charles green wrote: > what are the differences between one phase motors, two phase motors, and > three phase motors? > > > A single-phase motor needs something to get it started, as there is no phase rotation to cause the rotor to start turning. There are shaded-pole motors, resistive-start, capacitor start, capacitor-start/capacitor-run motors and capacitor-run variations. These generally have centrifugal starting switches that shut off the start winding when the motor is up to speed. The shaded pole and cap-run motors do not have the starting switch, though. The resistive start winding or the capacitor creates a phase angle shift that provides the rotation for starting. So, all of these except the shaded-pole are actually two-phase motors, but they generate the 2nd phase internally.
One problem with these motors is they are much less amenable to variable speed operation. When equipped with a starting switch, then you can't run it below the speed where the switch turns on the start winding, as it will overheat the start winding. When equipped with a capacitor, the proper phase angle shift is only obtained at one frequency. You won't find true two-phase motors run from the power line except in the most unusual cases. However, a stepper motor is usually a two-phase motor. Three phase motors have 3 sets of windings arranged around the stator, and the phase sequence provides the rotation for starting. So, no capacitors or switches are needed for starting, making the motors much simpler and more reliable. Since there are no special arrangements for starting, these motors are much easier to operate off a variable frequency supply to get variable speed. The voltage applied should be proportional to the frequency. Jon ------------------------------------------------------------------------------ Keep Your Developer Skills Current with LearnDevNow! The most comprehensive online learning library for Microsoft developers is just $99.99! Visual Studio, SharePoint, SQL - plus HTML5, CSS3, MVC3, Metro Style Apps, more. Free future releases when you subscribe now! http://p.sf.net/sfu/learndevnow-d2d _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
