Plug Socket with Emergency Lights

A BS1363 plug socket switched or un-switched has embedded emergency lighting, normal at the bottom of the plug socket. These are low voltage long-lasting light-emitting diodes that will illuminate when the mains electrical supply power to the socket is removed.
The plug socket has an internally mounted charging circuit board, this is powered via the plug sockets main 230vac power supply terminals. The bright white light emitting diodes used for the emergency lighting is powered via the 3.7V rechargeable battery and only switch on when the power to the socket is lost.

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2 Gang Emergency Socket Finish
Emergency Socket

LED Socket

The appliance operates similarly to the existing socket until it detects the power is removed when it automatically switches to battery operation and illuminates the bright light emitting diodes.
The rechargeable battery enables the light emitting diodes to stay on independently for up to a minimum of three hours or until the electrical power returns.

The idea was brought about after seeing the 24-storey Grenfell Tower fire which broke out on 14 June 2017. When a fire occures the electrical supply normally fails and if emergency light power sockets were installed, then you would have illumination close to the floor in a smoke filled area.

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Could Britian face a winter of power cuts?

Today experts warned that Britain must brace itself for power shortages if the country is hit by a severe winter.

After a rush to close coal-fired power stations to meet green targets, a deep freeze means mothballed oil and gas power stations could have to be restarted and factories paid to shut down to preserve power.

Business leaders warned that for too long, the UK has failed to plan properly to keep the lights on, as the National Grid revealed the average gap between supply and demand will be just 4.1 per cent - the narrowest in eight years.

The National Grid report said the country will be eating into its most basic reserve power if there is extreme weather.

Emergency Light Socket
Emergency Light Socket
Emergency Light Socket
Emergency Light Socket PCB
Emergency Light Socket
Emergency Light Socket Schematic

Type of battery

The battery used in this circuit is a 3.7v Li-ion battery 2000mAH.
Charging current in this circuit is 5.9mA, which is acceptable for slow charging since this circuit is for emergency lighting.

Emergency Light Socket

Further Information

A power socket with emergency light, comprising of a power socket front switched or unswitched with a circuit board behind the socket front, a rechargeable battery and emergency light emitting diodes embedded into the socket front.

The internally mounted circuit board being provided with an external power from the sockets power supply input terminals, the rechargeable battery and the emergency light emitting diodes being in electric connection with the circuit board respectively; when the power line is connected to the socket, the emergency lights are in an off state, not illuminated; when the power line is disconnected from the external socket, fuse tripped or power cut, the emergency lights are in an on / lighted state.

Transistor Info


The power socket cover has the function of emergency lighting as well as providing power supply to appliances, enabling the emergency lights to be powered and light up when the socket mains power supply is unexpectedly cut off.

The emergency lamp circuit charges the battery using the 230v AC electric line, when the 230VAC power is removed, the Light Emitting Diodes will illuminate automatically.

  • Working voltage: 13A, 250V
  • Working temperature: -15 to 40 C
  • UK 3 pin socket output: 13A, 250V
  • Fits any standard back box (minimum depth of 25mm)
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    Technical Information

    A 820nF 250/400 volt AC capacitor is dropping the 230volt AC to low volt AC.
    X Rated capacitor 0.82uf 400 Volt - X=1/{2xPIx50x0.82x(1/1,000,000)} = 38818.278 Ohms or 38.8 Kilo ohms. 230V/38.8 = 5.92mA

    Bleeder resistor 270R 2W is used to remove the stored current from the capacitor.

    BR IN4007 D1 through D4 rectifies the low AC to DC.

    The capacitor 470uF 16 or 25V makes the DC ripple free.

    This S9012 PNP transistor in TO-92 package is perfect for switching applications and switches power from the 3.7 volt battery to the light emitting diodes.

    Zener Diode is commonly used as a voltage regulator. Being a diode normally operated in the reverse bias and at the breakdown voltage, the zener diode allows the current to keep the voltage across the diode close to the zener breakdown 4.8 voltage. Therefore it protects other devices against voltage pulses.

    What Is Emergency Lighting?

    Emergency lighting is battery powered lighting which will switch on and illuminate when the power is cut from the mains. This is usually for the people inside the building to find their way out of the building in a safe manner. Guidelines now exist which mean all new larger buildings must have the correct emergency lighting fitted whilst older buildings must retro-fit emergency lighting to ensure the building is as safe as possible.

