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3 Simple Battery Voltage Monitor Circuits

3 Simple Battery Voltage Monitor Circuits

The post describes 3 simple battery charge monitor or battery status circuits. The first design is a 4 step LED 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.

1) 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

4 led battery charge monitor circuit

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.

2) 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

The article shows a simple method of using the IC LM3915 for monitoring battery voltages right from 1.5V to 24V in 10 discrete steps using 10 LED indicators.

3) Using a LM3915 IC for the 10 Step Function

The third circuit explained below allows you to visualize precisely what voltage your battery has at any particular instance while it's being charged.

The LM3915 is basically a 10 stage dot/bar mode LED driver circuit which provides a sequential 10 step LED display corresponding to the varying voltage levels set at its signal input pinout#5.

This input can be set with any voltage level right from 1 to 35V for acquiring a correspondingly sequencing readout of the voltages fed on that pin.

In the proposed 10 step battery charging indicator and monitor circuit we assume the battery to be a 12V which is to be monitored, the circuit functioning may be understood as follows for the aforesaid condition:

The transistor at the right end is configured as an emitter follower replicating a  high current, constant voltage zener diode, fixed at 3V.

This is required so that the LEDs are restricted from drawing excessive current, unnecessarily making the IC warm.

The battery voltage is also fed to pin#5 via a voltage divider network made from a 10K resistor and a 10K preset.

The outputs of the IC are all connected with 10 individual LEds for producing the required 10 step indications. The color of the LEDs can be as per your preference.

How to Set up the above explained battery status indicator Circuit.

  1. It's pretty simple.
  2. Apply the full-charge voltage level across the point indicated "to battery positive" and ground.
  3. Now adjust the preset such that the last LED just illuminates at that voltage level.
  4. Done! Your circuit is all set now.
  5. For calibrating, simply divide the above mentioned full charge level with 10.
  6. For the present case, let's assume the full charge level to be 15V, then 15/10 = 1.5V, meaning each LED would stand for an increment of 1.5V. For example with the 8th LED just ON would indicate 1.5 x 7 = 10.5V, 8th LED = 12V, 9th LED = 13.5V and so on.
  7. Similarly, the circuit can be used with any battery and just needs to be set as per the above guidelines for achieving the proposed 10 step battery level monitoring.

Circuit Diagram

Car Battery Voltage Monitor Circuit

The first concept above can be also modified as a 4 LED car voltmeter which will allow us to monitor the voltage level of the battery of our car at any instant, continuously.

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


About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!

39 thoughts on “3 Simple Battery Voltage Monitor Circuits”

  1. 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

    • 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

  2. 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.

    • 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.

      • 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?

          • 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.

  3. 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 ..to reduce the ampere for IC input (pin no 4)..

  4. 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.

    • 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

      • 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?

          • 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?

            • 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.

  5. 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.

    • 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 pulse….you can do it as shown in the following diagram


  6. 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?

  7. 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.

    • 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

  8. 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?

  9. Swagatam,
    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.

  10. 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?

  11. Greak Sir!
    I will definitly try this ciecuit.
    apart from its simplicity to build, its also smaller in size.

    Thank you very much.

  12. 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 faizan.hamayun@hotmail.com

    • 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.

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