Car Battery Voltage Monitor

This simple 4 LED car voltmeter is designed to allow us to monitor the voltage level of the battery of our car at any instant, continuously.

Submitted: R.K. Singh

Main Features

To achieve the above feature it must be placed somewhere in the dash of the car so that the group of 4 LEDs remain protruded, each with a label indicating the battery voltage having at that instant.The circuit is designed for executing the following:

- 1st LED lights with 11V battery
- 1st and 2nd LEDs light with battery 12V
- 1st, 2nd and 3rd LEDs light with battery 13V
- 1st, 2nd, 3rd and 4th (all) LEDs light with battery 14V

Operational Details

When the battery voltage drops to 11 or 12 volts, it may need charging. If its around 13 volts it is in acceptable condition. At 14 volts it is fully charged. The colors of the LEDs indicate these status.

The main components of the circuit are just a few operational amplifiers used as comparators.

The inverting inputs of these operational are set at fixed reference voltages: 5.1, 4.8, 4.4, 4.1 using zener diode D1 and resistor network: R1, R2, R3 and VR potentiometer.

The VR potentiometer is used to make minor adjustments to the above referenced voltages, which could vary because the resistors are not exact values.

The battery voltage is delivered to non-inverting inputs of the opamps through the shown voltage divider networks formed by R4 and R6 terminals.

Depending on the battery voltage, the voltage at the non-inverting terminal will vary and will put a high voltage level at the output of the comparator, activating the corresponding LED for the required indications.

Circuit Diagram

Parts list for the circuit

- IC1: LM324 integrated (quad opamps in a single integrated) Circuit
- D1: 3.3V zener diode, 1/4 watt
- D2 = D3 = D4 = D5: Diodes LED (2 red, 1 yellow or amber, 1 green)

- R1 = 1K
- R2.....R6: all 1K preset

+12V: is the car battery whose voltage is to be sensed

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lm3914 12v battery indicator circuit is also available.... which one is better sir?
Swagatam said…
lm3914 will give a 10 step indication, so it may depend on the users requirement and preference... whatever might suit better to his application.
Garry Gutierrez said…
can i use this for 24vdc battery sir?
1maniekx1 said…
R2 to R6 all 1K u are wrong!!

IMO R2 7.5K, R3 270ohm, R4 220ohm, R5 200ohm, R6 2.5k
Hi Swagatam,
I have been following your projects for quite a few years now and most of my small electronic project at home came inspired from yours. Great thanks from all your work. I am coming now with a request , I don't know if it's easily feasible in a single circuit something for my very old Peugeot diesel pick-up that I am restoring . All it's equipment is busted, and I would like to have an electronic box that will show water temp, oil temp, Amps for battery charging , battery voltage, break fluid level and water level. Do you have an idea? I was thinking of a press button that will display each request on a digital display.
Thank you so much.
Swagatam said…
Thanks Marika, It may be possible but not exactly as you have mentioned.

The temperature sensors can be configured using the following concept:

the meter could be replaced with a digital voltmeter.

or the same could be viewed through a LED bar-graph, as explained below

Water level could be also monitored using an LED based water level sensor, as discussed below:

break fluid is difficult and I do not have much idea regarding this subject
kazuki_chan8 said…
Hi author... can i use this for lead acid battery - 48V/12Ah
Swagatam said…
Hi Kazuki, yes it can be used..
Aurelian Cheregi said…
Hello what is BZI on the circuit diagram?
Swag said…
IT is the buzzer.
Bronsville tech said…
Do I have to change the value of the resistors to use on a 24 volt battery?
Swag said…
you can change all 1K values with 10K, and use 10K also with the LEDs
Bronsville tech said…

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