EP1842276A1

EP1842276A1 - Device for detecting an electrical power supply failure

Info

Publication number: EP1842276A1
Application number: EP05818480A
Authority: EP
Inventors: Anthony Pugh; Hugh Goodwin
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-12-16
Filing date: 2005-12-12
Publication date: 2007-10-10
Also published as: WO2006064209A1; GB0427505D0

Abstract

A device for detecting an electrical power supply failure comprises a plurality of electrical connectors for connecting the device between an electrical power supply and an electrical load, and a threshold monitor for detecting an electrical current and/or voltage from the power supply. The threshold monitor, which may be a comparator, is arranged to distinguish between: (a) a current and/or voltage having a magnitude greater than a predetermined magnitude, thereby indicating the presence of a current and/or voltage powering the load, or indicating the presence of a residual current and/or voltage from the supply when the load is not in use; and (b) a lack of a current and/or voltage having a magnitude greater than the predetermined magnitude, thereby indicating a failure in the power supply.

Description

Device for Detecting an Electrical Power Supply Failure

This invention relates to a device for detecting an electrical power supply failure, and in particular relates to a device for providing emergency lighting in the event of a power supply failure.

In commercial buildings, emergency lights are present which are installed with their own fixed wiring at strategic positions in the building, for example in a stairwell or in doorways. Such light devices can be emergency only lighting devices, or dual function devices that can operate as a normal lighting device when the mains is healthy and as a low-wattage emergency light when the mains supply fails. These dual function devices have a disadvantage in that they require two separate power supplies, one switched supply to allow the light to function as a normal light, and another supply that provides a constant supply of current in order to maintain the charge of an internal battery which upon failure of the power supply activates the emergency light. Having two supplies of power is a disadvantage in that it increases costs of wiring and ultimately building costs.

For the domestic market, emergency lights are known which are of a low wattage and which are themselves plugged into conventional domestic power sockets. This allows an internal battery to be charged but has a distinct disadvantage in that they will activate if they are unplugged or if the socket is switched off. By having a device that is constantly plugged into a socket, this also has a disadvantage that fewer power sockets are available to be used.

The present invention seeks to overcome the problems associated with the prior art by providing a self-contained device that discriminates between a true failure in a power supply and an electrical load (e.g. a lamp) merely being switched off (e.g. switched off at a wall socket or a wall-mounted switch). According to a first aspect of the invention there is provided a device for detecting an electrical power supply failure, comprising a plurality of electrical connectors for connecting the device between an electrical power supply and an electrical load, and a threshold monitor for detecting an electrical current and/or voltage from the power supply, wherein the threshold monitor is arranged to distinguish between: (a) a current and/or voltage having a magnitude greater than a predetermined magnitude, thereby indicating the presence of a current and/or voltage powering the load, or indicating the presence of a residual current and/or voltage from the supply when the load is not in use; and (b) a lack of a current and/or voltage having a magnitude greater than the predetermined magnitude, thereby indicating a failure in the power supply.

The invention has the advantage that because the device is able to determine whether a residual current and/or voltage from the supply is present or absent, then it is able to distinguish (discriminate) between a true failure in the power supply (on the one hand) and an electrical load merely being "switched off" by means of a switch situated in the electric circuit supplying the load (on the other hand). This is because the inventors of the present invention have determined that when an electrical power supply is functioning correctly but an electrical load connected to the supply is switched off by means of a switch (e.g. a wall-mounted switch) remote from the load, then a small residual current (or a "leakage" current) is detectable at the load. The invention monitors whether this residual current is present in order to distinguish between a failure in the power supply and the electrical load merely being switched off. This monitoring for the residual current may be a direct monitoring of electric current and/or it may be an indirect monitoring of electric voltage produced (for example across the electrical load) by the residual current.

In an alternating current (AC) electrical power supply, the residual electric current referred to above is normally due to an inherent capacitance between electrical conductors (wires or cables) providing power to the switch and/or due to an inherent capacitance between the switch contacts when the power supply is functioning.

