I’m running them in bipolar parallel(6 wire, 2 end wires and 2 center taps), and when increasing the current all the way to max on my stepper driver boards, the pololu stepper drivers with voltage regulators (2amps) with the potentiometer they start to make a vibrating whining noise, and then eventually start to pulse on and off slower and slower.
When I run the machine in this state the motors will actually pulse on and off, move, stop moving, start again, adjusting the current changes the frequency of the pulse until it becomes low enough that the motors move smoothly. Turning the pot in the other direction fully stops the motors from moving at all.
I’m driving them with a 24volt, 6.5amp supply
An arduino mega is supplying step and direction pulses, but even when the arduino is not on the motors make these vibrations
It sounds like your driver is overheating as you turn the current limit up, which is causing the thermal protection to kick in. If you don’t need the full stepper motor torqe, you can keep the current limit low enough to keep the driver from overheating. If you need more torque, you must take extra steps to keep the driver cool, such as mounting a heat sink. For more information on adding a heat sink, please see the following thread: