• Register
  • Login
  • Here is an energy saving solar inverter battery charger. It harvests solar energy to replenish 12 volt inverter battery. It has auto cut off facility to stop charging when the battery attains full charge. The charger uses a 24 volt solar panel as input.

    The circuit uses a variable voltage regulator IC LM 317 to set the output voltage steady around 16 volts. Variable resistor VR controls the output voltage. When the solar panel generates current, D1 forward biases and Regulator IC gets input current. Its output voltage depends on the setting of VR and the output current is controlled by R1. This current passes through D2 and R3. When the output voltage is above (as set by VR) 16 volts, zener diode ZD2 conducts and gives stable 15 volts for charging.

    Charging current depends on R1 and R3. Around 250 to 300 mA current will be available for charging. Green LED indicates charging status. When the battery attains full voltage around 13 volts, Zener diode ZD1 conducts and T1 forward biases.

    This drains the output current from the regulator IC through T1 and charging process stops. When the battery voltage reduces below 12 volts, ZD1 turns off and battery charging starts again.

    Solar Inverter Battery Charger Circuit Schematic

    solar inverter battery charger

    Connect the circuit to the solar panel and measure the input voltage. Make sure that it is above 18 volts. Connect the circuit to the battery with correct polarity and adjust VR till LED lights. This indicates the conduction of ZD2 and output voltage. Use heat sinks for LM317 and TIP 122 to dissipate heat.

    Note : The same circuit can be modified for charging different types of batteries. The only modification required is the change of ZD1 and ZD2. Select ZD2 value for the required output voltage and ZD1 for cut off voltage level. For example for 6 volt battery, ZD1 should be 6.1 volts and ZD2 6.8 volt. For Mobile battery, ZD1 should be 4.7 volts and ZD2 5.1 volts. All the other components remain same.

    attentionThe author D Mohankumar is not an active member anymore. Please take into consideration that the presented information might not be correct.
    ask a question

    84 Responses to "12V Solar Inverter Battery Charger"

    1. Sivanand says: on April 21, 2010 at 7:58 am

      Battery charging thru linear route that too using solar power is height of stupidity !!! what a waste…

      • Dear Sivanad,

        With a bit of circuitry knowledge you would not make such a statement.

        Most switching regulator will not get efficiency better than 85%. And for what price? DC2DC IC, Coil, power FET.

        The majority of the charge wil take place around battery voltage of 14V with input of 18V (even less when current is high). The Linear efficiency is therefor about:

        14/18*100 ~ 77%

        This circuit also accomodate for over charge and cost fraction of a DC2DC.

        If you have an alternative please provide a Schematic to discuss.

        The circuit posted by D.Mohankumar is sufficient and simple.


      • I agree with sivanand, This is an 80′s circuitry and there are a lot of voltage doubler that would cost much less and being in the Solar energy field would not recommend Mohans design .. The basic of Solar panels is undergoing change with most manufacturers configuring the voltage to be around 15V and thereby increasing the current in the panels.

        voltage doubler pro types are available for a cost.

        Charging a 6V battery through a 18 V panel seems out of place and line

      • Sebastian,
        This is about physics. This is not a religion of Linear V. Switching. Clearly, switching is better in a larger scale. However, when the gap voltage between input voltage to output voltage is small the Switching regulator is in disadvantage. Also, the switching will need additional circuitry to deal with the battery V/I chart when battery voltage is increasing.

        It is about charging a 12 Volt battery with 18 Volts solar panel and NOT A 6 V. If you have a better solution then please post a schematic and lets discuss this. So show me the money!!

        It is about the best optimized (price, performance) circuit to charge a 12 v battery with 18V solar panel.


      • For someone who is not aware of Solar energy and uses non efficient solutions You would be receiving an OScar for sheer waste and living in stone age devices.

        We provide solutions at cost and do not provide free solutions.

        Maybe you need to visit maxim and Texas Instruments to learn of the Boost Chips .

