Tuesday, April 10, 2012

How to Make a Solar Battery Charger Circuit

Solar panels are not new to us and today it's being employed extensively in all sectors. The main property of this device to convert solar energy to electrical energy has made it very popular and now it's being strongly considered as the future solution for all electrical power crisis or shortages.

Solar energy may be used directly for powering an electrical equipment or simply stored in an appropriate storage device for later use.
Normally there's only one efficient way of storing electrical power, and it's by using rechargeable batteries.
Rechargeable batteries are probably the best and the most efficient way of collecting or storing electrical energy for later usage.
The energy from a solar cell or a solar panel can also be effectively stored so that it can be used as per ones own preference, normally after the sun has set or when it's dark and when the stored power becomes much needed for operating the lights.
Though it might look quite simple, charging a battery from a solar panel is never easy, because of two reasons:
The voltage from a solar panel can vary hugely, depending upon the incident sun rays, and
The current also varies due to the same above reasons.
The above two reason can make the charging parameters of a typical rechargeable battery very unpredictable and dangerous.
But thanks to the modern highly versatile chips like the LM 338 and LM 317, which can handle the above situations very effectively, making the charging process of all rechargeable batteries through a solar panel very safe and desirable.
The circuit of a simple solar battery charger is shown below, using the IC LM338:


The circuit diagram shows a simple set up using the IC LM 338 which has been configured in its standard regulated power supply mode.
The specialty of the design is that it incorporates a current control feature also.
It means that, if the current tends to increase at the input, which might normally take place when the sun ray intensity increases proportionately, the voltage of the charger drops proportionately, pulling down the current back to the specified rating.
As we can see in the diagram, the collector/emitter of the  transistor BC547 is connected across the ADJ and the ground, it becomes responsible for initiating the current control actions.
As the input current rises, the battery starts drawing more current, this build up a voltage across R3 which is translated into a corresponding base drive for the transistor.
The transistor conducts and corrects the voltage via the C LM338, so that the current rate gets adjusted as per the safe requirements of the battery.

127 comments:

  1. Hi, Your blog is very cool. I'd like to contact you privately about a possible opportunity and can't seem to find a way to message you on this site. Do you have an email I could use or another way I can message you. Thanks!

    ReplyDelete
    Replies
    1. Hi,

      Thanks,
      Please contact me on this ID:

      hitman2008@live.in

      Regards.

      Delete
  2. Swagstram,
    Is the emmitter "floating", or is the solar panel negative not commoned with the battery negative. If they are commoned then the transistor will not do it's job.

    Regards

    Richard

    ReplyDelete
    Replies
    1. Richard,

      As shown in the figure the solar panel negative is connected with the negative of the circuit which includes the emitter of the transistor also.

      The battery negative is taken after the current sensing resistor so that the required over current is detected by the transistor.

      Regards

      Delete
  3. waht modification in the circuit is needed if i use lm317

    ReplyDelete
    Replies
    1. No modifications will be required, but the max current will be limited to 1Amp.

      Delete
  4. What happens when the battery is full? Thank you in advance for your help.

    ReplyDelete
    Replies
    1. The meter will show 0, the battery will then need to be disconnected manually.

      Delete
  5. Sir, if battery is not disconnected manually after full charge , whether battery becomes over charged or charging stops after full charge?
    Sir, as R3 =0.7/ charging current , how can i get some non standard value of resistors? Could i use variable resistors?

    ReplyDelete
    Replies
    1. Battery will get overcharged, you will have to remove it manually when the meter reads zero volts.

      You can adjust the value by adding a few resistors together in parallel or in series to reach the approximate value.

      Delete
  6. When the ammeter reads zero at the full charge of battery, then how it further charges to get over charged ? As the ampmeter reads zero means no current i.e. No charging am i right sir?

    ReplyDelete
    Replies
    1. The battery is not consuming any current because it's trying to obstruct the charging process, but the voltage from the charger is forcing the battery to get charged and therefore slowly after many hours the battery voltage will keep rising, crossing the danger mark and dangerous chemical reactions will start taking place inside the battery, reducing its life and efficiency.

