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12V Automatic Battery Charger Circuit with 4 LED Indicator

12V Automatic Battery Charger Circuit with 4 LED Indicator

A lead acid current controlled automatic 12V battery charger circuit with 4 LED indicators can be learned in the following post. The design also includes a 4 level charging status indicator using LEDs. The circuit was requested by Mr. Dendy.

12V Battery Charger with LEDs

I would like to ask and look forward to you to be made Automatic cellphone charger circuit 5 Volt and Automatic Lead Acid Battery Charger Circuit 12 V (in the schematic circuit and the first transformer CT) automatic / cut off by using a battery indicator and

LED lights red as an indicator were charging (Charging On Indicator) using IC LM 324, and

LM 317 and a full battery using a green LED and breaking electrical current when the battery is full.

For cellphone charger circuit 5 Volt I want to have levels of the following indicators:

0-25% battery is in the charger using a red LED.25-50% using a blue LED (red LED goes out)55-75% using a yellow LED (LED red, blue outages)75-100% using a green LED (LED red, blue, yellow outages).next to Lead Acid Battery Charger Circuit 12 V I want to use the 5 LED lights as follows:0-25% using a red LED25-50% using orange LED (red LED goes out)50-75% using a yellow LED (LED red, orange outages)75-100% using a blue LED (Led red, orange, yellow outages)more than 100% using the green LED (LED red, orange, yellow, blue outages).

I hope you, the components are common and accessible and made a circuit schematic above as soon as possible because I really need schematics details.

I hope you will help me to find a better solution.

The Design

The requested 12V automatic battery charger circuit with 4 LED indicators make use of  4 level status indicator and can be witnessed below.The TIP122 controls over-discharge of the battery while the TIP127 ensures an instant supply cut-of for the battery, whenever an overcharge limit is reached for the battery.

The SPDT switch can be used to select the battery charging either from a mains adapter or from a renewable energy source such as a solar panel.

Circuit Diagram

12V Automatic Battery Charger Circuit with 4 LED Indicator


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!

66 thoughts on “12V Automatic Battery Charger Circuit with 4 LED Indicator”

  1. Howdy, Friend! Interested to Learn Circuit Designing? Let's Start Discussing below!
  2. Hi Swagatam,
    Thanks for the post , its very useful for me.

    Can i use TIP122 in place of TIP127?
    I tried to use TIP122 for charging cutoff, Base -> LM324 output via 1kohm, Collector -> LM317 output i.e 14v , Emitter ->Battery +, so when TIP122 is conducting i could see only 10.7 volts at the Emitter of TIP122.
    Why is there drop ? And i am using 14v supply for LM324 , so output of comparator gives 10v.

    Thanks in Advance.

    • Thanks Ahmed, when you are using an NPN here it will work like an emitter-follower, which will create an emitter voltage 0.7V less than its base voltage. Since TIP 122 is a Darlington, this drop could be around 1.4V, so the emitter voltage will be = base voltage – 1.7V.
      Check the base voltage of TIP122 from LM324, you will find it to be 1.7V higher than the emitter voltage or vice versa.

      By the way when a discharged battery is connected the supply voltage will sink and attain the value of the discharge level of the battery, so in your case it could have reached at around 11V and that is why you are seeing 10V at TIP122 emitter.

      • Ahmed, sorry TIP122 will simply not work here, because when your battery is in the discharged state, the relevant LM324 output will be zero therefore the TIP122 will never be able to conduct

  3. Max can use the voltage and how many watt solar panels. Can use the 12v / 150Watt solar panel to charge the Betterie of ..12V / 7AH or 12V / 26AH…please help me sir.

    You have said to give 14v and 18v but I have 12v only to give me tips on how to charge bettery of 7ah / 26ah
    Can I use any regulator or have a circuit that changes 12v to 14v / 18v

    • yes you can use, just replace LM317 with LM338, and TIP127, TIP122 with TIP147 and TIP142 respectively, and the input must be rated at minimum 18V 3 amps

  4. Can use 12V / 10AMP supply in input as the SMPS will be around 13.5V..If using 12V 10AMP SMPS..
    So can it give me 10AMP in output..for LM317 which is 1.5AMP..what do I have to do.Can it be so.

