The single biggest engineering problem with standard single-phase alternating current motors is that they are inherently incapable of generating a rotating magnetic field on their own upon startup. Because single-phase power drops to zero voltage sixty times per second, a single-phase motor supplied with only main running windings experiences a pulsating magnetic field that causes it to buzz and stall rather than spin. To overcome this limitation, single-phase motors require auxiliary mechanical or electrical starting mechanisms—such as centrifugal switches, start capacitors, run capacitors, or shaded poles—to create an artificial phase shift and initiate rotation.
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