Friday, November 23, 2012

Solar Inverter/Charger Circuit 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 design:

The circuit mainly consists of two stages viz: the 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.



Circuit Description:

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

T1, T2 = 2N3055, MOUNTED ON SUITABLE HEATSINK

TRANSFORMER = 9-0-9V, 3 TO 10 AMPS

R5 = 10K

R6 = 0.1 OHMS 1 WATT

P1 = 100K PRESET LINEAR

D1, D2 = 6A4

D3 = 1N4148

T3 = BC547

C1 = 100uF/25V

RELAY = 9V, SPDT

LDR = ANY STANDARD TYPE

SOLAR PANEL = 17 VOLTS OPEN CIRCUIT, 5 AMPS SHORT CIRCUIT CURRENT.


63 comments:

  1. Hello Sir,

    Thanks for a nice project. Please explain how to
    connect battery more clearly.

    Thanks.
    Regards.


    ReplyDelete
    Replies
    1. Welcome Rashid,

      Battery should be connected to the shown points.

      For simplicity sake a low voltage cut off has not been included, so should be monitored using a suitable voltmeter.

      Delete
  2. Thank you Sir,

    I just over looked the diagram.

    Take care.

    Bye.

    ReplyDelete
  3. hello sir.. can you give me link of any porject which explains solar inverter using solar tracking system??

    ReplyDelete
    Replies
    1. Hello Udit,

      A solar tracker system is discussed here:

      http://homemadecircuitsandschematics.blogspot.in/2011/12/how-to-build-dual-solar-tracker-system.html

      And a solar inverter is given here, you can easily combine the two:

      http://homemadecircuitsandschematics.blogspot.in/2012/02/how-to-make-solar-inverter-circuit.html

      Delete
  4. Hello Sir,
    I am Marios and I have to say that your posts are really useful. I am experimenting with solar Cells and I find your information particularly useful.
    What I am wondering is what circuit designer have you used? I tried to simulate the circuit with LTspice but there is no relay component. I need to use the simulator because I am using a different solar panel and I need to consider other components' specifications and drag out safe working results and conditions.
    My solar panel has the following specifications:

    SOLAR PANEL, 1.2W
    Power Rating: 1.2W
    Power Voltage Max: 7.5V
    Current at P Max: 150mA
    Open Circuit Voltage: 10.3V
    Short Circuit Current: 160mA
    DC Power: 1.2W
    Nom Voltage: 6V
    Output Current Max: 0.15A
    Output Voltage Max: 8.4V

    Do you have any suggestions for which of the rest components need to change and what their value has to be?
    Also what is the purpose of the LDR? Isn't relay switch based entirely on the voltage reaching from the solar panel?
    I appreciate your help very much Sir!
    Ps. I don't want to transform the voltage to 230 V, I just want to convert it to a smooth AC

    ReplyDelete
    Replies
    1. Hello Marios,

      I do not depend on simulation softwares, I do it in my mind more efficiently.

      If you are planning to operate the above described circuit with your specified solar panel then I am afraid it will not work.

      Even if you are using the inverter without any load, it would require 12Volts for operating.

      Without the LDR the relay may remain switched on at voltages lower than 10V from the panel which won't operate the inverter properly, therefore the LDR is kept so that the relay can be forced to switch OFF below 12volts from panel. This operation will switch the inverter operation from panel to battery without interrupting the output AC to the conected loads.

      Delete
    2. Hello again Sir!
      What if I use two of these solar panels connected in series? Will that solve the problem and I can use the existing components with no change at all?

      Delete
    3. Yes it might solve the problem....as the voltage will then become around 15V

      Delete
    4. No change in the components would be required.

      Delete
    5. Ok Sir, thank you very much, I really appreciate your help!

      Delete
  5. any substitude for 2n3055 ?

    ReplyDelete
  6. Hello Sir,
    I am looking at your circuit and I am wondering what is the component that is connected in parallel with C1 and D3. Is that an inductor?
    And if yes what is it its purpose in the circuit and what should be its value?
    Thanks in advance! Merry Christmas by the way :)

    ReplyDelete
    Replies
    1. Hello,

      Merry Christmas to you!

      It's not an inductor it's the relay coil.

      Regards.

      Delete
  7. hi swagatam,

    could you please help me with 60watt smps based inverter circuit for commercial use.

    Regards
    Sriram

    ReplyDelete
    Replies
    1. Hi Sriram,

      I'll try to find a suitable circuit....

      Regards.

      Delete
  8. Hello Swagatam,
    What battery should be appropriate for this kind of circuit? And where is the Ah value based on?
    Kind Regards

    ReplyDelete
    Replies
    1. Any rechargeable type of battery can be used here, provided it's rated at 12V and above 7 AH

      Delete
  9. my name raju,
    i used 675w invertor or 150 ah battery, i cnvert my solar invertor 150w panel plese circut digram sir.......

