Lenze MC1000 Series - Manual (Page 52)

48 13435742_EDBM101_v24
12 DC BRAKE (DC BRAKE VOLTAGE)
DC braking creates a braking torque by injecting DC voltage into the motor. This
parameter sets 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 used 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:
MAXIMUM DC BRAKE VOLTAGE
MODEL M1100
240 / 200 Vac
MODEL M1200
240 / 200 Vac
MODEL M1400
480 / 400 Vac
MODEL M1500
590 / 480 Vac
24 VOLTS 24 VOLTS 48 VOLTS 59 VOLTS
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. If it is set to .0 seconds, it is disabled.
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.