power to that of the rated motor power, if the peak
braking power is greater that 1.5 times that of the motor, the deceleration time,
(t
3
- t
2
), needs to be increased so that the drive does not go into current limit. Use
1.5 times because the drive can handle 150% current maximum for 3 seconds.
Peak power can be reduced by the losses of the motor and inverter.
Step 3 – Calculating the Maximum Dynamic Brake Resistance Value
V
d
= The value of DC bus voltage that the chopper module regulates at and is
equal to 375V DC, 750V DC, or 937.5V DC
P
b
= The peak braking power calculated in Step 2
R
db1
= The maximum allowable value for the dynamic brake resistor
Choose a Dynamic Brake resistance value that is less than the value calculated in
Step 3. If the value is greater than the calculated value, the drive can trip on DC
bus overvoltage. Remember to account for resistor tolerances.
Step 4 – Choosing the correct Dynamic Brake Module
In the table above, choose the correct Dynamic Brake Module based upon the
resistance value being less than the maximum value of resistance calculated in
Step 3. If the Dynamic Brake Resistor value of one Dynamic Brake Module is not
sufficiently low, consider using up to three Dynamic Brake Modules in parallel,
such that the parallel Dynamic Brake resistance is less than Rdb1 calculated in
Cat. No. Resistance Wattage
240 Volt
KA005 28 ohms 666 watts
KA010 13.2 ohms 1650 watts
KA050 N/A N/A
460 Volt
KB005 108 ohms 1500 watts
KB010 52.7 ohms 2063 watts
KB050 10.5 ohms 7000 watts
600 Volt
KC005 108 ohms 1500 watts
KC010 52.7 ohms 2063 watts
KC050 15.8 ohms 8000 watts
R
db1
V
2
d
P
b
------- =