    ReplyDelete
    Replies
    1. Raju, please refer the following circuit, you can use it to control and charge the battery via the solar panel.

      http://homemadecircuitsandschematics.blogspot.in/2012/11/high-current-transistor-tip36-datasheet.html

      Delete
  10. hello sir pls help me
    i want to make inverter from 12v 7ah baterry
    and i want to charge battery from solar pannel of this specification
    SOLAR PANEL, 10W
    Power Rating: 10W
    Power Voltage Max: 17.6V
    Current at P Max: .57A
    Open Circuit Voltage: 21V
    Short Circuit Current: .61A

    pls give me circuit diagram to built this controller

    ReplyDelete
    Replies
    1. Hello admin,

      you can try the first circuit from the following link:

      http://homemadecircuitsandschematics.blogspot.in/2012/02/how-to-make-solar-inverter-circuit.html

      Delete
  11. Hello Swagatam,
    I am looking at your diagram and I am looking at the wire connection that comes down from the relay to the middle of the transformer on the primary side (LHS). Is this a tap transformer? And if I don't want to use a tap transformer (because I cannot understand why, I am new to electronics:) where shall I connect this wire?
    Is it ok to connect it on the top side of the transformer? Will it still work fine?
    I really appreciate your help!

    ReplyDelete
    Replies
    1. The transformer is a center tap transformer, it has three wires 12V-0-12V.

      The center wire is connected with the relay contact.

      Delete
    2. Yes, but can I use a normal transformer with two wires as an input and two wires as the output?
      Actually what I want to do, is to use the AC waveform just as it is, in 12V without transforming it. That's why I need to find a place for the wire from the relay :) Can you tell me where shall I connect the wire from the relay in the case I don't want to use either a tap transformer or a transformer? Thanks Sir!

      Delete
    3. A three wire transformer is also a normal transformer.

      Most inverters and also the above will work with three wire transformer only....by the way what is your requirement? do you want a 12V oscillator circuit or an inverter?

      The voltage from the the panel is DC and not an AC.

      Delete
    4. I would like just to get the AC Power at the output as 12V AC, I don't want to step it up to 240 V.
      Besides that, I cannot find to buy a transformer with 3 wires in the primary side. I can only find step down transformers, from 240 V to 12-0-12 V which are not useful I think.
      Can you suggest me anything else to help me?

      Delete
    5. OK. it means you need only the oscillator part, you can try the following configuration:

      http://homemadecircuitsandschematics.blogspot.in/2011/12/how-to-understand-ic-4060-pin-outs.html

      Delete
  12. Hey Sir, I am George,
    I like the staff that you publish and I find them really useful!
    I bought all the electronic components to built this circuit and I have a question.
    According to the relay diagram in page 3 (terminal arrangement, bottom right side) of the datasheet here http://datasheet.seekic.com/PdfFile/G5S/G5SB_G5SB14DC12_G5SB14DC24VDC_G5SB1.pdf
    I cannot realize which pin correspond to the N/C pin on your diagram. I assume that the coil has no polarity.
    Can you please help me find it out? Is it pin no.3 or no.4 that corresponds to the N/C pin on your relay circuit?

    ReplyDelete
  13. HI SIR, AM ERIC AND I THINK YOU ARE DOING A GREAT JOB BY SHARING WHAT YOU KNOW WITH US.I HAVE BEEN WONDERING IF I COULD OPERATE THE INVERTER DIRECTLY FROM THE SOLAR PANEL WITHOUT BACK UP AND YOU HAVE JUST ANSWERED THAT THANK YOU.

    ReplyDelete
  14. Hello Swagatam,
    My name is Tom. Thank you for posting this. My question is:
    Does this circuit gives a constant smooth output of 240 V or the output will vary? Does the variation in solar cell Voltage (due to sun intensity) affects the output, or the circuit with the transistor fixes this problem?

    ReplyDelete
    Replies
    1. Hi Tom,

      This circuit is quite a crude one, so surely it will not produce accurate 220V at the output....the output will be dependent on the supply voltage from the panel, and will vary according to the sun light intensities.

      Delete
  15. Hello again sir. So if I add a 12V voltage regulator before the transformation part, will the voltage be smooth and of constant value?

    ReplyDelete
    Replies
    1. I don't think a voltage regulator would be required for such a basic design, it would be rather better to use a panel with voltage specs around 12V to 18V max, this would roughly produce 200v to 260V from the inverter, which should be manageable.

      Delete
    2. Hello again Sir. I really appreciate all your stuff you publish and all the hard work you do. And I really thank you for that!
      I had tried to built this circuit but it doesn't work for me. It appears to have 2 problems..

