AntiSwitch triggers too early, how should I set the threshold?
Early cut-out is caused by setting the current threshold too close to the real operating current. The threshold must be placed clearly above the current measured at the heaviest normal load but below the stall current. On the PT500 the clockwise direction is set with the A1 pot and the reverse direction with the A2 pot independently, so the two directions are calibrated separately.
For current-based end point detection to work, there must be a distinguishable difference between the normal operating current and the stall current. The threshold is placed between these two values, not near the operating current but nearer the middle.
Calibration steps:
- Run the system under the heaviest real operating condition and measure the current. Include the worst case such as cold weather, a dirty guide rail, maximum load.
- Measure the stall current by letting the mechanism run against the end point.
- Set the threshold between these two values, clearly away from the operating current.
- Repeat the same measurement for each direction; the current differs in the down and up directions because of gravity. On the PT500, A1 and A2 are already separated for this purpose.
- Test the setting for 10–20 cycles, then mark the pot position with a label kit.
Causes of early cut-out other than the setting: the starting current surge exceeding the threshold (extend the ramp time), the current rising because of voltage drop (check the cable cross-section), mechanical jamming and lack of lubrication, and also increased friction in hot weather.
Raising the threshold excessively is not a solution; it loses its protective function and increases the risk of mechanical damage.
Full topic: DC Motor Driver Selection Guide