I'm having some problem powering my stepper motor through arduino motor shield with external power supply. I already cut the Vin trace on the motor shield, so the main board and the motor shield is not now powered separately. The stepper motor is rated at 12v, 1.7A.
Using a variable power supply, I've noticed some very odd things. When I restrict the power supply to 5V, 1A, the overall draw seems to be around 0.7-0.9A. When I upped the limit to 2A, the draw was around 1.6A. Understandably, when the stepper motor is braking, the full current is drawn.
However, when I supply 12V, the current draw seems to be whatever I set the limit to. If it is 1A, it always is 1A. When it's 2A or more, it always draws that too. at 12V 2A, the shield is reaching it's limit and gets very hot.
For now, i'm limiting my source to either 12V 1A, or using 5V (since the load isn't that much). But I want to figure out why is it behaving this way. I'm probably missing something very basic here, so any help is appreciated.
Motor Shield: http://arduino.cc/en/Main/ArduinoMotorShieldR3 Stepper Motor: http://www.phidgets.com/products.php?product_id=3319_1