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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.
16 CURRENT (CURRENT LIMIT)
This parameter sets the maximum allowable output current of the drive, which
also determines the torque capability of the motor. For most applications,
CURRENT is left at the maximum setting, which is 150% or 180% (of the drive’s
output current rating), depending on whether the input voltage to the drive is low
or high (see Parameter 0 - LINE VOLTS). Regardless of the CURRENT setting,
the drive is capable of delivering a maximum of 150% current for one minute, and
180% current for approximately 30 seconds, before tripping into an OVERLOAD
fault. See Parameter 17 – MOTOR OL below.
The drive will enter current limit when the load demands more current than the
drive can deliver, which results in a loss of synchronization between the drive and
the motor. To correct this condition, the drive will enter FREQUENCY
FOLDBACK, which commands the drive to decelerate in order to reduce the
output current and regain synchronization with the motor. When the overcurrent
condition passes, the drive will return to normal operation and accelerate back to
the speed setpoint. However, if FREQUENCY FOLDBACK cannot correct the
condition and the drive remains in current limit for too long, it will trip into an
OVERLOAD fault. If the drive enters current limit while accelerating, the time
required to reach the speed setpoint will be longer than the time programmed into
ACCEL (Parameter 8).
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