      Delete
    2. Thank you sir, thanks for explaination

      Delete
  7. SIR, What happens if i charge 12 volt 3 ah lead acid battery by giving exact 13.7 volt dc through LM 317 continuously i.e. unattended for more than 2 days? Charging current is 0.3 amps
    1. Whether the 12 volt battery charges or not ?
    2. Whether the battery over charges i.e. Whether the battery voltage raises more than 13.7 volt ?
    3. Whether Charging stops after the battery will attain 13.7 volt ?

    ReplyDelete
    Replies
    1. 1) Battery will get charged within 14 hours.
      2)Battery will slowly get overcharged and its life will deteriorate. Battery voltage will not reach above 13.7V but harmful chemical reactions will start taking place inside the battery.
      3) Charging process will not stop and the battery plates will start getting damaged slowly.

      Delete
    2. Unless battery voltage will not reach above 13.7 volt, how the harm full chemical reaction starts to deteriorate the cell? Because normally 13.8 or above up to 14 volt is taken as full charge for 12 volt battery , under charging

      Delete
    3. If the current is not reduced after 14 hours of charging, harmful chemical reactions will start taking place at 13.8V, which is the fully charged condition of a 12V battry. 300mA rate means 1/10th of 3AH which can be dangerous after 14 or 16 hours of charging.

      You can read this article for further info:

      http://www.operatingtech.com/lib/pdf/A%20Guide%20to%20battery%20Charging.pdf

      Delete
  8. Sir, as the battery voltage does not reach above 13.7 ( as you replied), then no chance of harmfull reaction. Isn't it? Ok, if it starts in 13.7 itself, what happens if i decrease the charging voltage as , say 13.5 volt. And even charging current also i.e. Say 200 mili amps. I know the charging is very slow. My aim is to find out whether battery become over chargied or not , in certain charging voltage and current condition, even in absence of auto cut off. Give your opinion

    ReplyDelete
    Replies
    1. If you reduce the voltage, the battery will attain only 75% charge but yes the battery will not get over charged.

      The right process is to charge the battery with high current up to 14.4 volts then switch the charging to very low current and continue for another few hours and then shut off the power, in this way the battery will reach at least 90% of its capacity.

      Delete
  9. your all full of your self ...

    ReplyDelete
  10. i want a battery which provides me 12volts for my oder circuit wat changes do i do?

    ReplyDelete
  11. Hello Sir,

    Solar panel should be of how many watts and volts ?
    Please reply.

    Thank you.

    ReplyDelete
  12. Sir,

    Also please explain how to get the value of R3 easily.

    Thank you again.

    ReplyDelete
    Replies
    1. The charging Current should be 1/10th of the battery AH, now you can calculate yourself.

      Delete
  13. The open circuit voltage of the panel should be around 30v and the short circuit current must be rated at 5 amps.

    ReplyDelete
  14. O.K Sir,

    It means according to W=V*I, it should be 150W.

    Thank you.

    Best Regards.

    ReplyDelete
    Replies
    1. Yes you are approximately correct....

      Regards.

      Delete
  15. Question on component P1 - Looks Like a 2K Pot is this a voltage adjustment? Can you say more on P1 Watts etc...

    ReplyDelete
    Replies
    1. Yes P1 can be either a 2K pot or preset, any normal type will do, high wattage is not required.

      Delete
  16. A series diode at output is needed to avoid battery discharging or LM damage when no input voltage at regulator..the only thing that was missed here.

    ReplyDelete
  17. LM338 as in LM338K or LM338T?

    ReplyDelete
    Replies
    1. yes that's right, all will work here.....

      Delete
  18. Hello Sir,

    In most of the panels, the Open circuit voltage, Voltage at maximum power and voltage at rated load are given. But I want to know whether the panel voltage drops to 10 volts, 9 volts or below which, I think can not be used to charge a 12V battery.

