I'm a student doing my Master Thesis and I have to use two stepper motors with an Arduino motor shield. My problem is that when I connect only one of them, it works. With one of them the LED is ON all the time (its nominal current is 1.6A), while with the other, it only lits when the motor moves (the nominal current is 1.2 A). When i connect both at the same time, the one which only lits with movement moves very slowly and the other one wants to move, but it can't.
I'm powering it with a USB power supply (5 V and 1 mA) and with the block of the shield (9 V and the current is limited to 1.25, I suposse that it's automatically cut by the Arduino). I have already taken off the VIN jumper.