Battery Voltage Status Monitor Circuit 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.

The Circuit Request

Hi Swagatam,

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 Circuit 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 Schematic


Battery Voltage Status Monitor Circuit using 4 LEDs

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.

32 thoughts on “Battery Voltage Status Monitor Circuit using 4 LEDs

  1. Have questions? Please feel free to post them through comments! Comments will be moderated and solved ASAP.
  2. Looking for a very simple circuit.. I have a voltage source that ranges from 0-60v DC. I would like to send this voltage/current to one load when the voltage is below 24v and to different load when it above 24v. I was planing on using 2 solid state relays a 5v signal to the (above 24v) relay to switch it from normal open to close, and the invert of that signal to the other relay. Unless there is a solid state relay that has normal open and normal close in the same package like a current steering device.

    • 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.

  3. 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?

  4. 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.

  5. 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, 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

  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. 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.

  8. 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.

  9. 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)..

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