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  • This battery level indicator offers (5) LEDs that light up progressively as the voltage increases:

    • Red: Power Connected (0%)
    • Yellow: Greater than 10.5V (25%)
    • Green 1: Greater than 11.5V (50%)
    • Green 2: Greater than 12.5V (75%)
    • Green 3: Greater than 13.5V (100%)

    Of course, you may select your own colors if desired.

    12 Volts Battery Level Indicator Circuit Schematic

    12V battery level indicator

    Operation of the battery level indicator

    D1 is the voltage reference zener. Tied to this is a string of divider resistors (R2-6) that set the various fixed voltage levels. R7 & 8 form a voltage divider to that reduces the battery voltage by a factor of 3. U1 is an LM339 quad comparator that compares the various voltages from the two dividers. The comparator sections have open collector outputs that simply function as switches to operate the LEDs. D7 protects against reverse battery connection.

    The LEDs are biased to operate at about 4mA which is quite bright if modern LEDs are used. This current can be adjusted simply by varying the series resistors (R9 through R13). The overall current drain as shown is about 25mA which tends to be wasteful for continuous operation. For energy conservation, connect to battery via a pushbutton (Push to Test).

    Printed Circuit Board

    I did a www.expresspcb.com SMT layout using 0805 size components, 1N753 zener and SOIC-14 IC. D7 is in a SOT-23 package. These components are about as small as I like to work with. The layout has not yet been carefully checked or built. Note that surprises abound when constructing prototypes.
    The circuit board measures only 0.5” x 1.5”.

    More recently, I located an inexpensive SOT-23 zener with a 2% voltage tolerance—this has not yet been incorporated.

    I have had good results with 0805 size LEDs purchased from China on eBay. They are both inexpensive and BRIGHT!

    12v battery level indicator photo

    The 12v battery level indicator unit in the photo has no reverse polarity diode and R2 is the calibration potentiometer.

    
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    60 Responses to "12V Battery Level Indicator Circuit"

    1. Marius Marian says: on July 26, 2012 at 8:00 pm

      Added to favorites, great article.

    2. .D circuits nt well post ..it nt work…

      • Iqbal singh says: on October 12, 2014 at 6:16 pm

        I built this project but not working.if do only red led glows.other i replace d7 with diode 4007 to pervent reverse effect.

    3. Jim Keith Jim Keith says: on August 15, 2012 at 2:50 pm

      The only detail not actually tested is the addition of D7. Try shorting D7 to see if it makes a difference. Otherwise, find your wiring error.

    4. SURAJMAHAGURU says: on August 18, 2012 at 10:56 am

      it works but after some changes

    5. K tanks…….d only fact is dat d circuits is terminated…hi will like to post circuit like dis (battery monitor) but d only different is dat…is very useful to monitor inverter battery during is charging process….

    6. yup. i agree with @SURAJMAHAGURU its works but need some customization.

    7. I would like to use the “above 13.5vdc” condition switch to turn on a relay which would enable a battery desulfator circuit. How would I modify this circuit to do so efficiently?

      • Jim Keith Jim Keith says: on October 20, 2012 at 2:16 pm

        Actually, it would be easier and simpler to start over. Let me draw up a circuit that will do this for you. Will attempt to post next week.

      • Thanks Jim!,

        Here’s the link to the circuit I want to build. I would like to interrupt the voltage supply source at S1 with a 13.5vDc voltage sensing switch like I implied above. Your help is greatly appreciated!

        http://www.instructables.com/id/Desulfator-for-12V-Car-Batteries-in-an-Altoids-Ti/

        Is there any concern for the pulsing circuit interfering with the sensing switch? I.E. the 56-80vDc pulses (obviously > 13.5vDc ) causing the interruptor circuit to switch on and off with every pulse?

        Thanks for your advice and help!

      • “Is there any concern for the pulsing circuit interfering with the sensing switch? I.E. the 56-80vDc pulses (obviously > 13.5vDc ) causing the interruptor circuit to switch on and off with every pulse?”

        OOPS! I just divulged my own ignorance! Yes, I took a moment to think… and now realize that the circuit would not be active and therefore would not be effected…never mind!

        Thanks for your advice and help!

      • Jim Keith Jim Keith says: on October 25, 2012 at 1:59 pm

        Actually, there is concern that something bad will happen. In a case like this, it may be best to latch the relay on via a 2nd set of contacts, and turn the level detection circuit off –use 2 two pole relay or power contactor.

        Still working on circuit…

    8. umesh_kirdat says: on November 27, 2012 at 3:34 pm

      This article is great but can we develop a similar circuit which displays the charge status/level on a small LCD display?

