Does the system reset itself after protection trips?

It depends on the model: some retry automatically after a set period, others stay latched until power is cycled. Since repeated attempts can make a mechanical problem worse, manual reset is safer.

Doesn't a fuse provide this protection?

A fuse protects against short circuits; it is not fast enough against sustained overload. Locked rotor current can stay below the fuse blow threshold, so separate thermal/current protection is still required.

The motor is heating up but still turning. Is that also locked rotor?

No, that is overloading. If the motor is turning, cooling still works partially. Even so, continuous overload shortens life; the load or the gearbox ratio should be reviewed.

What Is Locked Rotor? Why Thermal Protection Is Critical

When a motor is mechanically jammed and cannot turn, current stays stuck at startup level; this condition is called locked rotor. Without thermal protection, the driver and the motor are damaged within a short time.

Locked rotor is the condition where the motor is energized but cannot turn mechanically. Because the motor does not turn, no back-EMF is developed across it, and the only thing limiting current is the winding resistance: I = V / Ra. The result is that current settles at startup level — typically 3–10 times rated current — and stays there.

Why is it so dangerous?

Two effects stack up:

Current stays high: On a normal start, current falls as the motor speeds up because back-EMF grows; with a locked rotor it does not fall.
Cooling stops: If the fan or air circulation depends on motor rotation, cooling disappears exactly when the most heat is being produced.

When these two combine, the winding insulation and the driver's output stage are quickly stressed. Without protection, damage occurs within a short time.

Causes of stalling

Cause	Typical symptom
Mechanical jam / foreign object	Sudden stop, humming
Overload	Slowdown followed by stopping
Bearing failure	Gradual stiffening, heating
Gearbox seizure	Motor audible but no motion
Freezing / contamination	Failure to start in cold weather

How does protection work?

The driver measures current continuously. If current exceeds the threshold and stays high for a defined period, the output is cut. The subtlety here is time: current rises on a normal start as well, so protection must be time-delayed rather than instantaneous — otherwise it trips needlessly on every start. Soft start (ramp) makes this distinction easier, because it brings the startup surge down to 1.5–2 times rated current.

What to do about repeated stalling?

If protection is tripping, the system is working correctly; the real problem is on the mechanical side. Replacing the driver with a higher-current model hides the symptom, it does not remove the cause. Check the load, the gearbox and the bearings first.

For full coverage of this topic: DC Motor Driver Selection Guide

For measurement steps: DC Motor and Driver Troubleshooting Matrix

Knowledge Center