Power usage for Stepper Motor


I'm controlling a 28BYJ-48-5v Bi-Polar stepper motor from an Arduino Ethernet. I'm trying to work out what I need to power this motor. This link seems to have the most information on it:


Suggests it's 50ohm, I make that 100ma but from searching around I don't think it's that simple, but I don't entirely understand enough to be sure I'm right :-) From other things I've read I'm lead to believe the ULN2003 can't take more than around 500ma anyway which would suggest that's what the motor is likely to pull if that's what they're providing with it

I was wondering if I would be able to run this from the Arduino regulator's 5v Vout when powering it from a >7v external PSU. I've seen both 200ma and 1A given for the onboard regulator which is also a little confusing.

So my question is, can I run that stepper motor from the 5v Vout on an Arduino Ethernet board? I'd also be interested to know if I would be able to run 2 motors in the same way. If not I guess I'll need a 5v PSU with enough ampage or a >5v PSU that I can regulate to 5v for the motors.

Any advice greatly appreciated,


Only two coils will be on at any one time so that is 200mA per motor so yes you can get two to run from the arduino's on board regulator. http://www.thebox.myzen.co.uk/Workshop/Motors_3.html and http://www.thebox.myzen.co.uk/Workshop/Motors_4.html

I've seen both 200ma and 1A given for the on board regulator which is also a little confusing.

The 1A is the limit for the regulator component itself but that is not the limit, the limit is set by the power dissipation. http://www.thebox.myzen.co.uk/Tutorial/Power_Examples.html

Thanks Mike, I'd read the Power Examples page which is what led me to believe that I'd be better off not running more than ~200ma through the Arduino regulator. In that case are you saying that I can run two motors through the Arduino's regulator but perhaps shouldn't?

It depends on the voltage input, with 12V probably not but if you can drop that to just under 8V then yes.

Ah yes, i get you, thanks very much.