GB2076236A

GB2076236A - Controller for AC electrical apparatus

Info

Publication number: GB2076236A
Application number: GB8114633A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-05-15
Filing date: 1981-05-13
Publication date: 1981-11-25

Abstract

A controller is provided for controlling the energisation of electrical apparatus (3) from an a.c. supply, the apparatus (3) being of the type including a control device (7) having a first state in which it enables energisation of the apparatus from the supply and a second state in which it inhibits energisation of the apparatus. The controller includes a switch device (51) for connection into one line (15) of the supply circuit of the apparatus (3) and switchable between non-conducting and conducting states. The controller further includes indicator means (5) for providing an indication of the state of the control device (7) of the apparatus when the switch device (51) of the controller is in its non-conducting state. The controller is particularly suited to the control of a domestic immersion heater unit (3), the indicator means (5) being arranged to provide an indication of the state of the heater-unit thermostat (7). <IMAGE>

Description

SPECIFICATION Controller for AC electrical apparatus FThe present invention relates to a controller for a.c. electrical apparatus and in particular, but not exclusively, to a controller for control ling a thermostatically-regulated immersion heater unit.

Many pieces of electrical apparatus include control devices arranged to prevent energisa tion of the apparatus from a supply circuit in the presence of certain conditions; thus, for example, a domestic immersion heater unit includes a thermostat which prevents energi sation of the heater element of the unit when the water in the domestic hot water tank exceeds a certain temperature. Often, the ap paratus concerned is not provided with any means for indicating the state of the internal control device although such information would frequently be ueful to a user of the apparatus.

In the case of a domestic immersion heater unit, an indication of the state of the thermos tat would provide the user with an immediate indication of whether the water was in a fully heated condition. Of course, where the exter nal switch controlling the supply of electricity to the immersion heater unit is left perma nently closed, then the user can be sure that the water is either fully heated or is being heated.However, for economic reasons, the external switch will often be open and it is particularly in this condition that an indication of the state of the heater-unit thermostat would be useful as it would enable the user to determine whether the heater unit should be switched on; furthermore, an indication of the state of the thermostat with the heater unit switched off would enable the water hotness to be assessed even when an external heat source (for example, a boiler) was being used to heat the water.

According to one aspect of the present invention, there is provided a controller for controlling the energisation of electrical appa ratus from an a.c. electrical supply, said appa ratus being of the type including a control device having a first state in which it enables energisation of the apparatus from said supply and a second state in which it inhibits energi sation of the apparatus, said controller com prising a switch device for connection into a line of the electrical supply circuit of said apparatus and switchable between non-con ducting states in the latter of which the supply circuit to the apparatus is completed, and indicator means operative to provide an indi cation of the state of the control device of the apparatus when said switch device is in its non-conducting state, the sole electrical con nection provided, in use, between the indica tor means and said apparatus being via said electrical supply circuit.

In use of the controller to control a domestic immersion heater unit, the said switch device of the controller is constituted by the thermostat of the heater unit. In this application, the indicator means operates to provide an indication of when the thermostat is open in the condition of the switch device being open.

Controllers embodying the invention can implement various other control functions in addition to a simple conducting/non-conducting function of the switch device. Thus, the controller when used to control an immersion heater unit can be arranged to provide a "one-shot" function in which is can be operated to effect a single heating of water in the tank and thereafter place the switch device in its non-conducting state.

Accordingly, in a second aspect the present invention provides an immersion-heater controller for controlling the energisation of a thermostatically-regulated immersion heater unit from an a.c. electrical supply, said controller being arranged for connection into the electrical supply circuit of the heater unit and including switching means having a stable first state in which, with the controller connected into said supply circuit, that circuit is open, and a quasi-stable second state in which said supply circuit is closed, the switching means being temporarily settable into its second state by manual operation of a switch member of the switching means whereby to initiate energisation of the heater element of the heater unit if the instantaneous state of the heater-unit thermostat so permits, and the switching means being responsive to the state of energisation of the heater element to maintain itself in its quasi-stable second state only for as long as heater-element energisation continues uninterrupted, interruption of heater-element energisation causing the switching means to revert to its first state where it remains until a subsequent operation of said switch member, the controller further comprising first indicator means operative to indicate the state of the thermostat when the switching means is in its stable first state, and second indicator means operative to indicate when the switching means is in its quasistable second state, said electrical supply circuit providing, in use, the sole electrical connection between the first indicator means and the thermostat.

