3 LED Battery Voltage Level Indicator Circuit

A healthy battery is important for your car or any machine with a battery to run well and avoid problems.

This post shows you how to build a tool that checks your battery voltage and tells you if it is low, good or overcharged.

It works with most 12V car batteries, but with a small change, you can even use it on 24V systems.

The tool uses a special chip called a IC LM393 to measure the voltage accurately and light up LEDs to show you the batteries health.

What is a 3 LED Battery Voltage Level Indicator Circuit:

A 3 LED Battery Voltage Level Indicator Circuit is a simple electronic circuit that provides a visual indication of the voltage level of a connected battery.

This type of circuit is commonly used in various battery powered devices to give users an idea of the remaining charge in the battery.

The LED indicators typically represent different voltage levels or battery states.

Construction Steps:

Parts List:

Circuit Construction process is mentioned below:

• Gather all the required materials and ensure they are in working condition.
• Double check the specifications of the LM393, potentiometers, LEDs, zener diode, and resistors to match the design.
• Place the LM393 dual operational amplifier on the PCB.
• Connect the positive and negative power supply terminals to the PCB.
• Connect pin 4 of LM393 to the positive power supply and pin 11 to the negative power supply.
• Connect potentiometer P1 between pin 2 and pin 4 of LM393.
• Connect potentiometer P2 between pin 6 and pin 4 of LM393.
• Connect resistors and LEDs as per the circuit diagram
• Yellow LED between pin 2 and pin 7.
• Green LED between pin 6 and pin 7.
• Red LED between pin 2 and pin 12.
• Connect Zener diode between pin 8 and pin 4 of LM393.
• Connect series resistances for LED2 and LED3 if using a classic op Amp LM358, LM1458, or MC4558.
• Connect the controllable power supply to the positive and negative terminals on the PCB.
• Turn on the power supply and set it to the desired voltage range.
• Adjust potentiometer P1 until the yellow LED lights up at the low battery threshold around 9.5 to 10V.
• Adjust potentiometer P2 until the green LED lights up, indicating a sufficiently charged battery.
• Further increase the voltage to simulate overcharging and adjust P2 until the red LED lights up around 14 to15V.
• Connect the device through a suitable fuse to prevent potential hazards.

Testing

• Verify the indicators functionality by connecting it to the actual battery system.
• Ensure that the LEDs respond correctly to the battery conditions.

Warning:

• Exercise caution during the construction and installation processes to avoid any damage to the indicator.

Formulas:

Designing a 3 LED battery level indicator circuit with LM393 involves calculations for resistors:

Voltage Divider Resistors:

These resistors set the reference voltages for the LM393s comparators, determining when each LED turns on.

To calculate them, you will need following formulas:

• Battery Voltage (Vbat): Minimum and maximum voltage of your battery.
• Number of LEDs (N): here, N = 3.
• Desired Threshold Voltages (Vt1, Vt2): Voltages at which each LED should turn on (slightly higher than LED forward voltage).

Current Limiting Resistors Rled:

To avoid damage, these resistors limit the amount of current that passes through each LED.

What you will need is below mentioned formulas:

• LED Forward Voltage (Vf): Found in the LED datasheet at a specific current e.g. 20mA.
• Desired LED Current (Iled): Typically between 10mA and 20mA.

The formula uses ohms law:

• R_led = (V_bat – V_f) / I_led

where,

• Vbat = 3.7V
• VfLED1 = 2.0V (example LED forward voltage)
• Iled = 15mA (desired current)
• Rled = (3.7V – 2.0V) / 15mA
• Rled = 1.13k (Choose a close standard value like 1.1k)

Remember:

These are abbreviated instances, for information on precise pin connections and biasing specifications, see to the LM393 datasheet.

Calculations for resistors and voltage dividers can be made simpler with online calculators.

Circuit Working:

The heart of the circuit is the LM393 dual operational amplifier.

It is configured to measure the input voltage through potentiometers P1 and P2.

Potentiometer P1 is responsible for setting the voltage threshold at which the 2nd LED green lights up, indicating a well charged battery around 9.5 to 10V.

P2, on the other hand sets the threshold for the 3rd LED red to light up indicating overcharging around 14 to 15V.

The reference voltage for the operational amplifier is provided by the zener diode ensuring accurate voltage measurements.

Yellow LED Low Battery: In low battery conditions, only the yellow LED lights up.

Green LED Good Battery: When the battery is sufficiently charged, both the yellow and green LEDs light up.

Red LED Overcharging: If the battery experiences overcharging all three LEDs light up.

LED Connection:

• LEDs are connected in series to maintain a constant current ensuring that the current does not increase when multiple LEDs are lit simultaneously.
• If a classic op Amp is used e.g. LM358, LM1458, MC4558 series resistances are added to LED2 and LED3 to maintain proper functionality.

Calibration:

• The calibration process involves adjusting potentiometers P1 and P2 with a controllable power supply.
• P1 is adjusted until the yellow LED lights up at the low battery threshold.
• P2 is adjusted until the green LED lights up at the desired voltage indicating a well charged battery.
• Further increasing the voltage allows P2 adjustment until the red LED lights up indicating overcharging.

Warning :

• The device must be connected to a suitable point in the battery circuit and only through a suitable fuse to prevent fire or damage to the circuit.

Final Testing:

• Once calibrated the indicator is connected to the actual battery supply for final testing.
• LEDs should respond accurately to the battery conditions providing a visual indication of the battery status.

Conclusion:

The general charge state of your battery may be quickly and easily determined with the help of a 3 LED battery voltage level indicator circuit.

Depending on the battery voltage, it uses LEDs with various voltage thresholds to display a low, medium or high visual signal.

References

Battery Level Indicator 

Battery indicator