US3801889A

US3801889A - Control for well pump

Info

Publication number: US3801889A
Application number: US00359102A
Authority: US
Inventors: J Quinn
Original assignee: Individual
Current assignee: Individual
Priority date: 1973-05-10
Filing date: 1973-05-10
Publication date: 1974-04-02
Anticipated expiration: 1991-04-02

Abstract

A control for turning on and off a motor driving a well pump which includes high pressure and low pressure detectors. The detectors are coupled to the gate circuits of respective silicon controlled detectors, or SCR''s, which have their load circuits connected in a latching loop circuit which energizes a relay to operate the motor. To disable the relay when the pump is sucking air, an auxiliary SCR controls an auxiliary relay having normally closed contacts connected in the loop circuit. The auxiliary SCR is turned on by a source of positive voltage but a current transformer wired in a series with the pump motor sets up a negative control voltage which is of sufficient level under normal current conditions to overpower the positive voltage to maintain the auxiliary SCR turned off. A capacitor connected to the gate insures against premature actuation of the gate by positive inrush voltage.

Description

0 United States Patent [1 1 [111 3,801,889 Quinn I Apr. 2, 1974 CONTROL FOR WELL PUMP [57] ABSTRACT [76] Inventor: James L. Quinn, 6143 W. Touhy A control for turning on and off a motor driving a well Ave., Chicago, II]. 60648 pump which includes high pressure and low pressure detectors. The detectors are coupled to the gate cir- [22] Flled May 1973 cuits of respective silicon controlled detectors, or [21] Appl. No.: 359,102 SCRs, which have their load circuits connected in a latching loop circuit which energizes a relay to operate the motor. To disable the relay when the pump is 2? 8 318/481 gagsggg sucking air, an auxiliary SCR controls an auxiliary i 318/482 relay having normally closed contacts connected in E 1 0 318/481 the loop circuit. The auxiliary SCR is turned on by a source of positive volta e but a current transformer d h h wire in a series wit t e pump motor sets up a nega- [56] References Cited tive control voltage which is of sufficient level under UNITED STATES PATENTS normal current conditions to overpower the positive 3,252,420 5/1966 Sorensen 417/36 voltage to maintain the auxiliary SCR turned off. A 3,540,027 11/1970 6t 417/36 capacitor connected to the gate insures against prema- 3,667,022 5/ 1972 318/482 ture actuation of the gate by positive inrush voltage. 3,671,142 6/1972 Calabrese 417/36 Primary ExaminerB. Dobeck Attorney, Agent, or FirmWolfe, Hubbard, Leydig, Volt & Osann, Ltd. Tm

6 Claims, 2 Drawing Figures CONTROL FOR WELL PUMP It is an object of the present invention to provide a control for a well pump which is reliable in turning the pump motor on at a predetermined low pressure and off ata predetermined high pressure and which positively disables the motor when the pump begins to suck air. It is another object to provide a control system for awell pump which makes use of the solid state ,SCR devices but in which such devices are completely deenergized during the long periods of standby when the pressure in the tank is up to the rated level. It is a general object to provide a control circuit for a well pump which is capable of operating without care of maintenance for long periods of time.

Other objects and advantages of the invention will become apparent upon reading the attached detailed description and upon reference to the drawings in which:

FIG. 1 is a diagram showing a typical well pump system to which the invention is applied.

FIG. 2 is a schematic diagram illustrating a preferred embodiment of the invention.

While the invention has been described in connection with a preferred embodiment, it will be understood that I do not intend to be limited thereto but intend on the contrary to cover the various alternative and equivalent forms of the invention included within the spirit and scope of the appended claims.

Turning now to the drawings, a control package indicated at 10. serves to control a motor M driving a pump P which furnishes water under pressure to a tank T. Communicating with the tank are detectors H and L which are set to respond at respective high and low pressures, or water levels, and which are connected to terminals 11, 12, sharing a common terminal 13. The motor is powered through terminals 14, and power is received from lines L1, L2 via terminals l6, 17. The water W, keptunder head of air A, leaves the tank through an outlet 18.- Itwill be understood that detectors H and L include switches which show an open circuit when satisfied, a drop in pressure closing the circuit to call for water.

Turning now to FIG. 2, a'first SCR is provided having an anode 21, a cathode 22and gate 23. The gate is connected to the low pressure detector'L via a series resistor 24. The resistor 25 is the usual gate-cathode resistor and the diode 26 serves as a clamp to limit'the negative voltage which can be applied to the gate.

