Although they've been using singlephase, single-winding, twopole synchronous motors for decades, such motors can be inefficient and don't always generate enough torque to assure quick startups. Engineers at Johnson Electric, Shelton, Conn. (johnsonelectric.com), have devised a synchronous motor with split-phase windings for driving fluid pumps. Split windings set up a rotating magnetic field in the stator. This assures field alignment during each revolution and guarantees single-direction rotation and reliable start-ups at the proper times with enough torque to do the job.

The motor updates conventional two-pole motors in which a single winding is divided between stator poles set 180° apart. Alternating current energizes the winding and magnetizes the stator poles. At this point, the permanent-magnetic field generates a force that tries to line up the permanent-magnetic field with the stator field. But, depending on conditions, the fields aren't always aligned and the motor won't start, so it must recycle until there is enough force for start-up. And sometimes at start-up, the permanentmagnet rotor is already lined up with the stator and no starting torque is developed, so the motor will not run.