# DRV8825 driver - Current flowing through the winding is not as per datasheet

Dear All
I am using stepper motor driver (DRV8825) to control stepper motor (Model No:17HS3401) - Two phase Hybrid stepper motor with step angle 1.8 deg. I am operating with 12V power supply. Mode pins set as Full step mode configuration. V ref is setted by varying the potentiometer, such that V ref is setted as 1.029V. While operating the stepper motor, the maximum current obtained by the stepper motor was 1.25A. Since, as per datasheet; R sense = 100 mohms, I rated = V ref x 2.
As per datasheet in full step mode, Current through the winding shall be +/- 71%. If V ref = 1.029, Irated = 2.058A. Then, Current through the winding should be 0.71 x 2.058 = 1.46A.
I donâ€™t know why there is 200mA current value difference with respect to theortical data. Kindly suggest.

Hello.

Do you have the specifications for your stepper motor (i.e. rated voltage and current per phase)? From a brief internet search, it looks like it might be rated for 1.3A per phase, so if that is the case you should not be trying to run it at nearly 1.5A. Also, how are you measuring the current?

Brandon

Hello!

Yes, I am using 17HS3401 Stepper motor with 1.3A per phase as recommended. Thanks for remaining me.

Now, I have limit the current to 1A through Vref =0.5V. We were measuring current through current scope probe. Also, i am getting as expected current limit in the windings. What will be the impact of running the motor greater than the rated current?

Please clarify the below query:

I am operating the stepper motor with input voltage as +12V

Also, our Load inertia is about 1e-4 Kg m2 which is about 30 times higher than shaft inertia (34e-6 kg m2). What will be the maximum step frequency can be configured? (Note: I am using DRV8825 motor drive which supports up to 250kHz Maximum Step frequency input)

Please recommend, whether to operate the motor with variable frequency profile (Acceleration + Constant speed + Deceleration) or Constant speed profile - for rotating the shaft from point A to Point B with minimum possible time.

An appropriate current limit also ensures that your motor is not allowed to draw more current than it or your driver can handle. Running at a current limit higher than the motor is rated for risks damaging the motor.

As far as the maximum step rate you can achieve, the limitation will almost certainly be from your motor and not the driver. If you have a datasheet for your stepper motor, you might check to see if it has a pull-out torque curve to give you an idea of what the stepper motor is capable of; however, please note that there are a lot of factors specific to your setup that can affect the maximum achievable step rate. You can find some general tips for achieving higher step rates in this forum post by Ben.

Brandon