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Battery Status Indicator Circuit

If an LED indicator is present in battery powered gadgets such as Emergency lamps, it will consume power even if the gadget is not using. This will reduce the battery voltage since the LED takes around 2 volts. So it is necessary to charge the battery continuously to keep the battery voltage level. This circuit eliminates this and the LEDs turn on only in two conditions. That is in the over charged and over discharged conditions only.

The circuit is basically a voltage controlled switch using Zener diodes. Two state LED indication is provided using a Bicolour LED. Zener diode ZD1 and the PNP transistor T1 forms the over discharge indicator switch. When the battery voltage is above the breakdown point of ZD1 (around 5 volts), it conducts and keeps T1 out of conduction. So the Red half of the bicolur LED remains off. When the battery voltage reduces below 5 volts, Zener turns off allowing T1 to conduct and Red LED turns on. This indicates that the battery is going to the over discharged state.

Zener diode ZD2 and NPN transistor T2 forms the Over charge indicator switch. When the battery voltage is below 6.8 volts (maximum voltage level), ZD cease to conduct and T2 remains off. So that the Green half of the LED also remains off. When the battery voltage increases above 7 volts due to overcharging, ZD2 conducts followed by T2 and Green LED turns on. This is the over charged state. In short, if the battery voltage is between 5 and 7 volts, both LEDs remain off. This reduces the chance of power consumption.

Battery Status Indicator Circuit

Setting

A variable power supply is necessary for the calibration. Provide 5 volts and adjust VR1 till Red LED turns on. At this point, Green LED remains off. Increase the voltage to 7volts and adjust VR2 till Green LED turns on. At this point, Red LED should remain off. Reduce the voltage to 6 volts. Both LEDs should be in the off state.

34 Comments

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  • Saptaswa Dhara

    Dear Sir,
    I think there is something wrong for 6v battery. i have prepared the circuit but the red led does non shut off at 6v or higher. The emitter of T1 is higer tha the base as the base is feeding from a voltage devider point and the emitter direct from 6v. it needs some change.

  • Rizwan

    I want to open a shop so i want to learn how to build tubler led battary for inverter

  • v sambath kumar

    Hi mohan kumar,

    usually any zener diode requires an excess of 1.6v than its prescribed value to reach the break down threshold level.as per your

    circuit 6.8v z should be replaced by 4.5v z ie 4.5+1.6+ .7for T2 so
    the total voltage will be 6.8v and for 4.7v z you can go for a2.8v zener
    ie 2.8+1.6+ .7 for t1 will be equal to 5.1v low ind.

    Regards Sambath kumar.

  • Deepak

    Dear sir,

    I am Deepak mishra .i have completed B.Tech, I want to implement full charge indicator of a battery. therefore kindly suggest me about it.
    I am waiting for your positive response.
    Thankingyou

  • karthik

    Hello neon. Could you please tell me the parameter that a mobile phone battery level indicator uses. Is it current or voltage??

  • Kith angelo salamat

    sir what is the VR in the diagram? and can you post a picture of this on a breadboard thanks

  • Flightdream

    HI I m new in electronics. I wanna make 12V bettery level indicator kindly help me. i just want that when bettey has been full and low than device indicate me.

  • Aparna

    sir I am Aparna doing B.Tech(ECE) final year. I would like to know if i can make this as my final year project.

  • Shahrukh

    Sir this is a very usefull circuit for battery charging.can you please kindly give me this circuit modified to 12 volt car battery. I want to use it for emergency light.
    Thanks

  • aravind

    Sir,

    If I would like to implement your circuit for monitoring 3.7V battery (like typical smartphone battery), how do I modify the circuit?
    would you be able to help me choosing the correct resistor values for the circuit?
    I really appreciate your help

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