The second state of the switching means is termed quasi-stable since this state is a maintained one rather than one in which the switching means resides independently of an external maintaining influence.

It will be appreciated that each operation of the switch member of the controller is effective to cause the heater unit to heat up water in the hot water tank once only, thereby preventing unnecessary wastage of electricity.

The provision of the first and second indicator means enables the user (typically a busy housewife) to tell at a glance whether the water in the domestic hot-water tank is being heated, is in a heated-up state, or requires to be heated.

In one preferred form of the immersion heater controller, the switching means comprises an a.c. contactor connected into the supply circuit. The contactor has a winding which is arranged to be energised directly by the heating current to maintain the contactor closed (that is, in its second state). The switch member for temporarily setting the contactor into its second state comprises a single-pole rocker switch electrically connected across the contactor contacts and mechanically biased open; momentary closure of this rocker switch results in energisation of the contactor winding and closure of the contactor (provided, of course, that the thermostat contacts are closed).

The said first indicator means of the controller preferably comprises a three-arm star circuit the first and second arms of which each comprise a respective rectifier in series with an impendance, said first and second arms being connected in series across the contactor contacts with the rectifiers in series aiding relation, the third arm of the star circuit including a threshold circuit which, in use, is connected across the supply circuit via said first and second arms, and said threshold circuit being arranged to cause the first indicator means to take up a predetermined first output state only when supplied with a direct current or voltage above a certain value, the values of said impedances being such that:: a) when the contacts of the contactor are open and the thermostat of the heater unit is in a state allowing energisation of the heater element, the direct current or voltage supplied to said threshold circuit is below said certain value due to the loading effect of the heater element; and b) when the contacts of the contactor are open and the thermostat is in a state preventing heater-element energisation, the direct current or voltage supplied to the threshold circuit is above said certain value; closure of the contacts of the contactor being effective to supply alternating current or voltage to said threshold circuit through both said rectifiers.

An immersion-heater controller embodying the invention will now be particularly described, by way of example, with reference to the accompanying drawings, in which Figure 1 is a diagram illustrating the arrangement of the controller in a domestic immersion heater installation; Figure 2 is a perspective view of the controller; and Figure 3 is a circuit diagram of the control ler.

As shown in the Fig. 1, the immersionheater controller 1 now to be described is intended to replace the normal two-pole mains supply switch provided in a domestic immersion-heater installation between the mains switchbox 2 and the thermostatically-regula\,ed immersion heater unit 3 installed in the hot water tank 4. The unit 3 comprises a heating element 6 and a thermostat 7. No further connections additional to the normal power supply leads are required between the controller 1 and the heater unit 3. The purpose of the controller 1 is to cause the immersion heater unit 3 to fully heat water in the hot water tank 4 once only and thereafter to keep the immersion heater unit de-energised until the controller 1 is manually reset. This avoids the need for the operator (for example, a busy housewife) to remember to turn off the immersion heater unit 3.The foregoing mode of control of the immersion heater unit 3 is termed the "conserve" mode as it prevents electricity being wasted due to the immersion heater unit being unknowingly left on. The controller 1 is so arranged that the unit 3 can also be operated in a "constant" mode in which the immersion heater unit 3 is continuously energised with the heating element 6 itself being energised under the sole control of the thermostat 7 of the unit to maintain the water above a predetermined temperature.

The controller 1 is shown in perspective in Fig. 2 and, as can be seen, includes three front-panel switches S1, S2, and S3. Switch S1 is a two-pole mains supply ON-OFF switch the closure of which can be arranged to energise a "Mains On" neon indicator light (not shown). Switch S2 is a two-position, rocker switch and permits the mode of operation of the controller 1 to be selected, that is, whether the controller operates in the "conserve" or "constant" mode. Switch S3 (the "reheat" switch) is a spring-pole rocker switch which is spring biased into a normally-open position and which, with the controller operating in the "conserve" mode, is arranged, upon being momentarily pressed closed, to initiate a single heating of the water in the tank 4. Neon indicator lights 50 and 5 are provided to indicate respectively the state of energisation of the immersion heater unit 3 (and thus whether the water is being heated) and the state of the thermostat contacts 7 (and thus whether the water is fully heated and ready for use).

