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[Guest]

Can one use a stepper motor as a generator? In this application, the motor will initially be used as to spin a propeller up to a certain rpm. Once the prescribed RPM is attained, the motor will stop and the propeller should continue to spin by an underwater current, which will turn the shaft going into the stepper motor. The motor will hopefully generate power. The reason for using the stepper is due to the requirement of high-torque and low rpm -- a characteristic of stepper motors. A relay will be used to switch the motor/generator from the driver to load. Is this feasible? Several other candidate motors were rejected due to the need for low-RPMs; finding efficient designs are another problem since the motor needs to fit in a 9-in diameter pressure vessel.
This project is an alternative power-generation system. The stepper/generator will be used in a 1:10 prototype. Eventually this thing is intended to produce power to feed a grid. The smallest motor with the most power output is ideal for this situation.

[daqmaster]

There is a dilemma here. Slow speed operation needs many poles to work well at low speed.

Look at any prospective stepper motor's power torque-curves to determine how to match the propeller to the motor; otherwise, efficiency will suffer.

Also, consider a tiny sheave on the stepper, and a large one on the propeller shaft. Use a light, cogged belt. This should be quiet, simple, inexpensive, and relatively efficient and will go a long ways towards matching the motor to the load.