    I want to know whether a circuit can be designed to upscale the voltage in that situation to charge the battery however with small current. Or, is the circuit you have given here capable to do that?

    Incorporating the feature in the charger circuit would be best to use the maximum possible energy produced from the panel.

    Regards

    Gyanendra
    Nepal.

    ReplyDelete
    Replies
    1. Hello Gyanendra,

      As far as I know, as the voltage drops, current also drops in solar panels with decreasing sunlight.....though there are ways to step up or boost the voltage using boost converter circuits, the current will decrease proportionately and will be adequate may be just for trickle charging purpose of the battery.

      Regards.

      Delete
  19. can i know the wattages of the resistors used plz.

    ReplyDelete
    Replies
    1. All are 1/4 watt, except R3/R4 which may be 1 watt or more

      Delete
  20. good day sir! i dnt understand R3=2R3. can you please explain sir. please. i have no idea. hope you understand. im carrem from the philippines.

    ReplyDelete
    Replies
    1. Good day Carrem, actually R4 is not required according to me. R3 is sufficient, however in the datasheet both these resistors are included so I have provided exactly what's given in the datasheet of the IC338.

      Delete
  21. thank you sir. more power.. god bless..

    ReplyDelete
  22. hi sir i want to clear one thing i am looking for this type of batter charging ckt but i need auto cut-off ckt for this can u help me. are any reference

    i want develop my self but i dont have any guidance i hope u can help me

    ReplyDelete
    Replies
    1. Hi Syed,

      Please check out the last circuit in the following article:

      http://homemadecircuitsandschematics.blogspot.in/2012/07/making-simple-smart-automatic-battery.html

      Delete
  23. Good evening Sir
    I'm trying out your circuit which was previously posted and that circuit resembled the same like the above but 'dint have a diode' at the pin out of LM338 to the battery negative? so what diode should I place here?
    Then Sir I'm using LM317 , so please tell how to preset adjust to 7v at output? Please help me as I'm doing my undergraduate project in 'construction of solar panel regulator'.
    Thank You Sir

    ReplyDelete
    Replies
    1. Hello Sasikala,

      The diode prevents the battery from getting discharged in the absence of voltage from the IC or from the solar panel, so it is a must.

      LM317 and LM338 are similar with their operations, for 317 also you would have to adjust the given preset P1 to get the required voltage at the output.

      Delete
  24. HERE USING SOME DIODE AND AND RESISTER WHICH I CAN'T DEFINE THE VALUE OF R1,R2 AND DIODE.......SO PLEASE TELL ME SIR....THANK YOU.

    ReplyDelete
    Replies
    1. The diode current value will depend on the specified charging current at the output, same for the values of the resistors, calculate it using the given formula.

      Delete
  25. Hello Sir,

    I am a bit confusing in selecting the right solar cell.
    I have a small 12v 18AH battery. Please tell me the specs of solar panels, like volts and watts.
    Also please give me the formula to calculate it with different ratings of batteries.

    Thank you so much.

    Rashid

    ReplyDelete
    Replies
    1. Hello Rashid,

      you may use any type of panel which is able to provide more than 14 V for 6 hours at 1/5th current of the battery AH.

      Delete
    2. Hello Sir,

      Really appreciate your help.

      Thank you.
      Rashid

      Delete
  26. THANK YOU SO MUCH SIR .. I got the output and as you have already said that using LM317 will limit the output to 1 Amp. How can I utilize this 1 Amp current Sir?

    I'm so happy the I have completed the circuit Sir. Thank you so much and all the conversations helped me gather information. Thank you users for giving your views... Thank you once again Sir.

    ReplyDelete
    Replies
    1. You are welcome sasikala!

      you may use it for any circuit application like for driving LEDs, for charging a battery etc.

      to be precise the IC will limit anything above 1.5amps, but you can set R3 for any desired current of your choice.

