IES20080132A2 - Emergency light socket assembly - Google Patents

Abstract

An emergency light socket assembly comprises a permanent wall-mountable housing containing at least one power-supply socket having supply terminals connectable to mains power leads within the wall. The housing further contains a rechargeable battery which is charged up by the mains during periods of mains power and at least one lamp for illuminating exteriorly of the housing. A control circuit automatically applies battery power to the lamp in the absence of mains power.

Description

This invention relates to a socket assembly including an femergencyTight/’ FtS 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.

It is an object of the invention to provide an emergency light socket assembly which capitalises on the benefits whilst mitigating the disadvantages of the above conventional emergency light types.

According to the invention there is provided an emergency light socket assembly comprising a permanent wall-mountable housing containing at least one power-supply socket having supply terminals connectable to mains power leads within the wall and at least one lamp for illuminating exteriorly of the housing, the housing further containing a rechargeable battery which is 132 charged up by the mains during periods of mains power and a control circuit for automatically applying battery power to the lamp in the absence of mains power.

By “permanent” we mean that the housing is adapted for mounting to a wall of a building to provide a fixed power outlet socket.

Preferably the lamp is an LED.

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. Preferably, manual operation of the test means does not remove mains power from the battery.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figures 1a and 1b are front and top views of a two-gang socket assembly according to an embodiment of the invention.

Figure 2 is a diagram of a first embodiment of control circuitry of the assembly of Figure 1.

Figure 3 is a diagram of a second embodiment of control circuitry of the assembly of Figure 1.

Figure 4 shows a modification of the second embodiment of control circuitry of Figure 3.

KO so 132 Referring first to Figures 1a and 1b, a socket assembly 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 power-supply sockets 16 exposed at the front surface 14, one on either side of a central compartment 18. Within the housing 10 the sockets 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 sockets per se is essentially conventional and will not be further described.

The central compartment 18 contains a rechargeable battery 24, Figure 2, an emergency lamp L1 located behind a lens 26 in the front surface 14 of the housing, and a control circuit 28. When lit, the emergency lamp L1 shines through the lens 26 to provide a concentrated beam of light which illuminates at least the immediate surrounding in front of the socket assembly. The lens can be configured to provide wide or narrow beams as desired. There is also a test button 30 located on the front surface 14 of the socket assembly 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 socket, whereby an emergency light can be provided without sacrificing one of the sockets.

Figure 2 is a diagram of a basic control circuit for the emergency light socket assembly. As stated, the mains supply live and neutral conductors L, N are connected to the terminals 20, 22 to power the supply sockets 16 in conventional manner, and this connection is not shown. To power the *0 80 1 32 emergency lamp L1, which is a filament bulb, the mains conductors L, N are connected to a bridge rectifier X1 via a resistor R1. The rectified AC output from X1 is smoothed by a capacitor C1. A light emitting diode D1 and a resistor R2 are connected in series across C1 so that D1 will light up to provide an indication that the mains supply voltage is present. Resistors R3 and R4 form a potential divider whose junction is connected to the base of a transistor Q1. When the full mains supply voltage is present, Q1 is held turned off by the voltage at its base. A rechargeable battery 24 comprising one or more cells is connected across the output of the rectifier X1. A diode D2 prevents current flow from the battery 24 through R3 and R4.

Under normal supply conditions a current will flow from the mains supply to charge up C1, which in turn provides a current to charge up the battery 24.

On initial powering up, the battery 24 may take several hours to charge up fully. When the supply voltage is reduced below a certain threshold as determined by the ratio of R3 and R4, Q1 will turn on and connect L1 across the battery 24 which in turn will cause a current to flow through L1 and cause it to light. L1 will remain lit until the voltage across the battery 24 falls below a certain threshold, but typically L1 will remain lit for at least one hour.

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 28, and when the voltage at the base of Q1 falls below a certain level, Q1 will turn on and cause L1 to illuminate as before.

