Motor starting circuit

• US 4,801,858 A
• Filed: 08/04/1987
• Issued: 01/31/1989
• Est. Priority Date: 07/26/1984
• Status: Expired due to Fees

• Current Assignee: Rexnord Corporation
• Original Assignee: PT Components, Inc. (Regal Rexnord Corp.)
• Inventors: Min, Young K.
• Primary Examiner(s): Smith, Jr., David
• Application Number:
  US07/081,347
• Time in Patent Office: 546 Days
• Field of Search: 318/786, 318/778, 318/779, 318/809, 323/901, 323/300, 323/238, 307/647
• US Class Current: 318/786
• CPC Class Codes: H02P 1/426 by using a specially adapted frequency converter

Abstract

A solid state starting and control circuit for AC motors employing a single phase power source is disclosed in which the normal motor starting capacitor and speed responsive switch or similar means for energizing and deenergizing the start winding are eliminated by use of an all electronic, sparkless circuit which provides phase displaced current to excite the motor starting winding and in which there is time regulated gradual decreasing of the starting current pulse width to deenergize the start winding.

Claims

1. A starting control circuit for AC single phase motors having both running and starting windings each connectable to an AC power source, comprising:

an AC power source switchably connected to said running windings of said motor and to said starting control circuit, first full wave bridge rectifier means connected to said AC power source in parallel with said running windings, DC power source means connected at its input to the positive side of said first full wave bridge rectifier means, zero voltage inflection point detecting means connected to said first full wave bridge rectifier means and to said AC power source for providing signals indicative of said zero voltage inflection points, control pulse generating means connected to said DC power source means and responsive to the signal output of said zero voltage inflection point detecting means and adapted to provide control pulses selectively phase shifted from said zero voltage inflection points, and switching means connected to said starting windings of said motor and connected and responsive to said control pulses to switch said starting winding on and off each cycle of said AC power source for a time interval equal to each control pulses duration and off therebetween to thereby effect motor starting.

2. A starting control circuit for AC single phase motors having both running and starting windings each connectable to an AC power source, comprising:

an AC power source switchably connected to said running windings of said motor and to said starting control circuit,

first full wave bridge rectifier means connected to said AC power source in parallel with said running windings,

zero voltage inflection point detecting means connected to said first full wave bridge rectifier means and to said AC power source for providing signals indicative of said zero voltage inflection points, said zero voltage inflection point detecting means comprising;

first transistor means connected at its input to the positive output of said first full wave bridge rectifier means and responsive to each positive going output excursion thereof to turn on,

first and second series diode and capacitor means connected at said diodes inputs to the positive output of said first bridge rectifier means to effect charging of the capacitor associated with each diode, and

second transistor means connected at its input to the output of said first transistor means and in parallel to the capacitor of said first series diode and capacitor means to generate spiked pulses, one for each turn on of said first transistor means,

control pulse generating means connected to said DC power source means and responsive to the signal output of said zero voltage inflection point detecting means and adapted to provide control pulses selectively phase shifted from said zero voltage inflection points, and switching means connected to said starting windings of said motor and connected and responsive to said control pulses to switch said starting winding on and off each cycle of said AC power source for a time interval equal to each control pulses duration and off therebetween to thereby effect motor starting.

5. A starting control circuit for AC single phase motors in accord with claim 2 wherein said switching means comprises:

second full wave bridge rectifier means connected in series with said starting windings and said series is connected across said AC power source,

pulsed switching means connected at its input to said signal manager means and across said second full wave bridge rectifier means and responsive to said phase shifted control pulses to effect on and off switching of said starting windings for the duration of each control pulse.

6. A starting control circuit for AC single phase motors in accord with claim 2 wherein said DC power source means comprises diode means connected at its input to the positive side of said first full wave rectifier means and at its output in series with resistor means and zener diode means, said zener diode means connected in parallel with capacitor means.

3. A starting control circuit for AC single phase motors having both running and starting windings each connectable to an AC power source, comprising:

an AC power source switchably connected to said running windings of said motor and to said starting control circuit,

first full wave bridge rectifier means connected to said AC power source in parallel with said running windings,

DC power source means connected at its input to the positive side of said first full wave bridge rectifier means,

zero voltage inflection point deflecting means connected to said first full wave ridge rectifier means and to said AC power source for providing signals indicative of said zero voltage inflection points,

control pulse generating means connected to said DC power source means and responsive to the signal output of said zero voltage inflection point detecting means and adapted to provide control pulses selectively phase shifted from said zero voltage inflection points, said control pulse generating means including phase shifting means, comprising;

signal magager means connected and responsive to said voltage inflection point signals to generate positive going output pulses, one for each inflection point signal,

RC time delay means comprising first resistor means and capacitor means connected at its input to said DC power source means and at its output to said signal manager means to control the maximum duration of said positive going output pulses,

differentiator means connected at its input to said positive going output pulses to generate a phase shifted negative going trigger signal for said signal manager means based on the duration of said positive going output pulses, and said control pulse generator means within said signal manager means being responsive to said phase shifted pulse, one for each trigger signal, and

switching means connected to said starting windings of said motor and connected and responsive to said control pulses to switch said starting winding on and off each cycle of said AC power source for a time interval equal to each control pulses duration and off therebetween to thereby effect motor starting.

4. A starting control circuit for AC single phase motors in accord with claim 3 wherein said control pulse generator means further comprises:

first series RC time constant network means connected at its input to said DC power source means to regulate control pulse duration,

second series RC time constant network means connected at its input to said DC power source means and in parallel to said first series RC time constant network,

first transistor means coupling said first series RC time constant network means to said second series RC time constant network means to decrease the time constant of said second network as the capacitor of said first RC time constant network means increases in charge,

second transistor means coupling said second series RC time constant network to said signal manager means to discharge the capacitor of said second series RC time constant network and reset said signal manager means to thereby regulate the duration of each of said phase shifted control pulses.

7. A starting control circuit for AC single phase motors in accord with claim 3 wherein said signal manager means comprises an integrated circuit conforming to industry standard 555-556.

8. A starting control circuit for AC single phase motors in accord with claim 3 wherein said first and said second full wave bridge rectifier means each comprises diode means.

9. A starting control circuit for AC single phase motors in accord with claim 3 wherein said phase shift of said control pulses is substantially 90 degrees.

10. A starting control circuit for AC single phase motors in accord with claim 3 further comprising means for reversing motor direction on start-up comprising:

second resistor means connected to said DC power source network, and

switching means for connecting said second resistor means in series with the capacitor means of said RC time delay means in substitution for said first resistor means to increase the duration of said positive going output pulses and thereby the phase shft of said control pulses to a point where start-up is in the opposite direction from that achieved with said first resistor means.