Automatic Emergency Light Using Relay And 12 Watt LED

This project will show you an inverter type Automatic Emergency Light with 12 watt LED panel. Load shedding is a common problem in today’s developing countries. By keeping the problem in mind, I will make a simple automatic emergency light that is operated through AC mains. It can also operated through battery backup.

It can be operated by both AC mode and with 6V/5A battery. But when the AC mains resume, the battery supply will be automatically turned off and going to in charging mode. The whole circuit then glows the LED panel with an AC voltage supply. This emergency light can work for around 12 hours.

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Principle Behind The Automatic Emergency Light

In this circuit, we have three modes. The three modes are AC mode, Battery mode, and charging mode. In AC mode the LED turns on and the Battery in charging mode. In the charging mode, the LED turns off but the battery is charging. When there is no AC power, then the battery mode starts. That means the circuit auto cut the charging mode and the LED turns on with the power of the battery.


Automatic Emergency Light Using Relay

Circuit Diagram

Automatic Emergency Light Using Relay

Components Required

  • 9-0-9 500mA Step-Down Transformer
  • LED panel (6V, 12 watts)
  • 12V SPDT relay (single pole double through)
  • Regulator IC 7806
  • IN4007 Diodes (x4)
  • Switch (2 poles 2 way)
  • 1000uF/35V Capacitors (x2)
  • 470uF/16V Capacitor
  • 1K Resistor
  • Red LED (indicator)
  • 6V/5A battery

Circuit Connection

In this project, the components which are required and the design of this project are too simple. At first, we are going to explain the connection of this circuit. Two output side of the transformer explained is connected with two bridge rectifiers. One of the rectifiers (D2 and D3) is connected to the coil (1st terminal) and a wayside (4th terminal) of the SPDT relay ( single pole double through). Another rectifier is connected to the 7806 regulator ic input channel.

After completing the rectifier circuit, we take the battery. The positive (+VCC) side of the battery has connected the pole (1st terminal) of the relay. Then we take the switch( 2 poles 2 way ). Connect the second way (5th terminal) of the relay with the switch (1st terminal). The output terminal of the 7806 is connected to the other side of the switch (3rd terminal). The pole of the switch (2nd terminal) is connected to the +VCC side of the LED panel (6V, 12W).

Then we started to connect the ground lines. On the ground side of the transformer, the negative side of the battery and another side of the coil (3rd terminal) is connected to the ground. The base pin of 7806 ic and the negative pole of the LED are connected to the ground also.

At last, we added two filters C1 and C2 across the rectifiers (D1, D4, and D2, D3 ) and ground line respectively. We added a red led across C1 and with a 1KΩ resistor in series. Then we connect C3 across the output of the 7806 ic. Hence, we build the connection of the circuit.

Working Principle of Automatic Emergency Light

Now, we are going to explain the working of the automatic emergency light circuit.

In the AC mode bridge rectifier ( D2 and D3 ) supply the power to the coil. This rectifier also provides voltage to the battery. Because when the AC supply is turned on the pole (1st terminal) of the relay makes a connection between the battery and the DC voltage ( 5th terminal of the relay).

Another bridge (D1 and D4) supplies the voltage to the 7806 ic. The 7806 ic reduces the voltage from 9V to 6V. So when the switch connects the pole (switch) and 4th terminal (switch), the LED turns on. From the above, we see in the AC mode battery takes charge and LED turns on.

Now, what can we do when we do not need light but have to charge the battery for backup. We take the switch in the opposite position. This means the switch now makes a connection between the pole (switch) and 1st terminal (switch). In this situation, the LED is connected with +VCC of the 7806 ic, so the LED is off. But the battery remains in a charging position.

In the end, a question arises. How this circuit reacts as an automatic emerging light?

The answer is when we leave the circuit in the charging position the AC supply is on. But when the main supply is off, the pole of the relay is connected to the 5th terminal of the relay (N/O position). Now the source (battery) is connected to the LED and the LED turns on. When we do not need light or charging we just disconnect the AC and make the switch in 1st position (2nd and 3rd terminals of the switch are connected).

Features of This Automatic Emergency Light

  • Charging and LED turns on
  • Only Charging
  • As an automatic emergency light.

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