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Operational Overview
• A positive analog velocity or torque command (i.e., a higher voltage on the (+)
differential input than on the (-) input).
• A positive direction (+) pulse command.
• A positive preset velocity or torque command.
Current Foldback
Current foldback is used to protect the motor and drive from overload. There are two levels
of current foldback: RMS Foldback and Stall Foldback.
RMS and Stall Foldback are displayed on the diagnostic display as a "C" and "c" respectively.
RMS Foldback
RMS foldback protects the motor from overheating. The RMS Foldback parameter models
the thermal heating and cooling of the drive and motor based on the commanded current and
the motor velocity. On power-up, the RMS Foldback level is zero and is continually updated.
When the RMS Foldback level reaches 100 percent, current foldback is activated and the
Foldback Active output function is active.
Each drive is designed to deliver up to 300 percent of the motor’s continuous torque for no
less the two seconds when running at 100 RPM or more. If only 150 percent of continuous
torque is required, several seconds of operation before RMS foldback is typical.
During current foldback the Torque Command Actual will be limited to 80 percent
continuous motor torque. Current foldback is cancelled when the RMS Foldback level falls
below 70 percent. This could take several seconds or several minutes depending on the load.
The RMS Foldback value is dependent on both torque and velocity. At low speeds (<20
percent of maximum motor speed) the RMS Foldback will closely follow the Torque
Command Actual. At high speeds (>50 percent of maximum motor speed) the RMS Foldback
will read higher than the Torque Command Actual.
The time constant for RMS Foldback is 10 seconds. This means that if the load is 150 percent
of continuous, it will take about 10 seconds to reach the foldback trip point.
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