The circuit diagram of the controller 1 is shown in Fig. 3. Input terminals 8 of the controller 1 are arranged for connection to the live and neutral lines (L, N) of the mains supply while output terminals 9 provide connection to the immersion heater unit 3. The two-pole switch S1 is wired directly to the input terminals 8 and acts as a master ON OFF swich.

The controller 1 is built around a switch device in the form of a single-pole A.C. con tactor 51 comprising an operating winding 52 and a pair of electrical contacts 53 and 54.

The winding 52 and contacts 53, 54 are connected in series into the "live" line 1 5.

Both the contact pair 53, 54 and the winding 52 are arranged to pass the full heating curent drawn by the immersion heater unit 3, the winding 52 being designed to hold closed the contacts 53, 54 whenever this heating current is flowing.

The reheat switch S3 is electrically connected across the contacts 53 and 54 and can be manually operated against its spring bias to short together these contacts 53, 54.

The switch S2 can be manually set into an open or closed position both of which are stable. The switch S2 is electrically connected across the whole of the contactor 51 so that when the switch S2 is set in its closed position, the contactor 51 is effectively by-passed and exerts no control over the heater unit 3; this setting of the switch S2 corresponds to the "constant" mode of operation of the controller 1 in which energisation of the heater element 6 is regulated solely by the thermostat 7.

With the switch S2 in its open position, the controller will operate in its "conserve" mode.

In this mode, depression of the reheat switch S3 to momentarily shunt the contacts 53, 54 will (provided the thermostat 7 so permits) initiate heating current flow; as already mentioned, the heating current in passing through the winding 52 will maintain the contacts 53, 54 closed so that upon manual pressure being removed from the switch S3, the contacts 53, 54 will remain closed and current will continue to flow until interrupted by the thermostat 7. Subsequently, the heater unit 3 will remain de-energised regardless of whether the thermostat 7 is open or closed, until either the reheat switch S3 is again depressed to initiate a water re-heat cycle or switch S2 is set into its "constant" mode state.

In the above-described manner, a single heating of water in the hot-water tank 4 can be achieved simply by setting the switch S2 into its "conserve" mode state and thereafter pressing switch S3 once.

The state of energisation of the heating element 6 is indicated using the neon light 50 which is connected in series with resistors 68, 71 and diode 67 across the heater unit 3.

The resistor 71 is part of the assembly of the neon light 50 which is, for example, arranged to light up red. Whenever the heating element 6 is energised, the neon light 50 will be illuminated and, conversely, when the element 6 is de-energised the neon light 50 will be extinguished.

The state of the hotness of water in the tank 4 can be indicated using the circuitry associated with the neon light 5 in Fig. 3. This circuitry is arranged to cause illumination of the neon light 5 whenever the thermostat contacts 7 are open and comprises three circuit branches connected in a star arrangement with a common star point 60. The three circuit branches respectively comprise a resistor 61 and a diode 62 connected by its anode to the contact 53; a resistor 63 and a diode 64 connected by its cathode to the contact 54; and a threshold circuit constituted by a resistor 65 and the neon indicator light 5 connected between the star point 60 and the neutral line 1 6 and paralleled by a capacitor 66. The resistor 65 is part of the assembly of the neon light 5 which, for example, is green in colour.

Whenever the contacts 53, 54 are closed, the diodes 62 and 64 will conduct alternately resulting in an A.C. waveform appearing at the star point 60. The value of the capacitor 66 is so chosen that its reactance at the mains supply frequency is sufficiently low as to prevent the neon light 5 from lighting up when an A.C. voltage is present at point 60.

