MOTOR START WINDING SWITCH CONTROLLED BY PHASE OF MAIN WINDING CURRENT

• US 3,777,232 A
• Filed: 09/06/1972
• Issued: 12/04/1973
• Est. Priority Date: 09/06/1972
• Status: Expired due to Term

• Current Assignee: Richard E. Woods, William H. Hohman
• Original Assignee: Richard E. Woods, William H. Hohman
• Inventors: Woods, Richard E., Hohman, William H.
• Primary Examiner(s): Rubinson, Gene Z.
• Application Number:
  US05/286,761
• Time in Patent Office: 454 Days
• Field of Search: 318/22R,221R,221E,227
• US Class Current: 318/786
• CPC Class Codes: H02P 1/42 for starting an individual single-phase induction motor H02P27/04 takes precedence

Abstract

In a motor circuit for an AC motor having a main winding and a start winding, a control circuit utilizes a change in phase between the start winding current relative to the phase of another motor circuit signal to remove a trigger signal from a thyristor in series with the start winding in order to remove power from the start winding when the motor reaches a preselected cut-out speed. In one embodiment a change with motor speed of the relative phase between the main winding current and the applied voltage is utilized. Another embodiment utilizes the change with motor speed of the relative phase between the main winding current and the start winding current.

Claims

1. In a motor circuit for an electric motor having a main winding and a start winding both connectable with a source of periodic voltage, said motor circuit when connected with the source of periodic voltage providing a pair of signals including a main winding current signal, the relative phase between which varies with motor speed, a circuit for controlling the application of power to the start winding, comprising:

switch means connected with said start winding for causing current conduction through said start winding except when disabled; and

control means for controlling said switch means including disable means responsive to the phase of one of said pair of signals to disable said switch means, and disable preventing means responsive to the phase of the other of said pair of electrical signals for preventing said disable means from disabling the switch means until the relative phase between the pair of electrical signals assumes a preselected value corresponding to a preselected cut-out speed of the motor.

2. The control circuit of claim 1 in which said switch means includes a switch connected with the start winding and trigger means for enabling said switch to cause conduction through said start winding.

3. The control circuit of claim 2 in which said disable means comprises means for disabling said trigger means from enabling the switch, said switch being disabled when not enabled.

4. The control circuit of claim 2 in which said trigger means generates a trigger signal and said switch is responsive to said trigger signal to cause current conduction through said start winding until said trigger signal is removed, said trigger signal being removed when the trigger means is disabled.

5. The control circuit of claim 4 in which said trigger means comprises a relaxation oscillator.

6. The control circuit of claim 2 in which said switch is in series circuit with the start winding.

7. The control circuit of claim 2 in which said switch means comprises a thyristor having a gate input connected with the trigger means.

8. The control circuit of claim 1 in which said pair of signals includes the applied voltage.

9. The control circuit of claim 8 in which said one of said pair of signals comprises the main winding current.

10. The control circuit of claim 1 in which said pair of signals includes the start winding current.

11. The control circuit of claim 10 in which said one of said pair of signals comprises the main winding current.

12. The control circuit of claim 1 in which said one of said pair of signals comprises the main winding current.

13. In a motor circuit for an electric motor having a main winding and a start winding both connectable with a source of periodic voltage, said motor circuit when connected with the source of periodic voltage providing a pair of signals including a main winding current signal, the relative phase between which varies with motor speed, a circuit for controlling the application of power to the start winding, comprising:

switch means connected with said start winding for causing current conduction through said start winding except when disabled; and

control means for controlling said switch means including disable means for generating a disable signal in response to the said one of said pair of electrical signals passing through a first preselected phase angle, said switch means being disabled in response to reception of said disable signal, and disable preventing means responsive to the other of said pair of electrical signals passing through a second preselected phase angle prior to generation of said disable signal to prevent reception thereof by said switch means, said other of said pair of signals passing through said second preselected phase angle prior to said one of said pair of signals passing through said first preselected phase angle only until the relative phase between the signals assumes a preselected value corresponding to a preselected cut-out speed of the motor.

