IES20090435A2 - Emergency light socket assembly - Google Patents

Abstract

An emergency light socket comprises a permanent wall-mountable housing containing a power-supply outlet having supply terminals connectable to mains power leads within the wall. The housing also contains a rechargeable battery which is charged up by the mains during periods of mains power and a first lamp for emitting light through a window in the housing to provide exterior emergency illumination. A control circuit automatically applies battery power to the lamp in the absence of mains power. The control circuit also detects at least one failure mode of the battery, and a second lamp is illuminated in the case of a battery failure detected by the control circuit. The second lamp is positioned to emit light through the same window as the first lamp.

Description

This invention relates to a mains socket including an emergency Lign Emergency lights (EL) are widely used in commercial and industrial premises as well as airports, hospitals, theatres, etc. The basic principle of operation is that the EL contains a rechargeable battery which is charged up by the mains during periods of mains power and, when the mains supply fails, the EL switches from a charging mode to a lighting mode so as to provide temporary lighting during power failure conditions. These commercial/industrial ELs come in the form of a box which has to be connected to the mains supply, and they tend to be quite bulky in shape and size. They also tend to be very expensive, and usually need to be installed by skilled persons.

Portable ELs which plug into mains socket outlets are also quite common and are more likely to be used in domestic areas. These tend to be compact and relatively inexpensive but suffer from the problem that they can be removed or easily damaged due to their portability. Their portability and propensity for damage make them less than ideal as a reliable and viable means of providing emergency lighting.

UK Patent Application 2 255 242 describes a socket outlet incorporating a battery powered light which provides emergency lighting in the event of a power failure condition. This device is intended to be installed in any location where a standard socket outlet could be fitted, e.g., homes, hotels, offices, etc. When mains power is available, the battery will acquire a charge and remain fully charged until a power failure condition occurs, at which point the battery will discharge via an LED to provide emergency lighting. In the event of a major failure of the emergency light circuit, such as a battery failure, the user will have no way of knowing that the emergency 110 9 0 4 35 lighting will no longer be available. The user will only discover this condition if the device is tested by temporary removal of mains power, or when a genuine mains failure condition arises. Testing of the emergency light socket may not be convenient for a variety of reasons, e.g. the device may not be fitted with a test facility, intentional removal of mains supply may prove difficult or inconvenient, etc.

It is an object of the invention to provide an emergency light socket which can also indicate to the user one or more battery failure modes so that the user can make timely arrangements to have the socket repaired or replaced.

According to the invention there is provided an emergency light socket comprising a permanent wall-mountable housing containing: (a) at least one power-supply outlet having supply terminals connectable to mains power leads within the wall; (b) a first lamp for shining light through a window in the housing to provide exterior emergency lighting; (c) a rechargeable battery which is charged up by the mains during periods of mains power; (d) a control circuit for automatically applying battery power to the first lamp in the absence of mains power, the control circuit further including a battery-monitoring circuit for detecting at least one failure mode of the battery; and (e) a second lamp which is lit in the case of a battery failure detected by the monitoring circuit; wherein the second lamp is positioned to shine light through the same window as the first lamp.

By “permanent” we mean that the housing is adapted for mounting to a wall of a building to provide a fixed power outlet socket. q 3 0435 Preferably the monitoring circuit is arranged to detect a battery short circuit and/or a battery open circuit, and most preferably the control circuit is also arranged to detect a failure of the monitoring circuit.

Preferably the lamps are LEDs.

A manually-operable test means is preferably provided to simulate the removal of mains power from the control circuit to test the operation of the lamp. In such a case the test means may be latchable to allow use of the assembly as a night light powered by the battery.

An embodiment of the invention wilt now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a front view of a two-gang mains socket according to an embodiment of the invention.

Figure 2 is a top view of the socket of Figure 1 in which the positions of certain internal components are indicated.

Figure 3 is a diagram of the electronic control circuitry in the socket of Figures 1 and 2.

Referring first to Figures 1 and 2, a mains socket comprises a housing 10 adapted in any suitable manner for permanent fixing to a wall 12 of a building. In particular, the housing 10 is recessed into the wall 12 with a front surface 14 of the housing substantially flush with, or standing slightly proud of, the wall. The housing 10 contains two three-pin power-supply outlets 16 exposed at the front surface 14, one on either side of a central compartment 18. Within the housing 10 the outlets 16 are connected in parallel to live and neutral supply terminals 20, 22 respectively, the latter being exposed at the rear of the housing for connection to live and neutral mains power leads within the wall. The arrangement of the outlets 16 per se is essentially conventional and will not be further described.

The central compartment 18 contains a rechargeable battery B1, two lamps (in this embodiment in the form of light emitting diodes LED 1 and LED2) positioned behind a lens 26 in the front surface 14 of the housing 10, and a control circuit, Figure 3. When lit in response to a detection of mains failure by the control circuit, LED1 serves as an emergency lamp and shines white light through the lens 26 to provide a concentrated beam of light which illuminates at least the immediate surroundings in front of the socket. The lens 26 can be configured to provide a wide or narrow beam as desired.

LED2, which serves as a battery-failure warning lamp, is lit when the control circuit detects a battery failure, and shines red light through the same lens 26 as LED1. There is also a test button 30 located on the front surface 14 of the socket to facilitate manual testing of the emergency lamp from time to time.

The housing 10 is preferably dimensioned to be a direct replacement for an existing conventional double outlet socket, whereby an emergency light can be provided without sacrificing one of the outlets.

