Pacific Scientific PowerMaxII M21NXXA* Nema 23 8-lead stepper motors can be connected as:
Unipolar (100 oz-in at rated 4.0A/phase, 0.46ohm ph resistance)
Bipolar series (142 oz-in at rated 2.8A/phase, 0.92ohm ph resistance)
or Bipolar parallel (142 oz-in at rated 5.6A/phase, 0.23 ph resistance)
I'm happy that the lowest-possible current (2.8A/phase = 5.6A/motor) still gives the highest-possible torque.
I can understand how wiring the half-coils in a phase in parallel doubles the current drawn.
I can't understand why doubling the rated current doesn't increase the torque. I'm led to ask, "Why would anyone wire this thing to draw more current (unipolar or bipolar parallel) for same torque or even less?
I suspect the higher currents might have better speed-torque curves, meaning slower torque falloff at higher speeds?