In this article, we teach you how to design a simple Lead Acid Battery Charger circuit using an op-amp IC and some associated components. The core of this circuit is IC LM 317 – which is basically an operational amplifier IC. Apart from the IC, a transistor (BC 548) is used to control the charging current supplied to battery. You would need a properly designed DC power supply as a prerequisite to build this circuit.


Here is a lead acid battery charger circuit using IC LM 317.The IC here provides the correct charging voltage for the battery.A battery must be charged with 1/10 its Ah value.This charging circuit is designed based on this fact.The charging current for the battery is controlled by Q1 ,R1,R4 and R5. Potentiometer R5 can be used to set the charging current.As the battery gets charged the the current through R1 increases .This changes the conduction of Q1.Since collector of Q1 is connected to adjust pin of IC LM 317 the voltage at the output of of LM 317 increases.When battery is fully charged charger circuit reduces the charging current and this mode is called trickle charging mode.

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Battery Charger Circuit Diagram with Parts List.

Lead Acid Battery Charger
Lead Acid Battery Charger Circuit Diagram

Notes .

  • Connect a battery to the circuit in series with a ammeter.Now adjust R5 to get the required charging current. Charging current = (1/10)*Ah value of battery.
  • Input to the IC must be at least 18V for getting proper charging voltage at the output .Take a look at the data sheet of LM 317 for better understanding.
  • Fix LM317 with a heat sink.

We have more Battery Circuits that you may like to read and understand;Take a look:

1. Battery Monitor Circuit

2. Ni Cd Battery Charger Circuit

3. Simple Battery Charger

4. Battery Charger Using SCR

5. Battery Charging Indicator Circuit



  1. Suresh Ghorpade

    Dear Seetharaman,

    I am looking for the above charger circuit to charge 4V, 1.0 or 1.5AH lead acid battery. I have regulated output from 7805 which i can use for input to this LM317. Please suggest me the design for my requirement.


    • Vanessa Li

      We are a manufacturer of Lithium battery.Should you have any questions?Let me know.sales06 at

  2. Read this particular in 2nd semester of my degree course. Thanks for sharing.

  3. How to make a mobile charger testing circuit/machine in order to check voltage current and for any circuit problem or damage..? Please reply…

  4. Diodeman

    I’m interested, plz send me relevant details (cost, specs, etc) of this charger kit

  5. Sir can i use d same circuit for charging a 12 v 1.2 ah battery..can u sent me d ckt design via mail…

    • Vanessa Li

      We are a manufacturer of Lithium battery.Should you have any questions?Let me know.sales06 at

  6. Lorne Evans

    Can I use my ICP model 10008 (11-1582) solar panel (1 amp / 12 volt / 15 watt) as a continuous trickle charger for the deep cell batteries in my motor home while it’s stored over winter ? In Calgary we would get 5 or 6 hours direct sunlight during the winter months. Thanks, Lorne


    I will use this circuit to charge 3 X (12V, 16A Lead Acid Batteries) connected in series. I need the charger circuit urgently because the charger of my e-bike has got damaged and I need to charge the batteries.
    Please let me know the following things –
    1. What input voltage (dc) should I use with this circuit??
    2. Does this circuit has automatic over charge protection??

    Atonu Ghosh

    • Vanessa Li

      We are a manufacturer of Lithium battery.Should you have any questions?Let me know.sales06 at

  8. Hoa sen vàng

    Dear admin, it’s a circuit easily to follow, how to adjust POT r5 – 1k, and to its right with battery charger output. how you know it’s full without led indicator. thanks

  9. greetings! sir, for 6V 4.5 AH SLA Battery, what is the recommended charging voltage? is the circuit above also applicable to it? when should i charge my battery and stop it from charging. I am concern with undercharging and overcharging. i hope you can respond.

  10. hello. just wanna ask is it okay if i use other IC instead of LM317 in order to avoid using any heat sink? if i really need to use ic LM317, can u suggest any available heat sink for this ic?

  11. Seetharaman

    Hello you can use the 12X heat sink from ebay

    • I made the circuit without overcharge protection(I will made it after final testing of circuit).I want to know whether
      the R1 resistance is required of 5 watt. I have a 6 volt 5 ah sla battery which is showing 0.14 volt now . will it get recharged .