      • Charles would you be willing to pay for solutions where we use efficient devices instead of the crude outdated solution you offer.

        Research and learn about Solar energy and know the basic instead of giving an OSCAr TO A NON EFFICIENT DEVICE

      • A. I did not offer any solution. I was outrage for you name calling for no reason the post by D. Mohankumar; my point is be nice! If you have real knowledge then challenge me; I love to be challenged on this field, so please address the points I raised.

        B. I defended the linear circuit based on the objectives; so read the material and the analysis.

        As I said before, if you have something better to offer then show it. Also, play nice the internet playground.

        Charles B.

      • Cameron says: on June 26, 2012 at 11:42 pm

        I know you have a better solution, why do always assume P=IE = free

      • capacitor 1 is absent…

        if there’s other option if the P122 is not available in our area?

        thank you.

    2. D Mohankumar D.Mohankumar says: on April 21, 2010 at 11:33 am

      This circuit was posted on request by a student for his project.Alternate methods are plenty but individual choice and ideas vary.

      • d mohankumaar can you help me on how can i get 3 dc outputs 16 19 21 volts with a input of a battery rated volts is 11.1 volts with 4.3 amperes and its has a 220 inputs also for ac

      • Dear MohanKumr,
        What modifications reqd if I want to charge a 12V , 7.5Ah battery ?


      • what are the use of TIP122 in this circuit

      • I have 600w inverter with 80ah battery.

        Can I connect 100w solar panel control

        unit out put to battery leads.

        Please provide 12v 4.5ah battery charger with ldr circuit for 12v 5w solar panel
        for led light

      • prabhavathi says: on June 21, 2012 at 12:00 pm

        sir we wanted to do this as our mini project.can we do this?

      • jeffreybernardo says: on July 20, 2013 at 2:57 pm

        sir can you design a ckt using a 20 watts solar panel with different voltage regulators? (5v, 17v, etc)

      • sally koundoul says: on November 24, 2013 at 2:13 am

        hi can i use an NPN transistor D42D3 since i do not have TIP122 chip or what other transistor can i use in the place of TIP122. Also i would like to know how can we tell when the battery is full is the green LED is going to turn OFF ?

      • trusharkadu says: on November 2, 2014 at 5:23 pm

        Hello Sir.
        I just wanted to know of what maximum capacity battery can be used with this circuit.

    3. Sivanand says: on April 21, 2010 at 11:56 am

      Solar based battery chargers employ shunt type regulators, so the battery gets max charge and thrz no power loss during boost charge phase…the shunt comes into effect only at full charge and thr r SMPS based buck regulators, which can be easily implemented as the linear circuit,,with less parts count & more efficient & costing less…Students projects should not be based on circuits designed in the 70′s.

      Moreover the circuit around transistor TIP 122 (costly part) is not. necessary as we all know a fully charged battery will not draw current from a constant voltage limited to (13.8 volts for a lead acid 12 v battery) ..the GREEN LED will light as soon as the battery is connected..ie it wont show the actual charging process…it should be connected across R3 thru a current limiting resistor.

      • i TOTALLY AGREE. In fact we have designed a circuit that boost solar panel voltage using a boost circuit converting 10.5V to 15.5 volts and further using 317. automatic switching through 9015 and IRF . The use of ZD ensures the voltage to the battery is never above 13.5v. Further the use of a coil the battery output to the LED light it lights up a chain of 5 led’s in a series upto 10 . So 50 led giving 250 Lumens and consuming less than 2W.

