Battery Level Indicator

Outline

• Introduction
• Battery Level Indicator Circuit Principle
• Battery Level Indicator Circuit Diagram
• Circuit Components
• Battery Charge Indicator Circuit Design
  • LM3914 Features
• How to Operate Battery Level Indicator Circuit?
• Battery Charge Level Indicator Circuit Applications
• Limitations of the Circuit

Introduction

I will demonstrate how to construct a straightforward Battery Level Indicator Circuit using easily accessible components in this project. The battery level indicator employs illuminated LEDs to display the battery’s status. For instance, if there are six LEDs lit up, it signifies that 60% of the battery capacity remains.

This tutorial will walk you through the process of building a battery level indicator. This circuit can be utilized to assess the condition of various batteries, including car batteries and inverter batteries. Consequently, this circuit can help prolong the life of the battery.

This circuit is designed based on lM3914 IC (Integrated chip). This IC is LED dot/bar display driver.

Battery Level Indicator Circuit Principle

The core component of this battery level indicator circuit is the LM3914 IC. This IC takes in an analog input voltage and linearly illuminates 10 LEDs in response to that voltage. In this design, there are no resistors in series with the LEDs because the IC regulates the current.

To gain a deeper understanding, you may want to explore the related article titled “How Does an LM317-Based Automatic Battery Charger Work?”

Battery Level Indicator Circuit Diagram

Circuit Components

• LM3914 IC
• LED’s -10 (Red – 3, Yellow – 4, Green – 3)
• SPST Switch
• Resistors – 18KΩ, 4.7KΩ, 56KΩ
• Potentiometer – 10KΩ
• 12V Battery (to test)
• Connecting wires

Battery Charge Indicator Circuit Design

This circuit is designed to indicate the battery capacity using LEDs (D1-D10) in either dot mode or display mode. The selection between these modes is made using an external switch, sw1, connected to the 9th pin of the IC. A resistor connects the 6th and 7th pins of the IC to ground, and this resistor controls the brightness of the LEDs. Resistor R3 and POT RV1 form a potential divider circuit, and the calibration pot RV1 is employed here. It’s worth noting that this circuit doesn’t require an external power supply.

The circuit is designed to detect voltage levels between 10 and 15 volts DC, and it will continue to operate even if the battery voltage drops to 3V. The LM3914 IC has an operational voltage range from 3 to 25 volts DC and can be used to drive LEDs, LCDs, and vacuum fluorescents. Additionally, it features an adjustable reference and an accurate 10-step divider, making it suitable for sequencing applications as well.

LM3914 Features

• Internal voltage reference from 1.2 to 12v DC.
• Programmable output current 2mA to 30mA.
• LED driver outputs are current regulated.
• No multiplexing interaction between outputs.
• It supports wide range of temperature from 0 to 70 degree Celsius.
• For bar graph display – connect 9^th pin of IC to the supply
• For dot display – leave the 9^th pin of IC

You can also use different colored LEDs to convey various battery status messages. For instance, connect red LEDs (D1 to D3) to signify that the battery is in a shutdown state, utilize green LEDs (D8 to D10) to indicate that the battery is within the 80 to 100 percent charge range, and employ yellow LEDs to signify that the battery is currently charging.

With some minor adjustments, you can adapt this circuit to measure additional voltage ranges. Initially, remove resistor R2 and connect the input to the upper voltage level. Next, adjust the resistance of Pot RV1 until the D10 LED illuminates. Afterward, replace the upper voltage level input with the lower voltage level, and substitute resistor R2 with a high-value variable resistor. Adjust this variable resistor until the D1 LED lights up. Once done, disconnect the variable resistor, measure its resistance, and replace R2 with a resistor of the same value. Your circuit is now configured to monitor a broader range of voltage levels.

This circuit is particularly well-suited for gauging the status of a 12V battery, with each LED representing a 10 percent increment in the battery’s charge level.

How to Operate Battery Level Indicator Circuit?

• Connect battery to be tested to the input of the circuit.
• Now adjust the pot RV1 so that LED D1 just starts glowing.
• Now increase the input Dc voltage slowly and observe the LED’s
• First led will glow for 1.2V and second LED is for 2.4 V and so on.

Below table shows the status of LED’s with input voltage level.

BATTERY LEVEL	PERCENTAGE	STATUS OF LED’S
1.2V	10	D1 – ON
2.4V	20	D1, D2 – ON
3.6V	30	D1, D2, D3 – ON
4.8V	40	D1, D2, D3, D4 – ON
6.0V	50	D1, D2, D3, D4, D5 – ON
7.2V	60	D1, D2, D3, D4, D5, D6 – ON
8.4V	70	D1, D2, D3, D4, D5, D6, D7 – ON
9.6V	80	D1, D2, D3, D4, D5, D6, D7, D8 – ON
10.8V	90	D1, D2, D3, D4, D5, D6, D7, D8, D9 – ON
12V	100	ALL LED’s – ON

Battery Charge Level Indicator Circuit Applications

• We can use this circuit to measure car battery level.
• This circuit is used to calibrate inverter status.

Limitations of the Circuit

• This battery level indicator works only for small voltages.
• This circuit is theoretical and may require some changes to work in practical.