Battery Voltage Status Monitor using 4 LEDs

The post describes a simple battery 4 step LED DC voltage monitor circuit using the versatile IC LM324. The idea was requested by Ms. Piyali.

Technical Specifications

I've a project, if you could help me out:
1. basically its a battery voltage detector cum indicator circuit.
2. the output from a transformer is 6V, 12V, 24V resp., depending on the supplied input. O/p is A.C.
3. by converting it into D.C. I've to design a circuit which will detect and indicate the voltage o/p by colored LED lamps. Such as,
Blue LED - 6V
Green LED - 12V
Red LED - 24V
4. Circuit should be compact in nature as much as possible.
1. should we be using comparator circuit ?
2. how to detect the diff. voltage levels ?
3. Is relay required ?
Please consider at earliest.

Thanks & Regards

The Design

The proposed battery voltage status monitor circuit using 4 LEDs makes use of comparators in the form of opamps from the IC LM324.

This IC is much versatile than the other opamp counterparts due to its higher voltage tolerance level and due to the quad opamps in one package.

In the proposed LED battery voltage monitor/indicator circuit all the four opamps have been used, although a few of them may be eliminated in case they are not required or depending on the specs of the individual users.

As can be seen the circuit diagram, the configuration is simple yet the outcome too effective.

Here the inverting pins of all the four opamps are clamped to a fixed reference level determined by the value of the zener diode which is not critical and can be any value close to the suggested one in the parts list.

The non-inverting pins of the oipamps are configured as the sensing inputs and are terminated with variable resistors or the presets.

How to Adjust the Thresholds

The preset should be adjusted in the following manner:

Initially keep all the presets slider arm shifted toward the ground end so that the potential at the non inverting pins become zero.

Using a regulated variable power supply apply the first voltage to be monitored starting from the lowest value to the circuit.

Adjust P1 such that at the above level the white LED just lights up. Fix P1 with some glue.

Next apply the second higher voltage or increase the voltage to the next level which is to be monitored and adjust P2 such that the yellow LEDs just switches ON. This should instantly shut OFF the white LED.

Similarly proceed with P3 and P4. Seal of all the presets after they are set.

The shown battery indicator circuit is configured in the "dot" mode meaning only one LED glows at any instant indicating the relevant voltage level.

If you want to make it respond in a "bar graph" mode, simply disconnect the cathodes of all the LEDs from the existing points and connected them all with the ground or the negative line.

Circuit Diagram

Parts List for the battery status monitor circuit

R1---R4 = 6K8
R5 = 10K
P1---P4 = 10k presets
A1----A4 = LM 324
z1 = 3.3V zener diode
LEDs = 5mm, color as per individual preference.

Modifying the above 4 status Battery Indicator with Flashing LEDs

The above explained 4 LED battery status indicator can be modified appropriately for enabling it with flashing LED indicators, as shown in the following diagram:

flashing battery indicator circuit 4 LED

R1 = 2k2

R2 = 100 ohms

LED = 20mA 5mm type

C1 = 100uF to 470uF depending on flashing rate preference

Need Help? Please send your queries through Comments for quick replies!


Swagatam said…
it can be implemented with an ordinary electromagnetic relay and an opamp, not sure about solid state relays.
Faizan Hamayun said…
HI can this circuit be designed for 4.2V lithium ion rechargeable battery.
3 steps LED
Green works from 4.2-3.8V
Yellow works from 3.7-2.8V
Red works from 2.8-2.4V respectively.
What parts are needed for this.
Reply at
Swagatam said…
Hi yes it can be done by replacing the LM324 with a low voltage opamp.

the LED resistors may be decreased a bit for getting brighter illumination, no other changes would be required.
Greak Sir!
I will definitly try this ciecuit.
apart from its simplicity to build, its also smaller in size.

Thank you very much.
Swagatam said…
thank you Aminu, keep up the good work
Dave W said…
Hello Swagatam,
What wonderful work you do for us beginners. Thank you for sharing what you know, and making it easy to understand.

In reference to the low power op amp; Can an lm358 be used for monitor of a 6v supply?
Dave W said…
Thank you for sharing what you know. It is very easy to follow for a beginner like me. What a wealth of knowledge. Keep up the great work.

In reference to a low power op-amp; can i use an lm358 for a 6v supply monitor in this circuit?

Thank you.
Swagatam said…
Thanks Dave, yes you can use an LM358 IC, although it has only a couple of opamps.
Dave W said…
My mistake Mr.Majumdar, i meant to say lm339. It has all 4 opamps...

Thanks again.
Swagatam said…
yes LM339 can be used.
Aminu Yahaya I said…
Morning Sir,
I built this circuit since, and my design was working in bar LED mode. Now I want improve it by adding a relay in the last LED (that indicate below 11v level), so that if the last LED turn off relay will turn off too.
Sir how can I add a relay?
Aminu Yahaya I said…
My desing is in bar form and I'm operating 12v battery with it. What I need an addintion of relay to the last LED that will turn off together with the relay.
Thanks very much Sir.
Swagatam said…
Aminu, you can do it by connecting the base of a PNP transistor such as a BC557 with the output of A1...the relay can be attached across the collector and ground with a diode parallel to the coil.

