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Solar Inverter/Charger for Science Project

The following article explains a simple solar inverter circuit consisting of it's own battery charger and an automatic changeover relay system for switching the battery to the inverter in the absence of solar energy. The circuit was requested by Ms. Swati Ojha.

The Circuit Stages

The circuit mainly consists of two stages viz: a simple inverter, and the automatic relay changeover.

During day time for so long the sun light remains reasonably strong, the panel voltage is used for charging the battery and also for powering the inverter via the relay changeover contacts.

The automatic changeover circuit preset is set such that the associated relay trips OFF when the panel voltage falls below 13 volts.

The above action disconnects the solar panel from the inverter and connects the charged battery with the inverter so that the output loads continue to run using the battery power.

Simulation and Working:

Resistors R1, R2, R3, R4 along with T1, T2 and the transformer forms the inverter section. 12 volts applied across the center tap and the ground starts the inverter immediately, however here we do not connect the battery directly at these points, rather through a relay changeover stage.

The transistor T3 with the associated components and the relay forms the relay change over stage  The LDR is  kept outside the house or at a position where it can sense the day light.

The P1 preset is adjusted such that T3 just stops conducting and cuts off the relay in case the ambient light falls below a certain level, or simply when the voltage goes below 13 volts.

This obviously happens when the sun light becomes too weak and is no longer able to sustain the specified voltage levels.

However as long as sun light remains bright, the relay stays triggered, connecting the solar panel voltage directly to the inverter (transformer center tap) via the N/O contacts. Thus the inverter becomes usable through the solar panel during day time.

The solar panel is also simultaneously used for charging the battery via D2 during day time so that it charges up fully by the time it gets dusk.

The solar panel is selected such that it never generates more than 15 volts even at peak sun light levels.
The maximum power from this inverter will not be more than 60 watts.

A MOSFET  based solar inverter can be witnessed HERE

Parts List for the proposed solar inverter with charger circuit intended for science projects.

R1,R2 = 100 OHMS, 5 WATTS
R3, R4 = 15 OHMS, 5 WATTS
R5 = 10K
R6 = 0.1 OHMS 1 WATT
D1, D2 = 6A4
D3 = 1N4148
T3 = BC547
C1 = 100uF/25V

Need Help? Please leave a comment, I'll get back soon with a reply!


  1. Hello Swagatam,
    Can u give me the description of the solar panel that u use for this project in more detail please ?

  2. Hello eron,

    You can use a 18V/6amp solar panel for this application.

  3. im sorry again... My lecturer told me to made this project but I do not know much about the solar panel. So how much the rated max power for this solar panel?

  4. you can try a 15V 100watt panel for the above application.

  5. ok swagatatam...thanx again :)

  6. sir i need a solar mppt 5ams to 40ams charge controler circuit

  7. Dear sir,
    I want to know that what change should be there in above describe circuit if I take different ratting solar panel like 20 watt,40 watt,75 watt, 100 watt ,150 watt and 250 watt?
    please reply me and send these detail on my email account ,if possible.

  8. Dear Abhishek,

    It will depend on the load current and the max panel voltage rating, pls specify these two parameters.

  9. Namaskar Mr. Swagatam
    This is Ahmad
    I want to make an inverter of 500wats or more for my office, can please give me specification of Solar panel and other components to be used. Please help

  10. Hello Ahmad,

    Please provide the maximum load wattage and battery AH that you would be using, this is essential for the calculations.

  11. Dear Sir ,
    I am newbie about this , but i am realy interested ,
    About output from inverter , could it be made to be pure sine wave?

  12. Dear investasi, the above design is too basic, it cannot be made into a sine wave inverter.

  13. Hello Good sir,
    I'm an engineering student in the U.S. and i'm doing a final year research project on anything of my choice. I'm interested in anything solar so I came upon your design. I found a cheap solar panel online with the following specs:

    Dimensions (H x W x D) in mm: 284 x 350 x 17

    Weight in Kg: 1.38

    Cell Type: Poly

    Number of cells: 18 pcs

    Power max. (Pmax): 10 W

    Voltage max. 9.01 V

    Current max. (Imp): 1.11 A

    Open circuit voltage: 11.25 V

    Short circuit current: 1.36 A

    Module efficiency: 15.05%

    Maximum System Voltage: 600 V

    Do you think this would be a good fit for your circuit?
    Thanks in advance for your time.

  14. Hello Francois, I don't think a 9V battery would work with the shown inverter'll need a 12V battery and a minimum 18V solar panel for implementing the project with optimal results....

  15. I appreciate your prompt reply, and i found another one matching your suggestion

    5W waterproof epoxy solar panel W/ battery clip 12V battery charge


    Related power






    Short circuit current (Isc)


    Working current (Iop)


    Output Tolerance


    Temperature range

    -40℃to +80℃

    SLA Battery Voltage


    Dimensions (L x W x H)mm


    NET Weight (KG )


    Thanks for the help sir.

  16. the shown inverter will require at least a 10AH battery to produce a meaningful output, and a 10AH battery will require at least a 2amp charging current for getting charged within 5 hours (day time optimal range)

    so a minimum input of 2 x 12 = 24 wats will be required...your panel should be rated at around 18V, 36 watts, for getting proper results from the shown system.

  17. Related power 40W
    Open circuit voltage (Voc) 22.41V
    Max power voltage (Vpm) 17.9V
    Short circuit current (Isc) 2.48A
    Max power current (Ipm) 2.23A
    Output Tolerance ±3%
    Temperature range -40℃to +80℃

    I think this will do??

  18. Also what i understand from the article is that if I build the circuit (correctly), I should be able to power whatever device that uses a 12v battery, while at the same time at the other end of the circuit, recharge any 12v my understanding correct?

