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Publication numberUS3796061 A
Publication typeGrant
Publication dateMar 12, 1974
Filing dateDec 15, 1972
Priority dateDec 15, 1972
Also published asCA988185A1
Publication numberUS 3796061 A, US 3796061A, US-A-3796061, US3796061 A, US3796061A
InventorsS Weihl
Original AssigneeEssex International Inc
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Protective device for refrigeration compressors
US 3796061 A
Abstract
A protective device for protection of a refrigeration compressor from burnout caused by short cycling. A time delay means is provided which prevents the compressor motor from being started again until a predetermined time interval has elapsed after the system thermostat has opened. If a power failure should occur, the compressor motor is prevented from being started until a predetermined time interval has elapsed after power resumption to the refrigeration system.
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Description  (OCR text may contain errors)

United States Patent [191 Weihl [451 Mar. 12, 1974 PROTECTIVE DEVICE FOR REFRIGERATION COMPRESSORS [75] Inventor: Steven P. Weihl, Logansport, Ind.

[73] Assignee: Essex International, Inc., Ft. Wayne,

Ind.

[22] Filed: Dec. 15, 1972 [21] Appl. No.: 315,341

[52] US. Cl 62/158, 307/293, 318/484 [51] Int. Cl. G05d 23/32 [58] Field of Search 62/158; 318/484; 307/293 [5 6] References Cited UNITED STATES PATENTS 3,127,754 4/1964 Mobarry 62/158 3,707,661 12/1972 King 62/158 Primary Examiner-Meyer Perlin Attorney, Agent, or Firm-Robert D. Sommer [5 7 ABSTRACT A protective device for protection of a refrigeration compressor from burnout caused by short cycling. A time delay means is provided which prevents the compressor motor from being started again until a predetermined time interval has elapsed after the system thermostat has opened. If a power failure should occur, the compressor motor is prevented from being started until a predetermined time interval has elapsed after power resumption to the refrigeration system.

6 Claims, 1 Drawing Figure PATENTEUMAR 12 um M OTOR PROTECTIVE DEVICE FOR REFRIGERATION COMPRESSORS BACKGROUND OF THE INVENTION The present invention is concerned with refrigeration systems and, in particular, is concerned with preventing burnout of the compressor motor caused by short cycling.

in the past, refrigeration systems have been protected from compressor short cycling. However, these previous protective devices do not always afford complete protection.

In one prior art system a timing motor in conjunction with a cam is used to prevent compressor short cycling. When the system thermostat opens, the timing motor is actuated and prevents the compressor from being started until the timing motor has timed the proper interval. However, if a power failure should occur while the system thermostat is closed, it is possible that the compressor motor will be restarted when power is resumed to the system. And if the power failure is short enough in duration, the compressor can short cycle, possibly burning out the compressor motor.

Another prior art device employs a bimetallic element as a time delay means. When the system thermostat opens the bimetallic element prevents reenergization of the contactor controlling the compressor motor until the time interval has elapsed. If a power failure should occur while the thermostat is closed, compressor short cycling is still possible.

SUMMARY OF THE INVENTION This protective device recognizes the opening of the system thermostat or other limit device. Then in response to this opening a time delay means is energized. The purpose of the time delay means is to prevent the contactor which controls the compressor motor from being energized until a predetermined time interval has elapsed after the thermostat or other limit device has opened. A first relay and a time delay circuit are both energized when the system thermostat or limit device opens. After a predetermined time interval has elapsed, the time delay. circuit acts to deenergize the first relay allowing the contactor to be energized upon thermostat closure. The contactor can be energized only when the system thermostat and all limit devices are closed and the first relay is deenergized. A second latching relay is provided to prevent compressor short cycling when a power failure has occurred.

Further features and advantages of the invention will be apparent from the following description and accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING The single drawing FIGURE illustrates schematically a wiring diagram of a refrigeration system including a presently preferred form of a compressor motor protective device.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, there is shown an electric motor I for driving the refrigerant compressor of a conventional compressor-condensor-evaporator type refrigeration system. The motor 1 is connected to alternating current electric supply lines 2, 3 and 4 through contactor switches 5a, 5b and 5c. The contactor switches are closed by a contactor coil 5 connected in a control circuit which may have its terminals connected to the supply lines 3 and 4. The control circuit further includes a thermostat 6 or another suitable condition responsive switch responsive to refrigeration system demand and may also include one or more safety or limit switches 7 such as a low-pressure switch, a high-pressure switch and a motor thermal overload switch.

