sorry If I don't answer quit well.
In fact, I obtained the 12 volt by division with 2 same resistor on a 24V/5A power supply.
I decided to remove the 2 resistors and supply directly with 24V and everything worked well!
So I decided to use the original stepper motor that I want to use from the begining which is 1A/phase and 14ohm/phase.
I measured Vref and i obtained 0.125V which correspond to 0.250A, I said ok I can connect the motor there no risk, so connected if and the motor turned perfectly!!!
I don't know why I decided to turn a very, very little the Pot on the DRV8825, I powered and nothing happened, I get back to the initial position and nothing again, I decided to check continuity with multimeter, and I find continuity between Vmot and GND!!!
Is my DRV KO?