  12. jalal fares

    remember max amperage can be supplied by lm317 is 1.5

  13. jalal fares

    the current required can be calculated using this formula :
    R = ohm, I=amp

  14. jalal fares

    this charger circuit is not good for SLA battery! SLA battery need constant voltage charge, this circuit is good for Lead-acid batteries!!! R5 set the float
    voltage not the current!! current is limited by R1.

    • Seetharaman

      This is a constant voltage & current limited charger for SLA batteries. set max voltage (13.8 volts)with R5 and the max charge current (1.5A)is limited by R1.

      • jalal fares

        this circuit is not constant voltage! if the current exceed the set limit it will pulldown the voltage!!!! it will pull the adj pin to ground! sla nead 14.5~15.0 volts to be charged at 13.8 they will just float, not charged!!!! sorry…,

        • Seetharaman

          you cannot have infinite charging current the battery will blow. for charging yes if battery terminal voltage is low the charger voltage also will get reduced to that level and charge at the set limited current of 20% of the rated current of the battery. as the terminal voltage raises the reg voltage also will raise up to the max set voltage and afterwards the charging current will start reducing and finally to the level of top up current. This is the charging theory and practice. 13.8 volt is the limit for cycle use and 14.4 is for stand by use and 15.2 is for boost charge.

  15. please mail me, the detail working principle of this 12 v lead acid battry charger circuit.

  16. Did anyone built one for an 8v batterie? or would know what would be the change in resistance values to achieve it.


    • Seetharaman

      Hi you can use for 8volt lead acid dry fit batteries (SMF) adjust output voltage for 9.6 to 10 volt, with R5 pot. the charging current eill be 1.25 amps with the value of R1 shown. that is you can use this charger for charging battery up to 8volt 10AH rating.

  17. Did anyone have built one for 8v batteries or would have the specs for the resistance value for such.

  18. Hello Mr. seetharaman Thanks for your circuit where can i find the PCB layout could you mail me pls>>

    Thanks in advance

  19. Hello There,,

    Thanks for nice website,

    I have an engine generator with output voltage 80 Vdc power 1kW

    If I want to make Charger 72Vdc 50Ah Batery with my Generator , What do I need ?


    Best regards


  20. Do you have any Mobile Battery Charger circuit using solar energy.

  21. Hi Seetharaman,
    I am going to do a presentation about lead acid battery charger in one of my university courses, and your circuit really helps me, but i am not sure why you use BC 548, what direction of current flows around BC 548, and how does it works before and after battery fully charged.

    Thanks you very much !

    • Seetharaman

      Hi Chenwie a lead acid battery should be charged through constant voltage with the current limited 30% of the rated capacity of the battery or with limited 10% for 12 hours. Here LM317 with R3 R2 & R5 takes care of regulating the voltage to 14 volts. To limit the current to 10% of the capacity R1 Q1 R4 is used. Q1 will conduct once the drop across R1 is >0.65volts. That is 0.65 / 0.5 1.3 amps. 12volts 13AH battery can be charged with the above circuit.

  22. Srinivas.G

    Dear Sir,

    In continuation to my previous reply, my email id is, please email me the connections for showing the charging LED indicator which lights up during the charging mode.

    Thank you.

  23. Srinivas.G

    Dear Sir,

    I am bit confused about the charging LED indication, Can you Please email me the connections for showing the Charging LED indicator which lights up when in the charging is in progress.

    Thank you.

  24. Hi Seetharaman!

    Your circuit diagram is very useful to me.

    I have a 12V 5AH conventional (the one with cell caps where you may add distilled water) lead acid battery.

    Please bear with as I am not an engineer. If I may ask, can you provide me with a circuit diagram for a ‘rectified dc voltage in’? Kindly include parts and their values.

    Further, what is the minimum required transformer voltage and current to get at least 15V rectified DC and 1.5A maximum charging current?

    Furthermore, can you provide me with a pictorial diagram of your battery charger circuit diagram?

    Finally, do you have any updates on how to add LED indicators in this battery charger circuit diagram?

    Thank you very much and more power to you!

  25. Hi,
    I’ve built the above circuit but i see something very weird.
    the current thru the battery fluctuates.
    It starts at 0.3A rises to 1.4 approximately and drops down.

    may it be the battery is dead ant cannot be recharged or is it something else?

    • and finally it drops to 0.12-0.13 and stays there…

      • I played with it a little bit and what i got is this:
        when i set the output voltage to 13.8V (which is the charging voltage) the current thru the battery is 3.5A instead of the 1.6 i need.

        The simulation i ran (Pspice) shows a max of 2Amp when the battery is empty (0V).


