Appendix A
Appendix A-1MN715

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) +1.02x 2
ǸxV
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 +LoweringTime
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