LEDs are used as emergency light bulbs in this system, The important specialty of this Emergency circuit is an automatic charge controller which recharge the battery if the voltage is below the threshold level and cut off the charging supply to the battery, if the voltage reach at the pre-set level, two LEDs are used to indicates the of presents of main power and activation of charger.
This circuit mainly focus to lead acid battery life, in this circuit design we limit the maximum charging voltage is 13.8V as per lead acid battery manufacturers.
Circuit diagram of Automatic Emergency Light
- IC 555
- Transistor BC 548
- Diode (6A4 x4, 1N4007x2)
- Zener diode (13.8V)
- LED (red, green, white)
- Capacitor 4700μF, 25V
- Resistor (1KΩ x 3, 820Ω, 5Ω 10W x 2)
- Variable resistor 10KΩ
- Relay (12V, 10Ax2)
- Transformer 230V/0-15,5A
Working Automatic Emergency
- The main component of this circuit is 555 timer IC which control the automatic charger circuit.
- Two 12V relays are used to switch the charger and emergency LED lights accordingly.
- Consider the main supply is on, then the step down transformer reduce the ac voltage level to 15V AC
- Bridge rectifier converts this to 15V DC and 4700μF capacitor remove the ac ripples to make a perfect DC.
- Green LED indicates the presents of main power, 1KΩ resistor used as current limiting resistor for LED.
- The relay connected to the LED is always ON if the main power is present, so the LEDs are remain in OFF since those are connected to NO (Normally Open) terminal of the Relay. (Read our Relay connection diagram to know more about Relay connection and configuration)
- The variable resistor is meant for set the voltage level for the charger activation, a 13.8V Zener diode is used to turns off the charger circuit if the battery voltage reach at 13.8 volt which helps to Lead Acid battery’s long life.
- Negative terminal of the lower comparator is connected with battery voltage to compare the battery voltage level is below the pre-set level (voltage level to ON the charger can be set by varying the variable resistor).
- If the battery voltage reach at below the pre-set level the lower comparator will reset the flip flop in the 555, which turns ON the charger.
- The battery is also connected with positive terminal of the upper comparator, which compare the battery voltage level with the reference voltage 13.8V, if the battery voltage reach at this level which set the flip flop thus turns OFF the charger.
- LEDs provide long life, because LEDs drawn very low current which depend on the number of LED connected in parallel.
- At the time of power failure all the charger circuit will inactive and the relay RL2 connects the battery to LEDs, thus it glows.