    9. onionterror says: on December 11, 2012 at 11:52 am

      I just assembled this circuit on bread board. The leds work but when I change the voltage they all work at the same time. Effectively it works as a dimmer. Anything common that I may have got wrong?
      Thanks

      • When building this stuff, all kinds of things can go wrong. I intend to write an article on troubleshooting soon.

        Perhaps the zener is connected reverse–that could cause the symptoms.
        Measure the various points on the voltage dividers –they do not have to agree with the values on the schem exactly, but should be progressive. Also the 2nd divider divides the source voltage by a factor of 3 –this can be checked. IC wiring is easy to screw up. Check and recheck your work.

        As I previously indicated, D7 is an afterthought to protect against accidental battery reverse connection. Try shorting it out to see what happens.

      • onionterror says: on December 12, 2012 at 11:07 am

        Thanks, I found that my zener was popped and so I got it to work.
        Thanks again.

      • Same problem with me, except all the LED’s light up besides R10.

    10. Hi, I have a question. I was wondering if it would still be possible to use this circuit for a 9V operation if I subtracted the last LED that indicated a full 12V. If you are wondering what I may be using it for, well then, I was plan on adding this as a side circuit to that simple solar battery charger circuit that you posted the schematics for, (which works great by the way) so that I could see roughly how full the battery was, without having to hook up the volt meter every time. Though I was planning on adding a pushbutton switch to the indicator, so that the circuit wouldn’t be pulling allot of power away from charging the battery.

      If you wouldn’t mind responding back to my comment I’d highly appreciate it. But if you do, then Thank You for taking time out of your busy day to answer it.

    11. asreejithmenon says: on January 13, 2013 at 3:36 pm

      Sir i was thinking of showing the output in a 7 segment display.Also i would like to have a 1voltage accuracy.So that means 12 comparator needs to be used.So basically it would be working as a flash adc as the voltage divider would give the reference voltage and the battery voltage would be the input.I was thinking if i could replace the flash adc with a succesive approximation adc as the number of comparators required would be less.Can you please help me on this ? I dont mean to use a IC of succesive approximation adc,rather use the circuit on whole.Please help me sir.

    12. Dams4ever says: on February 14, 2013 at 1:54 pm

      Please how do I design this circuit for 24v (two 12v batteries in series) to monitor the battery levels?

    13. spyclub says: on June 10, 2013 at 4:43 pm

      Great circuit, I have put a simulation of it online at https://www.circuitlab.com/circuit/9d22db/12v-battery-detector/

    14. Akhil.k says: on July 27, 2013 at 3:30 am

      sir ,
      Is there replacement available for the zener diodes … ? how much voltage zener should be used .. ??

    15. Can you be my teacher and please teach me im eager to learn thanks e mail me thanks

    16. Navjot Singh Sains says: on September 30, 2013 at 11:18 am

      Hi Jim,

      Thanks for the wonderful post and sharing out your designs.

      Actually I’m willing to make this circuit, but I’ve a ques in my mind –

      http://www.electroschematics.com/6899/12v-ldo-solar-charge-control/

      I’ve made this circuit of yours a 12v LDO Solar Charge Control and I’m thinking of attaching the 12V Battery Level Indicator Circuit with the battery.

      Considering that the battery is permanently attached with the solar charge controller. How can I connect the 12V Battery Level Indicator in addition to that. Wouldn’t that always show the charging voltage being supplied to the battery?

      What I’ve in mind is to connect a push to test button which will disconnect the solar panel from the battery and will connect the Indicator Circuit with the battery.

      Can you please suggest me a better option?

      Thanks in advance!

      Best,
      Navjot

      • Yes, you are correct–when the solar panel is actively generating power and the battery almost fully charged, the voltage is at max.

        The push button is a great idea to conserve power–especially when the solar panel is not generating.

        Another idea that I have toyed with is a 555 astable oscillator that puts out a low duty cycle pulse every 2 or 3 seconds or so–perhaps 0.25 seconds duration. This pulse gates a MOSFET transistor that switches the battery level monitor on briefly, thus reducing power consumption by a factor of 10. On top of that, use ultrabright LEDs so that the LED current may be greatly reduced and remain visible. This would make another good project.

      • A little more info–disconnecting the battery briefly in order to measure voltage is troublesome in that it takes a while for the voltage to decay to normal. It may require a dummy load to accelerate this process.

    17. Navjot Singh Sains says: on September 30, 2013 at 6:44 pm

      Hi Jim,

      Thanks a lot for the info, I am overwhelmed by the support provided by you.

      I would like to know your thoughts on – which is the better option? Also, is it too much if I ask for the circuit diagram for the 555 astable oscillator?

      Thanks in advance!

      Grateful,
      Navjot

    18. kasi viswanadh says: on October 6, 2013 at 6:39 pm

      hello sir i have everything except zener diode can i replace zener by any other elements ?means any modifications in the circuit can i made?
      thanks for advance .