  26. Hi
    can i use this circuit to charge 12v,26amh SLA batteries.
    I need to charge 2 batteries which is connected in series (in total 24v,26amh)
    if so how long it will take for full charge

  27. Hello Sir
    i want a circuit diagram for batteries connected in series to 110vdc each of the battery is 65amp that is 650amp
    the circuit diagram that can charge all the batteries at once. I have a step down of 220v/110v 3000W,I love practical

    From ABRAHAM

  28. Hello Sir
    i want a circuit diagram for batteries connected in series to 110vdc
    the circuit diagram that can charge all the batteries at once. I have a step down of 220v/110v 3000W,I love practical

    From ABRAHAM

  29. Seetharaman

    You can use 0.47 ensure that it is disc type. With LM317 with infinite heat sink it can deliver 1.5 Amps absolute maximum. For your charging requirement of 12 volt 44AH battery a charger of 14.2 volt 12Amps is the requirement. With flat battery it will start at 12 amps and it will start tapering of as the terminal voltage increases slowly. Normally 10 to 12 hrs will be the requirement for SLA batteries. They go by constant voltage charging with current limiting. R5 is or setting the max voltage output to 14.2 volt without connecting the load. Current is limited by Q1 and R1.

  30. Hi,
    Its not mentioned here but that’s a 12v battery charger, am I right?. I was wondering if it would work with a 14AH SLA battery, and approximately how much time will it take to charge the battery completely if I increase the charging current with R5 POT.

  31. gangadhar

    i cant get 0.22uf capacitor thus planning to use 0.47uf electrolytic capacitor what may be the effect?

  32. Hello Sir,
    I have a Well Understanding of Lead Acid Batteries charging after reading certain circuits over the internet.

    I have made a circuit to charge my 12V 44AH Lead Acid Battery.
    The Problem is that i have used LM317 ic to control the voltage to 14.7V (2.45 / cell ) but getting a Current more than 0.7 Amp ( Cheked with an Ammeter in series during charging )
    I want to get 5 Amp Atleast.

    Please note that i have made almost the same circuit but without the transistor in it. I mean without Q1,R4 and R1 in it.

    Please let me know Why transistor is used here and for what purpose,
    and what if we don’t put Transistor and it’s biasing resistors R1 and R4 in this circuit.

    Should i need to change the IC with more Ampere Rating Ic of 5A like LM338 or LM138..?
    Awaiting reply !

  33. Hi sir,
    I use 24v solar panel as input.
    how can i increase the charging current so that the charging time can reduce ?

  34. Seetharaman

    Hi Dipen 14 volt is the regulated output. unregulated input should be 18 volt atleast.

  35. thanks a lot! by 14.0 volts you mean send it to the ‘rectified dc voltage in right? and again thanks

  36. Seetharaman

    Hi Dipen Use a 14.0 volt regulated power supply with a maximum current limiting of 360mA.

  37. I have a 12v 1.2amp battery how much should i limit the current?please help!

  38. Seetharaman

    Hi Vikram what is the input DC voltage. it can be around 18volts. For LM317 you have to provide an extruded alloy big size heatsink. the power dissipated with a flat battery will be (18-10.7) X 1.0 = 7watts.

  39. Hi Seetharaman

    i connected my 12V/7Ah SLA battery across the ouput for charging, lm317 becomes so hot.

    Is this charger compatible with 12V 7AH battery?

    what is the max. charging time for 12V 7AH SLA battery?

  40. I want to make battery charger circuite 6amps for 100ah/24volts (2 batteries) kindly sugest the circuite & the proper parts with transformer capacity required. Sir plz help me

  41. vijay kumar

    i am having 1 KVA (36V DC input) online ups (they have recomented 75AH 12V battery 3 nos) iam using output 300watts, how can i calculate the backup time

  42. I pulled apart a 24V charger for an elec mower that wasn’t working. It used this same LM317 charger ciruit and for a charge indicator they simply cut the circuit at the transistor’s collector and joined it up again using a red LED.

    What follows are a few numbers to see how this might work. In these calcs the highest output voltage is the open circuit output voltage, which is set to 13.8V, and the lowest output voltage is the voltage of a flat battery, for which I’m using 12.4V.