    • The battery terminals must receive around 14V to charge anything below this will not charge it correctly. LM317 will need to be replaced with a LM338 current controller, or some other current controller module depending on your battery Ah rating

    • Deepak, To charge a 12V battery you will require a minimum 14V, so 12V will not work, 10 amp will be OK if the BJTs are upgraded accordingly

  5. Hi Sir,

    I find your blog very interesting. I’m also an electronics enthusiasts. And i think you can help my problem now.
    I have a laptop battery rated 11.1v 4400mah, I removed the cover of the battery which shows 6 individual battery inside. Now i want to charged it using my 12v charger (I’m not charging it individually). My question is, is it okay if i will connect the directly to the terminals positive to positive and negative to negative? How will i know if the battery is fully charged? Actually I’m using this to power my brushless motor my rc plane.

    Expect more questions from because I want to learn more about electronics.

    Thank you in advance sir

    • Thanks Jakecorn,

      I am assuming the cells are connected in parallel inside the pack, in that case you can connect your charger directly with the parallel connection, however for a 11.1 V battery, the charging input must be 12.6V.

      Therefore make sure your charger output is set at this voltage level.

      If your charger is not equipped with an automatic cut-off then you must keep the input fixed at 12.5V, instead of 12.6V, this will ensure that your batteries are never able to reach an overcharge situation.

      Once the battery pack reaches the 12.5V mark you can assume them to be almost full charged and remove them from the charger

      • Thank you for the reply sir. may I know how you come up with 12.6v value?
        Did you mean sir if I will supply 12.5v or less to my 11.1v battery wont harm my battery regardless of how long I will charge my battery?
        If I will supply a fix 12.5v to my 11.1v battery, how long it will take to reach the maximum voltage of the battery?
        In choosing the charger for this battery do I need to consider the mah of the battery?

        Thank you so sir.

        • Jake, for a 3.7V cell the maximum charging limit is 4.2V, so with this proportion a 11.1V battery must have a charging limit of 12.6V.

          yes if you control the voltage below this maximum limit then you can keep it connected infinitely without the fear of getting it overcharged, however it is not recommended, because a continuous chemical reaction may cause some deterioration to the cells in the long run.
          the current rating of the charger must be 50% of the battery Ah rating ideally

  6. Hello, excellent project, Thanks for sharing

    I can use this innovative solar charger, only to charge the battery acid 12 V / 700 Amp, with the C.I LM-324 tells me the battery status by adjusting the 4 outputs (A1, A2, A3, A4).

    A1 indicates 10.5 v (Unloaded), Red Led
    A2 indicates 12.5 v (Charged), Yellow Led
    A3 indicates 13.9 v (Optima Load), Green Led
    A4 indicates 14.2 v (Over Load), Red Led

    I have to change some component of the circuit, where I have to do the calculations?

    • Thank you… I am glad you liked it.
      By 12V/700amp do you mean a 700Ah batt or a 7Ah battery?, for 7 Ah battery you can use the same circuit which is explained above, for a 700 Ah, the specs will need to be changed significantly…please clarify on this…

        • Hi Andrew, for a 12V 7AH battery nothing will need to be modified, except the 1 ohm resistor which can be changed to a 0.66 ohm 1 watt resistor.

      • The TIP122 controls the excessive discharge of the battery and TIP127 ensures an instantaneous supply cut for the battery.
        What is the function of BC 547?

        • It is for controlling or limiting current to the battery, the 1 ohm resistor determines the amount of current that may be allowed to pass across the battery terminals (for a 7AH battery at 0.1C rate). If it tries to exceed the set value, BC547 is initiated gradually which in turn gradually switches OFF the LM317 and in this way current control feature is executed…

  7. Hi Sir
    Where should I modify the circuit for charging 12v 8Ah battery?
    And can I connect inverter to the load terminal?
    After the battery is fully charge will it take power from solar panel or battery?

