Simple 2 LED Battery Status Indicator Circuit

This circuit is like a tiny gas gauge for your batteries.

It uses lights LEDs to show you how much juice is left.

One light might mean the battery is full, another might mean it is half full, and another might mean it is time to recharge.

This circuit uses parts like resistors and special diodes zener diodes and transistors to measure the batteries voltage and light up the LEDs accordingly.

So you will always know when it is time to plug in and keep your devices going.

Circuit Working:

Parts List:

If an LED indicator is included in battery powered devices like emergency lamps it will consume power even when the device is not in use.

This can lead to a reduction in battery voltage, as the LED typically requires around 2V.

Therefore, continuous charging of the battery is necessary to maintain the voltage level.

However, this circuit addresses this issue by ensuring that the LEDs only turn on under two conditions: when the battery is overcharged or when it is overdischarged.

The circuit functions as a voltage controlled switch using zener diodes.

It provides a two state LED indication using a bicolor LED.

Zener diode ZD1 and the PNP transistor T1 form the overdischarge indicator switch.

When the battery voltage is above the breakdown point of ZD1 around 5V, ZD1 conducts keeping T1 from conducting.

As a result, the red half of the bicolor LED remains off.

When the battery voltage drops below 5V, ZD1 stops conducting allowing T1 to conduct and turn on the red LED.

This indicates that the battery is approaching an overdischarged state.

Zener diode ZD2 and NPN transistor T2 form the overcharge indicator switch.

When the battery voltage is below 6.8V the maximum voltage level, ZD2 stops conducting keeping T2 off.

Consequently, the green half of the LED remains off.

If the battery voltage increases above 7V due to overcharging ZD2 conducts followed by T2 and the green LED turns on indicating an overcharged state.

In summary, when the battery voltage is between 5 and 7V, both LEDs remain off reducing power consumption.

Calibration requires a variable power supply.

Provide 5V and adjust VR1 until the red LED turns on while the green LED remains off.

Increase the voltage to 7V and adjust VR2 until the green LED turns on with the red LED remaining off.

Reduce the voltage to 6V, both LEDs should be off at this point.

Formulas:

The following is the formula for a resistive divider, which is frequently used in such as battery status indicators circuit.

For calculating the output voltage V_out of a resistive voltage divider circuit is:

V_out = (Rb / (Ra + Rb)) * V_in

Here,

• Vout refers to the LED voltage at which the LED will just illuminate, which should be around 3V.
• In our circuit diagram, Rb = VR1 for red LED and Rb = VR2 for the green LED; Ra = R1 for red LED and Ra = R3 for the green LED.

How to Build:

To build a Simple Battery Status Indicator Circuit follow the below mentioned steps:

Connect Zener diode ZD1 and transistor T1 for overdischarge indicator:

• Connect the anode of ZD1 to the base of T1.
• Connect the cathode of ZD1 to the positive terminal of the battery.
• Connect the emitter of T1 to the negative terminal of the battery.
• Connect the collector of T1 to one terminal of the red part of the bicolor LED.

Connect Zener diode ZD2 and transistor T2 for overcharge indicator:

• Connect the anode of ZD2 to the base of T2.
• Connect the cathode of ZD2 to the positive terminal of the battery.
• Connect the emitter of T2 to the negative terminal of the battery.
• Connect the collector of T2 to one terminal of the green part of the bicolor LED.

Connect the variable resistors:

• Connect VR1 between the base of T1 and the negative terminal of the battery.
• Connect VR2 between the base of T2 and the negative terminal of the battery.

Connect the resistors for current limiting:

• Connect a resistor in series with the red part of the bicolor LED.
• Connect another resistor in series with the green part of the bicolor LED.

Connect the other terminals of the bicolor LED to the positive terminal of the battery.

Calibration:

• Apply a voltage of 5V to the circuit and adjust VR1 until the red LED turns on.
• Increase the voltage to 7V and adjust VR2 until the green LED turns on.
• Reduce the voltage to 6V, both LEDs should be off.

Note:

• Remember to use appropriate resistor values for current limiting based on the specifications of the bicolor LED.

Conclusion:

A Battery Status Indicator Circuit is a useful electronic circuit that utilizes LEDs to visually indicate the charge level of a battery.

By monitoring the battery voltage these circuits can provide users with valuable information about the status of their batteries, helping them manage their power needs more effectively.

References:

 Battery Level Indicator