On Tue, 2009-01-06 at 11:23 -0600, Jon Elson wrote: > 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. > > Jon
I think alternators are very inefficient even as alternators. Using them as motors seems less than productive considering that there are cheap alternatives. All of the alternators I have worked on have had cast finger cores so that eddy currents must get pretty high with a load. I think these are meant to operate at a high load just long enough to replace the charge used up during engine starting, and then mostly idle while running lights, etcetera. I have noticed some new alternators, that are smaller than normal which might have a more efficient construction, maybe so they can run under a higher load all the time , and to save space. -------------- Kirk http://www.wallacecompany.com/machine_shop/ ------------------------------------------------------------------------------ Check out the new SourceForge.net Marketplace. It is the best place to buy or sell services for just about anything Open Source. http://p.sf.net/sfu/Xq1LFB _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
