This lead acid battery charger circuit is designed in response to a request from Mr.Devdas .C. His requirement was a circuit to charge two 12V/7AH lead acid batteries in series.Anyway he did not mentioned the no of cells per  each 12V battery. The no of cells/battery is also an important parameter and here I designed the circuit assuming  each 12V battery containing 6 cells. When two batteries are connected in series, the voltage will add up and the current capacity remains same. So two 12V/7AH batteries connected in series can be considered as a 24V/7AH battery.

The circuit given here is a current limited lead acid battery charger built around the famous variable voltage regulator IC LM 317. The charging current depends on the value of resistor R2 and here it is set to be 700mA. Resistor R3 and POT R4 determines the charging voltage. Transformer T1 steps down the mains voltage and bridge D1 does the job of rectification. C1 is the filter capacitor. Diode D1 prevents the reverse flow of current from the battery when charger is switched OFF or when mains power is not available.

Circuit diagram.

24V lead acid battery charger circuit


  • Assemble the circuit on a good quality PCB.
  • T1 can be a 230V primary, 35V/3A secondary step down transformer.
  • If 3A Bridge is not available, make one using four 1N5003 diodes.
  • LM317 must be fitted with a heat sink.
  • R2 = 0.85 ohm  is not a standard value. You can obtain it by combining a 6.2 ohm and 1 ohm resistors in parallel.
  • F1 can be a 2A fuse.
  • To setup the charging voltage, power ON  the charger and hook up a voltmeter across the output terminals and adjust R4 to make the voltmeter read 28V. Now the charger is ready and you can connect the batteries.
  • This charger is specifically designed for two 12V/7AH/6 cell lead acid batteries  in series OR a  24V/7AH/12 cell lead acid battery.


  1. Sir,can u design circuit for indicator or energize the relay when battery is faulty/stolen .I use two 12V/150Ah lead acid batteries in series.My problem is i can’t separete the source from charger battery when i dismantel the battery,the relay selfholding because get supply from charger.I think i must use elctronic look like at panel suppression firefighting have indicator power supply DC trouble

    • Doug L.L

      According to what I see in the circuit in terms of a series circuit is that the polarity shown at the batteries are actually in parallel to the source voltage, not in series.

      Meaning that the positive side is connected to positive on the battery negative is connected to negative on battery, which results in making the battery into a load device not a storage device.

      That means the battery and your source voltage are going to be opposing one another .

      In series the battery would be connected from positive of the source to the negative of the battery and positive of the battery to negative of the source.

  2. Thayumanavan KS


    I want to charge 24v 26ah battery so pls give the circuit. Or tell the formula for which Ah battery how much ohms should the R2 resistor should have.

  3. Md Rubel Hossain

    Need a 24v 2.5ah charger circuit diagram with cutoff

  4. Hi The given charging circuit are tested circuit

  5. Aakash KS

    Hello Seetharaman,
    I am looking for charging circuit for 2nos of 4V 0.5Ah lead acid batteries connected in series . could you please publich a circuit for the same or you can provide the basic details like the voltage and current required for the same

  6. Hi i have 30vdc power suply,can i use this circuit to charge 24v lead acid btrs.
    Thank you a lot

  7. Sir i have a ups system which is back up by three 12v batteries (17Ah)connected in series. I want to construct a charger circuit for this by using transformer. Help me


    Hello sir, i have the input dc voltage ranging from 15V to 36V. But i have to charge the 24V Lead acid battery constantly What are the modification i have to do from this circuit?

  9. mohammed mohzin

    hi,I am trying to build a charger for a 24v(two,12v 100Ah batteries connected in series). Each 12v battery consists of 6 cells. I have been trying hard with various configurations and failed in getting a proper design. Kindly suggest me a circuit to build a charger of the above mentioned characteristics.

  10. Shashant Vijay

    Sir, I need to make a 24 Volt (6v X 4) 1.5 Ah charger, what necessary changes is required?

  11. Sudip Dhara

    Can anyone please explain the working of transistor in this circuit? Thanks in advance!

  12. Mohd Arif Khan

    Sir, nice to study your guidance. I just want to confirm, It will auto cutoff after complete charging of battery & start after discharge..Thanks in advance & appreciate your reply

  13. Sir,
    i am having 12V 7Ah Exide SMF Battery i need charger for it so please suggest me how may amp Charger its require for better performance, and make me available for details for solar charger for same.

  14. sir, please suggest me a circuit for charging 12v,15ah lead acid battery..

  15. I Have 36 volt 10 AH lithium battery, can I modif 24V lead acid battery charger circuit, to charger my 36 volt lithium battery?

  16. kalaiselvan

    Hi Seetharaman,

    Thanks for the above circuit for charging 24V,7Ah lead-acid batteries.
    You have suggested that for 48V, 7AH battery we have to make two of the above circuit.
    My requirements is to charge 48V 7AH (4 nos of serially connected 12V,7AH )
    batteries with charge and dry indication,in a single circuit. I hope you can help reg this.

  17. Hi I am Manic new to the designing part …. I need to charge my lead acid battery in series of 24v…it this circuit is enough or still i need some more modification in it…but i need to use SMPS for input supply please give the regarding information

  18. Hello engr,in this your design.can i use it to charge two 12V,26AH lead acid battery connected in series?.if no,what is the implication? thanks

    • seetharaman

      Two 12 volts batteries of similar type and conditions can be charged up to a maximum of 7 AH only. As per your requirement of 26 AH a power pack capable of maximum current limit of 7 amps (9 amps preferred) is required.