    The LM317 works by keeping the voltage drop across R3 at 1.25V. For R3 = 120 this means that the current through R3 is always around 10.4mA.
    When the charger is not connected to a battery the voltage across R2+R5 = 13.8-1.25 = 12.55V. The current is 10.4mA so R2+R5 are going to be adjusted to about 1207 ohms.
    When the charger is connected to a flat battery the voltage across R2+R5 = 12.4-1.25 = 11.15V. 11.15v across 1207 ohms = 9.2ma.
    This gives 1.2mA as the max current going into the collector of Q1, which will only be this high at the start when you charge a 100% flat battery.

    This does mean that the indicator LED will turn off before the battery is fully charged. As you charge the battery the current limiting action of R1 will gradually reduce this current until Q1 (and the LED) is turned off when the circuit switches to from it’s current limiting mode to it’s constant voltage mode.

    A search on the element14 website for through-hole LEDs with forward current If=1mA comes up with one 2mcd, three 3mcd and one 10mcd LED!

  43. hi, you have done a good job with this circuit , but i want to know how to add LEDs to indicate normal charge and trickle charge state, and also add a dc voltage digital display…. thanks for your co-operation

  44. Seetharaman

    Hi Tasawar 3.5 amp @ 13.8volt is just correct.

  45. sir,
    what required of amp charging for 2 parallel 12v 7amp batteries?
    best is 1.5amp or 3.5amp for slow charging
    pls replay urg thanks.

  46. can this circuit is capable to charge sla battery 6 volts 4.5 ampares and how much rectified dc voltage in schematic

  47. Tej Savsani

    Sir,I Made a acid battery charjing circuit
    in this circuit we also charge more then 1 battery
    pleas help me….

  48. Seetharaman

    Hi Ganesh kindly read my comment on march 22nd for all your required details.

  49. Sir, kindly tell me the actual voltage i need to set as output by tuning the pot for a 12v 7.2ah battery? How to determine whether the battery is getting correctly charged also one more question what’s equation used for determining required voltage and ampere for charging my battery? Kindly answer to the 3 questions above..

  50. Sir, a small request. My relations are comes to my house due to DEBAVALI festival. So I cannot attend the two in one radio. After festival I will tell what is the fault of in it. Thanking Sir for your kind attention.

  51. seetharaman

    Hi Mani I have at home in India, I can send you by Jan 2012 end as I am away in the US. you may send a mail to me to that i will attach the scanned circuit diagram. if you can give me details of the problem i can suggest the remedies also.

  52. OK Sir, Thank you very much. And another one question Sir. May I ask you? I have a Sanyo Two in one. Model No. M1700AH It is given by my friend as a last attempt to me. Its cabinet is appear as a new one. But printed board was collapsed by many other mechanics. If I get its circuit diagram by you I will make it good condition approximately. Thank you Sir for your kind attention.

  53. seetharaman

    Hi Mani you can raise the voltage to 15.2 volt and try to charge. if it is conducting even small current leave it for few minutes if the current is raising the battery is getting activated leave it, will get charged. if no conduction at all the battery has lost its life you may trash it. Normally these batteries are properly maintained will work for 2 to 3years, if not they loose their life very fast may within a year also it can fail.

  54. I have two 12 volt 7.6 AH batteries. One of them is a new one. one year old. I recharge it for eight hours. But no charge is in it. What can I do Sir? Please answer me Sir? Thanking Sir.

  55. It is very very simple. I will try it very soon. Thanking Sir.

  56. seetharaman

    Hi AL It is for decoupling power supply against common impedance due to cable resistance.(as the power supply internal resistance will increase due to cable resistance)

  57. seetharaman

    Hi AL C1 & C2 are must to take care of length and gauge of wire used between power pack and charger.

  58. Got it,
    Also are you using C1 to screen the supply noises?
    If i have a very stable power supply do i still need it?

  59. seetharaman

    Hi Al it is to set minimum to maximum voltage in such a way the required voltage will be around center of the pot, such that the setting will be quite easy instead of setting the pot at extreme ends.

  60. Hi,
    I was wondering why do you need R2?
    why not use a bigger R5?


    if i need to charge a cellphone with 12v motorcycle batery, which circuit to do it? i need the right scheme, with auto “on” if plug is conected to the phone, an auto “off” if batery was fully charge with the indikator. thanks for help.

    i’m Sugiman, glad to know you all.

  62. Seetharaman

    Hi John you may already using a switching regulator for charging from solar panel. before the output there will be an isolating diode for the battery from the same point add another isolating diode and use for your other equipment.

  63. The quick and dirty:

    I am using a 17.6 volt .290mA solar panel to keep a 6vdc 4.5aH battery charged, while also providing power to a 6vdc device on the output side.

