Overcurrent Protection
Electronic protection that continuously measures motor current and cuts movement when it exceeds a set threshold. When the mechanism jams or the cable snags, current rises quickly; the protection stops the motor long before the fuse does. AXI LFT54 has current-protected drive, AXI LFT20 does not have this protection.
In a DC motor the current is directly proportional to the applied load. While the shaft turns freely the current is low; when the shaft is held the motor goes to stall current, and that value can be several times the normal operating current. The temperature rise is rapid, which is why the winding insulation can be damaged within minutes.
- Threshold and duration: the protection looks not only at the current level but also at how long that level lasts. The short high current at start-up must not cause a nuisance trip.
- Difference from a fuse: the fuse protects the cable and the supply line, the overcurrent protection protects the motor and the mechanism. Neither replaces the other.
- Symptom: if the protection trips frequently, look for a jam on the mechanical side, cable friction or a frozen mechanism.
For the LFT20 the manufacturer declares an average current of 10 A; this value is the basis for fuse selection. For the LFT54 no current value is declared, only that it is protected; for this reason no amperage value is attributed to the LFT54.
Context in which this term is used: Converting a tractor hydraulic lever to electronic control
For its application on levelling legs and its relation to ground-contact detection, see the entry Overcurrent Protection — On a Levelling Leg.