May 20, 2014

6V Solar Battery Charger Circuit

In this post we discuss a simple 6V solar battery charger circuit with an automatic cut-off feature using 4 way LED indication, and an overcurrent protection. The system can be operated through a solar panel or via an AC/DC mans adapter unit. The idea was requested by Mr. Bhushan Trivedi.


The Request


Dear Swagatam,

Greetings, I trust you are well. 

I am Bhushan, and I am working on a hobby project currently. 

I am very impressed by the knowledge you share at your blog, and was hoping if you would like to guide me a bit with my project.  

My project is around charging a 6V 4.5 Ah sealed battery with grid and solar panel. This battery will supply power to led lights and a mobile phone charging point.


Actually, the battery will be kept in a box. and box will have two inputs for battery charging. These two inputs are solar (9V) and AC (230V) for charging the 6V Battery. 



There will not be any automatic switchover. Its like the user has an an option to either charge the battery from solar or grid. but both the input options shall be available. For example, if on a rainy day or for some reason the battery can't be charged from a solar panel, then grid charging should be done. So I am looking for an option of both the inputs to the battery. Nothing automatic here

The battery level indicator LED should indicate in red yellow and green on the battery level. Automatic battery cut off after voltage goes down certain limits to ensure long battery life.

I am attaching a short problem statement along this email for your reference. I am looking for a circuit for the arrangement shown in it. 

I am keen to hear from you on this

Kind Regards,


Bhushan






The Design

The required 6V solar battery charger circuit can be witnessed in the diagram presented below.

Referring to the diagram, the various stages may be understood with the help of the following points:

The IC LM317 which is a standard voltage regulator IC is configured to produce a fixed 7V output determined by the resistances 120 ohms and 560 ohms.

The BC547 transistor and its base 1 ohm resistor ensure that the charging current to the 6V/4.5AH battery never exceeds the optimal 500mA mark.

The output of the LM317 stage is directly connected with the 6V battery for the intended charging of the battery.

The input to this IC is selectable via a SPDT switch, either from the given solar panel or from an AC/DC adapter unit, depending whether the solar panel is producing sufficient voltage or not, which could be monitored through a voltmeter connected across the output pins of the LM317 IC.

 The four opamps from the IC LM324 which is a quad opamp in one package are wired up as voltage comparators and produce a visual indications for the various voltage levels at any instant, during the charging process or during the discharging process through the connected LEd panel or any other load.

All the inverting inputs of the opamps are clamped to a fixed reference of 3V through the relevant zener diode.

The non-inverting inputs of the opamps are individually attached to presets which are appropriately set to respond to the relevant voltage levels by making their outputs high sequentially.

The indications for the same could be monitored via the connected colored LEDs.

The yellow LED associated with A2 may be set for indicating the low voltage cut-off threshold. When this LED shuts off (white lights up), the transistor TIP122 is inhibited from conducting and cuts off the supply to the load, thereby ensuring that the battery is never allowed to discharge to dangerous unrecoverable limits.

A4 LED indicates the upper full charge level of the battery....this output could be fed to the base of the LM317 transistor in order to cut-off the charging voltage to the battery preventing overcharging (optional).

Please note that since the A2/A4 do not have hysteresis included could produce oscillations at the cut-off thresholds, which won't necessarily be an issue or affect the battery performance or life.


6V solar battery charger circuit with an automatic cut-off feature using 4 way LED indication,

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62 comments:

  1. good circuit diagram...thanks.........

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  2. is that p1 to p4 resistor?how to connect that one end with opam also with gnd?
    pls make me clear.
    thank u sir.

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    Replies
    1. those are presets, the center lead goes to opamp pins while the remaining two to positive and negative rails

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    2. thanks a lot sir...what are the voltage rating of the four LED???

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  3. P1-p2 how much watt is used...and R1-R2 also..

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  4. Replies
    1. all are standard 1/4 watt types,

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    2. Thank you so much....i wana battery monitering indicator for this ckt...and also auto discharge cut off is available ...for safe of battery

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    3. All these features are already included in the above design...

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    4. Sir,which type of p1-p4 resistor are used...? Is that resistor having 3 terminal???

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  5. P1 to P4 are which type resistor....they have three terminal...(is that resistor having 3 terminals)..

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    Replies
    1. those are called presets, or variable resistors

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  6. Hi.
    What is the procedure to set the appropriate values to p1-p4 presets?
    Thanks

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    Replies
    1. Hi, without the battery connected, you'll need to supply the relevant voltages from the lowest to the highest levels and go setting the p1 to p4 correspondingly, and confirm the same by looking at the respective LEDs getting illuminated.

      Please note that while you go on setting the subsequent preset, the previous LED will shut off and the one which is being adjusted will light up ....and so on.