Whenever the contacts 53, 54 are open with switch S1 closed, (that is, after the completion of a single heating cycle when the controller is in its "conserve" mode), only diode 62 is connected to the A.C. mains. As a result, a D.C. voltage will be developed across the capacitor 66. Whenever the contacts of the thermostat 7 are open (water "ready"), the magnitude of this D.C. voltage is sufficient to cause illumination of the neon light 5 whereby to indicate that the water has been heated to the required temperature. However, when the thermostat contacts are closed, the capacitor 66 is shunted by the circuit path comprising the resistor 63, the diode 64, the thermostat 7 and the heating element 6, the effect of this shunting being to reduce the capacitor voltage to a level insufficient to cause illumination of the neon light 5.Provided the switch S1 is closed, the neon light 5 will provide an indication of when the water is fully heated even when heating is effected by means other than the unit 3 (for example, by a central heating boiler).

From the foregoing it will be appreciated that the threshold circuit constituted by the neon light 5, the resistor 65 and the capacitor 66 operates to provide a particular output (lighting up of the neon light 5) only when a direct voltage above a certain value is applied thereacross, this output being absent in the presence of alternating voltages or direct voltages below said certain value. It would of course, be possible to provide a threshold circuit responsive to current rather than voltage values.

In the illustrated circuit, the values of the resistors 61 and 63 and of the capacitor 66 should be chosen to give short charging and discharge time constants to prevent undesired oscillations of the neon light 5; typical values suitable for use with a 240 v, 50 Hz supply are 33K for resistors 61, 63 and 0.68 I1F for capacitor 66. If desired the values of the resistor 61 and capacitor 66 can be selected to give flashing indication that the water has been heated to the required temperature.

The provision of the diode 67 in series with the neon light 50 prevents illumination of the latter via diode 64 when the voltage across the capacitor 66 is sufficient to cause illumi nation of the neon light 5.

A removable link 69 is provided in series with the resistor 65 to enable the insertion of an external "water-ready" alarm in addition or as an alternative to the neon light 5.

In order to provide for disablement of the "constant" mode of operation, a link 75 is provided which is normally connected to ter minal 72 of switch S2 but which can be connected instead to a terminal 73 and thereby effectively render S2 inoperative to shunt the contactor 51.

In addition to the terminals 72, 73, the controller is also provided with terminals 72, 73, 76, 77, 78 79, 80 and a link 81 which facilitate rnodification or expansion of the basic controller and, in particular, enable remote control, paraileling of circuit portions, and time-switch control to be implemented.

Various modifications to the described controller are, of course, possible. Thus, for example, instead of using the neon light 50 to provide an indication of the state of energisation of the heating element 6, a mechanical indicator could be provided physically linked to the moving contact 5a. of the contactor 51.

Claims

1. A controller for controlling the energisation of electrical apparatus from an a.c. electrical supply, said apparatus being of the type including a control device having a first state in which it enables energisation of the apparatus from said supply and a second state in which it inhibits energisation of the apparatus, said controller comprising a switch device for connection into a line of the electrical supply circuit of said apparatus and switchable between non-conducting and conducting states in the latter of which the supply circuit to the apparatus is completed, and indicator means operative to provide an indication of the state of the control device of the apparatus when said switch device is in its non-conducting state, the sole electrical connection provided, in use, between the indicator means and said apparatus being via said electrical supply circuit.

2. A controller according to Claim 1, wherein said indicator means is arranged to take up a predetermined first output state only when said switch device is in its non-conducting state and said control device is in its second state in which it inhibits energisation of the apparatus.

3. A controller according to Claim 2, wherein said indicator means comprises a three-arm star circuit the first and second arms of which each comprise a respective rectifier in series with an impedance, said first and second arms being connected in series across said switch device with the rectifiers > series aiding relation, the third arm of the star circuit including a threshold circuit which, in use, is connected across the supply circuit via said first and second arms, and said threshold circuit being arrange to cause said indicator means to take up its first output state only when supplied with a direct current or voltage above a certain value whereby, in use:: a) when the said switch device is in its conducting state, the indicator means is otherwise than in its first output state due to the threshold circuit being supplied with an alternating current or voltage via said first and second arms; b) when said switch device is in its nonconducting state and the said control device of the apparatus is in its second state, the indicator means is in its said first output state due to a direct current or voltage above said certain value being supplied thereto via said first arm; and c) when said switch device is in its nonconducting state and the said control device of the apparatus is in its first state, the indicator means is otherwise than in said first output state due to the loading effect of the electrical apparatus via said second arm causing the direct current or voltage supplied to the threshold circuit to be less than said certain value.