    Can I use a 7806 to regulate this voltage with a blocking diode on the input side???
    Or do you have another suggestion???

  64. Seetharaman

    Hi Yugan VRLA and SLA are same the same, hence charging rules are same. Please see my previous reply.

  65. Seetharaman

    Hi Naveed LA and SLA are having the same characteristic of constant voltage with initial charging current limited to 30% of the rated current of the battery.
    without battery set the output voltage to 6.9volt. use rectified DC input of 10 volts to 12 volts. no other modification is required.

  66. Lead Acid Battery Charger

    can this charger charge 6volts 4.5 ampare sla battery
    what is the changes in schematic

  67. Seetharaman

    Hi Dina you can add series pass transistors (3nos 2N2955) with LM317 and increase the current to 10Amps and also by reducing R1 to 0.06 ohms.

  68. hello Seetharaman, can I modify this circuit to give 13.5v/10A?
    If possible, kindly provide the solution.

  69. Seetharaman

    Hi Pritam R3,2 & 5 will take care of terminal voltage (not to exceed the safe limit – 115% of rated voltage) R1, R4 and Q1 to limit the maximum safe current for charging. The basic requirement of Lead Acid battery is constant voltage with current limitation to 30% of the rated AH capacity.(at this point charger will become constant current mode). The principle involved is initially charge through constant current and change over to constant voltage variable current mode.

  70. Pritam Shete

    what is the use transistor in this circuit? can please explain us working of this circuit?

  71. Please I need a help on the construction of a lead acid charger capable of charging up to 200AH. Its input supply should be 220vac while its output should be 12vdc. thanks.

  72. i hav built the ckt on board.. the output is around 16.5V.. how to reduce it to 13.5v

  73. Seetharaman

    Hi Srinivas you can make it into 4 groups of 75 each in series. That will be 150Volt @ 20mA per group. the requirement is 150Volt @ 80mA. you have to drop 80 volt at 80mA. you can calculate the capacitor etc, refer to our mains operated LED.
    If you want to use standard 12volt switched mode mains adapter, you can use 50 groups of 6nos in series, that will be 12volt at 1000mA. For protection use 2.2 ohms 1/2 watt, in series with every group of 5. 10nos of 2.2 ohms are required.

  74. p.srinivas

    sir, i want to make a board for 300 red leds and each led voltage is 2v so wich smps ican use for this board please send me massage as soon as possible, i can connect leds in series

  75. also can i build this circuit on a bread board

  76. hi… i’m gona build this circuit to charge my sealed lead acid battery.. will it support it.. thnx

  77. helo
    pls how can i build a 12V 30A regulator circuit with LM338k.Thanks. pls i hope to here you soon

  78. Seetharaman

    Hi Valetinas sorry for the typographical error the ic is LM338K and in T03 casing.


    Thanks, but i cant find LM388K. I found only LM338K TO3.

  80. Seetharaman

    Hi Valentinas you can use LM388K TO3 casing can be used for 5Amps rating. Ensure in-coming supply is capable of this current. Reduce R1 to 0.125 ohms 5watts or use 0.5 ohms 2watts 4 nos in parellel.


    Hello. If i change LM317(1.5A) with more powerfull LM338(5A)? Will it work and be able to give 5A?

  82. am still waiting for reply over my last post.hope to hear from you soon.
    thank you

  83. thank you for your respond,can you pls give me circuit diagram that will charger 12v 200ah deep cycle battery or inverter circuit diagram with charging system. thank you

  84. Seetharaman

    Hi Peter deep cucle batteries require initially 30% of rated current to charge a flat battery. that is 60amp is your requirement. and then 10 to 20 amp is requirement. it will not be possible by this circuit.

  85. can i charge 12v 200ah deep cycle battery with this charger.moreover how can i include battery level indicator

  86. Seetharaman

    Hi Turan Kindly go through my nov 4th comment

  87. Furkan Turan

    I have built that circuit but the output was lower than 12V. While testing there was no battery load, connected to the circuit.
    So I want to ask if connecting load results in accurate output.
    And I also want to ask that, you have said output is 12V. Is it needs to be higher than 12V to charge 12v battery.

  88. Seetharaman

    Hi John you can use for 6 volt battery also you reduce the value of R2 to zero ohms(shot R2). reduce the rectified DC input to 10volts. use a good heat sink for IC. you can charge upto 6volt 10 amp battery. flat battery only upto 6 v 7AH rating.