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  7. Sir.I need a circuit that it should disconnect the battery when its fully discharged.I made the circuit that u posted with single opamp successfully but I need this additional application on the circuit.can u help me sir

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    Replies
    1. vijay, you can incorporate the last circuit from the following article for implementing it:

      http://www.homemade-circuits.com/2011/12/how-to-make-simple-low-battery-voltage.html

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  8. Thanks for your reply sir.The circuit u mentioned above is to autocutoff the battery when its fully charged.
    http://www.homemade-circuits.com/2012/07/make-6v-4ah-automatic-battery-charger.html?m=1


    I made the second circuit in a link successfully.thanks for the circuit.now I need a circuit that should turn off the load when the battery voltage is to low this will increase the lifetime of battery.please suggest any circuit sir.I need to complete my project soon.pls reply as soon as possible

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  9. Sir.shall I use this circuit for charging 48v.20ah battery

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    Replies
    1. yes you can use it, but the LM317 will not work, you may have to feed the input from a 50V source ...........and make sure the supply input to IC 324 is stepped down to around 12V

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  10. Sir can u post the circuit for 48v 20ah battery with same model like more led to indicate the voltage as same as the above circuit with constant voltage.overcharge protection and deep discharge prevention please help me sir I need this for my project please help me sir

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    Replies
    1. Vijay, you just have to replace the LM338 stage with a 50V source, that's all

      ...if i have time I'll try to draw it.

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  11. Please make it fast sir. I am waiting for your post sir.I want to complete my project with in this month sir.help me sir

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    Replies
    1. It is not so difficult, you can make the LM324 stage as shown in the above diagram, and remove the LM338 stage...and feed the voltage to the LM324 stage from a 50V DC source.

      just make sure you connect pin4 of the IC through a 10k resistor and connect a 12V zener across pin4 and ground...also connect a 22k resistor between the common terminal of the presets and the positive

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  12. Thanks for the sudden reply sir.I will try it

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  13. Sir please say how to use this circuit for 12v battery charging what all are the elements I need to change it sir. I am waiting for your reply sir

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  14. Say the resistor I need to use at lm317 stage sir to get 13v output to charge 12v battery

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    Replies
    1. Vijay, you don't have to change anything in the design, just replace R2 with a 10K pot, and adjust it to get 13V or 14V after the diode (without a battery connected)

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  15. Sir I tried I didn't get more than 12.3v even if I vary the pot please help me sir

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    Replies
    1. try connecting a 4k7 resistor in series with the pot, if still it doesn't work then you can be sure of the IC to be faulty or some other hidden fault in the assembly.

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  16. Sir. I did the above circuit with the help of rps easily but there is one problem in turning off of one particular LED 2.I have set 11.5v in rps by adjusting the pot I turned on the first led. Next I have set 12v in rps by adjusting the pot I turned on the second led now both LEDs are turned on. Next I have set 12.5v in rps by adjusting the pot third led is turned on now three LEDs are in on state. Finally I have set 13v in rps by adjusting the pot fourth LED also be turned on. Now all my LEDs are in on state. Sir the problem faced here is when I reduce the rps voltage to 12.8v one LED has been turned off. After that when a rps voltage reaches 12.4v the another led has been turned off. But now as per I did the next led should turn off at the voltage of 11.9v or 12v but the led is turned off at 9.8v. What is the reason behind this sir.please reply me if u don't understand it. I need your help sir

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    Replies
    1. Vijay, At a time ONLY ONE LED should glow, two LEDs can never glow together.

      because if any of the LEDs has two opamps with high outputs across it, then that LED can never glow due to the absence of a ground path (both sides high)

      with the first opamp output high, its LED glows because the upper subsequent opamp's output is low, but as soon the upper opamp's output becomes high, the first LED shuts off, and the second glows and the sequence continues.

      something could be wrong in your circuit or the IC is faulty

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    2. Sir. How it is possible. By using zener diode and transistor we have set the reference voltage to each comparator as same value in the range of 5v. Now each pot is directly connected to the 13v supply. Initially the pot is at maximum position that means that preset voltage is zero .when my rps voltage is at 11.5v by adjusting the pot of first led I have changed my preset voltage above the reference voltage due to this opamp output become high. Next I have set 12v in rps at this stage by adjusting the pot of second led the second opamp preset voltage goes above the reference voltage due to this second led also be turned on at this stage my first led also at turn on position sir. Because the first comparator preset voltage is high sir. As per your idea how the first led gets turn off sir???

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    3. Oh sir your right. I didn't connect the wire between two LEDs that's while all my LEDs are in turn on state. Am I right sir??. Now my question is what happen if I didn't connect the wire between two LEDs it works well sir but all my four LEDs are glow when the battery is full charged. Each led should turn off as per the decrease in battery voltage. Am I right sir

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    4. Sir even I didn't connect the wire between two LEDs it work well sir but my 2nd opamp in the ic lm324 is not a reliable one. When I set the ic preset at 12v. After that I turn off the supply and turned on again all other opamp are working perfectly but my second opamp is not working properly. What is the reason for that sir?? Please give me a suggestions sir I am awaiting for your next comment

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    5. Vijay, The opamp might be OK, either the LED or the preset could be faulty, or there could be a loose contact somewhere.