      Delete
  27. hello sir
    could u please mail me the complete operation of solar battery charging circuit
    mail id: ayyappareddy239@gmail.com

    ReplyDelete
    Replies
    1. Hello ayyappa,

      I have explained everything in the article, if you have specific questions you can ask them here.

      Delete
  28. sir i did this circuit and using for 100watts panel the voltage is regulated and output is ok but the LM338,TIP36 and all other components including resistors were getting too hot with in a minute. why? will this affect circuit components.

    ReplyDelete
    Replies
    1. which circuit are you referring to? show me the circuit diagram I'll check it.

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

      this charge regulator circuit.

      Delete
    3. what is the voltage from the solar panel, LM338 cannot handle more than 32V

      Delete
    4. what is the value of R3, the transistor or the IC will become hot only in case the current exceeds their limits.

      R3 must be dimensioned properly, make it 0.05 ohms/ 10 watts

      use two 0.1 ohms 5 watt in parallel

      R4 can be removed, short it with a wire link.

      Delete
  29. hello sir,

    can i use this cct for a small scale wind turbine which gives an output ranges from 5V to 15V?... i need to charge a battery using that. so please help me on this sir.

    ReplyDelete
    Replies
    1. hello Rizmy,

      you may use it to get a fixed maximum voltage output as per the setting of the preset, but you won't get any voltage boost from this circuit.

      Delete
  30. Sir,
    Then the maximum output will not be sufficient to charge a battery ryt... Then how to boost the voltage here sir?,

    ReplyDelete
    Replies
    1. For boosting the voltage upto the battery level you will require the following circuit, but the current from the turbine source should be strong otherwise the boosting will not take place.

      http://homemadecircuitsandschematics.blogspot.in/2013/03/how-to-convert-12v-dc-to-220v-ac-using.html

      Delete
  31. i want ask if i can use LM7812 instead of LM338

    ReplyDelete
  32. hi sir,
    how can i charge a 12v 130AH battery with solar plates can u show the circuit diagram

    ReplyDelete
    Replies
    1. hi jaguar,
      you will need a 200 watts 24V solar panel for this....do you have it?

      Delete
  33. sir,how can we increase the current at the output if the output voltage is 6.52 but in my case current is too low?

    ReplyDelete
    Replies
    1. current cannot be increased, it will be always equal or less than the input source.

      Delete
  34. is this circuit can be use to charge 4.7v mobile battery by using 12v solar plate? and how long will it take to charge my battery?

    ReplyDelete
    Replies
    1. yes it can be used, calculate R3 = 0.7/battery AH

      it will take about 1 and 1/2 hours to charge it fully.

      Delete
  35. What is the modifications in the circuit if i want to charge 24 v battery with 12 v of solar panel input.

    ReplyDelete
  36. sir,
    i want to charge a 12 volt 5 amp battery using this circiut in your blog..what would be the specification of the solar pannel..plz help.

    ReplyDelete
  37. sir,
    I have to drive robot which require 12 v,1.5 amp to operate .So,please help me to decide which solar panel and rechargeable battery i have to use.

    ReplyDelete
    Replies
    1. battery can be a 12V 7.5ah and the solar panel = 14v, 1amp

      Delete
  38. sir,
    I want to design a solar battery charger,all components should be SMD type and my aim is to reduce PCB size as much as possible...pls help me...

    ReplyDelete
    Replies
    1. Vipu, what specifications do you want for the solar charger circuit?

      Delete
    2. still we are not finalised,but mostly it wiil be 5V/6V battery charger....but i need a circuit for my reference,can u send me?....pleaseee

      Delete
    3. should it be automatic, or manual?

      Delete
    4. you can try the second circuit from the following link, except LM317 all other parts could be SMD

      http://homemadecircuitsandschematics.blogspot.in/2012/07/make-6v-4ah-automatic-battery-charger.html

      Delete
    5. hiii...
      I have 1 more doubt,how to connect a temperature sensor TMP100 with a CC2541 IC.Should i use I2C pin or any other digital I/O pin???? thanks

      Delete
    6. I'll have to do some research on it before suggesting.....

