Stuart Stevenson wrote: > Gentlemen, > I have seen (youtube) the conversion of an automotive alternator to > a stepper motor. The fields are pulsed and no motion occurs until the > rotor has dc voltage applied. Would it be possible to use this type of > stepper to overcome some of the speed and torque limitations of a PM > stepper? The problem/advantage of the alternator is it has much lower pole count. I suspect the pole count is WAY too low for it to be much use as a step motor. I think most of them are around 4-8 poles. What you can do with them is use them as brushless motors. Whether the torque ripple and velocity ripple makes them useful as a servo motor can be debated. My guess is the ripple is pretty bad, but a tight control loop could make them work. I know some people have done it. > Could you reduce the voltage at faster speeds and get better > performance. Maybe you could size it so more voltage to the rotor > could give more torque during the cut? > Just thoughts of someone who knows NOTHING about stepper motors. :) > The step driver is basically a current source, and everything it does to the motor is based on current, not voltage. You need enough supply voltage to overcome the motors generated voltage (back EMF) at any particular speed.
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