Any one has another idea how to protect my motor driver ?
Since you only have access to the bidirectional motor wires (if you don't wanna hack into the PCB), the easiest solution I can think of is this:
You'll have to experiment a bit with how many windings are needed to trigger the Reed at 1A, as there is a plethora of Reeds and they come in many different sizes. The larger the physical reeds (the arms in the glass tube that gives it its name), the stronger a magnetic field is required. In your case, even the tiniest reed will do.
Wind it on a tight fitting plastic tube and use a wire gauge suitable for the motors.
More windings will make it trigger at a lower current and vv.
Here's what a Reed Switch looks like:
When the current through the motor and hence the coil around the Reed reaches a certain magnitude, the magnetic field inside the coil will trigger the switch and the terminal marked "I/O" will go low.
Then you have to make a routine to alter the PWM to say 30% max. whenever the I/O pin is low.
That way it will still be able to handle the start surge in a reasonable way, which it has to, or it will be very slow starting.