      • Hello
        Is your circuit for sale?
        I have 18V 150W PV panels and 120Ah batteries.
        I am testing many different charge controllers.
        Can your circuit be scaled up to high charge currents?
        Many thanks
        Manchester UK

      • rashid omar says: on May 10, 2012 at 10:31 pm

        yes its true this circuit doesent do what is design for waste of money … just like the other design circuit using lm317….6volts 4ah charger it does not work…. i change the ZD 6.8v to 13.8v…. toi charge my …. 12v battery… but still have that 7.20volt out put…..i tried this im really disappointed …. it wAS A waste of my money…. really …

      • sir, it is possible to connect 2 led indicators red and green? the green led for the charging status, once the battery is fully charged it will be close. and the red one is show it will have a voltage flow across the battery?
        help me please.
        thank you.

      • sssomnath474 says: on March 29, 2015 at 6:24 pm

        hello sir i want a circuit for charging 24 volt battery using solar panel can you please help me out?

      • Colin Mitchell Colin Mitchell says: on March 29, 2015 at 9:52 pm

        “J want a circuit for charging 24 volt battery using solar panel can you please help me out?”

        How much current?

        How many watts for the solar panel?

      • sssomnath474 says: on March 30, 2015 at 9:47 am

        energy rating for solar panels are currently unknown to me but it must be something that can run 24 volt dc brush less motor of 250 watts

    4. Dear Sivanand, i think u’r design for the above circuit will b much effective. Please send me the circuit diagram for the same concept.

    5. Dear Sivanand, i think u’r design for the above circuit will b much effective. Please send me the circuit diagram for the same concept.

    6. Hi Mr D.Mohankumar, i need a charge controller circuit for my solar powered garden light. Can you give me a charge controller circuit for to charge up a 12V battery please?
      Also can i use a solar charger circuit instead?

      Thank You

    7. great circuit sir

    8. Dear Mr D.Mohankumar and Sivanand,

      I need to design a solar battery charger for an academic project. The design should be simple and cheap.

      I was going to use this circuit, but after the recent comments on it, it is true that it can be improved.

      Could you please send me the design of this circuit, taking in consideration the comment of Mr Sivanand?

    9. I found this circuit, which charges 12V batteries, what do you think of this design? http://simpleelectronic.com/wp-content/uploads/2009/06/solar-charger-control.gif

    10. badejo emmanuel says: on April 4, 2011 at 3:40 pm

      pls i need 2kva inverer circuit diagram

    11. Kartik Joshi says: on April 5, 2011 at 2:12 pm

      What is the function o f Dc motor?

    12. Jose Vieira says: on June 9, 2011 at 8:07 pm

      Dear D. Mohankumar
      Please information: Can i replace LM317 by component LM7815 (78XX) in your project page.
      I am a great admirer of his schemes electronics (The Best), i live in Brazil, South America. Thank you for your attention.

      José Vieira

    13. Please Information:
      How to build a circuit to take charge in three (3) lithium batteries with total voltage of 11.1 V-DC (True TrustFire Protected 18650 3.7V 2400mAh Rechargeable Lithium Batteries) with solar panel (Kyocera KS10-10W) 12V?
      D. Mohankumar is one of the best of the Internet in electronic circuits. Thank you for your attention.

    14. radheshyam says: on July 14, 2011 at 7:12 am

      d.mohankumar i wanna design simple and cheap solar inverter battery please could u provide me information

    15. Kazi Faruk says: on August 12, 2011 at 11:37 pm

      Dear D. Mohankumar
      can i charge a 12V/120-150ah via this circuit design. Please help me.

    16. Dear Mr D.Mohankumar I need to design a solar battery charger for an academic project.
      The design should be simple and cheap.I was going to use this circuit, but after the recent comments on it, it is true that it can be improved.
      Could you please send me the design of this circuit, taking in consideration

    17. Mr D Mohan kumar… i need design a solar battery charger for project.until now I still have not got a suitable circuit. Could you please send me the design of this circuit.

    18. i have an idea..no need a circuit. just connect 9v battery directly for charge ur mobile..i did like this oly..

