How do I control a DC linear actuator with these drivers?

The driver reverses the actuator's polarity without contacts; with no built-in limit switch, the KS250 and PT500 AntiSwitch detects the end of travel.

The DC motor inside a linear actuator turns the other way when the supply polarity changes; the shaft extends or retracts accordingly. That is exactly the driver's job: it reverses the polarity without contactors or relays and, where needed, sets the speed and the ramp. If the actuator has no built-in limit switch, or if you do not want it straining at the end of travel, the current-threshold AntiSwitch function on the KS250 and PT500 detects the end of the movement and stops that direction.

Installation steps

1. Determine the current requirement. Measure the actuator's current at full load or take the label value. The KS250 is defined for continuous current up to 15 A and the PT500 up to 30 A. If you will drive two motors independently and 4 A per channel is enough, the ST42 can be used; its speed and ramp are adjustable, but the ST42 has no AntiSwitch.
2. Match the voltage. The modules work with 12V and 24V DC; do not exceed the actuator's nominal voltage.
3. Connect the direction inputs. On the KS250, IN1 is clockwise start, IN2 is reverse start, IN3 and IN4 are stop; on the PT500 the A–D digital inputs are used. The command source can be a button, a panel signal or an RF receiver.
4. Choose the end-point strategy. If the actuator has a built-in limit switch, the movement is already cut off there. If not, the current threshold for each direction is set separately with the A1 and A2 pots on the PT500 and no external limit wiring is needed.
5. Set the ramp and the speed. The HIZ and RMP pots on the PT500 and the soft start/stop function on the KS250 smooth the movement; this reduces the shock on the shaft and the screw thread.

Which method should cover the end point

On an actuator with built-in switches the switch already cuts the current, so AntiSwitch may never trigger; that is not a problem but two protections overlapping. Where the limit switch is wired is a separate decision: if the switch cuts the command signal the driver stops on its ramp, and if it cuts the power the movement stops dead.

Situations met in the field

The most frequent complaint is an actuator that stops in one direction and will not start in the other. The reason is usually a threshold set too low: while the shaft rests at the end point the current is still high, and the threshold trips again the moment the reverse command is given. If AntiSwitch engages too early, open the threshold up step by step and try each direction separately. The second common situation is two actuators connected in parallel with synchronous movement expected of them; unless their loads are equal, the shafts do not advance at the same speed. Oil thickening in cold weather also raises the current and trips a setting made in summer too early in winter.

Where this method is not enough

A current threshold is not a position sensor; it only tells you the movement has been strained. In applications needing repeatable stops at an intermediate position or position feedback, a DC linear actuator with a potentiometer or an encoder and a control to match are required. Outdoor use is a separate decision as well: the KS250 is defined as IP45 and the PT500 as IP67, and the choice between IP45 and IP67 is made according to the mounting location.

What to do

Measure the current, match the voltage, and choose the end-point strategy before installation. Once the installation is done, calibrate the threshold under load; a setting made on a cold, unloaded mechanism must always be reviewed again with the real load and at low temperature.

The full topic: DC Motor Driver Selection Guide

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