Per phase current from V and R

I have a Kollmorgen NEMA 17 motor that is just labeled 6V 7.5R.
Does this imply that the amps per phase would be .8?
If I connect it to a 12v power supply, would I set the driver for .4 amps?


Yes, the current per phase of your motor is probably 0.8A, assuming the resistance of your motor is given per phase or per coil. For stepper motors the rated current is generally the maximum current the motor can handle and the rated voltage is just the voltage at which the motor draws the rated current.

If you use a current limiting stepper motor driver like our carriers and Tic controllers, you should set the current limit at or below the motor’s rated current regardless of the supply voltage. More details on this can be found in the first FAQ on any of our stepper motor carrier product pages. For your motor that means you could set the current limit up to 0.8A even with a 12V supply. However, if your driver does not actively limit the current, you should not use a supply voltage over the motor’s rated voltage.


The motor is 6 wire unipolar. The tag doesn’t specify if the resistance is per coil so I measured it and it’s 7.5r to the center tap and 15r across the entire coil. Since I plan to wire it bipolar, I expect I should use the 15.
I have a pair of TB67S249FTG full breakout carriers coming just because I was drawn to the features like AGC, ADMD and ACDS. If I can figure out how to set them up properly, it should make for a very smooth system.

I have a similar follow up question. I also have a Sanyo NEMA 17 motor that’s rated .85A per coil at “up to 36 volts”. Sound a bit ambiguous. At any rate, it seems to follow that if I drive this motor with my 12 volt source, I could set the driver to 2.55A. That seems more than a bit excessive.

Thanks for your help.

As I mentioned in my previous post, the rated current is the maximum current the motor can handle. It should not be exceeded (regardless of voltage) or you risk over heating and damaging the motor. Using a different voltage with a current-limiting driver does not change the maximum current that the motor can handle.

I suspect the “up to 36V” rating is probably when using a current limiting driver. You could measure the coil resistance to calculate the actual rated voltage that would cause a 0.85A draw.