# Thread: Stepper Motor (Rated Current ?? )

1. ## Stepper Motor (Rated Current ?? )

Hi all

I am currently selecting stepper motors for my system. To begin with I have calculated my load torque and final torque at my final required PPS. The supplier has also provided the torque vs Speed curve for a NMB stepper motor (at a rated current of 500 mA & 24 VDC). Now I am trying to see what will be the max current required.

My doubt is whether this rated current of 500 mA is when the torque is max and speed minimum? As my speed increases does the current (torque) in my motor decrease?

Or

does this rated current mean the motor always draws this current irrespective of the speed, for the provided torque Vs Speed curve.

Thanks

2. If the rated current of the motor is 500mA then thats what you should supply to it, if you give it more you may get excess motor heating, poor linearity and premature failure of the motor. If you were using three of these motors then your power supply should be rated to deliver 2/3 of the total current ie 1A. I have three 6A 2.0V rated steppers on my machine. My power supply delivers 60V dc at 12A to three gecko drives, these are then current limited to 6A with a resistor.

Hope this helps a bit!

Haydn

3. depending on your drive, current may decrease at high speeds (ideally, steppers are constant power motors, thus, increasing speed and decreasing torque should have measured 24V at 500mA all throughout the curve, but that is pretty far from reality). 500mA is the maximum current the motor can handle and this is normally rated at motor standstill.