  19. Once I build the circuit, and connect everything, I'd like to test it on a small simple battery. Can you recommend anything? I looked up the 10AH batteries but they look too big and are for electric bicycles and whatnot.

  20. yes it is possible, but then that will demand a proportionately higher watt panel in order to allow an external load operation as well as the battery to be charged simultaneously from panel power

    you can power anything which is 12V rated but the total wattage must not exceed above 50% of the solar panel wattage.

    if you have a panel that's able to produce much higher voltage than the required load voltage in that case you can opt for a buck converter circuit.....otherwise it would be better to use a panel with lower voltage and higher current....for example a 15V 7amp panel etc

  21. don't build the entire thing together...first build and confirm the inverter stage separately...if it works as per the expectation then you can move ahead with the remaining integration.

    the inverter design can be learned below in greater details:

  22. Hallo sir iam looking for an invertor circuit capable to produce 300w

  23. hello mushi, please use the search box to find the one of your choice.....

  24. Hello Sir my name is Arun Yadav from india. Sir I want to know that there is two batteries discussed in the circuit one is beside the solar panel and one is at the transformer is both batteries are same? If not then how I will connect the battery with the transformer. And I have a transformer 0-9, 3-amps having two wires at primary side and two at output side will it work on the circuit?

  25. Arun, both are one and the connect the battery across the arrow signs shown at the top.

    0-9V will not work, it should e 9-0-9V...and preferably 5amp

  26. Hello sir I am again having a problem that is now I had used the transformer 9-0-9V and of 5amps but it is not working. The transformer is not damaged. In circuit 2 there are only transistors and resistors and could they convert the DC to ac. My all components are fixed correctly then after I am not getting the output power. Please Sir upload a video it will be thankful to please sir.

  27. Arun, Please make the inverter circuit separately first and confirm its working, once it's confirmed then you move on with the solar panel circuit integration

    you can refer to this article:

    this has been tested by me many times and it works wonderfully well but only if the transformer is of very good quality...low quality transformers with wrong winding configuration will produce inefficient and low outputs...and also the battery should be fully charged with 7AH capacity minimum.

  28. ...a good quality 9-0-9 5amp will weigh around 4kgs....

  29. Can you brief us how this circuit is changing DC to AC ?

  30. the details can be found here:

  31. Is D1 connected to NO part of the relay?And kindly elaborate the switching technique of the relay.

    Manish Kumar

  32. yes D1 is connected to N/O of the relay....the relay deactivates at N/C when there's no light on the LDR and towards N/O during daytime.

  33. After completing the circuit, it runs well with a battery but when it is connected with a solar panel the bulb(as load) connected just blinks once. Please help, what could be the possible reason ? Could you also help with the connection of potentiometer.

    Thank You.

  34. if you connect the solar pannel while the battery is also connected then there should be no flicker on the load...can't judge the fault precisely from here.

    check if the relay is clicking while you connect the solar, this could be causing the blink.

    for the pot, short the center and one of the outer leads, connect this to the negative line, and connect the other free lead with the R5

  35. hello sir, could u plz tell me the approx cost of this solar inverter project with the equipments u have mentioned, also is it neccessary to solder the ciruit connections and should we connect anything to the output circuit to know if the inverter circuit is working or not.

  36. Hello Rohit, it could be around Rs.600/- excluding the battery...

  37. hi sir im finding it difficult to find a proper transformer of ur given specifications is it ok if i try out a transformer with with a lesser current rating as im making just a small model i would also prefer to use a lower voltage battery for charging plz give ur opinion...

  38. Rohit, you can use a low current trafo, but since the output power is directly proportional to the transformer current and the input supply current....if these are low then the output watt will be also low and you will have to select the load as per these specs.

  39. Sir could u plz tell the function of the capacitor C1 in parallel with D3 in the relay change over ciruit

  40. It's for preventing or controlling relay chattering during twilight zones.

  41. Sir could u plz tell where to the circuit connections bcoz it did not fit on a breadboard im doing it as a small project also it would be of great help if u could post any picture of the assembled circuit

  42. Rohit, please make it stage wise, make the inverter first and test it with a battery and then attach the solar panel once the inverter is successfully built.

    the inverter details are provided here:

  43. sir pls give me the block diagram of the above circuit.

  44. Hi sir, can I use solar panel with these specification.
    Open ckt voltage_21.5V
    Maximum system voltage 600v

  45. Hi Prabhath, yes you can use the mentioned solar panel for this project...

  46. Hi sir, can I use solar panel with these specification.
    Output DC voltage: 18V, 1.5W .

    Output Current: 83mA ( depend on the power of sunlight ).

    Size: 11cm x 14cm x 0.2cm.

    Package Included:

    1 x 18V 1.5W 83mA Solar Panel

  47. Hi Idave, you can use it to charge a small battery only, but operating an inverter might not be possible...

  48. Hai.
    I want to make DC to AC with solar charger and AC power charger with control for output 220 volt 500 watts.Kindly help for the same

  49. Hi, there are plenty of inverter circuits presented in this website, you can select any one of them as per your preference and build it...if you have doubts you can ask them through comments

  50. sir can I modify a 240v to 240v avr trafo into 240v to 15v?

  51. if it has a 0-15V tap then you can...

  52. sir can i use only the solar side and add my inverter circiut to it
    and is there any chang that can be made to it to work with 24v battery and inverter lastly can i remove the LDR because it scarce in my side of the world
    thanks sir for your quick reply

  53. sir can i used this for a 24v battery if no what are the things i need to change to push it to 24v sir

  54. Abioye,
    the inverter cannot be used with a 24V supply, but you can replace it with a IC4047 based inverter circuit and use it in the similar way.
    make sure to supply the IC through a 7812 IC regulator


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