The ability of the device according to the invention to determine whether a residual current is present provides the great benefit that the device can function while being remote from a switch (e.g. a wall-mounted switch) that connects an electrical load to the electrical power supply. For example, if the electrical load is a lamp, the device can be situated adjacent to the lamp in the electric circuit powering the lamp, and remote from a wall-mounted switch connecting the lamp to the power supply. The invention consequently avoids the need for the device to be attached to the switch, or to be part of a replacement switch component, in order to monitor the current (or voltage) on the supply side of the switch (which is the case with some prior art devices). The invention also has the great advantage that, for example, if the electrical load is a lamp, the device is able to constitute an emergency lighting device located actually at the lamp fitting, rather than being located remote from the lamp fitting (e.g. at a wall-mounted switch or socket). The emergency lighting device can thus provide emergency lighting from the same location as a lamp that is not functioning due to a power failure, thereby providing more convenient and suitable emergency lighting than emergency lights that are situated in different locations to the normal lighting. Also, the emergency lighting device of the invention can have the capability to be retro-fitted, i.e. connected to an existing lamp fitting (e.g. by being inserted between the lamp fitting and the lamp).

In preferred embodiments of the invention, the threshold monitor comprises a comparator. Preferably, the comparator comprises a voltage comparator, e.g. arranged to distinguish between: (a) a voltage having a magnitude greater than the predetermined magnitude; and (b) a lack of a voltage having a magnitude greater than the predetermined magnitude. The predetermined magnitude of current and/or voltage preferably is a reference value stored in the device. The device may advantageously include an amplifier arranged to amplify the current and/or voltage from the supply, the device being arranged such that the current and/or voltage that the threshold monitor detects is the current and/or voltage that has been amplified by the amplifier. Preferably, the amplifier is arranged to amplify a residual current and/or voltage from the supply when the load is not in use, such that the residual current and/or voltage is amplified to a magnitude that is greater than the predetermined magnitude and consequently is detected as such by the threshold monitor. A current and/or voltage powering the load in use will normally be amplified such that the amplifier is driven substantially to saturation, and consequently the current and/or voltage detected by the threshold monitor has a magnitude that is greater than the predetermined magnitude. Preferably the device includes an amplifier protector that is arranged to protect the amplifier by attenuating the current and/or voltage from the supply before it is amplified by the amplifier if the current and/or voltage from the supply has a magnitude greater than a particular magnitude, which particular magnitude is greater than the predetermined magnitude. In this way, the amplifier may be protected when the power supply is functioning normally.

In particularly preferred embodiments of the invention, the device includes a power source arranged to provide electrical power in the event of a power supply failure being detected by the device. The power source preferably comprises one or more batteries, for example Nickel-Cadmium (NiCd) batteries or any batteries of a similar power-to-weight performance. Preferably the battery or batteries (or other power source) is/are arranged to be charged by the electrical power supply.

The device may beneficially include a power supply failure indicator, arranged to signal the existence of a power supply failure in the event that the threshold monitor fails to detect a current and/or voltage having a magnitude greater than the predetermined magnitude, which power supply failure indicator is itself powered by the power source. For example, the power supply failure indicator may comprises one or more lights and/or a device arranged to emit an audible alarm signal in the event that the threshold monitor fails to detect a current and/or voltage having a magnitude greater than the predetermined magnitude.

In an especially preferred aspect of the invention, the device is an emergency light device, arranged to provide emergency lighting powered by the power source, in the event that the device detects a failure in the power supply. For example, the emergency lighting may be provided by at least one light of the device arranged to illuminate in the event that the threshold monitor fails to detect a current and/or voltage having a magnitude greater than the predetermined magnitude. The (or each) light may for example comprise a light-emitting diode (LED). Additionally or alternatively, if the electrical load comprises a lamp, the lamp may be powered by the power source in the event that the device detects a failure in the power supply, thereby providing the emergency lighting by means of the existing lamp.

A second aspect of the invention provides an electrical apparatus including a device according to the first aspect of the invention. The electrical load preferably comprises a part of the electrical apparatus, and/or it may comprise an external electrical load that is electrically connected to the apparatus. The electrical apparatus may generally comprise any electrical appliance, but preferably the apparatus comprises a light fitting, in which case the electrical load preferably comprises at least one lamp (e.g. at least one light bulb) of the light fitting. Thus, in some preferred embodiments of the invention, the invention provides a light fitting incorporating a device according to the first aspect of the invention.

