Nema 17 and A4988 Stepper Motor Driver Carrier

I am building 3d printer and i have problem with motors on z axis.
I am running NEMA 17 motors - []
on controller A4988 Stepper Motor Driver Carrier and I have ramps1.4 - []
On the axes x,y motors are running perfectly with vref set to 0,46
Problems are starting when I am plugging two of them, I increased vref to 0,94 and check other values but it didn’t help.
I have read that maximum output current 2 A on motor driver.
And two run two motors at the same time i need minimum vref 0,92 V, that means 2,3 A
Is this could be a reason ?? Do you know what could cause this problem ?

I will be grateful for any suggestions.


Exceeding the current rating of the driver can damage the board, and is likely the cause of the problem you are having. Our A4988 Stepper Motor Driver Carrier is only rated for 1A continuous current per phase without additional cooling. Even with sufficient cooling, the A4988 has a maximum of 2A per phase.

- Grant