      It seems you have connected the LED ends to ground, this will make all the LEDs to glow one after the other together, not one at a time as suggested in the above article.

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  17. Yes sir. I connected them to a ground. OK sir I change the particular opamp pot and try again later. If I get a good or bad result I will share with you sir please help me if I get a bad result. Thank you very much sir for your support.

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  18. Connection of all led to a ground will affect the circuit operations sir?? I hope it will not affect it

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    Replies
    1. It will not affect the circuit....

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    2. Sir I did it successfully. Thanks for your support.

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  19. Hi Sir!
    i want to charge a 12v battery using this circuit, so can i use a fixed 13v voltage regulator instead of LM317 and a diode instead of TIP122..ill b waiting for your reply. Thank you!

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    Replies
    1. Hi Sarosh,

      you can use 14V fix supply instead of the 317 stage.

      if you don't want the automatic cut off feature then you can replace the TIP122 with a diode.

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    2. so R2 and the 120 ohm resistor remains the same??...and why are we using BC547?? cant we directly connect the solar panel to the battery??1

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    3. BC547 is positioned for limiting current to the battery at the required safe level...

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    4. Sir I have two 12v,1amp transformer. Can I able to use this two 12v 1 am transformer by connecting them into parallel as 12v 2 amp supply for charging my 12v 8ah battery

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    5. Vijay, you can do it by including two bridge rectifiers for the two trafos and then joining the outputs of the rectifiers together (positive with positive, and negative with negative)

      by the way 1 amp is sufficient for charging an 8ah battery

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  20. Hi Swagatam,
    I measured current from solar panel i have and see it to be 6V, 100 mA across panel terminals as per the specification of panel.
    But when i connect 2 AA 1.2V batteries (1000mah) in series with Panel, i see current drop to 85mA.
    When i connect 4 AA 1.2V batteries in series, i see current drop to 50mA.
    Why is this happening?

    Also how do i know if batteries are fully charged by solar panel?

    Regards,
    Nishanth

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    Replies
    1. Hi Nishanth, It's due to the internal resistance of the battery.....try brand new cells, and probably you will be able to witness more efficient results....by the way 85mA from a 100mA source quite OK.

      when the battery voltage reaches 2.86v across the series then you can assume them to be fully charged.

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    2. Hi Swagatam,
      But when i connect 4X1.2V batteries instead of 2X1.2V batteries, current drops from 85mA to 50mA. Is this Ok?

      Can you tell me how you arrived at 2.86V across batteries when fully charged?

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    3. Nishanth, I am not entirely sure, but it looks OK to me, just keep them on for 10 hours minimum.

      for a 12V batt the full charge level is supposed to be around 14.4V, so with that proportion I calculated it to be 2.86V for the two cells in series.

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    4. Hi Swagatam,
      I have LED light of 3.2V/350mA (1 Watt) which i am planning to power up with 3.6V, 2000mah battery.
      But i see that current flowing through LED with fully charged battery does not cross 180mA. When i change the battery to 4.8V, current increases to 260mA.
      What is the ideal voltage for battery so that constant current of 350mA flows through it for 5 hours and start dropping there after.
      Sorry for asking many basic questions. :)

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    5. Hi Nishanth, the ideal voltage should be exactly as specified for the LED, that is 3.5V.

      at 3.5V the current consumption should be around 300 to 350mA..provided the battery is able to deliver that much amount of current.

      check the voltage of your battery while its connected to the LED, I am sure it must be dropping significantly to around 3V.....if not then your LeD quality would be in question.

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    6. Hi Swagatham
      Have a query.
      I want to shutoff solar supply using TIP120, once battery is fully charged.
      I am using a micro controller which operates on same battery voltage which is a reference of ADC within micro controller.
      Microcontroller does not have bandgap or Fixed voltage reference.

      Can you suggest a way to detect VDD value itself by ADC which does not have reference voltage?

      Regards,
      Nishanth

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    7. Hi Kancharia, sorry I do not have any idea regarding this.

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  21. Hi swagatam
    Thank you for this amazing circuit. Please I want to use this circuit to charge my phone. It takes 5v 750mA from it charger. So,how can I set this circuit to give me 5v 750mA. And could you tell me how to include a battery full automatic cut off.thanks.

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    Replies
    1. Hi Ezekiel, use the given formula for calculating the "1 ohm" resistor value with regards to your 750mA specification....

      once the current is limited the 5v regulation may not be required...and the output can be connected directly with your phone.

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  22. Thank you sir for the quick response. Which formula are you taking about? Is it R=0.7/load current? Again, sir the panel I have is a 17.3v,6W panel. How do I use it for this circuit? Sir please help me out. The power problem in this part of the world is becoming unbearable.

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    Replies
    1. Yes the mentioned formula is the one which needs to be implemented.

      if your panel is 17V then you can use the same circuit that's shown and the pot can be used for adjusting the output as per the cellphone specs

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  23. Thank you sir, I will get back to you when i'm done with it.

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