It will therefore be appreciated that the present invention may comprise an electrical component suitable for incorporation into an existing electrical apparatus (e.g. for incorporation into an existing light fitting), or the invention may comprise a self-contained unit suitable for connection to an existing electrical apparatus (e.g. for connection to an existing light fitting), or the invention may comprise an electrical apparatus (e.g. a light fitting) which includes a device according to the first aspect of the invention. The invention thus provides great versatility, such that embodiments of the invention may be provided in substantially any convenient form.

The device according to the invention may include a delay circuit and a switch component, which switch component preferably connects and disconnects the power source of the device, e.g. to emergency lighting of the device. The delay circuit preferably is arranged to maintain the switch component in an "off" condition while the threshold monitor detects a current and/or voltage having a magnitude greater than the predetermined magnitude, and is arranged to cause or allow the switch component to adopt an "on" condition if the threshold monitor fails to detect a current and/or voltage having a magnitude greater than the predetermined magnitude. In this way, for example, the emergency lighting of the device may be switched on in the event of a power failure being detected. The switch component may comprise a transistor, e.g. a field-effect transistor (FET), especially a MOSFET.

The electrical connectors of the device may generally comprise any electrical connectors. However, for embodiments of the invention in which the device is intended to be fitted to a lamp fitting, e.g. with a lamp connected to the fitting via the device, the electrical connectors of the device preferably comprise lamp fitting connectors, e.g. bayonet or screw-thread connectors. The device may generally be used in conjunction with any form of lamp, e.g. filament lamps, fluorescent lamps, low-energy lamps, light-emitting diodes (LED's), etc.

In at least some preferred embodiments of the invention, the device includes a visual indicator to show that the device (preferably the power source) is receiving electrical charge, in use. In a preferred arrangement the device includes a visual and/or an audible indicator to alert that the power source is below a predetermined level of electrical charge. Such an indicator can therefore provide a warning that the electrical load must be switched on in order to charge the power source of the device and/or that the power source must be replaced, for example.

In a further arrangement, the device may include a test switch to simulate a failure of input power supply, thereby allowing the device to be tested.

Preferably, the device includes a light detector whereby the device is deactivated when light levels are above a given illumination threshold. By limiting the device to be active only when light levels are low, this will conserve the stored charge available for use during low light levels or darkness.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying figures, of which:

Figure 1 is a perspective view of a device in accordance with the present invention;

Figure 2 is a schematic diagram of electrical circuitry associated with the use of the device illustrated in Figure 1; and

Figure 3 is a schematic diagram of the electrical circuitry of the device itself.

Referring to Figure 1, the power failure detecting device according to the invention is indicated by the reference "A". The device comprises a main body 1 comprising a housing which contains electrical circuitry. A series of lights 4 (preferably six lights) are arranged around the periphery of the housing. On an upper surface of the housing there is a plug-type electrical connector 2, which is shown as a bayonet plug (although, as mentioned, a screw type plug could be used) for fitting into a light bulb socket. On the underside of the device, there is another electrical connector 3 so that the device can be attached to an electrical load, which in this case is a lamp such as a light bulb 5. The device also includes an attachment 12 between the housing 1 and the connector 3. An indicator light 6 is incorporated in the housing to provide a visual indication that power is being supplied to the device from the mains supply to charge a rechargeable battery contained in the housing 1.

In operation, the power failure detecting device A is plugged into a ceiling lamp fitting (not shown) connected to the "mains" power supply. In the event of a power failure, there will no longer be current supplied to the light bulb 5. As explained above, the device detects the power failure and illuminates (by means of the rechargeable battery) the lights 4 spaced around the upper surface of the housing, thereby providing emergency illumination. Positioning the emergency lights around the upper surface of the housing provides the advantage that the emergency lighting will be reflected from the ceiling, thereby spreading the illumination over a wide area. To enhance the affect of the illumination, a reflector or lens may be positioned above the emergency lights 4. It will be appreciated that the emergency lights 4 may be positioned on other faces of the device to increase the spread of illumination. (For example, the lights 4 may be positioned so that there is both upward and downward illumination.)

