Eugene Robert Schmit

US Patent:

39709086, Jul 20, 1976

Filed:

Dec 9, 1974

Appl. No.:

5/530768

Inventors:

James E. Hansen - Oak Creek WI
Eugene R. Schmit - Elm Grove WI

Assignee:

Cutler-Hammer, Inc. - Milwaukee WI

International Classification:

H02P 144

US Classification:

318221E

Abstract:

A single-phase induction motor is provided with a simple capacitor-start control system. A precision current detector (reed relay) is used in the main winding circuit to fire a bidirectional thyristor and precisely control the starting and stopping points of energization of the start winding to cause the motor to accelerate to the desired speed. Although this small reed relay is a fast acting device that picks up on the leading side and drops out on the trailing side of each current half-cycle, chopping up of the current wave is avoided by the combination used. Thus, in view of the nearly 90 degree phase-shift between the main winding and start winding currents, the reed relay, with its dropout point being lower in current value than its pickup point on each half-cycle due to the inherent differential in its magnetic characteristics, applies a wide firing pulse to the thyristor at the most desirable time, that is, it widely overlaps the point where the start winding current passes through zero. Thus, the thyristor is force-fired at the beginning of each half-cycle for symmetrical triggering. And since the thyristor conducts for the remainder of each half-cycle, this start winding thyristor affords full-cycle conduction even though the reed switch itself is not closed throughout each half-cycle of main winding current thereby avoiding chopping up of the start winding current wave.