SINGLE-PHASE MOTOR-STARTING CONTROL APPARATUS

• US 3,624,470 A
• Filed: 01/26/1970
• Issued: 11/30/1971
• Est. Priority Date: 01/26/1970
• Status: Expired due to Term

• Current Assignee: A. O. Smith Corporation
• Original Assignee: Richard A. Johnson
• Inventors: Johnson, Richard A.
• Primary Examiner(s): Rubinson, Gene Z.
• Application Number:
  US05/005,849
• Time in Patent Office: 673 Days
• Field of Search: 318/221R,221G,227
• US Class Current: 318/789
• CPC Class Codes: H02P 1/44 by phase-splitting with a capacitor

Abstract

A starting circuit for a single-phase electric motor is provided that includes solid-state circuit means connected with the auxiliary winding for developing a signal proportional to motor speed and controlling an electromechanical relay that permits application of line power to the auxiliary winding only upon predetermined speed conditions.

Claims

1. A starting control circuit for a single-phase motor comprising:

an electromechanical relay having a coil and a pair of contacT members serially connected to a motor starting winding;

a solid-state switching element connected in series with said coil;

circuit means for controlling the firing of said solid-state switching element in response to changes of a motor speed-dependent electrical parameter of said motor-starting winding;

said circuit means comprising first means for producing a first rectified current proportional to a single-phase supply voltage, second means for producing a second rectified current proportional to said motor speed-dependent electrical parameter, and means to apply to an electrode of said solid-state switching element a signal representing the difference in magnitude between said first and second rectified currents.

2. The subject matter of claim 1 wherein:

said solid-state switching element is a thyristor whose gate is said control electrode and having two main electrodes in series with said coil; and

said circuit means maintains said thyristor in a turned on condition and said relay closed when single phase voltage is supplied until said second rectified current is large enough to cause said thyristor to turn off.

3. In combination, a single-phase electric motor having a main winding and an auxiliary winding;

solid-state circuit means connected with said auxiliary winding for sensing a speed-dependent electrical parameter across said auxiliary winding;

an electromechanical relay connected to be controlled by said solid-state circuit means to permit application of line voltage from a single-phase voltage supply to said auxiliary winding only until occurrence of predetermined motor speed;

said solid-state circuit means including a solid-state switching element electrically connected in series with a coil of said electromechanical relay across conductors of the single-phase voltage supply with contacts of said relay electrically coupled in series with the auxiliary motor winding so said relay blocks application of voltage to said auxiliary winding when said contacts are in their open position.

4. The subject matter of claim 3 wherein a voltage divider with variable resistance provides means for selecting pullin and dropout speeds of said motor.

5. The subject matter of claim 1 wherein latching circuit means is provided within said solid-state circuit means for providing feedback control of the switching characteristics of said solid-state switch.