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.


Solar Inverter Charger Circuit for Science Project

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.


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88 comments

comments
November 23, 2012 at 6:15 PM delete

Hello Sir,

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

Thanks.
Regards.


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November 23, 2012 at 8:18 PM delete

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.

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November 26, 2012 at 5:51 PM delete

Thank you Sir,

I just over looked the diagram.

Take care.

Bye.

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November 28, 2012 at 1:57 PM delete

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

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November 28, 2012 at 3:14 PM delete

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

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Anonymous
December 6, 2012 at 10:59 AM delete

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

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December 6, 2012 at 12:08 PM delete

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.

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December 7, 2012 at 5:27 AM delete

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?

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December 7, 2012 at 3:48 PM delete

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

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December 7, 2012 at 3:49 PM delete

No change in the components would be required.

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December 7, 2012 at 9:02 PM delete

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

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Anonymous
December 11, 2012 at 8:24 PM delete

any substitude for 2n3055 ?

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Anonymous
December 26, 2012 at 5:30 AM delete

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 :)

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December 26, 2012 at 8:52 AM delete

Hello,

Merry Christmas to you!

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

Regards.

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January 7, 2013 at 5:23 PM delete

hi swagatam,

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

Regards
Sriram

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January 7, 2013 at 9:55 PM delete

Hi Sriram,

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

Regards.

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Anonymous
January 8, 2013 at 9:18 AM delete

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

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January 8, 2013 at 9:54 AM delete

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

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January 10, 2013 at 10:32 PM delete

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

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January 11, 2013 at 8:00 PM delete

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

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January 25, 2013 at 11:00 AM delete

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

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January 25, 2013 at 7:41 PM delete

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

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Anonymous
February 5, 2013 at 2:56 AM delete

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!

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February 5, 2013 at 9:56 AM delete

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

The center wire is connected with the relay contact.

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Anonymous
February 5, 2013 at 5:40 PM delete

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!

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February 5, 2013 at 9:05 PM delete

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.

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Anonymous
February 5, 2013 at 9:57 PM delete

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?

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February 6, 2013 at 10:45 AM delete

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

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Anonymous
February 20, 2013 at 8:59 AM delete

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?

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February 20, 2013 at 2:19 PM delete

4 = N/C

3 = N/O

2 = pole

1 and 5 = coil

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BEE
February 22, 2013 at 6:04 PM delete

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.

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Anonymous
March 8, 2013 at 7:30 AM delete

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?

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March 8, 2013 at 10:38 AM delete

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.

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April 12, 2013 at 7:32 PM delete

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

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April 13, 2013 at 9:13 AM delete

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.

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Anonymous
April 22, 2013 at 5:41 PM delete

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!

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April 23, 2013 at 7:55 AM delete

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.

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Anonymous
April 23, 2013 at 9:14 PM delete

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.

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April 24, 2013 at 10:30 AM delete

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.

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Anonymous
April 29, 2013 at 2:54 AM delete

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?

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April 29, 2013 at 9:23 PM delete

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.

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Anonymous
April 30, 2013 at 3:11 AM delete

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!

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April 30, 2013 at 2:00 PM delete

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.

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May 2, 2013 at 7:41 AM delete

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

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May 2, 2013 at 7:48 PM delete

Hi edalcor,

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

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May 12, 2013 at 7:44 AM delete

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.

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May 12, 2013 at 8:12 PM delete

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.

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July 18, 2013 at 2:39 PM delete

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

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July 19, 2013 at 12:08 PM delete

Hello eron,

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

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July 19, 2013 at 7:40 PM delete

okey Swagatam.. Thanx :) ~

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July 19, 2013 at 8:03 PM delete

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?

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July 20, 2013 at 11:31 AM delete

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

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July 20, 2013 at 7:39 PM delete

ok swagatatam...thanx again :)

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July 21, 2013 at 8:59 PM delete

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

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January 21, 2014 at 12:17 AM delete

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

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January 21, 2014 at 11:37 AM delete

Dear Abhishek,

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

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May 22, 2014 at 8:21 PM delete

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

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May 23, 2014 at 12:27 PM delete

Hello Ahmad,

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

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July 25, 2015 at 5:42 PM delete

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?

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July 26, 2015 at 9:52 AM delete

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

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September 5, 2015 at 10:04 PM delete

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.

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September 6, 2015 at 5:56 PM delete

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

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September 7, 2015 at 1:45 AM delete

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

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

Specification:


Related power

5W

Voc

18.2V

Vop

17.3V

Short circuit current (Isc)

0.29A

Working current (Iop)

0.27A

Output Tolerance

±3%

Temperature range

-40℃to +80℃

SLA Battery Voltage

12V

Dimensions (L x W x H)mm

200*210*3mm

NET Weight (KG )

0.25

Thanks for the help sir.

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September 7, 2015 at 10:17 AM delete

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.

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September 8, 2015 at 1:35 AM delete

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??

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September 8, 2015 at 1:56 AM delete

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 battery...is my understanding correct?

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September 8, 2015 at 3:44 AM delete

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.

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September 8, 2015 at 12:58 PM delete

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

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September 8, 2015 at 1:01 PM delete

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:

http://www.homemade-circuits.com/2012/02/how-to-make-simplest-inverter-circuit.html

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January 19, 2016 at 5:53 PM delete

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

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January 20, 2016 at 8:11 AM delete

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

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February 8, 2016 at 8:24 PM delete

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?

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February 9, 2016 at 8:24 AM delete

Arun, both are one and the same....so 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

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March 17, 2016 at 8:50 AM delete

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.

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March 17, 2016 at 12:30 PM delete

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:

http://www.homemade-circuits.com/2012/02/how-to-make-simplest-inverter-circuit.html

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.

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March 17, 2016 at 12:31 PM delete

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

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April 25, 2016 at 12:08 PM delete

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

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April 26, 2016 at 7:29 AM delete

the details can be found here:

http://www.homemade-circuits.com/2012/02/how-to-make-simplest-inverter-circuit.html

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May 2, 2016 at 5:20 PM delete

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

Regards
Manish Kumar

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May 3, 2016 at 8:21 AM delete

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.

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May 5, 2016 at 12:17 PM delete

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.

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May 5, 2016 at 4:06 PM delete

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

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