Under the control of the high pressure'detector H is an SCR device 30 -having anode 31, cathode 32 and gate 33, the latter being connected to-the high'pressure detector via a seriesresistor 34 and with the gate being provided with a shunting resistor 35 and a clamping diode 36. i i

For thepurpose of furnishing load current, a transformer :is provided having a primary winding 41 and a secondary winding 42. Connected in series, that is, in a loop, with the loadcircuits of the SCRs and with the transformer secondary winding is a motor relayhaving I an input circuit, or-windin'g,-50- and 'normally open contacts 51,52 which are connected in series with the a.-c. supply lines. A protective diode 53 connected across the relay protects the SCRs against'the inductive kick which occurs when the relay is deenergized.

In order to make the SCR 20 operate in the latching mode, such SCR, and the relay winding 50 which is in series with it, are shunted by a capacitor 54. Thus during positive pulses of current, the capacitor is charged to a voltage which corresponds to the sum of the voltage drops through the relay winding and anodecathode circuit. The capacitor has a sufficiently high capacitance so as to maintain a positive voltage between the anode 21 and cathode 22, thereby to maintain the SCR 20 in the conductive state, bridging the negative half cycles supplied from the upper end of the transformer winding 42.

For the purpose of protecting the pump against the hazardous condition of sucking air, means are provided for disabling the pump motor when the motor is turned on but when substantially less than rated current is flowing through the motor. This is accomplished by a current detecting circuit which employs an auxiliary SCR 60 having an anode 61, cathode 62 and a gate 63, the latter having a shunt resistor 64. The auxiliary SCR 60 is connected to operate an auxiliary relay having input and output circuits in the form of coil 65 and a normally closed contact 66. The relay is of the mechanically latching type having a latch 67 which serves to hold in the relay armature following energization with a reset button 68 provided for manual release. Connected in parallel with the relay coil is a protective diode 69.

For controlling the auxiliary SCR 60, that is, for keeping the same non-conductive as long as normal current is drawn by the motor M, a current transformer 70 is provided having a primary winding 71 which is wired in series with the motor and a secondary winding 72. Voltage from the secondary winding is rectified by a diode 73 and the level of the rectified voltage is set by a potentiometer 74 having a wiper 75, which wiper is connected via a series resistor 76 to the gate 63 of the auxiliary SCR. The diode 73 is so polarized that rated current, drawn by the motor, is effective to produce a negative voltage at the gate 63 of the auxiliary SCR which is sufficiently high as to keep the SCR turned off. However, for turning on the SCR when ,ower values of motor current are drawn, indicating the condition of sucking air, a positive source of voltage is provided which is made up of a diode 80 and series resistor 81. The diode 80, and the auxiliary transistor are powered through

input terminals

82, 83 which are connected to the switched" side of the contacts 51, 52 so that the current detecting circuit is completely dead and unresponsive during the times that the motor M is turned off.

In order to prevent the auxiliary SCR 60 from responding to an inrush of positive voltage when the contacts 51, 52 are initially closed, and before negative control voltage is developed by the current transformer and its associated diode, a high value capacitor, indicated at 90, is connected to the gate terminal of the SCR and specifically'between the gate and cathode terminals. The capacitor increases the effective time constant of the gate circuit since no positive voltage can be developed atthe lower end of the resistor .81 until the capacitor has had opportunity to charge, and the rate of positive charging is limited by the value of the resistor'8l. Once the initial inrush condition has been taken care of,'the voltage across the capacitor will stabilize at a voltage and polarity which depends upon the relative magnitude of the voltages being supplied via the negative diode 73 and positive diode 80, the negative voltage normally predominating.

While the operation of the circuit will be apparent from the foregoing description, it will be helpful to review a typical operating sequence. Let it be assumed that the system occupies the initial condition shown in FIG. 1 with water at a low level within the tank and with a low pressure in the space above it, causing both of the detectors to be turned on, or closed, calling for water. It is apparent that closure of the contacts L and H (FIG. 2) provides a path for positive control voltages to pass to the

gates

23, 33 at the same time that positive pulses are applied to the anodes so that both SCRs conduct, and serve with one another, to energize the winding 50 of the motor relay, closing contacts 51, 52 and'turning the motor on. The resultant operation of the pump then causes water to flow into the base of the tank to raise the water level and the pressure of the contained air.

When the pressure of the air becomes sufficient to satisfy the detector L, the latter becomes open circuited, thus deenergizing the gate terminal 23 of the SCR 20. However, because of the latching effect of the capacitor 54 the SCR will continue to remain conductive and pressure will further increase until the high pressure detector H is finally satisfied opening its circuit (FIG. 2) and deenergizing the gate 33 of the SCR 30. Since the latter operates in the non-latching mode, such SCR will become non-conductive and no further current will flow through the loop circuit formed by the SCRs, causing the motor relay 50 to drop out, opening contacts 51, 52 and denergizing the motor. This causes the control circuitry to go'into the quiescent state.

