Sep 18, 2012

Easy Driver with Arduino Part II (How to adjust the maximum Stepper Current)

Go to Part I
Part II
Go to Part III

   How to adjust the maximum current with Easy Driver.

Easy Driver let's you adjust the maximum current for the motor coils.
But what does this mean:

      More current ==> more torque / more Heat / less Speed  / more motor noise
      Less current  ==> less torque   / less Heat   / more Speed / less noise

Then the best choice is to adjust it to the minimum current given the needed torque.

I did it by trial and error; i expenrienced that when there's not enough torque, some (or all) steps where dropped, then i adjusted the current to the point at witch i never loose an step.

To adjust the current, simply turn the potentiometer (3):
CCW ==> less current
CW   ==> more current
Yes, the SilkScreen is wrong for squarish white box pot (schmalzhaus, says that for some Easy Driver with other pot, the silkscreeen is right) .
To know the actual current for each coil of the steper:
     Take a meter and monitor the voltage between points (1) and (2).
     Take a meter and monitor the resistance between points (4) and (5).
     then aply the following formula:
                 Imax = VREF/8RS                                     (page 5 of Allegro's A3967 Data Sheet)
        Imax is the  max current for each coil (obviously Imax has never to exceed the maximum current  suported by your stepper)
        VREF is the voltage you read in the meter
        RS      is the resistance you read in the meter (in the EasyDriver's schematic sheet Rs is 0.75 Ohm, but in my board i meter this and found that Rs is 1.5 Ohm) 
     For example i read:
          VREF = 1.7V
           RS    = 1.5 Ohm
          Then Imax = 1.7 /(8 * 1.5) = 0.141 A = 141 mA