I need to drive a stepper motor powered by a low voltage (12V) source, connected by a thin and long cable (about 15m of 2x0.14mm^2). The voltage drops by about 2 volts, which is acceptable.
Now the motor operation gets extremely noisy.
The driver used is an Allegro A4988 in this case, which automatically limits the motor current. I think this may be the reason for the problem, as the high resistance power source forces the control to constantly change reacting on voltage variations introduced by the whole circuit powered. The constantly adapting control results in wildly meandering frequency and noise sounds. I just wonder why the control frequencies are so much louder than on a stable power supply, where the same meandering occurs, but much more silent.
I tried different capacitors up to 1000u in total, but it seems I would need tons of them to fully stabilise the input.
What could be the exact reason of the noise, and what to do about it?