      Delete
  39. sir, what is the charging current of 12v 7Ah battery? what is the diode use in here?and what is the watt of resistor to be use?..thanks

    ReplyDelete
    Replies
    1. Erns, R4 is not needed, you can remove it.
      the ideal charging current of a 12V 7ah battery is around 1amp.
      the diode is for preventing accidental polarity reverse conditions at the input.

      Delete
  40. Sir me bhanu can u plese tell me how to calculate charging current easily....
    You have given a formula i.e 0.6/Charging current
    Can i use 0.6/ battery Ah or i will take 1/10th of battery Ah

    ReplyDelete
    Replies
    1. 0.6 should divided by 1/10th of battery AH.

      Delete
  41. Thanks sir i have assembled all the components except this resistor.... taking your suggestion i will progress the circuit and tell you about the output ....
    Sir do you have a of DC 12v to 18v or 24v DC converter circuit i am not not getting this in your site...can you please help me...once again thank u ...

    ReplyDelete
    Replies
    1. Bhanu, you can try the following converter circuit:

      http://homemadecircuitsandschematics.blogspot.in/2012/09/led-emergency-light-circuit-using-boost.html

      Delete
  42. hii sir,
    Is there any single chip IC for dust sensor and sound sensor??? If no please suggest me a simple circuit... thanks

    ReplyDelete
    Replies
    1. hi Vipu, sound can be sensed by a mic, I am not so sure about dust detection.

      Delete
  43. Sir, i have 70Ah 12volt battary and i'm about to buy 100Ah solar panel to charge it. there need to be solar charging system(circuit)? could i connect battary directlly from solar panel for charging? it will harmfull for battary?

    ReplyDelete
    Replies
    1. Dev, solar panel current is not rated with AH, its rated with amps....a controller can be avoided by selecting a correctly rated solar panel for the battery.

      for a 12V 70ah battery use a 18 V, 10amp solar panel....18v is the peak rating of the panel and 10amp is the short circuit current of the panel

      Delete
  44. have a good day sir!!!
    plz help me about my question that, is it possible to charge 12 volt 1.5A battery from 6 volt 250 mA solar panel?????

    ReplyDelete
    Replies
    1. good day Tejas,

      No that's not possible, the voltage should be minimum 14 V

      Delete
  45. thank you for your reply...
    but sir if i will place a boost converter in between solar panel and battery.....is it true??

    ReplyDelete
    Replies
    1. ....for that your solar panel supply should be rated to generate at least 1amp output, 250mA will not do.

      Delete
  46. ok... so according to you i should connect two 6 volt, 250 ma panels in series... then i will get 12volt 250ma.... am i true sir??

    ReplyDelete
    Replies
    1. yes that will do but the voltage will need to be at least 14V to initiate the charging....

      Delete
  47. actually i want to make charging my 24 volt 1.5 Ah battery to supply 24 volt, 600 mA STEPPER MOTOR.....
    is this possible from 12 volt 250 mA solar panel using 12-24 volt boost converter???

    ReplyDelete
    Replies
    1. No it won't, it's the same situation as previously explained...

      Delete
  48. Hi sir,
    I realised the circuit of this article but I can manage only the voltage at the output with the potentiometer, not the current. What could it be wrong? I didn't put the R4 and I switched the multimeter as ammeter and connected it in series the output of circuit with the battery.

    ReplyDelete
    Replies
    1. Hi Daniele

      R4 is not required anyway, so the current limit will still work for you depending upon the selection of R3

      Delete
    2. ...the pot is only for varying the voltage not current, current can be managed by altering R3 as explained in the article.