Figure 3 is a diagram of a control circuit for the emergency light socket. As stated, the mains supply live and neutral conductors L, N are connected to the terminals 20, 22 to power the supply outlets 16 in conventional manner, and this connection is not shown.

The mains supply is applied to the control circuit via a resistor R1 and a dropper capacitor C1, which in turn feed a bridge rectifier BR1. The resultant DC voltage is smoothed by a capacitor C2 and clamped to a safe operating level by zener diode ZD1. This DC voltage is fed to the battery B1 via diodes D1, D2, D3 and D4 and provides a continuous current to charge B1 and keep it fully charged to approximately 1.2V. An LED driver integrated circuit (IC) U2 can, when active, draw a controlled level of current through emergency lamp LED1. However, U2 is held in an inactive state by a bipolar transistor Q2 which is held in the turned on state via a voltage on its base derived via a diode D11 and resistors R11/R12. A diode D7 supplies a DC voltage to C3, and also via a diode D8 to an FET Q.1 to keep it turned on.

When the mains supply falls below a certain level, Q2 will turn off and thereby allow U2 to switch to the active state. The charge on C3 keeps Q1 in the on state temporarily and with U2 now active, B1 battery voltage is drawn through LED1 to light it. The battery voltage is also fed to Q1 via a diode D10 to keep Q1 turned on. Diode D8 now prevents C3 from being charged by the battery voltage. Current will be drawn through LED1 in a controlled manner by U2 so as to ensure that LED1 provides an optimum level of light for a given period of time. When the mains supply is restored, Q2 will turn on again and deactivate U2, allowing the battery to recharge and return the circuit to its quiescent state.

The control circuit also includes circuitry to monitor the state of the battery B1. Under normal conditions, battery B1 will have a charged voltage of about 1.2 volts with a charging current of about 30mA. With these values, B1 can be represented as an effective impedance of about 40 ohms. The two main battery failure modes are short circuit or open circuit, so if the battery goes short circuit its effective impedance will fall to a substantially lower value, and if it goes open circuit its effective impedance will rise to a substantially higher value. The battery monitoring circuit exploits this behaviour to alert the user to a battery fail condition.

Under normal conditions and with B1 fully charged, the voltage at the junction of D1 /D2 will be about 3.3v, and the voltage at the junction of D2/D3 will be at about 2.6V. U1a and U1b are comparators with a common reference voltage Vref determined by a zener diode ZD2. The voltage at the junction of D1 /D2 is monitored by U1 b, and the voltage at the junction of D2/D3 is monitored by U1a. The outputs of U1a and U1b are low under normal conditions. If B1 goes into short circuit failure mode, the -ve input of U1b will be pulled lower than Vref with the result that the output of U1b will go high and light LED2. Likewise, if B1 goes into open circuit failure mode, the +ve input of U1a will go higher than Vref with the result that the output of U1a will go high and light LED2. Thus for either failure mode of battery B1, LED2 will light to alert the user to a battery failure condition. Also, a failure of any of the diodes D1 - D4 will also cause LED2 to be lit.

Switch Sw1 is a test switch to verify the correct operation of the circuit.

When Sw1 is opened, by pressing the test button 30, mains supply is removed from the control circuit, thereby simulating a power failure condition and causing LED1 to light. Preferably the test switch Sw1 is of a type that can be latched open, so that the assembly could be left in the emergency lighting mode, for example as a night light.

The foregoing shows an embodiment of the invention providing a double gang socket outlet, but the emergency light function could readily be incorporated into single or multiple gang socket outlets.

Amongst the advantages of the embodiment of the invention are that it is compact, low cost, easy to install and permanently wired. Ί 110 9 04 3» Clearly, if several such assemblies were fitted strategically around a house or other premises instead of conventional socket outlets, a simple but effective means of providing emergency lighting would be provided.

While the embodiments above have been described in terms of a power socket for receiving a portable appliance plug, it will be seen that the present invention could equally be implemented in power sockets for receiving, for example, fuse holders. These are known as spur units or Fuse Connection Units (FCU) and are typically used to provide a fused supply to hand dryers and dispensing machines, etc. When the fuse blows, the fuse holder (acting as a plug) is removed from the power socket and once a replacement fuse is fitted, the holder is again plugged into the socket. As such, an FCU incorporating the invention can either provide an alternative or supplement emergency lighting in houses or other premises, in particular in bathrooms where portable appliance sockets are typically not used.

The invention is not limited to the embodiments described herein which may be modified or varied without departing from the scope of the invention.

Claims (5)

Claims
1. An emergency light socket comprising a permanent wall-mountable housing containing: (a) at least one power-supply outlet having supply terminals connectable to mains power leads within the wall; (b) a first lamp for shining light through a window in the housing to provide exterior emergency lighting; (c) a rechargeable battery which is charged up by the mains during periods of mains power; (d) a control circuit for automatically applying battery power to the first lamp in the absence of mains power, the control circuit further including a battery-monitoring circuit for detecting at least one failure mode of the battery; and (e) a second lamp which is lit in the case of a battery failure detected by the monitoring circuit; wherein the second lamp is positioned to shine light through the same window as the first lamp. 20
2. 2. A socket as claimed in claim 1, wherein the window comprises a lens.
3. 3. A socket as claimed in claim 1 or 2, wherein the monitoring circuit is arranged to detect a battery short circuit and/or a battery open circuit.
4. 4. A socket as claimed in claim 1, 2 or 3, wherein the control circuit is arranged to detect a failure of the monitoring circuit.
5. 5. A socket as claimed in any preceding claim, wherein each lamp is an 30 LED.