    19. can i connect to the inveter battery 12v and 150ah

    20. how can i connect the display inside of lights

    21. thanks for d ckt,it’s working perfectly….

    22. Hi Jim,

      In looking for a solution for a different application (motorcycle gear indicator), I came across your design and would be interested in your thoughts on how it may be applied to this:

      There are different voltages presented on a wiring connector depending on which gear you are in as follows:

      Gear Voltage
      1st Gear Approx. 1.36 V
      2nd Gear Approx. 1.77 V
      3rd Gear Approx. 2.49 V
      4th Gear Approx. 3.23 V
      5th Gear Approx. 4.10 V
      6th Gear Approx. 4.55 V

      The idea is to light a simple seven segment LED, displaying a 1 for 1st gear, 2 for 2nd gear etc. up to 6 for 6th gear based on these voltages. Your thoughts and guidance would be greatly appreciated…

      Thanks,

      Mike

      • This would be a neat exercise for you arduino guys –read the voltage with the A-D converter and light the proper segments in a 7segment LED display so it indicates the proper numeral.

        Otherwise, this appears to be a neat project and some of the circuit techniques used here are useful for your application. The main issue is the blanking of lower order LEDs this is not actually required for effective operation.

    23. is there any code for lm339?

    24. Thanks for answer. How can i change voltage for example when the battery voltage decreasing?

      • R7 & R8 reduce the the input voltage level by a factor of 1/3. So the voltage threshold to be compared must be equal to this voltage.

        To obtain the proper voltage to the other comparator input terminal simply adjust the resistances in the fixed voltage divider (R2 to R6). Now this can get very tricky because changing one resistor affects all voltages outputs. To get around this, make a separate voltage divider for each comparator input. Suggestion: Use a 100K potentiometer for each input and set the output to 1/3 * the desired input voltage. Or if you have an adjustable lab power supply, you may simulate the battery voltage and then adjust the pot to the visible LED threshold. Good luck!

    25. I’m building a 12volt powered DC fan blower, for cooling rc electric motors. Currently Ive wired it up with a on/off rocker switch and a variable resistor in series, to allowed it to be turned off and to control fan speed. I would like to add a series of say 5 leds that will light up indicate fan speed. Would this cicuit work, as the variable resistor alters the input voltage in theory.

      • This should work OK for your speed indicating application where speed is controlled via a variable resistor.

        It will not work in pulse width modulation speed controls where the the voltage is reduced via turning the power on /off at a high rate –in that case the voltage to the control must be filtered via an R-C filter.

    26. Would it be possible to use this same comparator circuit with modifications to the resistor values for a lower voltage output such as 3.7V from a LiPo?

      • No, this circuit (as it is) cannot not work down to that voltage level. However, this would make a good project –will attempt to post a low voltage circuit this week.

    27. Thanks Jim,

      To alter the voltage that the led’s indicate would I just alter the resistor in series with each LED? Meaning I would want the led’s to indicate say 13volts, 11volts, 9 volts, 7volts. Think my variable resistor drops the voltage down to 5 volts at max resistance.

      Im sure Jim will clarify but I would assume it might work Farad but the component values might need altered to suit lower voltage?

      • The resistance in series with each LED merely affects the brightness –simply adjust for adequate brightness.

        The thresholds are modified via the input voltages as divided by the resistance voltage dividers. To obtain the kind of voltage range you need, a better voltage reference is required –the zener shunt voltage regulator simply does not have adequate input voltage range. Watch for new post:
        “Voltage /Speed LED Indicator”
        I will make it more versatile. Another low voltage issue is turning on white or blue LEDs that require 3V.

    28. Many thanks Jim, my gcse and A level electronics knowledge has slid after 12 years!

    29. Hasan Basri says: on June 13, 2014 at 8:14 pm

      Respected Sir,

      What if I connect a 3.7V (Lit-ion) general purpose battery instead of 24V lead acid battery? Will the circuit work the same as for 24V lead acid battery
      Thanks you..

    30. No the circuit will not work for a 3.7V battery. The following circuit will work provided that the battery voltage never drops below 3.0V.
      http://www.electroschematics.com/10436/low-voltage-battery-level-indicator/
      Next month I will be posting a circuit that designed for 3V applications.

    31. Hello…. am stuck I can’t figure it out…. Someone please help…… I have a volt meter like the top Schematics and I want it to check 5Volts instead of 12V….. I have connected it and it will not turn on LEDs…. Each LED has a 1K resistor…. can that be it? Do I lower those resistors? Do I have to change all the resistors or just one? Thanks…

    32. If we use a 12v 150ah battery, should we not consider the wattage value of the resistors. Because excessive amount of current will flow from 150ah battery.

    33. Jim, thanks!

      One question, the LM339N in the picture requires a min 18volts. How does this work with a 12v batt?

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