Referring to Figure 2, the relationship between the device A and a typical domestic lighting installation circuit is shown. The incoming main AC power supply 7 (comprising live ("L"), neutral ("N") and earth ("E") conductors) is connected to a "loop-in" ceiling rose 8, which connects a pendant lamp holder 9 to a wall-mounted light switch 10 which is in series with the live feed to the lamp holder via cable 13. The power failure detecting device A is fitted between the lamp holder 9 and the light bulb 5. The device A includes a PCB (printed circuit board) containing circuitry to allow for monitoring of the in-coming mains power supply, as explained above. As mentioned above, Figure 3 is a schematic diagram of an example of the electrical circuitry of the device A. During normal operation with the electrical load (e.g. a lamp) switched "on", the AC supply is connected to a charger circuit 52 which produces a DC charge current suitable for continuous "trickle" charging of rechargeable batteries 59 and 60 (which are typically 2.4V Nickel-Cadmium batteries). A re-settable thermal fuse 61 protects the batteries from abnormally high charge and discharge faults. The battery voltage (VBAT), is applied to a low voltage regulator 62 which supplies a stable voltage (VA) for amplifier and detector circuits 54, 55, 56. The AC supply is also connected to amplifier overload protections circuits 50, 51, 53. The amplifier 54 amplifies the AC voltage, which is prior reduced by resistor 51 and diode network 53, and is driven to saturation by the AC voltage. A voltage comparator 55 (the "threshold monitor") detects that this large AC voltage is greater than a fixed reference voltage (the "predetermined magnitude") and holds-off a delay circuit 56 which keeps a Metal Oxide Semiconductor Field Effect Transistor (MOSFET) 57 in an "off" state.

When the wall light switch 10 is in its "off" state, the inherent capacitance due to its construction Cx and the parallel wire capacitance Cy (shown in Figure 2) will pass a small residual AC current which will flow through the filament of the lamp 13 producing a microvolt- 1 eve I AC voltage. This residual voltage is too small to be attenuated by the effects of the protection circuits 50, 51 and 53. However, the high voltage gain amplifier 54 is arranged to amplify the residual voltage to ensure that it is detected by the comparator 55 as greater than the fixed reference voltage, which again keeps the MOSFET 57 in an "off" state.

When mains power supply failure occurs, the device A fails to detect a voltage higher than the reference voltage, because there is now no residual voltage being amplified. Thus, either no voltage is now presented to the comparator 55, or any voltage that might still be presented to the comparator is now below the fixed reference magnitude. Consequently, the delay circuit 56 no longer maintains the MOSFET 57 in the "off state", but causes or allows the MOSFET 57 to adopt an "on state", which in turn causes the emergency LED lights 4 to be illuminated.

The arrangement of the present invention has the advantage that where the mains supply to the device has an external series on/off switch which may be in the off position, the device is uniquely able to distinguish this condition from a true supply failure.

It is to be appreciated that the description of the specific embodiment of an emergency lighting device and the references to the accompanying figures are intended solely to illustrate the underlying invention. The skilled addressee should be equally minded of alternative embodiments which do not depart from the theme of the invention. Furthermore, the described embodiment and figures are not intended to be limiting on the invention, which is defined in the claims.

Claims

1. A device for detecting an electrical power supply failure, comprising a plurality of electrical connectors for connecting the device between an electrical power supply and an electrical load, and a threshold monitor for detecting an electrical current and/or voltage from the power supply, wherein the threshold monitor is arranged to distinguish between: (a) a current and/or voltage having a magnitude greater than a predetermined magnitude, thereby indicating the presence of a current and/or voltage powering the load, or indicating the presence of a residual current and/or voltage from the supply when the load is not in use; and (b) a lack of a current and/or voltage having a magnitude greater than the predetermined magnitude, thereby indicating a failure in the power supply.

2. A device according to claim 1, in which the threshold monitor comprises a comparator.

3. A device according to claim 2, in which the comparator comprises a voltage comparator arranged to distinguish between: (a) a voltage having a magnitude greater than the predetermined magnitude; and (b) a lack of a voltage having a magnitude greater than the predetermined magnitude.

4. A device according to any preceding claim, in which the predetermined magnitude of current and/or voltage is a reference value stored in the device.