However, as water is drawn through the connection 18 from the tank the pressure will be gradually reduced until the detector H will, calling for water, close its circuit. No current will, however, flow through the loop circuit since the SCR 20 remains deenergized. However, when the water pressure falls an additional differential amount, the low pressure detector L, too, calls for water by closing its circuit thereby energizing the gate 23 so that the condition for conduction is satisfied in both of the SCRs thereby energizing the motor relay 50, closing contacts 51, 52 and turning on the motor.

The initial positive inrush through the diode 80 to the gate 63 of the auxiliary transistor is defeated by the capacitor 90. At rated motor current, the voltage generated in the current transformer and rectified by the diode 73 insures that a net negative voltage will exist at the gate 63 thereby maintaining the auxiliary SCR 60 turned off, and the auxiliary relay deenergized so that the loop circuit, including contact 66, remains intact.

However, let it be assumed that water cannot be replenished at a'sufficient rate withint the well to keep up with the rate of withdrawal by the pump, in which case the pump will suck air. Such-sucking of air'effectively unloads the pump, and hence the motor,-so that the current through the motor falls to only a fraction of rated value. This condition is reflected by,a drop in voltage at the output of the current transformer and hence a drop in the negative voltage produced by the diode 73, so that the positive voltage from the diode 80 prevails, causing the auxiliary SCR to become conductive. This opens the contact 66 in the loop circuit, drop ping out the motor relay50 and opening the contacts 51, 52 to turn off the motor. In carrying out the invention the auxiliary, undercurrent relay is of the latching type so that the contact 66 remains open circuited, thus disabling the motor until the reset push button 68 is depressed, whereupon normal operation and control of water pressure will resume.

It has been found that in a normal installation, in which the leads of the detectors run closely parallel to one another, it is possible for the closing transient which occurs when the high pressure detector calls for water to induce a signal in the low pressure control line 11 which is sufficient to jar the SCR 20 permaturely into conduction. In order to avoid this possibility the time constant of the gate circuit of the transistor 20 is increased by addition of an auxiliary capacitor 95.

The term detector used herein is used in a generic sense to include both pressure-responsive devices which provide an indirect measure of water level or means to detectlevel directly. Also while the invention has been described as applied to a well pump it will be apparent that it is applicable to any pump which serves to replenish a reservoir.

I claim as my invention:

1. In a control for a motor driving a well pump having an associated tank and intended for operation from the regular a.-c. supply line, the combination comprising a low pressure detector including a switch, a first SCR having a gate and load circuit and in which the gate is connected to the low pressure detector, a highvpressure detector including a switch, a second S CR having a gate and load circuit and in which the'load circuit is connected to the high pressure detector, a transformer having a primary winding connected to the a.-c. supply line and having a secondary winding, a relay having input and output circuits, the load circuits of the SCRs and the relay input circuit being connected in series with the secondary winding in a loop circuit, the load circuit of the first SCR having a capacitor connected in shunting relation thereto for latching such SCR so that the motor once energized is maintained turned on after the low pressure detector is satisfied and until the high pressure detector is satisfied and so that the motor once deenergized is maintained turned off after the high pressure detector calls for water and until the low pressure detector calls for water.

2. In a control for a motor driving a well pump having an associated tank and intended for operation from the regular a.-c. supply line, the combination comprising, a low pressure detector including a switch, a first SCR having a gate and load circuit with the gate being connected to the low pressure detector, a high pressure detector including a switch, a second SCR having a gate and load circuit with the gate being connected to the high pressure detector, a transformer having a primary winding connected -to the a.-c. supply line and having a secondary winding, a relay having input and output circuits, the load circuits of the SCRs and the input circuit of the relay being connected in series with the transformer secondary to form a loop circuit, the load circuit of the first SCR having means to place such SCR in thelatching mode so that the'motor is turned off by operation of the high pressure detector, a current transformer having its primary winding wired in series with the pump motor and having a secondary winding, an auxiliary latching type relay having an input coil and having a normally closed output contact connected in series with the loop circuit, a current detector circuit having an auxiliary SCR including a gate and load circuit, the load circuit being coupled to the coil of the latching relay and the gate circuit having means for coupling to the secondary of the current transformer, the current detector circuit having power input terminals connected in shunt with the motor so that the latching relay is actuated only when the motor is energized and when the current in the current transformer is less than rated current for the motor indicating that the pump is sucking air.