    • Hi Kunal,

      replace the 1 ohm resistor with a 0.6 ohm 2 watt resistor, this will charge the 8 AH battery with the required 1 amp rate.

      For an inverter to run you may have to replace the TIP122 with a TIP35 along with a 2N2222 to make a Darlington pair, and connect the base of this pair with the top red LED cathode (by disconnecting the cathode from the ground).

      I would recommend to connect the inverter manually once the red LeD illuminates.

      • Thankyou sir!
        Is it compatable with 12V 100W solar panel?
        Basically this my project “Photovoltaic based irrigation system” in this we are taking power from solar panel of 12V 100W and by using charge controller we store that in battery from that we give that 12V DC to the inverter and after that the output 12V AC of inverter is given to transformer to step up it upto 230V AC and finally that 230V AC supply is given to our pump.
        So can you give me some suggestion for above stated model. Your suggestion will be very benificial for us. Thankyou!

        • Yes it will work with a 100 watt panel for your purpose. You can directly replace the LM317 with a LM338 for better current gain…make sure to use a heatsink for it. And in place of the TIP127 use TIP147, again use heatsink for it.

          However I think a 8Amp battery will not be able to drive a standard water pump, and could quickly get drained within 1 hour. You must use at least a 25 AH battery and a 200 watt inverter.

  8. hi sir,
    can i use this circuit to charge higher ratting batteries such as 180 amp.and also explain if i want to use LCD display instead of led.thanks

  9. sir , i can't understand anything from above comment…. please tell me what will be changed for 12v 7.2Amh battery… and what is the adapter means.. can i use there a 12-0-12 1amp transformer with bridge rectifier? pls send me all parts list, and also the solar plate ratting

    • nanigopal, you can build the circuit exactly as shown in the diagram…set the respective presets and pots as per the specifications of the battery….the solar panel can be a 18V, 1amp panel

      yes a 12-0-12 trafo with bridge and filter cap can be used for the adapter…..use the 0-12V tap…do not use the 12-12 taps

  10. Sir I tried this same circuit I don't know why its not functioning full load cutoff but deep discharge is working well…even my opamp output is high battery is still charging .suggest some idea for me sir. If there is any circuit to test tip 127 suggest me I wiwill try that too

    • Vijay, you said you had done some modifications, so i am confused whether you did you build it exactly as above or modified something in it?

      and what is "full load"? do you mean full charge?

      TIP127 will switch OFF only when battery voltage becomes equal to its emitter voltage

      and one more thing the TIP127 will rapidly switch ON/OFF at the threshold because there's no hysteresis control in the design.

      do one thing add a 1M resistor across pin14 and pin12…this will allow you to witness the TIP127 switch OFF for some moment clearly.

    • Vijay, you can use the same circuit for 12V also, just change the LM317 resistor for setting a 14.4V charging output for the 12v batt

  11. Thanks for your reply sir. I did a circuit with small modification on your above circuit. From LM 324 I have used only three opamps instead of using 4 opamp. I used the first opamp for deep discharge protection as u mentioned in your circuit. Next I use my second opamp only for full voltage indication I just connect the second opamp to ground through resistor and led so that I get full charge indication. In my third opamp I just invert the inverting and non inverting terminal of an opamp so that opamp produce high output at preset is low and it produce high when preset passes over the reference…. Output from the third opamp is given to tip122 transistor that I have used instead of tip 127 but I connect the tip 122 in negative polarity as same as low voltage cut off. Everything is working fine but full load cutoff by third opamp is not disconnecting the tip 122 which is used in the battery side battery is still charging.i am using 12vbattery. I know some basic concepts please help me sir

    • Vijay, connect an LED in series with the TIP122 base and see what response it's giving, this will clarify the situation regarding how the opamp may be switching the transistor….or regarding any other issues.

    • Sorry sir for making you to confuse. I am using tip 122 in full load cutoff at negative terminal. I connected a led series to the base of tip 122 from opamp output. When I adjust my preset opamp become high this make me to fell that opamp is working well. I noticed following points during the operation…

      At first when I switch off the input power supply led in a base of tip122 blinks only an opamp produce high output

      When I turned on my power supply the led is illuminating even my opamp produces an low output. What is the reason for this sir????

