SINGLE PHASE MOTOR STARTING CONTROL APPARATUS

• US 3,671,830 A
• Filed: 06/24/1970
• Issued: 06/20/1972
• Est. Priority Date: 06/24/1970
• Status: Expired due to Term

• Current Assignee: A. O. Smith Corporation
• Original Assignee: Andrew P. Kruper
• Inventors: Andrew, P. Kruper
• Primary Examiner(s): Gene Z. Rubinson
• Application Number:
  US05/049,397
• Time in Patent Office: 727 Days
• Field of Search: 318/221R,221E,227
• US Class Current: 318/786
• CPC Class Codes: H02P 1/44 by phase-splitting with a capacitor

Abstract

A starting circuit for a single phase electric motor, particularly a capacitor start motor, is provided that includes a solid state switch connected in series with the motor starting winding and the capacitor for controlling the supply of power to the starting winding in accordance with switching signals that are developed by a triggering circuit one of whose inputs is a signal proportional to the voltage in the starting winding and is produced by means directly electrically connected across the starting winding. The improved reliability of solid state switching is provided as compared with mechanical relays as has previously been used. Pull in and drop out points may be readily set.

Claims

1. In combination:

a single phase electric motor having a main winding and a starting winding;

a three terminal solid state switch means having a pair of terminals in series circuit connection with said starting winding;

a voltage sensing circuit directly connected across said starting winding to develop a first voltage signal proportional to motor speed;

a trigger circuit connected to receive said first voltage signal and to apply or remove a switching signal to a third terminal of said solid state switch means only when said first voltage signal is of preDetermined magnitude.

2. The combination of claim 1 wherein:

said solid state switch means has a characteristic breakdown voltage, in the absence of signal on said gate electrode, that is greater than line voltage used to operate said motor; and

further comprising a starting capacitor in series circuit connection with said switch means and said starting winding.

3. The subject matter of claim 2 wherein:

said solid state switch means is a triac.

4. The subject matter of claim 1 wherein:

said means for directly electrically sensing voltage across said starting winding has an output proportional to the speed of the motor regardless of load conditions on said motor.

5. The subject matter of claim 4 wherein:

said output of said voltage sensing circuit is supplied to said trigger circuit and changes the state of the output of said trigger circuit between two potential values that are in inverse relation to voltages from said voltage sensing circuit to which said trigger circuit responds.