12 DC BRAKE (DC BRAKE VOLTAGE)
DC braking creates a braking torque by injecting DC voltage into the motor. This parameter set the
magnitude of that DC voltage. The point at which the drive applies DC braking to the motor depends on
which STOP mode is programmed (either COAST or RAMP, see Parameter 26 - STOP).
If the drive is set to COAST, DC braking is activated when the stop command is given. In this case, DC
braking helps decelerate the motor. This is useful in applications where a quick deceleration is desired on a
load that would normally take a long time to coast to a stop.
If the drive is set to RAMP, DC braking is activated when the output frequency reaches 0 Hz. In this
case, the drive decelerates the load to a near stop and then DC braking is sued to stop and hold the motor.
This is useful in applications where the load needs to be stopped in a certain position. Similar applications
with high-inertia loads utilize both dynamic braking and DC braking. The dynamic braking allows the
high-inertia load to be decelerated quickly, while the DC braking stops the load in the desired position.
Due to heat generated in the motor, DC braking should only be used in applications where the load is
stopped infrequently. In high duty-cycle applications, dynamic braking is recommended because the heat is
dissipated through external resistor banks, rather than in the motor. When used, DC BRAKE should be set
to the lowest voltage that provides satisfactory operation in order to minimize motor heating. The maximum
voltage available depends on the voltage rating of the drive. Refer to the table below:
13 DC TIME (DC BRAKE TIME)
This parameter determines the length of time that the DC braking voltage is applied to the motor. DC
TIME should be set to the lowest value that provides satisfactory operation in order to minimize motor
heating.
NOTE: If this parameter is set to 999.9 seconds (the maximum value), the DC braking will be continuous.
14 DYN BRAK (DYNAMIC BRAKE)
This parameter enables the dynamic braking circuit. Set this parameter to ON only if the optional
dynamic braking circuit board and resistors are installed.
Dynamic braking is used in applications where high-inertia loads need to be decelerated quickly. When
this is attempted, the motor regenerates voltage back into the drive, causing the DC bus voltage to rise,
eventually resulting in a HI VOLTS fault. With the dynamic braking option, the DC bus voltage is
monitored, and when it reaches a certain level, a transistor is switched on that connects an external resistor
bank across the DC bus. This allows the regenerated energy from the motor to be dissipated through the
resistors as heat, which keeps the DC bus voltage below the trip level.
51
MAXIMUM DC BRAKE VOLTAGE
240/120 Vac 240/200 Vac 480/400 Vac 590/480 Vac
24 VOLTS 24 VOLTS 48 VOLTS 59 VOLTS
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