5. A device according to any preceding claim, further comprising an amplifier arranged to amplify the current and/or voltage from the supply, the device being arranged such that the current and/or voltage that the threshold monitor detects is the current and/or voltage that has been amplified by the amplifier.

6. A device according to claim 5, in which the amplifier is arranged to amplify a residual current and/or voltage from the supply when the load

5 is not in use, such that the residual current and/or voltage is amplified to

, a magnitude that is greater than the predetermined magnitude and consequently is detected as such by the threshold monitor.

7. A device according to claim 5 or claim 6, in which the amplifier is 0 arranged to amplify a current and/or voltage powering the load such that the amplifier is driven substantially to saturation, and consequently the current and/or voltage detected by the threshold monitor has a magnitude that is greater than the predetermined magnitude.

8. A device according to any one of claims 5 to 7, further comprising an amplifier protector that is arranged to protect the amplifier by attenuating the current and/or voltage from the supply before it is amplified by the amplifier if the current and/or voltage from the supply has a magnitude greater than a particular magnitude, which particular magnitude is greater than the predetermined magnitude.

9. A device according to any preceding claim, further comprising a power source arranged to provide electrical power in the event of a power supply failure being detected by the device.

10. A device according to claim 9, in which the power source comprises at least one battery.

11. A device according to claim 9 or claim 10, in which the power source is arranged to be charged by the electrical power supply.

12. A device according to any one of claims 9 to 11, further comprising a power supply failure indicator, arranged to signal the existence of a power supply failure in the event that the threshold monitor fails to detect a current and/or voltage having a magnitude greater than the predetermined magnitude, which power supply failure indicator is itself powered by the power source.

13. A device according to claim 12, in which the power supply failure indicator comprises at least one light arranged to illuminate in the event that the threshold monitor fails to detect a current and/or voltage having a magnitude greater than the predetermined magnitude.

14. A device according to claim 12 or claim 13, in which the power supply failure indicator comprises a device arranged to emit an audible alarm signal in the event that the threshold monitor fails to detect a current and/or voltage having a magnitude greater than the predetermined magnitude.

15. A device according to any preceding claim, which is an emergency light device, arranged to provide emergency lighting in the event that the device detects a failure in the power supply.

16. A device according to claim 15 when dependent upon claim 9, arranged to provide emergency lighting powered by the power source, in the event that the device detects a failure in the power supply.

17. A device according to claim 15 or claim 16, in which the emergency lighting is provided by at least one light of the device arranged to illuminate in the event that the threshold monitor fails to detect a current and/or voltage having a magnitude greater than the predetermined magnitude.

18. A device according to claim 13 or claim 17, in the (or each) light comprises a light-emitting diode (LED).

19. A device according to claim 15 when dependent upon claim 9, in which the electrical load comprises a lamp, and the lamp is powered by the power source in the event that the device detects a failure in the power supply, thereby providing the emergency lighting.

20. A device according to any one of claims 9 to 19, further comprising a delay circuit and a switch component, wherein the delay circuit is arranged to maintain the switch component in an "off" condition while the threshold monitor detects a current and/or voltage having a magnitude greater than the predetermined magnitude, and wherein the delay circuit is arranged to cause or allow the switch component to adopt an "on" condition if the threshold monitor fails to detect a current and/or voltage having a magnitude greater than the predetermined magnitude, and wherein when the switch is in the "on" condition the power source provides its electrical power.

21. A device according to claim 20, in which the switch component comprises a transistor, e.g. a FET, especially a MOSFET.

22. A device according to any preceding claim, which includes a visual indicator to show that the device is receiving electrical charge, in use.

23. A device according to any preceding claim, which includes a visual and/or an audible indicator to provide an alert that a power source of the device is below a predetermined level of electrical charge.

24. A device according to any preceding claim, which includes a test switch to simulate a failure of the power supply, thereby allowing the device to be tested.

25. A device according to any preceding claim, which includes a light detector whereby the device is deactivated when surrounding light levels are above a given illumination threshold.

26. A device substantially as illustrated in, and/or substantially as described herein with reference to, the accompanying figures.

27. An electrical apparatus including a device according to any preceding claim, in which the electrical load comprises a part of the electrical apparatus and/or comprises an external electrical load that is electrically connected to the apparatus, in use.