3. In a control for a motor driving a well pump having an associated tank and intended for operation from the regular a.-c. supply line, the combination comprising, a low pressure detector including a switch, a first SCR having a gate and load circuit with the gate being connected to the low pressure detector, a high pressure detector including a switch, a second SCR having a gate and load circuit with the gate being connected to the high pressure detector, a transformer having a primary winding connected to the a.-c. supply line and having a secondary winding, a relay having input and output circuits, the load circuits of the SCRs and the input circuit of the relay being connected in series with the transformer secondary to form a loop circuit, the load circuit of the first SCR having means to place such SCR in the latching mode so that the mode is turned on by actuation of the low pressure detector and turned off by operation of the high pressure detector, a current transformer having primary wired in series with the motor and having a secondary winding, an auxiliary latching type relay having a coil and having a normally closed output contact connected in series with the loop circuit, a current detector circuit having an auxiliary SCR including a gate and load circuit, the load circuit being coupled to the input of the latching type relay, the current detector circuit having power input terminals connected in shunt with the motor, the current detector circuit further having a source of positive voltage supplied by the power input terminals and capable of turning the SCR on and having a source of negative voltage supplied by the secondary of the current transformer, means for coupling the gate of the SCR to both sources, the source of negative voltage varying in accordance with the motor current and of such magnitude as to keep the SCR turned off as long as rated current is drawn by the motor but which permits the SCR to be turned on when less than rated current is drawn by the motor with resultant actuation of the latching type relay and interruption of the loop circuit for disablement of the motor under conditions when the pump is sucking air.

4. The combination as claimed in claim 3 in which means are provided for preventing inrush of positive voltage to the auxiliary SCR when the motor is turned on so as to permit development of negative voltage corresponding to rated motor current to maintain the auxiliary SCR turned off.

5. The combination as claimed in claim 3 in which a capacitor is connected from the gate to the cathode of the auxiliary SCR so as to prevent the gate from going positive and hence turning on the SCR prior to the time that negative voltage is applied at the gate by reason of voltage induced in the secondary of the current transformer.

6. In a control for a motor driving a well pump having an associated tank and intended for operation from the regular a.-c. supply line, the combination comprising, a low pressure detector including a switch, a first SCR having a gate and load circuit with the gate being connected to the low pressure detector, a high pressure detector including a switch, a second SCR having a gate and load circuit with the gate being connected to the high pressure detector, a transformer having a primary winding connected to the a.-c. supply line and having a secondary winding, a relay having input and output circuits, the load circuits of the SCRs and the input circuit of the relay being connected in series with the transformer secondary to form a loop circuit, the load circuit of the first SCR having means to place such SCR in the latching mode so that the motor is turned on by actuation of the low pressure detector and turned off by operation of the high pressure detector, a current transformer having a primary wired in series with the motor and having a secondary, a latching type auxiliary relay having an input coil and a normally closed output contact with the latter being interposed in series with the loop circuit, a current detector circuit having an auxiliary SCR including an auxiliary gate, anode and cathode, the auxiliary anode and cathode being connected in series with the input of the latching relay, the current detecting circuit having power input terminals connected in shunt with the motor, a first rectifier connected to the power input terminals and coupled to the auxiliary gate for producing a positive voltage on such gate capable of turning on the SCR, means including a second rectifier connected to the secondary of the current transfonner and coupled to the auxiliary gate for delivering to such gate a negative voltage upon flow of normal current to the pump motor which is sufficiently high as to overpower the source of positive voltage and thereby keep the SCR turned off when the motor is normally loaded by the pump, and a high value capacitor connected between gate and cathode of the auxiliary SCR for increasing the time constant of the gate circuit and thereby effectively delaying application of the positive voltage to the gate until such time as the overpowering negative voltage produced by the second rectifier has had opportunity to be developed.

Claims

1. In a control for a motor driving a well pump having an associated tank and intended for operation from the regular a.-c. supply line, the combination comprising a low pressure detector including a switch, a first SCR having a gate and load circuit and in which the gate is connected to the low pressure detector, a high pressure detector including a switch, a second SCR having a gate and load circuit and in which the load circuit is connected to the high pressure detector, a transformer having a primary winding connected to the a.-c. supply line and having a secondary winding, a relay having input and output circuits, the load circuits of the SCR''s and the relay input circuit being connected in series with the secondary winding in a loop circuit, the load circuit of the first SCR having a capacitor connected in shunting relation thereto for latching such SCR so that the motor once energized is maintained turned on after the low pressure detector is satisfied and until the high pressure detector is satisfied and so that the motor once deenergized is maintained turned off after the high pressure detector calls for water and until the low pressure detector calls for water.