also make sure to connect a 10k resistor between the base and the A1 output and a 4k7 resistor across base/emitter...emitter will connect with the positive line
Aminu Yahaya I said…
I did it... It's quite simple.
Aminu Yahaya I said…
Sir, am building an inverter circuit using SG3524 IC.
So, My mind told me that, I can supply the Negative power to the inveter circuit through this LM324 by connecting A4 output of the LM324 to the negative supply to the SG3524. So that, the inverter will shut down if the final LED, that is A4 output short down.
Is this feaseble Sir?
Aminu Yahaya I said…
Secondly, can I replace the relay by connecting the emiter of PNP transistor to the Positive power of the IC SG3524?
So that, the inveter will shot down when the A4 LED gone off.
Swagatam said…
Aminu, it can be done, but as far as I know pin#10 of the SG3525 or 3524 requires a positive pulse for shutting down, not a negative can do it as shown in the following diagram
Aminu Yahaya I said…
Sir I need a circuit that can ON a fan if the temperature go up and switch OFF a fan if the temp go down.
Swagatam said…
Aminu, you can try the following concept
Godson said…
Hello sir Swagatam,
Thank you very much for this schematic. I'll like to incorporate it in my inverter design. From what i see, it appears to be for 12V battery. If i want to use it for 24V, 36V, 48V, 60V and higher voltages (for higher inverter capacities), what part do i need to change? And please could you tell me the upper and lower threshold voltages for 24V, 36V, 48V, and 60V e.g upper and lower threshold voltage 12V are 14.5V and 10.5V respectively. Thank you sir.
Swag said…
Hello Godson, you can can easily use it for 24V monitoring also, just change the zener with a 6V or 9V zener diode. For higher than 30V, you can still use the same design but make sure the IC supply pins are supplied with a regulated 24V.

after this you can simply adjust the relevant presets for enabling the LED switch ON at the desired thresholds
Godson said…
Thank you for the prompt reply sir. When voltage is above 30V and i use a 24V regulator like you said, how will the circuit be able to monitor the fall in voltage since the circuit will keep getting a constant 24V?
Swag said…
the 24V should be separately fed only to the (+) supply pin of the IC, that is to pin#4 of IC LM324....
Godson said…
Very well then. So that means that R5 and P4 will now be connected to the positive terminal of the battery in question and the settings will be done. Thank you for the info sir. I want to design mine in a "bar graph" mode and use it to power off the inverter when the last LED turns off. Can i connect a 10K resistor from pin#1 of the IC to the base of an NPN transistor such that a relay-diode assembly will be connected between the collector and positive terminal and the emitter to ground, keeping R1 and the associated LED in their place and then use the relay contacts as the inverter switch?
Swag said…
Yes that's correct R5/and the presets can remain connected with the battery voltage.
you can use pin#1 with a 10k/BC547/relay stage for initiating the mentioned operation.
N.Kesav said…
Sir i have few doubts...
* For 12v battery zener value 3.3
For 6v battery zener value ?
For 4v battery zener value ?
Pls tell sir....
Low voltage op amp ic also pls tell

* 12v btry 7aH I'm using...if i give directly to IC +ve (pin no 4) voltage source.IC will be damage or i need to connect IN4007 diode reduce the ampere for IC input (pin no 4)..
Swag said…
Kesav, it is not critical, you can use any value lower than the minimum threshold of the battery...the zener is only for providing a fixed reference based on which the presets are adjusted for the intended cut offs.

for low volatge operation it is better to use a BJT based circuit as given below:

the IC can tolerate upto 19v so 12V cannot be a problem, you can connect the batt directly, and a diode is not for reducing current, it's job is to only block reverse voltage....
N.Kesav said…
Thank u sir...

If u have LM3914 battery circuit sir...
I find many circuit not working proper sir...
Pls find me the good circuit sir...
Swag said…
You are welcome Kesav,

all circuits from this website will work but only if it's done with proper understanding...if you do it without understanding then you will keep struggling even with the simplest of the circuits, ....and anyway electronics is all about understanding and implementing.

You can check the following design which uses LM3915
Godson said…
Hello sir Swagatam,
What modifications do I need to make to the above schematic (first one) so as to use it for both battery charging indicator and discharging indicator? I want to use it for both in a project.
Thanks in anticipation.
Swag said…
Hello Godson,

the first circuit will work for both, as a full charge indicator when the red LED lights up, and a full discharge indicator when all LEDs shut down except the white one which shows the last discharge level of the battery and indicates that the battery needs to be recharged immediately.

Green indicates battery is moderately charged.
Godson said…
Hello sir Swagatam,
Thanks a lot for the reply. What I actually meant was using the circuit when the LEDs are in the bar mode, i.e when battery is charging, the LEDs turn on one after the other until the last one is lit, meaning that the battery is fully charged, and when the battery is discharging, the LEDs go off one after another until the last one is turned off, meaning that the battery has discharged. Is it possible for the schematic to work that way?
Swag said…
Hi Godson,

It is possible by connecting the respective LED ends with the ground line instead of the opamp outputs...
Godson said…
Hello sir Swagatam,
Thanks a lot for the reply. According to the datasheet, LM324 has a maximum supply voltage of 32V. How do I use it on a 48V battery? What modifications do I need to make?

Please sir, could you suggest a schematic for 0-50V variable power supply. I am urgently in need of it. Thanks a lot in anticipation.
Swag said…
Hello Godson, you can regulate the positive supply pin of the IC with a 24V zener diode. Connect a 4k7 resistor from it Vcc to positive supply line, and a 24V zner from its Vcc pin to the negative line (ground line)

Link for the power supply
Amit padole said…
Dear sir,
I want to design battery level indicator for 48 volt battery with 5 led. Can you send circuit diagram, rating of components used and mathematical calculation
Swag said…
Dear Amit, you can easily use the first circuit from the above article, and add one more opamp for getting the 5 LED output.

Just make sure to connect the positive pin of the IC with a stabilized 12V, while the preset output may be connected with the 48V, preferably add a 10K resistor in series with each preset.

The presets and the 10K resistors will form a resistive divider and ensure that the sensing voltage at the input is kept well within 12V range.

All resistors will be 1/4 watt rated, opamps can be from any standard opamp IC

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