Since L1 is a filament type bulb, an arrangement needs to be made to facilitate replacement of the bulb from time to time. Filament bulbs require a substantial amount of current to produce effective light with the result that relatively large batteries will be required in order to produce an effective ΙΕο 80 1 32 light for a given period of time. Filament type bulbs usually require a voltage of 2.5V or higher to be effective, and therefore are generally not suitable for operation from a single 1.5V battery cell. The rate at which the battery discharges through L1 will determine the duration of effective light that can be produced by the circuit, but this rate of discharge is not controlled. As a result the brightness of the bulb will decrease rapidly over time and may cease to be sufficiently effective even when the battery is not substantially discharged.

Figure 3 shows an embodiment of control circuit which mitigates these and other disadvantages and which provides a significantly more effective solution to the problem of providing emergency lighting. Figure 3 uses the same reference numerals as Figure 2 for the same or equivalent components.

In the circuit of Figure 3, the mains supply is rectified and smoothed by X1 and C1 respectively. U1 is a constant current driver integrated circuit (IC) intended to drive high brightness LEDs from a battery supply. Under normal supply conditions the voltage on C1 will be above a certain threshold and Q1 will be held in its on state. As a result, control pin CTL of U1 is held low and Vout is disabled. When the voltage on C1 falls below a certain threshold, e.g. due to a power failure on the mains supply, Q1 will turn off, and as a result CTL will be pulled high by the battery voltage. This in turn will drive a current into the high brightness light emitting diode LED1 to light it and provide emergency lighting from the socket assembly. When the battery voltage drops below a certain threshold, the drive current to LED1 is automatically reduced to a lower level so as to maintain a reduced level of light whilst maximising useful battery life. Diode D2 prevents the battery 24 from maintaining a charge on C1 under power failure conditions. Resistor R2 is connected in series with the battery 24 so as to provide a suitable voltage to illuminate a light emitting diode LED2 when the battery is charging. A Κθ Mi Zener diode Z1 clamps the voltage across the battery to a safe level in the event of the battery going open circuit.

As before, test switch Sw1, operated by pressing the test button 30 on the front surface of the housing, provides means for testing the circuit by removing the supply to the control circuit and thereby simulating a power failure condition.

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. However, the arrangement of Figure 3 will only provide effective light for a relatively short period of time based on the initial charge state of the battery and the rate at which it is drained. The “night light” period can be extended by moving Sw1 to the location shown in Figure 4 (which is otherwise identical to Figure 3) so that it is in series with R4. In this arrangement, the mains supply remains connected and the battery continues to be charged regardless of the position of Sw1. When Sw1 is opened, Q1 is turned off and the circuit switches to the lighting mode as before. The drain on the battery will be offset to some extent by the continuously available charging current from the mains supply with the result that the lighting period will be extended to facilitate the night light function.

In Figures 3 and 4, R1 could be replaced with a capacitor to provide wattless power if power dissipation was a problem in any mode of operation. The circuit of U1 can be configured to operate from one or more battery cells. The maximum drive current to LED1 can also be controlled by suitable component selection and configuration of the circuit so as to maximise useful battery operation. 80132 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.

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.

The invention is not limited to the embodiments described herein which may be modified or varied without departing from the scope of the invention. 801 $2 BO 1 J 2 IE L Fig 3 IE L Fig 4 The following Claims were filed on 4th November 2008

Claims (5)

Claims:

1. An emergency light socket assembly comprising a permanent wallmountable housing containing at least one power-supply socket having supply 5 terminals connectable to mains power leads within the wall and at least one lamp for illuminating exteriorly of the housing, the housing further containing a rechargeable battery which is charged up by the mains during periods of mains power and a control circuit for automatically applying battery power to the lamp in the absence of mains power.

2. A socket as claimed in claim 1 wherein the lamp is an LED.

3. A socket as claimed in claim 1 or 2 further comprising a manuallyoperable test means actuable to simulate the removal of mains power from 15 the control circuit to test the operation of the lamp.

4. A socket as claimed in claim 3 wherein the test means is latchable to allow use of the assembly as a night light powered by the battery. 20

5. A socket as claimed in claim 3 wherein manual operation of the test means does not remove mains power from the battery.