  89. john mark lacar

    can i use this circuit to a 6v lead acid battery?

  90. i am irani .i want one circuit lead acid battry charger with show voltage&corrent onthe lcd &with unconnect aotomative when charged full, i wait your ansver.thanks

  91. HI there, Im looking for a way to have reverse polarity protection in case of the battery being connected the wrong way and power being applied.
    Any thoghts on that?

  92. Seetharaman

    Hi Valentinas without any load switch on and adjust R5 for an output of required 14.8 volts (may be you are planning to boost charge). your battery is 1.3AH you cannot exceed 30% of 1.3 amps, that is 390mA. the value of R1 to be adjusted. that is 0.65 / required current, in this case 390mA. 0.65 / 0.390 ohms. That is 1.67 ohms not a standard value hence use 3nos 5 ohms in parallel. your charger is ready to charge a 12volt 1.3AH battery in boost charge mode.

  93. Valentinas

    Hello. I cant’t understand how to adjust charging voltage. I have 1.3Ah battery and charging voltage must be 14.4-15V. I want about 14.8 Volts. Do I need to change some resistor values or what? I still dont have that circuit because i want to know everything before i start building it. Thanks.
    P.S. sorry for my bad English

  94. Sir
    I want to make battery charger circuit for 180 AH / 12 volt battery kindly suggest the circuit and the parts with transformer capacity required.

  95. As anyone made progress on including LED indicators for this circuit? please i need assistance soonest

  96. Seetharaman

    Hi Sathish the same circuit can be used increase R5 to 2.5 K pot. Increase input supply to 30volts.

  97. helow, i m looking for a 24V battery charger circuit with LED indicator. can anybody help me on this???

  98. Seetharaman

    Hi Samy I will post the modifications soon. I am testing the improvement on my prototype.

  99. its still the same, maybe the battery needs a change. i want to include full charging and trickle charging indicators.where do i connect my LEDS please.

  100. Seetharaman

    Hi Sammy the rating is sufficient. with the present setting you charge for 3 hours and then advance the pot and try to achieve 1.3amps if it fails check the battery may be it is running out of life.

  101. Seetharaman

    Hi Mudu You can use this charger for lead acid batteries only. not for other types.

  102. can i use this circuit directly to charge nokia mobile battery?

  103. the transformer indicates a rating of 15V at 2A i.e 30VA. It sure meets the criteria or is they any need for change?

  104. Seetharaman

    Hi Sammy what is the rectified DC in is it atleast 5 volt greater than the load voltage at the rated current. That is the transformer must be rated atleast for 16volt at 1.5 amps (minimum 24VA rating)

  105. Thanks Seetharaman for your assistance so far. i just implemented the circuit on the breadboard. after setting the output voltage to 13.8V, the no load current read 1.13A for a while and then displayed 0A.Is this supposed to happen?on connecting a 12V SLA battery of 7AH in series with a multimeter, the current read no more than 150mA. the battery’s voltage before connection was 11.6V. I need a current of 0.7A. What am i to do?

  106. Seetharaman

    Hi Sammy both the transistors are smae with different casing, BC148 is lock fit type and BC548 is with long fly leads. 548 will be more suitable.
    Hi Mudu this is suitable for Lead Acid batteries only not for other types as they require different type of charging, with this you may damage your battery permenantly or shortening its life cycle.

  107. Seetharaman

    Hi Sammy without this transistor added. once the battery is flat and the IC output is 13.8 volt there is no current limitting in th circuit like series ressistancve between IC output and the battery, hence battery can draw current to the full current capacity of the incomming power supply / IC internal capability. to avoid such a situation this transistor is provided to limit the current output of the IC to around 1300mA.( once the current exceed 1.3A the drop across the resistance R1 the transistor will start conducting hence the IC output will fall down so no current flow can take place. Kindly add a 1N5404 diode between R3 and + output terminal to battery. this is required to avoid back flow current from battery to IC.

  108. hii,can i use this circuit directly to charge nokia mobile battery?

  109. Thanks Seetharaman. Am considering this circuit to be designed by you. My supervisor wants me to reference the source of the design am working with. My initial reference had “Admin” as the author’s name, is my conclusion that you are the author of the circut right? One more thing please, i can’t still comprehend the role of BC548 there. I’ll appreciate a little theoretical explanation more.