    What Buildings Am I Likely To See Emergency Lighting In?

    All buildings which have a large footfall or are reliant on artificial lighting are obliged to have emergency lighting installed as a legal requirement. This is usually so the people inside can find their way out in the event of an emergency. Hotels, theatres, cinemas, apartments, flats, warehousing, retail shops, pubs and restaurants are just some of the places you will find emergency lighting.

    Stairwells and exit routes are the places which are most likely to be illuminated when the power is cut along with first aid areas, refuge points and fire equipment areas.

    What Is The Difference Between Maintained & Non-Maintained?

    When looking for the emergency lighting fitting you require, you are likely to come across the terms 'maintained' and 'non-maintained'. These phrases are terminology usually associated with emergency lighting products, but what is the difference?

    Maintained fittings are ones which can be operated with a lighting controller (such as a switch) and can be left permanently on or can just operate when there is a power cut.

    Non maintained fittings will not illuminate unless there is a power cut, this is the emergency socket type we supply.

    What Types Of Emergency Lighting Are There?

    There are a variety of different types of emergency lighting which are available to suit whatever lighting need you may have. The most traditional type of emergency lighting are the internal and external bulkhead emergency fittings. These usually have a polycarbonate body and tray which houses all the components and most of these will operate for three hours without any mains power and will recharge when the mains power has been restored.

    There are a variety of different shapes, however the most popular by far are the circular and rectangular shaped bulkheads which will stretch from 8W to 28W usually. In recent times, more decorative products have hit the market. Interior and exterior bulkheads which can be purchased with emergency gear inside so they will light when there is a power cut.

    LED emergency lighting is now starting to become very popular thanks to its energy saving benefits. A lot of illuminated exit signs are now LED and are virtually maintenance free thanks to the fact the LEDs in the fitting will last for around 30,000 hours without needing to be replaced.

    20mA LED Resistor Calculation

    LED Type Forward Voltage Qty Max current Ohms Hours with 2AH Battery
    Standard Size - T1 ¾ 5mm 3.2v-3.4v 5 100mA 5 Ohms 20 Hours
    Standard Size - T1 ¾ 5mm 3.2v 5 100mA 5 Ohms 20 Hours
    Standard Size - T1 ¾ 5mm 2.7v 10 200mA 5 Ohms 10 Hours
    Standard Size - T1 ¾ 5mm 2.2v 15 300mA 5 Ohms 6.67 Hours
    Standard Size - T1 ¾ 5mm 1.7v 20 400mA 5 Ohms 5 Hours

    Characteristics of the bipolar transistor S9012

  • Type - p-n-p
  • Collector-Emitter Voltage: -25 V
  • Collector-Base Voltage: -40 V
  • Emitter-Base Voltage: -5 V
  • Collector Current: -0.5 A
  • Collector Dissipation - 0.625 W
  • DC Current Gain (hfe) - 64 to 300
  • Transition Frequency - 150 MHz
  • Operating and Storage Junction Temperature Range -55 to +150 °C
  • Package - TO-92
  • Pin Configuration (Pinout)

    The S9012 is manufactured in a plastic TO-92 case. When looking at the flat side with the leads pointed downward, the three leads emerging from the transistor are, from left to right, the emitter, base, and collector leads.

    Classification of hFE

    S9012 can have a current gain anywhere between 64 and 300. The gain of a S9012D will be in the range from 64 to 91, S9012E - range from 78 to 112, S9012F - range from 96 to 135, S9012G - range from 112 to 166, S9012H - range from 144 to 202, S9012I - range from 190 to 300.

    Replacement and equivalent transistor for S9012

    You can replace S9012 with 2SA708, 2SA709, BC527, BC528, KSA708, KSP55, KSP56, KSP92, KSP93, MPS3702, MPS4354, MPS6652, MPS6652G, MPSA92, MPSA93, MPSW51, MPSW51A, MPSW51AG, MPSW51G, MPSW55, MPSW55G, MPSW56, MPSW56G, MPSW92, MPSW92G, PN4354, ZTX554, ZTX555, ZTX556, ZTX557


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