Time delay means 8 is provided to prevent energization of contactor coil 5 until it has been deenergized for a predetermined time interval. Diode 9 provides suitable rectification..Resistors l0 and 13 and capacitors 12 and 14 provide filtering for the time delay circuit 16 which is described later. An impedance relay coil 15 .has corresponding normally closed contacts 15a and normally open contacts 15b in series with contactor coil 5, thermostat 6 and safety or limit switches 7. A latching relay with coil 17 and normally open contact 17a protects the refrigeration system in case of a power failure.

Time delay circuit 16 employs a programmable unijunction transistor (PUT) indicated generally by reference character 18 having anode electrode 18a, cathode electrode 18k, and gate electrode 18g. Resistor 19, capacitor 20, resistor 21 and resistor 22 act in conjunction to fire the PUT 18 after the proper time interval has elapsed. Resistor 25 limits the current through the anode cathode circuit of SCR 26, and resistor 23 and I 24 bias the gate electrode of SCR 26 properly.

The time delay circuit 16 operates in the following manner:

When power is applied to the system or when thermostat 6 or limit'switch of switches 7 open, the time delay circuit is actuated. Capacitor 20 begins to charge and when the voltage at the gate electrode 18g of PUT 18 becomes slightly negative with respect to the voltage at 18a, PUT l8 fires closing a conduction path between the anode 18a and the cathode 18k. This applies a voltage to the gate of SCR 26, allowing the SCR 26 to conduct and latch.

The operation of the protective device for refrigeration compressors is as follows:

Upon application of power to the system through power lines 3 and 4, relay coil 15 and time delay circuit 16 will both be energized. Since time delay means 8 does not draw enough current, contactor coil 5 will remain deenergized. When relay coil 15 is energized contacts 15a and 15b will transfer. This allows relay coil 17 to be energized, closing contacts 17a. After the predetermined time interval has been timed by the timing circuit 16 as previously described, SCR 26 will latch, deenergizing relay coil 15 and restoring contacts 15a and 15b to their normal positions. Assuming thermostat 6 and limit switch 7 are closed, a current path will be created through contactor coil 5, thermostat 6, limit switch 7, normally closed contacts 15a and closed contacts 17a. Contactor coil 5 is energized through this path. If the thermostat should be open when relay coil 15 is deenergized by SCR 26, the circuit will remain in this condition and contactor coil 5 will be energized when thermostat 6 closes.

It can be seen that contactor coil 5 cannot be energized after the thermostat 6 opens until the time delay circuit 16 has timed the proper interval and deenergized relay coil 15.

If a power failure should occur, contactor coil 5 cannot be reenergized until relay coil 15 has been energized, relay coil 17 has been energized and relay coil 15 has been deenergized by SCR 26.

As a specific example, the following circuit components operated as previously described although certain changes can be made without departing from spirit of the invention:

Diode 9 lN 4002 Resistor 10 22 ohm Capacitor 12 3.3 mfd.

Resistor 13 I000 ohm Capacitor 14 3.3 Mfd Relay Coil 15 Essex Controls Division Type M564 Relay Coil 17 Essex Controls Division Type 184 PUT 18 2N6027 Resistor 19 14.7 Megohm Capacitor 20 20 Mfd.

Resistor 21 2.2. Megohm Resistor 22 3.9 Megohm Resistor 23 22 ohm Resistor 24 1000 ohm Resistor 25 22 ohm SCR 26 General Electric C 106 F What is claimed is:

1. A protective device for use with a refrigeration system having a refrigerant compressor driven by an electric motor, a contactor switching device including a contactor coil and a contactor switch for closing an energizing circuit to saidmotor when said contactor coil is energized, a condition responsive switch means responsive to refrigeration system demand, and a control circuit for energizing said contactor coil having two terminals for connection to a source of electric power, said control circuit including said contactor coil and said condition responsive switch means in series with said contactor coil being connected to one of said terminals, said protective device comprising:

an impedance relay having an impedance coil and a normally closed switch which opens when said impedance relay coil is energized;

means for connecting said normally closed impedance relay switch in said control circuit between said condition responsive switch means and the other of said terminals to prevent energization of said contactor coil when said normally closed impedance relay switch is open;

means for connecting said impedance relay coil across said other terminal and the junction of said contactor coil with said condition responsive switch means for energization of said impedance relay hail from said source of electric power through said contactor coil;

' and time delay means connected in parallel with said impedance relay coil for deenergizing'said impedance relay coil a predetermined interval of time after said time delay means is energized.