  110. Seetharaman

    Hi Sammy BC148 is the current limitter when the charging current reaches (0.65 / 0.5) 1.3amps LM317 will act as a contant current source. (Without this resistance R1 this action cannot be achieved)once the terminal voltage reaches 13.8 volts R5 will reduce the charging current to zero. Whenever the battery terminal voltage falls below 13.8volt IC will start topping up the battery till its terminal voltage reaches 13.8 volts.

  111. Nice circuit! can anyone please tell me how the transistor BC548 trickle charges the battery when full? again, what is R1 doing there? what’s wrong if i do without it? thanks

  112. Great info, but, can I use a 24v NIMH charger to charge 24 volt lead acid batterys. We were just given a used handicap scooter that has NIMH batterys (2 x 12v)and I would like to convert to lead acid.

  113. hye there anyone who can help to find out with my wind battery charger controller. i need a suitable circuit to my wind turbine project…

  114. seetharaman

    Hi Mounica no you have to use the above circuit as the lead acid battery requires constant voltage charging with current limitting.

  115. can i use directly computer SMPS to charge the lead acid batteries with out using above circuit

  116. seetharaman

    Hi Nurudeen no it is for to limit the maximum charging current to 1.2amps, if the battery is flat. the output set voltage pot will take care of limitting the voltage. this is the recommended mode of charging for lead acid batteries

  117. Thanks. will check the ic. Again, is Q1 is supposed to turn off the LM317 when battery is fully charged? And can you help me out with an led connection to show full gharge. Thanks again!

  118. seetharaman

    Hi Nurudeen check the pin connection of the ic LM317. i tried with 1K pot at extreme end, open circuit voltage is 15.4 volt and other extreme end voltage is at 5volts. short citcuit current is around 1.2 amps. check your connections or replace the ic, may be defective.

  119. Hi- Tested the circuit with a 30v 2A transformer, could not get a no load charging voltage greater than 12.8v till I changed R5 to 10k. But my charging current was 130ma. I need about 1.1A charging current for the battery. Pls help out!

  120. pls how do I calculate value of R1 to suit the battery I may have?

  121. Marissa Pickerill

    I do believe diferrent because my friends and family use another brand name.It’s pleasant and i love it’s very much.But next drill driver I am going to think of this as drill driver stuffs you present.Appreciate!!!

  122. Hi threadstarter,
    If i am using an input solar panel rated 45Watts [Voc = 18Volt & Isc = 3.45Ampere], what should be the changes in component values to your circuit and which type of battery [12volt xx?? Ah] should i purchase?

    regards, Pillow

  123. seetharaman

    Hi M7amad please send the ups details like for what voltage, for how many hours of use if there is a power break down.

  124. seetharaman

    Hi Martins use 20Amps charger per battery for 3 to 4 hrs to charge. At this charge rate do not charge for more than 5 hrs the battery will loose its usable life fast.

  125. Please help me design a charging system for two 12V/60AH lead acid batteries. please note the charging must be fast.

  126. seetharaman

    Hi Power you can use LM138. If you want to charge with 5amps current you have to reduce the value of R1 to 0.12 ohms 5 watt

  127. Hi, may I just change LM317 to LM138 for a 5A current for the battery charger? thanks

  128. seetharaman

    Hi yes it is a must, that will protect IC, against accidental polarity reversal of battery.

  129. kindly tell me how to construct a 12v lead acid battery charger,tools required,maintenance and how to connect it to the battery

  130. i want to know that using this battery charger circuit in order to charge a batter of 12 v, 7AH how will i know that the battery is fully?What changes i have to made in this circuit if i want to charge batteries of different current rating like 3amp hour or other?

  131. daniel ale

    kindlly send me the schematics of a 12volt, 14ampere battery charger, thanks


    i need circuit diagram of bosch GBM 13-2 drill machine.

    Thanks / Regards



    i need an idea to design a battery run emergency fan with a circuit n components list…
    thank u … :))


    hi … i need a 6v,4.5ah sealed lead acid battery charging circuit….
    thank u in advance… 🙂

  135. gangstastick

    hi, really interested in your circuit, but the problem is i would like for it to supply more than just the rated 1.5amps. someone mention putting a power transistor in parallel, could you clarify more on that? thanks in advance.

  136. Thank so much for the 12v charger circuit but how can i modify it for 24v or 36v purposes? Kindly help me out.

  137. Hello,

    Thanks for sharing this circuit…

    I want to charge a 6V / 7Ah battery with this, what modifications are necessary.

