Hi Sargon - can you explain this a bit more please. I just don't get how a current limiting device (a chopper in this case) would LIMIT current to LESS than it was set to. (Not to be confused with not being ABLE to drive the "set" current after the motor reaches stall speed).
I'm not sure I understand the question. I don't think I said a chopper would "limit" the current to less than the max setting. That doesn't mean the stepper will always draw maximum current. Of course, once the stepper has stalled the power coupling between the rotor and stator will drop off to almost nothing - the motor will, at that point, only be able to provide a small fraction of it's normal torque.
On an aside, after re-reading the post I did mis-speak in calling, or at least alluding to the idea that a chopper is a constant voltage source - which isn't true. The chopper is being fed constant voltage and then typically uses PWM to "chop" the power into pulses in an attempt to provide constant current - with limited success when compared to a linear supply.
If there are any errors here please don't hesitate to correct me! I'm always willing to learn, and I'm not an electrical engineer so I will admit that my understanding of the theory may not be complete or necessarily correct.
Tweakie:
Please specify what you think would be acceptable capacitance, and what would be considered too large. If I were to use a capacitor for this purpose I would be thinking somewhere in the range of 100uF - 500uF. Am I correct? Also, thank you for clarifying where the problem is in using too much capacitance - makes sense to me - can't respond to changing conditions if you can't see them.