      Delete
    3. Thanks, I really appreciate your help, the circuit works, finally! ;) I have just one more question: there is any ways to evaluate the charging current? I have two batteries in parallel, one is 10Ah e another one 4.5Ah. The solar panel produce 1,7A and the R3 is 0.47ohm. I guess I made the correct calculation but I would check the real current that pass on the circuit. Any suggestions? Thanks in advance for any answer :)

      Delete
    4. Thanks Daniele,

      Usually it's AH/10 for lead acid batteries and AH/1 for Li-ion batts, but if you have two batts in parallel with different AH rating in that in case you may have incorporate separate current limiting circuits for each batts.

      You may have to make two of the above circuits, and calculate R3 separately in order to feed the respective batts...the ground will be common for both the circuits.

      Delete
  49. Hi sir
    I wanna ask if i can use this circuit to charge a 12v 40W lead acid battery ti powerup an LED lamp during the night. I'm planning to use this for a streetlight.

    ReplyDelete
    Replies
    1. Hi Nine, did you mean a 40 AH battery? Yes you can use the above circuit for charging a 40AH batt, make sure to put the IC LM338 on an adequately large heatsink

      Delete
  50. sir can you explain the role of each component in the circuit? i wanna understand how each of them function.. and how did you come up with the computation R3=0.7/chg. current? thank you so much sir!

    ReplyDelete
    Replies
    1. The upper resistors are as per the IC datasheet...the BC547 is responsible for grounding ADJ pin of the IC and disabling it when an over current is sensed, and this happens when the potential across R3 exceeds 0.7V which is the switch ON (saturation) voltage of the transistor

      Delete
  51. sir what is the maximum Ah that this circuit can handle? and can you teach me how to add an overcharge protection circuit to this one because i need the circuit to automatically stop the charging when battery is full.. thank you

    ReplyDelete
    Replies
    1. Nine, the LM338 IC used in the circuit can handle up to a 50 AH battery for charging.

      Delete
  52. correct me if I'm wrong sir, but you're assuming that the battery is rated @10 hr. I will be using a battery that will be rated @20 hr, so i can use a maximum of 100Ah because 100/20= 5A, which is the maximum output current of LM338..

    ReplyDelete
    Replies
    1. I don't know if a lead acid battery can be charged at AH/20 or C/20 rate, so I can't say much about this calculation...C/10 is considered as the minimum optimal range for charging lead acid batts.

      Delete
  53. ok sir i'll research more on that.. anyways can I use a 24V 50W panel to charge a 55Ah 22V battery, by the way the battery will supply a 12V 45W LED Lamp.. what's your opinion about this sir?

    ReplyDelete
    Replies
    1. Nine, you will require a minimum 125 watt panel for charging the specified battery....50 watt will not do it satisfactorily.

      Delete
  54. sir if that's the case, can I still use the above circuit? by the way it's 12V 55ah battery

    ReplyDelete
    Replies
    1. for a 12V battery a 50 watt panel can be used, but the panel peak voltage should not be above 15/16V for an optimal response,

      yes the above circuit will just fit in.

      Delete
  55. sir this is the current setup of the project..
    12V 50W solar panel to charge a 12V 40Ah lead acid battery, the load will be 12V 24W LED lamp
    what are your thoughts about these adjustments? and can the circuit above can charge a deep cycle battery? thank you so much sir for answering my questions

    ReplyDelete
    Replies
    1. yes a 12V 50 watt panel can be used for charging a 12V 40AH deep cycle battery, but will require around 10 hours to get fully charged.

      a 12V panel during peak should be producing 15 to 16V, so according to me you can connect it directly with the battery through a 6A4 diode...the above circuit may not be required.

      Delete
  56. for the current rating of the solar panel (12V 50W), what do you suggest I use sir? a 12V 40Ah lead acid battery or a deep cycle battery?

    note: the battery should be able to supply enough power to the LED lamp for the whole night (12 hours at most). thank you sir

    ReplyDelete
    Replies
    1. deep cycle batteries are also lead acid batteries, so you can use a 40AH lead acid battery for the said purpose.

      The mentioned 24W lamp can be operated for not more than 6/7 hours at stretch with a fully charged 40AH batt.

      Delete

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