    Also can I put solar panels at the input to chage the battery ? or i will need to use solar charge controller before the input ?


  138. twits4twats

    mansoor says:
    November 5th, 2008 at 9:08 pm

    What is the charging current capability of this circuit?I want to charge @5Amp.

    A LM317 can handle a maximum of 1.5A. Although this circuit doesn’t show it, a power transistor can be wired in parallel to increase the current handling capacity. Google the datasheet.


    can you tell me that
    How to change a 12v battery charger into 24v battery charger?

  140. Electrocub

    Thanks for the nice circuit. How can I add LEDS to indicate full charge and and trickle charge. Thanks

  141. How can I change my UPS’ output (square wave) to sine wave. Is it possible to rectify or change square wave to sine wave?

  142. Hi Sreenivasulu,

    Sorry I messed up the question numbers.

    2. Designing a transformer is very tricky. Is it a single phase or a three phase transformer?

    Simple rule is, for 220V you have to wind 540 feet of wire on each bobbin if it is thick wire. But if it is thin wire it has to be 650 feet or more. Core size and iron quality are also important factors, the best is 4% silicon steel.

    Calculation of turns i.e. wire length, I don’t know.


  143. Hi Sreenivasulu,

    I am trying to answer your questions even if I am not a electrical guy, because it has been long time nobody answered your questions.

    1. V = CR or V = IR, very basic formula

    2. Watt = VI = R*I^2 = V^2/R
    In DC (direct current) capacitors are shown as open circuit i.e. infinite resistance. But in AC its resistance depends on the frequency.
    Resistance of a capacitor: R = 1/jwC,
    w = 2*pi*frequency

    3. I don’t know what T/R & SMPS are.


  144. Hi,

    Can this charger be used to charge sealed lead acid batteries?


  145. aregawi kidanemariam

    i need to design 1kv ups but i need 12 v with a high rating batteries then can it be appicable for charging the batteries effectively with by passing the Lm317 to increase the chargig current

  146. sreenivasulu

    I want to know about some basic formulas
    1.Relation between capacitence and power(watts) to design a transformer
    3.working action of a hi frequency T/R in SMPS

  147. Expandable Cordless Phone System

    Hey, Good post. I love anything to do with phones and technology etc, so posts like this prove interesting to me. Your site has been bookmarked. Thanks.

  148. hello dear
    i want to know something description and calculation such like that non average current of half wave rectifier for assignment,can you help me, any website?


  149. What is the charging current capability of this circuit?I want to charge @5Amp.

  150. i am trying to build a mobile phone charger, that includes a voltage sensor that cuts off the power to the charger when the battery is charged. i’m assuming the voltage drawn is significantly less when the battery is fully charged. i’m hoping that the voltage sensor can be adjusted to cut off power when this drop in voltage occurs. any advice would be greatly appreciated, especially if given in extremely simple terms as i’m only a beginner.

  151. If i use 9VDC as an input voltage will the circuit work to charge a 6VDC Battery?

    Thanks for the Schematic!

    Reply:This circuit is designed to charge a 12V battery.

  152. Dear authority,
    Firstly take thanks for helpfull web site and i see all of circuit and get help from your web sit. anyway, Arinze i request you to if you have any chanch to help me like Fire Alarm Control Panel cuircuit for 8Zone control panel circuit diagram with component list and details. It is very helpfull for me. I am weating for return mail please.

  153. Dear,
    Firstly take thanks for helpfull web site and i see all of circuit and get help from your web sit. anyway, Arinze i request you to if you have any chanch to help me like Fire Alarm Control Panel cuircuit for 8Zone control panel circuit diagram with component list and details. It is very helpfull for me. I am weating for return mail please.

  154. kindly give me an information on how to design or repair 18V Battery Charger.The is meant for Cordless Drilling Machine that am usings.
    Also,send my some power related web site,for me to know more about building of control panel for electric Motor (AC Motor).E.g Direct on Line Starter,Forward & Reversed Starters,etc

  155. Pot R5 should be used to set the no load output voltage to 13.8-14V. This sets the maximum charge voltage so the battery is not overcharged. Current limiting is determined purely by R1.

  156. arinze :
    i need tutorials on house installation ,house wirelings.

    house installation & house wirings is a very broad will take a long time to teach you from the basics.if you need any specific tutorial on the above said (like how to wire in a room ,trouble shooting or modifying a wiring etc) i can help you.comment here with your exact need.i will surely help you.

    thanks for the comment.