I am rebuilding my printer, a hold Prusa/Mendel that has been boxed for years. I have changed the board ( I am using a Rumba) and the drivers (I am using Pololu 8225) with heatsinks and 1/16 microsteps.
5 motors type 42BYGHW811, rated: 2,5 A, R 1,25 Ohm. I have set the stepper voltage at 0,8 V for XYE which gives a current of 0,64 A and they seems to work without problems.
To get the same current on Z, where I have 2 motors in parallel, I should set it at 0,4 V but the motors do not turn at such low voltage. They just make noise, no turn. I have M8 rods nicely lubricated on such axis and I can turn them easily by fingers. If I go up to 1 V the motors turns but then the driver gets very hot and I loose steps. May be I should play with the acceleration too?
I am not sure if the above settings are correct. Your hints from your actual settings and experiences will be appreciated.