      • Vijay, when you say full load cut off do you mean to say "battery full charge cut-off"?

        an NPN will not work optimally if used in place of the TIP127….I assume you have connected the emitter towards the battery positive and the collector towards the LM317??

    • No sir I know the difference between tip 122 and tip 127.I connected my tip 122oon negative terminal the emitter of a tip 122 is in LM 317 side and a collector is in battery side… Sir in my circuit I use transformer(12v) with parallel capacitor instead of lm317 to get a constant voltage . please help me sjr I think it is only a minor fault in my circuit I can't able to identify it correctly…

      • Vijay, did you do any changes in the above diagram?

        If yes then you may have to provide me the drawing of it, only then I would be able to troubleshoot it.

    • Sir I shared the image with you on Google plus please spend sometime to see my image to find out the mistake that I did in the circuit

      • Vijay, I have seen it, it looks OK to me. actually a similar problem is happening with another circuit:


        I think the problem could be arising because the transformer negative is "more negative" than the battery negative, which is preventing the switch OFF of the left side TIP122 in your diagram.

        did you try connecting a zener with pin8?

        connect a 4.7V zener at pin8 and check the response….cathode will go to pin8

        and also connect a 1K between base and emitter of the left mosfet

    • OK sir I will try it in today..sir voltage across the capacitor near to transformer is 14.5v shall I use LM 317 to regulate the voltage to 12.8v. I have a doubt sir LM 317 can handle the current flows in 12v. 7.5ah battery??? Because LM 317 can handle up to 1amp maximum right???weather 7.5ah battery absorb more than one amp current at any situation???

    • Sit its not working do u have any idea to solve this problem?? I think using separate driver circuit for the operation of tip122 will solve this problem am I right sir??? If u have any driver circuit suggest me sir I will try it today

      • OK do it in this way:

        1) first swap the inputs of the opamp, meaning now (+) will go to the preset just like the other opamps.

        2) connect a BC547 with this opamp, base to opamp out via a 10k, collector to positive rail via a 10K, emitter TO THE NEGATIVE OF THE POWER SUPPLY NOT BATTERY.
        and base of TIP122 to the collector of this BC547

        this should do the job.

    • Sir.The circuit is working when I connect a led series with an opamp output that means anode is connected to opamp output and cathode of a led is connected to base of tip122.when my opamp output is low battery is not charging and it charging when my opamp output is high. My question how it works well by connecting a led to the base of tip122 .I didn't understand the operation but its work well sir…

      • Vijay, I had suggested the same LED idea initially but you said it wasn't working using a base LED…
        and then I advised a zener at the base for the very same reason and you said it didn't work either, so how come it's working now?

        The idea behind using an LED or zener buffer is to stop whatever biasing voltage the TIP122 might be receiving from the opamp while its output is in the switched OFF condition.

    • Yes sir this is your idea. I don't know why it didn't work on first time but it works very well sir. I am continuesly monitoring my battery voltage about 5hrs it never changed thanks you very much sir I can't do this successfully without your help sir.thank you very much sir I learned one new concept from you today….

    • Sir using led series to the opamp works well for improving my knowledge I have a doubt sir what I need to do next if led fails at this situation. Do u have any other suggestion to overcome this problem. If u know any concept share with me sir it will help me on future… Sir one more question… Shall I replace led with someother devices because led illuminating in this case I didn't need a illuminating if there is any other idea other than using led share with me sir otherwise I use a led in the circuit. Thanks for your support sir

      • you can try connecting a 1k preset between base and emitter of TP122 and adjust it until the transistor just switches OFF, (when opamp output is at zero volts)

  12. Sir if I didn't connect the 14th pin of opamp to ground. Weather the full load cut off will work????? Is its more important to connect them to a ground

    • Vijay, pin14 is not connected to ground, it is connected with the green LED. the ground is meant for the red LED illumination, if it's removed red LED will not respond…so it's not related to the opamp functioning..

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