4. A controller according to Claim 3, wherein said threshold circuit includes a neon indicator light paralleled by a capacitor the reactance of which at the normal supply frequency is such that the light remains extinguished when said switch device is in its conducting state, said light being arranged to be energised only when said switch device is in its non-conducting state and the control device of the apparatus is in its second state.

5. An immersion-heater controller for controlling the energisation of a thermostaticallyregulated immersion heater unit from an a.c.

electrical supply, said controller being arranged for connection into the electrical supply circuit of the heater unit and including switching means having a stable first state in which, with the controller connected into said supply circuit, that circuit is open, and a quasi-stable second state in which said supply circuit is closed, the switching means being temporarily settable into its second state by manual operation of a switch member of the switching means whereby to initiate energisation of the heater element of the heater unit if the instantaneous state of the heater-unit thermostat so permits, and the switching means being responsive to the state of energisation of the heater element to mainain itself in its quasi-stable second state only for as long as heater-element energisation continues uninterrupted, interruption of heater-element energisation causing the switching means to revert to its first state where it remains until a subsequent operation of said switch member, the controller further comprising first indicator means operative to indicate the state of the thermostat when the switching means is in its stable first state, and second indicator means operative to indicate when the switching means is in its quasi-stable second state, said electrical supply circuit providing, in use, the sole electrical connection between the first indicator means and the thermostat.

6. An immersion-heater controller according to Claim 5, wherein said switching means includes a switch device which, in use, is inserted into one line of said electrical supply circuit, ssaid switch device being normally in a non-conducting state corresponding to said first state of the switching means but being holdable in a conducting state corresponding to the quasi-stable second state of the switching means, the switching means further including means responsive to the flow of heating current to the heater element to hold said switch device in its conducting state.

7. An immersion-heater controller according to Claim 6, wherein said switch device is constituted by a pair of normally-open contacts.

8. An immersion-heater controller according to Claim 7, wherein said switch member comprises means for manually closing said contacts.

9. An immersion-heater controller according to Claim 5, or Claim 7, wherein said switch member comprises a normally-open switch in parallel with said switch device.

1 0. An immersion-heater controller according to any one of Claims 5 to 9, wherein said first indicator means includes first warning lamp means arranged to be illuminated only when the switching means is in its first state and the thermostat is in a state inhibiting energisation of the heater element, and said second indicator means comprises second warning lamp means arranged to be energised only when the switching means is in its second state and the heater element is energised.

11. An immersion-heater controller according to any one of Claims 6 to 9, wherein said first indicator means comprises a threearm star circuit the first and second arms of which each comprise a respective rectifier in series with an impedance, said first and second arms being connected in series aiding relation, the third arm of the star circuit including a threshold circuit which, in use, is connected across the supply circuit via said first and second arms, and said threshold circuit being arranged to cause the first indicator means to take up a predetermined first output state only when supplied with a direct current or voltage above a certain value, the values of said impedances being such that:: a) when the switch device is in its nonconducting state and the thermostat of the heater unit is in a state allowing energisation of the heater element, the direct current or voltage supplied to said threshold circuit is below said certain value due to the loading effect of the heater element; and b) when the switch device is in its nonconducting state and the thermostat is in a state preventing heater-element energisation, the direct current or voltage supplied to the threshold circuit is above said certain value; the placing of said switch device in its conducting state being effective to supply alternating current or voltage to said threshold circuit through both said rectifiers.

1 2. An immersion-heater control to Claim 11, wherein said threshold circuit includes a neon indicator light paralleled by a capacitor the reactance of which at the normal supply frequency is such that the light remains extinguished when said switch device is in its conducting state, said light being arranged to be energised only when said switch device is in its non-conducting state and the thermostat of the heater unit is in a state preventing energisation of the heater element.

1 3. An immersion-heater controller substantially as hereinbefore described with reference to Figs. 1 and 3 of the accompanying drawings.