I have an Atmega 1280 with a Adafruit Motor Shield.
I'm using these motors: http://www.ebay.com/itm/5-Stepper-motor ... 748wt_1413
The comments say "I have had RepRap owner state to me that they run these at 12 volts and .8 to 1 amp."
Current per Phase: 1.2A unipolar .85A bipolar
When I power these using the stepper demo using the USB they move nicely (and honestly unexpectedly - I wouldn't have thought the USB was enough to move these at all).
When I remove the PWR_EXT jumper and hook up a 12V 1A power supply, the motor ICs get very hot and the motors move erratically.
I've tried substituting the L293D with SN754410NE which also work fine at USB levels and erratically and too hot at 12V 1A.
What I am I missing? Is that power supply incorrect?