Why going for a complex circuit to make an Emergency Light automatic? Now different types of low cost Portable LED Emergency lights are available but these are not automatic in function. A Mobile charger like adapter is supplied along with these for charging. But we have to turn on / off the light manually using the switch. We can easily convert these kinds of Emergency lights into automatic so that when the power fails, the light turns on and when the power resumes, it turns off and enter into charging mode. We need only one relay and a diode for this. The advantage of the relay is that, full current will flow to the LED panel to get maximum brightness.
Open the cover of the LED Emergency light. You can see a battery connected to the LED panel through a switch. The charger socket is connected to one contact of the switch. There may also an LED connected to this contact to indicate the charging process. Now remove all the connections and do the following connections.
2. Connect the Common contact of the relay to of the one switch contact. Connect the battery +ve to the second contact of the switch. So that, when the switch is in the On position, battery will be connected to the common contact of the relay. Connect the battery –ve to the –ve of the charger socket.
3. Identify the NO (Normally Open) and NC (Normally Connected) contacts of the relay through continuity test with the Common contact.
4. Connect the +ve of the LED panel to the NC contact and the –ve to the –ve of the charger socket. So when the Relay is in the de-energized state ( No power from the charger ) LED panel gets current from the battery through the closed switch – Common – and the NC contact. So the LEDs light.
5. Connect the charger + pin to the NO contact, through a 4007 diode. So that, when the relay energize, charging current flow through the diode to the NO contact – Common – closed switch and the battery.
Working is simple. The switch should be in the closed position for automatic working. At this time, the lamp lights using the battery power because the LED panel gets current from the battery through the NC – Common contacts. When the charger is connected, relay energizes and the Common contact move towards NO contact. As a result, the NC contact breaks and lamp turns off. Now the Common contact is connected with NO and current from the charger goes to the battery.
Lamp On position current flow
Battery – closed switch – Common contact – NC contact – LED panel
Lamp Off position current flow
Charger – Diode – NO contact – closed switch – battery.
Use 5V Cube relay for 4 Volt battery, 6V relay for 6 volt battery and 12V relay for 12 volt battery. Using the same arrangement, you can make a Homemade automatic LED light with a battery, charger and the relay.