      1. It doesn't realise the solar panel input when there is light. I tried to vary the potentiometer but nothing happens. It stays triggered on the battery to supply the circuit with power.

      2. The inverter part doesn't work at all. Though there is a 12V supply from the battery, I can get no signal at the ends of the transformer. Can you help me fixing these two problems?
      Thanks in advance sir!

      Delete
    3. you will have to make and check the stages separately, then join them together.

      first check the inverter separately, with a 12V 7 ah battery.

      Next check the LDR circuit, the relay will only operate if the LDR resistance is at least 25% less than the P1 value in the presence of light.

      the inverter is a tested design and will start working immediately if everything's done correctly.

      Delete
    4. Ok, thank you! I will check them again.
      I will go through the inverter part. But can you give me any values of the voltage that I should get at the tree terminals of the transformer, before the scaling up? those at the Right hand side of the transformer as it is on the diagram. Because my transformer might be the problem.

      Delete
    5. The voltages at the tap is not important actually.

      The working condition will be indicated with a low buzzing sound inside the transformer and 220V at the output terminals.

      The transformer should be kind of bulky, weighing at least 3 to 5 kgs.

      Delete
    6. Hello again sir, as you said the inverter works fine! but the problem that I have with the changeover is still there. LDR doesn't seem to interact at all. I have change 3 different LDRs, with 3 different resistance ranges to light response, but there is no response from the relay itself. I can only manually adjust the relay changeover through the potentiometer. do you have any idea what may go wrong?

      Delete
    7. Hello, check the resistance value of the LDR at ambient light, it should be at least 25% to 50% less than the set resistance of the preset P1, and this should allow a base votage of 0.6V to develop at the base of the transistor, only then the relay will operate.

      Once activated the relay will deactivate only when it's sufficiently dark.

      Delete
    8. Hello Sir, thanks for the advice, I will check them tomorrow.
      Also I have two issues with the AC wave output of the transformer.
      With the battery feeding the inverter:
      When there is no load I get 510 volts peak-to-peak (255 V from axis to peak) but as soon as a load is connected the voltage drops to 400 V peak-to-peak. Is this normal?
      Also when there is no load the frequency is 37 Hz but when I connect the load it drops to 32 Hz? Shouldn't it be around 50 Hz in both cases?
      p.s. I get pretty much the same results when I connect a power supply to test it instead of the battery.
      Thanks once again Sir!

      Delete
    9. The load rating should be 30% less than the transformer wattage rating, otherwise the voltage will drop below the normal level proportionately.

      Frequency may be altered by adjusting one of the collector resistances of the inverter, try slightly reducing it or increasing it.

      Delete
  16. hi sir good day. i have a solar panel and here is the description:
    Rated Max Power: 10 Watts
    Voltage at Power Max: 17.5 Volts
    Current at Power Max: 0.57 Amps
    Short Circuit Current: 0.63 Amps
    my question is can i use this solar panel in this project?
    thank you

    ReplyDelete
    Replies
    1. Hi edalcor,

      yes it can be used but only for charging the battery, it cannot be used for driving the inverter simultaneously.

      Delete
    2. hi sir i have a question again. how long does it takes if i'm using a car battery rated (1SM MOTOLITE maybe you can help me how to identify the A/H rating because here in the Philippines if you buy a battery it will labeled 1SM,2SM,3SM,6SM,2D,AND 4D and please can you provide me the formula for computing how long will it last if i'm using 10 watts CFL before it will drain my battery? and,can this solar panel:Rated Max Power: 10 Watts
      Voltage at Power Max: 17.5 Volts
      Current at Power Max: 0.57 Amps
      Short Circuit Current: 0.63 Amps will be charged my battery for how long? thank you again sir for your kindly entertaining my questioned and i appreciate your reply.

      Delete
    3. Hi edalcor,

      In India the lead acid batteries are clearly given with AH ratings so I am not sure about your batteries, you can consult an auto electrician in your area regarding it.

      There's no specific formula for knowing the discharge rate because it depends on many factor which may be different for different batteries, like efficiency, age, condition etc.

      You can connect a voltmeter to monitor the level, when the voltage drops to 11.5V, then you can remove the connection and check the time how long it took to reach this level.

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

    ReplyDelete
    Replies
    1. Hello eron,

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

      Delete
  18. 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?

    ReplyDelete
    Replies
    1. you can try a 15V 100watt panel for the above application.

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

      Delete
  19. ok swagatatam...thanx again :)

    ReplyDelete
  20. 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.
    email-abhisekanand@sify.com

    ReplyDelete
    Replies
    1. Dear Abhishek,

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

      Delete
  21. 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

    ReplyDelete
    Replies
    1. Hello Ahmad,

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

      Delete

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Readers are advised to proceed with the construction of the presented circuits only after understanding the concepts from the core. Not adhering to this can lead to failures and frustrations.