Appendix A
Appendix A-1
MN715
Dynamic Braking (DB) Hardware
Whenever a motor is abruptly stopped or forced to slow down quicker than if allowed to
coast to a stop, the motor becomes a generator. This energy appears on the DC Bus and
must be dissipated using dynamic braking hardware. Dynamic braking (DB) hardware
can be a resistor or transistor load. Table A-1 provides a matrix of DB turn ON and turn
OFF voltages.
Table A-1
Parameter Description
Control Input Voltage
Nominal Voltage
230VAC
460VAC
575VAC
Overvoltage Fault (Voltage exceeded)
400VDC
800VDC
992VDC
DB ON Voltage
381VDC
762VDC
952VDC
DB UTP *
388VDC
776VDC
970VDC
DB OFF Voltage
375VDC
750VDC
940VDC
* DBUTP (DB Upper Tolerance Peak)
+
1.02 x
2
Ǹ
x V
L
*
L
Braking torque and time should not exceed the available drive braking torque and time
rating. The drive braking torque is limited to the available peak current and peak current
time rating of the control. If the peak current or peak current time limit is exceeded during
braking, the control may trip on an over voltage or a regen power fault. Selecting an
oversized control or a line regenerative control should be considered in these cases.
Selection Procedure
1.
Calculate the watts to be dissipated using the following formulas for the
appropriate load type.
2.
Identify the control model number and determine which braking hardware is
required based on the model number suffix: E, EO, ER, MO or MR.
3.
Select appropriate braking hardware from Baldor 501 Catalog or Tables A-2,
A-3 and A-4.
Hoisting Load Calculations
1.
Calculate braking duty cycle:
Duty Cycle
+
Lowering Time
Total Cycle Time
2.
Calculate braking watts to be dissipated in dynamic braking resistors:
Watts
+
duty cycle
lbs
FPM
efficiency
44
where:
lbs = weight of load
FPM = Feet Per Minute
efficiency = mechanical efficiency
i.e., 95% = 0.95
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