2; A protective device according to claim 1- wherein said time delay means comprises:

semiconducted switching means connected said impedance relay coil and operative to substantially 1 short out said impedance relay coil when said semiconductor switching means is in a conductive state;

and a time delay circuit connected to said semiconductor switching means and operative to render said semiconductor switching means conductive a predetermined interval of time after said time delay meansis energized.

3. A protective device according to claim 2 wherein:

a diode member connects said impedance relay coil and said time delay means to the junction of said contactor coil with said condition responsive switch means;

said semiconductor switching means is a silicon controlled rectifier having anode andcathode electrodes connected across said impedance relay coil;

and said time delay circuit comprises a resistancecapacitance timing circuit and a programmable unijunction transistor responsive to energization of said resistance-capacitance timing circuit for a predetermined interval of time to provide a firing signal to the gate electrode of said silicon controlled rectifier.

4. A protective device according to claim 1 further comprising:

alatching relay having a coil and a normally open switch which closes when said latching relay coil is energized;

a normally open impedance relay switch which closes when said impedance relay coil is energized;

means for connecting said latching relay switch and said normally open impedance relay switch in parallel with each other in said control circuit between said normallyclosed impedance relay switch and said other terminal;

and means for connecting said latching relay coil between said one terminal and the junction of said normally closed impedance relay switch with said latching relay switch and said normally open impedance relay switch. I

5. A protective device according to claim 4 wherei said time delay means comprises:

semiconductor switching means connected to said impedance relay coil and operative to substantially short out said impedance relay coil when said semiconductor switching means is in a conductive state;

and a time delay circuit connected to said semiconductor switching means and operative to render said semiconductor switching means conductive a predetermined interval of time after said time delay means is energized.

6. A protective device according to. claim 5 wherein:

a diode member connects said impedance relay coil and said time delay means to the junction of said contactor coil with said condition responsive switch means;

said semiconductor switching means is a silicon controlled rectifier having anode and cathode electrodes connected across said impedance relay coil;

rectifier. v

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3127754 *Oct 4, 1962Apr 7, 1964Honeywell Regulator CoRefrigeration control apparatus with time delay means
US3707661 *Mar 22, 1971Dec 26, 1972Cmd Electronics IncElectrical drive motor protective means
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4000450 *Mar 15, 1974Dec 28, 1976Robertshaw Controls CompanyLubricant pressure responsive control circuit
US4142375 *Nov 28, 1977Mar 6, 1979Hitachi, Ltd.Control apparatus for air conditioning unit
US4176388 *Mar 30, 1978Nov 27, 1979Towmotor CorporationControl circuit for a contactor
US4315413 *Dec 31, 1979Feb 16, 1982Whirlpool CorporationSelective temperature control system
US5448175 *Dec 28, 1993Sep 5, 1995Kabushiki Kaisha Tokai-Rika-Denki-SeisakushoCurrent detecting circuit
US5455469 *Oct 12, 1993Oct 3, 1995Watsco Components, Inc.Comparator controlled delay-on-break devices
US5524448 *Feb 10, 1995Jun 11, 1996Schwanebeck; James W.Minimum off-time device for protecting refrigeration compressors after a power interruption
US5666081 *Mar 31, 1993Sep 9, 1997The Nippon Signal Co., Ltd.On-delay circuit
US5809793 *Dec 12, 1996Sep 22, 1998Ssac Inc.Timer circuit for heating or air conditioner unit
Classifications
U.S. Classification62/158, 361/22, 318/484, 361/28, 327/402, 327/398
International ClassificationH02H7/08, F25B49/02, F04B49/10
Cooperative ClassificationF25B2600/23, H02H7/0816, F04B49/10, F25B49/025
European ClassificationF04B49/10, H02H7/08D, F25B49/02C
Legal Events
DateCodeEventDescription
Mar 1, 1985ASAssignment
Owner name: UNITED TECHNOLOGIES CORPORATION, A CORP OF DE
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:ESSEX GROUP, INC.;REEL/FRAME:004371/0645
Effective date: 19840815