# How to decide run current and hold current in stepper motor

Posted by KevinQ
 How to decide run current and hold current in stepper motor May 01, 2012 04:34PM Registered: 12 years ago Posts: 1
I am programming a motor controller where I have to specify the run current (coil peak current) and hold current (coil hold current) of the motors. The motor I used is a bipolar stepper motor, with a whopping 1.86Kg/cm of stall torque at 1.5Amp current (0.75A per winding) at 1.8 degree stepping angle.However, the table in the specification makes me confused: It lists a different current for a different torque.Here is a link to that motor controller: www.nex-robotics.com/products/micromouse/stepper-motors/high-torque-bipolar-stepper-motor.html How could I determine run current and hold current from this specification?

Edited 1 time(s). Last edit at 05/01/2012 04:42PM by KevinQ.
 Re: How to decide run current and hold current in stepper motor May 07, 2012 10:41AM Registered: 12 years ago Posts: 72
What is confusing is how they give a combined current rather than the current per winding.

Anyway, for full power you'd want a peak current of 0.75A and a hold current of around half that to prevent excessive heating when they are stopped. Having said that running it at full power will make it warm up, so for a machine where the stepper motors are mounted on plastic mounts you'd want to lower the peak current.

It all depends on what you're driving and how fast you want it to be able to accelerate.
 Re: How to decide run current and hold current in stepper motor November 12, 2012 08:26PM Registered: 14 years ago Posts: 27
I know this happened a few eons ago, but...

In any motor, torque is current. What this manufacturer has done is to apply a voltage on the winding and measure how much torque they need to move the shaft away from position. Notice in this case what they are using is an LR Drive. That is, the voltage is applied to an inductor and a resistor, and the current is equal to the equivalent V/R once the inductance has saturated. Where does the R comes from? The motor resistance, which in this case is 8 Ohms. Is the application voltage were higher, you would add higher resistance in order to limit the current.

I think they give combined current as it seems this stepper is meant to be used on battery operated applications. Makes sense to know how much current the motor will be consuming at all times, as this will dictate how long the robot will be operational.

If you use a current chopper driver, as most people use nowadays, you would regulate current to the one that you need. Notice they are running this test on what is full step. If you use microstep, you will need to divide the 0.75A by 0.707 in order to get the sine wave peak. This will give you an RMS value of 0.75A.

JIQ
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