    19. Dear mohankumar,
      Am kaluya moses,
      I have just got to this website , it so interesting because i like electronics so much and I want to be every powerful person in electronics. But am requesting you to help me to design for a high current 10-20amps Automatic Battery charger for a 200AH circuit

    20. vidyasagar says: on January 29, 2012 at 8:56 am

      dear sir
      can you plz show a circuit using lm 324 for charging 12v battery with under over voltage cut off solar panel used here is 10watts

    21. Navpreet says: on March 22, 2012 at 1:25 pm

      dear all, i have two exide tubalar battery and microtech and locally made inverter. now i want to buy exide solar panels. i want all heavy load to work on it. please tell me what options i have?

    22. CN BALASUBRAMANYAM says: on April 6, 2012 at 7:46 am

      dear friends,
      i want to have a inverter battery with solary energy backup. Iam a new man with commerce backup.(perhaps i require more details). my requirements are 1 light and two fans only. Iam not happy with the present electric charging inverters. can any one guide me with details plus cost factor.

    23. what modification can i do to charge a 12v 200ah deep cycle battery.

      thank you

      • what modification can i do to charge a 12v 200ah deep cycle battery using inverter and not solar power. thank you

    24. Use a power transistor of the required current u want take the output of lm317 to on it and ofcourse donot forget to choose a base resistor u can parallel them to ur destination load

    25. yagnesh says: on May 13, 2012 at 1:25 pm

      Require constant 13.70 output voltage battery chrger with 10 Amp

    26. Presumably to charge a 100Ah battery i presume

    27. prabakaran.v says: on June 6, 2012 at 8:26 pm

      sir, it is possible to integrate a inductor in small silicon chip.in marget a 9 volt,1 amps cellphone battery avilible or not.can you give practical oscilltor circuit with 50MHZ frequency please please please please please please please please please please please please please…………….

    28. prabakaran.v says: on June 6, 2012 at 8:39 pm

      sir, while i am converting 10MHZ frequency into voltage i got 10 voltage(dc) with 10 picco amps current,how can i increase my current……….

    29. Allwin M.A. says: on July 4, 2012 at 8:11 pm

      I like to know the rating and cost of solar panel and battery used in this ckt.

    30. Dear Sir
      Please send me a solar battery charger circuit diagram.

    31. vediyappan says: on July 31, 2012 at 11:26 am

      sir, how to simplyfy solar charger ckt i want small size of inverter but maximum power please please please please please please please please please
      reply me sir

    32. Plz sir wat type of solar panel is require for dis project plz i nid better understanding of dis circuits plzzzzzzz

    33. I do not recommend this circuit to anyone as its inefficient and a waste but try the link above

    34. sir,we have selected solar inverter battery charger as our mini project.can you please suggest some references regarding this project.

    35. othman says: on May 16, 2013 at 8:36 pm

      Sir,Can you help me. this circuit I can use for 70-100Ah ?

    36. ganesh chettery says: on July 14, 2013 at 6:36 pm

      Dear, sir,
      I need such a circuit diagram of solar charge
      controller,for cut the charging current when battery
      get full charged with the help of relay.actully i want
      to use this circuit for high voltage(96v,180v,192v)can this circuit work for it.or you have another circuit
      diagram for this project.Plz.suggest me(plz..plz..help
      me sir)
      with best regards
      ganesh Nepal.

    37. Johan Wei says: on August 1, 2013 at 8:40 am

      Good day

      Im sending you this mail from South Africa

      I did find diagram’s on how to build a solar battery charger.
      I got a 220v , 21v double outlet charger .
      Can you assist me in the correct diagram to build a battery charger for solar battery’s of 600Amp/hour and more

    38. It all sounds very scary to me. Why not go for a ready made proven and tested solution? Or is it the challenge?

    39. rami sharif says: on October 22, 2013 at 9:32 am

      Hi how many Amps can charge this circuit and what is the maximum rating of battery AH can be used ?
      also what about charging time / Hr for the selected rating battery ?


