Stepper motors are rated for a specific current and sometimes the stepper drivers are not set correctly to match the stepper motor of if you change your motors this may need to be adjusted. The v2 version of the DupI3 have been known to ship with steppers that are rated at a lower current (0.95amps) but the drivers are still set for the other higher current motors (1.2amps). This can cause the stepper motors to overheat or sound loud and harsh. With the extruder motor this can also lead to more heat creep from the heat transferring from the stepper to the cooling block.

Tools Required

  1. DC Voltmeter
  2. Small screwdriver (insulated preferred)
  3. Allen keys (to open the controller and remove the Melzi board)


Identify which stepper motors you have. We have seen -095 (0.95amp), -120 (1.2amp) and (-150 1.5amp). You will need to know the stepper motor current specs to make these adjustments.

Most v1 units shipped with these stepper motors:
X, Y, E, Z Motors – part# BOHONG 42HB34F103AB (1.3 amps)
Most v2 units are shipping with these stepper motors:
X, Y, E Motors – 42HS34(L)-0954-JA05 (0.95 amps)
Z Motors – 42HS34(L)-1204-JA05 (1.2 amps)
Decoding model numbers
42           HS   34(L)      – 095            4
Diameter(mm) Type Length(mm) – Max Current(A) Number of connectors
HS = Hybrid stepper, in case you wanted to know
Watch the video for a complete walk through and explanation. The formula for calculating the VREF for the Melzi board is:

For absolute Max current: VREF = Current(A) x 8 * Sense_Resistor (.1ohm RS)
Optimal setting is 90% of Max. VREF = Current(A) x 8 * Sense_Resistor (.1ohm RS) * 0.90

Motors with -0954 should use the Corrected VREF 0.684 = 0.855 amps (90% of 0.95 amp max)

Motors with -1204 should use the Corrected VREF 0.864 = 1.080 amps (90% of 1.20 amp max)


Video Guide

(video by Jim Shank)