42 SF01U
P25 CURRENT LIMIT
This sets the maximum allowable output current of the drive. The maximum setting is either
180% or 150%, depending on whether LINE VOLTAGE SELECTION (Parameter 01) is set
to HIGH or LOW.
The drive will enter current limit when the load demands more current than the CURRENT
LIMIT setting. When this happens, the drive will reduce the output frequency in an attempt to
reduce the output current. When the overload condition passes, the drive will accelerate the
motor back up to the speed setpoint.
P26 MOTOR OVERLOAD
The SCF Series is UL approved for solid state motor overload protection, and therefore does
not require a separate thermal overload relay for single motor applications.
The drive contains an adjustable thermal overload circuit that protects the motor from excessive
overcurrent. This circuit allows the drive to deliver up to 150% current for one minute. If the
overload circuit “times out”, the drive will trip into an OVERLOAD fault (displayed as "PF").
MOTOR OVERLOAD should be set to the ratio (in percent) of the motor current rating to the
drive current rating in order to properly protect the motor. See the example below.
Example: A 3 HP, 480 Vac drive with a 4.8 Amp rating is operating a 2 HP motor with a
current rating of 3.4 Amps. Dividing the motor current rating by the drive current rating yields
71% (3.4 / 4.8 = 0.71 = 71%), so this parameter should be set to 71%.
P27 BASE FREQUENCY
The BASE FREQUENCY determines the V/Hz ratio by setting the output frequency at which
the drive will output full voltage to the motor. In most cases, the BASE FREQUENCY should
be set to match the motor’s rated frequency.
Example: A 460 Vac, 60 Hz motor requires a V/Hz ratio of 7.67 (460 V / 60 Hz = 7.67 V/Hz)
to produce full torque. Setting the BASE FREQUENCY to 60 Hz causes the drive to output full
voltage (460 Vac) at 60 Hz, which yields the required 7.67 V/Hz. Output voltage is proportional
to output frequency, so the 7.67 V/Hz ratio is maintained from 0 - 60 Hz, allowing the motor to
produce full torque from 2 Hz (below 2 Hz there is less torque due to slip) up to 60 Hz.
NOTE
If this parameter is changed while the drive is running, the new value will not
take effect until the drive is stopped.
P28 FIXED BOOST
FIXED BOOST increases starting torque by increasing the output voltage when operating
below half of the base frequency, which increases the V/Hz ratio (see diagram below). For
better out-of-the-box performance, SCF Series drives are shipped with a setting that is different
from the factory default, as seen in the table below. If a factory reset is performed, FIXED
BOOST will default to 1.0 %.
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