    40. What is the value of that capacitor connected parallel to 15V Zener diode ?
      Someone please tell me.

    41. How can we modify the circuit above if we have only 16v to 18v as input? please help me.

    42. C3 value is absent.

    43. jishnuraj says: on June 24, 2014 at 5:43 pm

      I has a solar panel 12 v and 20 w . I want a charger circuit for charging 12 v 7ah battery. The circuit must include over charge protection and deep discharge protection. Can u make a circuit for me. Thanku

    44. This circuit DOES NOT WORK. The output voltage is 13.6v 13.6v will not charge a 12v battery.

    45. Cesar Alla says: on July 7, 2014 at 10:49 am

      I want power amp.circuit diagram for my sound system

    46. Vasilis says: on July 9, 2014 at 4:28 am

      I will not enter the dispute, on account of limited knowledge. What I need is a 12V DC-12V DC charger for low Ah lead-acid Pb battery. Altenatively another 12V (different) battery charger system would be acceptable. My application: My Pioneer car radio/CD player is difficult to adjust the sound parameters of. When I take my car for servicing the battery is usually disconnected and the sound settings on the radio are lost. I need a way to preserve settings and that would be another battery that remains connected to the radio power terminals. Besides, thius battery should be kept charged at all times, by the car alternator. Any suggestions? Thank you.

    47. Just buy a 1.2A-Hr battery and connect it to your car with a diode placed so the anode is connected to the positive of your battery. Now put a 100R across the diode.

      • Vasilis says: on July 9, 2014 at 4:57 am

        Thanks for your reply, Colin. This sort of battery is also my idea, but I feared that connecting it to an alternator intended to charge a much larger battery might destroy it. Is protecting it the reason for using 100 Ohm resistor?

    48. How can we modify the circuit above if we have 12.6v and 9800mah Li-Ion battery?
      Help me please.
      Thank you.

    49. The circuit above can be simplified to the solar panel with diode D1 connected directly to your battery.It will take many days to charge your battery.

      Just buy a 1.2A-Hr battery and connect it to your car with a diode placed so the anode is connected to the positive of your battery. Now put a 100R across the diode.

      should be:

      Just buy a 1.2A-Hr battery and connect it to your car with a diode placed so the cathode is connected to the positive of your battery. Now put a 100R ONE WATT RESISTOR in series with the diode and see how hot is gets by feeling it. Reduce the resistor to 47R or 22R until it gets very hot. This is an indication that the battery is charging at one watt and will take 15 hours to charge.

      Here is a very clever circuit to find the charging current, if you don’t have a multimeter.

      Connect a 22R 0.25 watt resistor in series with the battery and hold your finger on the resistor. The resistor will get very hot if 100mA or more is flowing.
      This resistor will indicate ONE WATT of energy is flowing into the battery, but we are using a 0.25 watt resistor to measure the heat as this represents “LOST ENERGY” and we want to keep the losses to a minimum.
      To get some idea of 0.25watt of heat, place a 560R 0.25watt resistor across the terminals of a battery.
      This is 250mW of heat and is your reference.

      A 1.2A-Hr 12 volt battery has 14 watts of energy and if you are charging at ONE WATT, it will take about 16 hours to fully charge the battery.

      This circuit can be used when charging a battery from your car, from a solar panel, a battery charger or a pulsed solar-charging circuit. It is also a SAFETY CIRCUIT as it will limit the current to 100mA. If the current is higher than 130mA, the resistor will hot and start to smell.

      Note: when the 22R is removed, the current flowing into the battery WILL INCREASE.
      The increase may be only 10% from some chargers, but can be as high as 100% OR MORE if the battery is connected to the cigarette lighter plug in your car.

    51. Good day.
      I want to know what’s the value for C1. Kind regards

    52. The circuit DOES NOT WORK. It does not matter what value you use.
      The circuit WILL NOT WORK.

    What do you think about this article? Leave a comment!

    You may add a picture too (related to electronics)