If the current intensity is set too high, motors and drivers can overheat, leading to step losses. In the worst case, stepper motors or drivers may fail. If the current intensity is set too low, step losses may occur more frequently. In this guide, I will show you the best way to adjust a A4988 motor driver.
All you need for this is a small crosshead screwdriver and a multimeter to measure the voltage.
How to Adjust the Current Intensity
First, find out how much amperage your stepper motors can handle.
- Then turn on your 3D printer and make sure the motors are not powered (send motor off signal).
- Now connect the negative pole of your multimeter to any ground pole of your power supply (usually the black wires).
- Measure the voltage directly at the potentiometer (the small adjustment screw on your A4988 motor driver). The measured voltage is a reference voltage.
The following formula applies:
A = VREF / (8 * RS)
By default, a 0.05-ohm resistor (= RS) is installed. Now, rearrange the formula to insert the desired current intensity and obtain the corresponding reference voltage.
VREF = A * 8 * RS Replace A with the desired current intensity Replace RS with the resistance value (usually 0.05)
My stepper motors can handle a maximum current intensity of 0.38A; we now insert this into the formula and get a reference voltage of approximately 0.152V.
0.152V = 0.38A * 8 * 0.05Ohm
Adjusting A4988 for 28BYJ-48 Stepper Motors
For my current project, the Backpack – Mini Delta 3D printer, I use the 28BYJ-48 stepper motors. After converting these unipolar stepper motors to bipolar, I also had to adjust the current intensity of the A4988 stepper motor drivers here.
The motors can handle a power of 0.5 watts.
5V / 50Ohm = 0.1A 0.1A * 5V = 0.5W
This means that the motors would only tolerate 0.0416A at 12V. Therefore, you should set the reference voltage of the A4988 drivers to 0.016V. In the test, it was found that the reference voltage for the 28BYJ-48 motors can be set to 0.105V without the stepper motors overheating.