2. In a control for a motor driving a well pump having an associated tank and intended for operation from the regular a.-c. supply line, the combination comprising, a low pressure detector including a switch, a first SCR having a gate and load circuit with the gate being connected to the low pressure detector, a high pressure detector including a switch, a second SCR having a gate and load circuit with the gate being connected to the high pressure detector, a transformer having a primary winding connected to the a.-c. supply line and having a secondary winding, a relay having input and output circuits, the load circuits of the SCR''s and the input circuit of the relay being connected in series with the transformer secondary to form a loop circuit, the load circuit of the first SCR having means to place such SCR in the latching mode so that the motor is turned off by operation of the high pressure detector, a current transformer having its primary winding wired in series with the pump motor and having a secondary winding, an auxiliary latching type relay having an input coil and having a normally closed output contact connected in series with the loop circuit, a current detector circuit having an auxiliary SCR including a gate and load circuit, the load circuit being coupled to the coil of the latching relay and the gate circuit having means for coupling to the secondary of the current transformer, the current detector circuit having power input terminals connected in shunt with the motor so that the latching relay is actuated only when the motor is energized and when the current in the current transformer is less than rated current for the motor indicating that the pump is sucking air.

3. In a control for a motor driving a well pump having an associated tank and intended for operation from the regular a.-c. supply line, the combination comprising, a low pressure detector including a switch, a first SCR having a gate and load circuit with the gate being connected to the low pressure detector, a high pressure detector including a switch, a second SCR having a gate and load circuit with the gate being connected to the high pressure detector, a transformer having a primary winding connected to the a.-c. supply line and having a secondary winding, a relay having input and output circuits, the load circuits of the SCR''s and the input circuit of the relay being connected in series with the transformer secondary to form a loop circuit, the load circuit of the first SCR having means to place such SCR in the latching mode so that the mode is turned on by actuation of the low pressure detector and turned off by operation of the high pressure detector, a current transformer having primary wired in series with the motor and having a secondary winding, an auxiliary latching type relay having a coil and having a normally closed output contact connected in series with the loop circuit, a current detector circuit having an auxiliary SCR including a gate and load circuit, the load circuit being coupled to the input of the latching type relay, the current detector circuit having power input terminals connected in shunt with the motor, the current detector circuit further having a source of positive voltage supplied by the power input terminals and capable of turning the SCR on and having a source of negative voltage supplied by the secondary of the current transformer, means for coupling the gate of the SCR to both sources, the source of negative voltage varying in accordance with the motor current and of such magnitude as to keep the SCR turned off as long as rated current is drawn by the motor but which permits the SCR to be turned on when less than rated current is drawn by the motor with resultant actuation of the latching type relay and interruption of the loop circuit for disablement of the motor under conditions when the pump is sucking air.

6. In a control for a motor driving a well pump having an associated tank and intended for operation from the regular a.-c. supply line, the combination comprising, a low pressure detector including a switch, a first SCR having a gate and load circuit with the gate being connected to the low pressure detector, a high pressure detector including a switch, a second SCR having a gate and load circuit with the gate being connected to the high pressure detector, a transformer having a primary winding connected to the a.-c. supply line and having a secondary winding, a relay having input and output circuits, the load circuits of the SCR''s and the input circuit of the relay being connected in series with the transformer secondary to form a loop circuit, the load circuit of the first SCR having means to place such SCR in the latching mode so that the motor is turned on by actuation of the low pressure detector and turned off by operation of the high pressure detector, a current transformer having a primary wired in series with the motor and having a secondary, a latching type auxiliary relay having an input coil and a normally closed output contact with the latter being interposed in series with the loop circuit, a current detector circuit having an auxiliary SCR including an auxiliary gaTe, anode and cathode, the auxiliary anode and cathode being connected in series with the input of the latching relay, the current detecting circuit having power input terminals connected in shunt with the motor, a first rectifier connected to the power input terminals and coupled to the auxiliary gate for producing a positive voltage on such gate capable of turning on the SCR, means including a second rectifier connected to the secondary of the current transformer and coupled to the auxiliary gate for delivering to such gate a negative voltage upon flow of normal current to the pump motor which is sufficiently high as to overpower the source of positive voltage and thereby keep the SCR turned off when the motor is normally loaded by the pump, and a high value capacitor connected between gate and cathode of the auxiliary SCR for increasing the time constant of the gate circuit and thereby effectively delaying application of the positive voltage to the gate until such time as the overpowering negative voltage produced by the second rectifier has had opportunity to be developed.