How to use a 3.8V stepper with Marlin / RAMPS?
The 3.8&nbsp;V rating does not mean what you think it does. "Rated voltage" has a very specific technical meaning. For a 3D stepper motor to work properly, the rated voltage of the stepper motors actually needs to be significantly lower than the supply voltage of the stepper drivers.

These steppers are perfectly compatible with a standard 12V RAMPS setup with A4988 system. You do not need to and should not mess around with buck converters. All you need to do is adjust the potentiometer on your stepper drivers to limit the current to at most 0.8&nbsp;A.

The rated voltage in some sense refers to the average voltage the stepper motor should see, but to actually run them at reasonable speeds you need to supply short bursts of higher voltage. A stepper driver and motor actually form a sort of buck converter themselves, and in some sense do the conversion from 12V to the rated voltage for you.