The answer to "DC Motor as a Generator Voltage and Current" from Olin Lathrop included:
"Sometimes these parameters can be inferred from other specs. For example, consider a motor that puts out 100 W of mechanical power at 60 Hz rotation (3600 RPM) speed, at 24 V applied, and is 90% efficient. The electrical input power is (100 W)/90% = 111 W. That means the current is (111 W)/(24 V) = 4.6 A. The winding resistance is then (11 W)/(4.6 A)² = 518 mΩ, which is dropping (11 W)/(4.6 A) = 2.4 V. That means the back EMF at 60 Hz is 21.6 V, or 360 mV/Hz.
If you were to drive this motor mechanically at 40 Hz, it would look like a 14.4 V source with 518 mΩ in series. If you were to put a 1 Ω load on it while still keeping the rotation rate at 40 Hz, you'd get 9.5 V and 90 W."
My question: is there any way to know what current I could get out of this stepper motor at 200/300/400 RPM? 65V 5.1A Bipolar parallel, 176W, 5.1A, 1.8DEG/STEP, not variable reluctance.