14. The control circuit of claim 13 in which said switch means includes a switch connected with the start winding and a trigger means for enabling the switch to cause conduction through said start winding, said trigger means being disabled in response to reception of said disable signal.

15. The control circuit of claim 13 in which said first phase angle comprises zero degrees.

16. The control circuit of claim 13 in which said one of said pair of electrical signals comprises the main winding current.

17. The control circuit of claim 16 in which said other of said pair of signals comprises the applied voltage.

18. The control curcuit of claim 17 in which said disable preventing means includes a switching device means having first and second states connecting between said switch means and said disable means, and means for switching said switching device means from its first state to its second state in response to the applied voltage passing through said preselected phase angle, said disable signal being prevented from being received by said switch means when said switching device means is in said second state.

19. The control circuit of claim 18 in which said second state comprises a low impedance state and said disable signal is shunted away from said switch means through said switching device means when in said low impedance state.

20. The control circuit of claim 19 in which said switching device means comprises a semiconductor controlled rectifier gatable into a low impedance state in response to the applied voltage passing through said second phase angle.

21. The control circuit of claim 16 in which said other of said pair of signals comprises the start winding current.

22. The control circuit of claim 21 in which said disable preventing means includes a switching device means having first and second states connecting between said switch means and said disable means, and means for switching said switching device means from its first state to its second state in response to the start winding current passing through said preselected phase angle, said disable signal being prevented from being received by said switch means when said switching device means is in said second state.

23. The control circuit of claim 22 in which said second state comprises a low impedance state and said disable signal is shunted away from said switch means through said switching device means when in said low impedance state.

24. The control circuit of claim 22 in which said switching device means comprises a semiconductor controlled rectifier gatable into a low impedance state in response to the start winding current passing through said second phase angle.

25. The control circuit of claim 13 in which said disabling means includes a switching device means in series with the main winding for conducting main winding current therethrough, said switching device means developing a voltage pulse thereacross at the beginning of each positive half-wave of main winding current to produce said disable signal.

26. The control circuit of claim 25 in which said switching device comprises a thyristor.

27. The control circuit of claim 25 in which said switching device means includes means response to the temperature of the motor for removing power from the main winding.

28. The control circuit of claim 13 in which said disable preventing means includes a switching device means having first and second states connecting between said switch means and said disable means, and means for switching said switching device means from its first state to its second state in response to one of said pair of signals passing through said preselected phase angle, said disable signal being prevented from being received by said switch means when said switching device means is in said second state.

29. In an electric motor having a main winding and a start winding both connectable with a source of periodic voltage, said motor when connected with a source of periodic voltage developing a pair of signals comprising the main winding current and the start winding current, the relative phase between said pair of signals varying with motor speed, a control circuit for controlling the application of power to the start winding, comprising:

switch means connected with the start winding for causing current therethrough except when disabled; and

control means for disabling said switch means in response to said relative phase assuming a preselected value corresponding to a preselected cut-out speed of the motor.

30. The control circuit of claim 29 in which said control means includes disable means responsive to the phase of one of said pair of signals to disable said switch means, and disable preventing means responsive to the phase of the other of said pair of electrical signals for preventing said disable means from disabling said switch means until said relative phase assumes said preselected value.

31. The control circuit of claim 29 in which said switch means includes a switch connected with the start winding and trigger means for providing said switch with a trigger signal, said switch being enabled to cause current conduction when said trigger signal is generated and disabled when said trigger signal is not being generated.

32. The control circuit of claiM 31 in which said disable means includes means for disabling said trigger means from generating said trigger signal.

33. The control circuit of claim 30 in which said disable means includes means for generating a disable signal in response to one of said pair of signals passing through a first preselected phase angle, said switch means being disabled in response to reception of said disable signal, and said disable preventing means includes means responsive to the other of said pair of signals passing through a second preselected phase angle prior to generation of said disable signal to prevent reception thereof by said switch means.

34. The control circuit of claim 33 in which said one of said pair of electrical signals comprises the main winding current and the other of said pair of signals comprises the start winding current.

35. The control circuit of claim 30 in which said one of said pair of electrical signals comprises the main winding current and the other of said pair of signals comprises the start winding circuit.