    • seetharaman

      Hi joe Two 12 volts batteries of similar type and conditions can be charged up to a maximum of 7 AH only. As per your requirement of 26 AH a power pack capable of maximum current limit of 7 amps (9 amps preferred) is required.

  19. Hello engr,in this your design.can i use it to charge two 12V,26AH lead acid battery connected in series.if no,what will be the implication? thanks

  20. Hello would you be kind enough to publish a 48v 5 to 10 amp lead acid battery charger circuit ? along with full charge indicator if possible. I need it for my project.
    thanks in advance !

  21. sir can please give me the design for 24 v lead acid battery charging circuit

    • Seetharaman

      This charger can be used for single 24 volt 7 AH battery or 2nos 12 volts 7AH batteries in series.

  22. Good day sir,
    May you please help me with an inductive charging circuit diagram to charge 12v,7a/h lead acid battery.
    Your help will highly appreciated


    Good day. Pls I need your urgent assistance in responding to these questions to enable me modify this circuit to do something else. (1) Pls analyze the function of the BC547 in the circuit (2) What is the output of the LM317 (3) what could be the effect on the charger if I use a bigger transformer that is used for welding machine? Pls your response is urgently needed. Thanks

  24. Thuy Tran

    Hi Sir,

    This circuit can charger for dry 24V/1.3Ah batteries?
    What parameter of components for this batteries?

    Thanks and best regards,

    • Seetharaman

      Hi Tran you can charge 24volt 1.3AH battery (hope dry means dry fit lead acid gel cell) also.

      • Thuy Tran

        Yes, that I mean.
        How can I addd a LED to recognize when charge batteries or discharger batteries?

        • Seetharaman

          For charge indication you can one more transistor across R2 similar to Q1 R! and connect the collector through 2.7 K ohms 1/4 resistance in series with an LED (may be green for charging)to bridge rectifier positive. But for battery discharged indication you have to use an opamp similar to 741 and with a zener you can use it as a comparator when battery terminal voltage falls below 10.8 volts to indicate through red led..

          • Seetharaman

            For 12 volt battery read it as 10.8 volt and for 24 volt battery it should be 21.6 volts.

          • Thuy Tran

            Thanks a lot.
            I am beginner in circuit designer. So could you send me a full diagram?

          • Please send us the same circuit but with red & green led indicators as explained.

  25. does it work with proper component sizing, on a 48V battery bank (sealed lead acid)?

  26. hola estoy precisando hacer algo asi pero para cargar 5 baterias de 12v 25amp conectadas en serie, seria como una bateria de 60v.
    serias tan amable de indicarme que tengo que cambiar o modificar ?
    y tambien me gustaria agregarle leds indicadores. muchas gracias

  27. Can i use a 18v 5w solar panel instead of the T1 to charge a ups 12v/7ah battery

  28. Maung PRU

    Thank you very much for the charger circuit, i would like to use this circuit for charging two lead acid (12v 150A X 2)battery, for inverter.

    what will be the changes for the 200 or 300 Ah battery charging?

    Thank you once again and regards

    Maung Pru

  29. Sir can i use this circuit to charge my 12v SLA battery?

  30. Sir can i use this circuit to charge my 12v lead acid battery?

  31. i have chosen 24v battery charger as my project . i would like you to give me a handsome description of it so that i can understand it well and present it more clinically . if u can tell me the working of each component
    and the whole circuit it would be a great help for me . plz reply on my email cz i got my valuable marks on it..

  32. hi friends
    How to make an Inverter of 1600 VA circuit diagram with neat specifications?

  33. Umer Chawla

    Can you please give any alternative of IN5003 diode and can I use 0.82 ohm resistor instead of 0.85 ohm.

    • Seetharaman

      You can use any in 1N500X series or any 3amps 100PIV rectifier diode. you can use 0.82 ohms which is a standard value available of the shelf.

  34. Umer Chawla

    Can you please give any alternative of IN5003 diode and can I use 0.82 ohm resistor instead of 0.85 ohm.

  35. Michael Yanni

    we need 48 lead acid battery Charger
    knowing it consists of 4 Sealed Batteries (12 V / 7Ah )
    can you help us with that !?

    • Seetharaman

      Hi Yanni you can use two of the above chargers, for each pair in series for charging.

  36. I want to use this charger to charge 2 lead acid battery 12v 2ah in series.
    How can i limit the current to 200ma?
    Changing the R2 to 3 ohms?

    Is it possible to add a led for fully charged?

  37. hi I want to make a circuit for charging of 2*12volt 40Ah batteries I can I use this circuit.
    please mention that what is the purpose of BC547 in this circuit.
    I have checked this circuit in Proteus & if I remove BC547 circuit still works/
    PLEASE send me a circuit having indication when batteries are fully charged.
    please reply me as soon as possible. THANKING you very much in anticipation

  38. HI,

    Sorry, I can’t quite follow how the resistor R2 provides 700mA, can you explain how the calculation is done please?


    • Seetharaman

      The PD across transistor Vbe required is 0.65 volt. Hence 0.65 / 0,85ohms is 700 mA appoximately

  39. I am looking to make an in-car charging system for an electric mobility scooter – it uses a 24v 10Ah battery. The charger that I have (for use indoors) charges at 28.5 volts 1.6 amps. I have two questions –

    1) can I substitute a 12v step-up DC-DC converter for the transformer and bridge rectifier section of your circuit to give me the DC input to the regulator, and what output voltage would the converter be required to supply?

    2) what if any of the components of the regulated charger section would need to be changed to provide the correct output current and voltage?

    many thanks!

  40. Talal Haj Najeeb

    Hi Mr. Seetharaman:
    I’m a big fan of your circuits,and I would like to ask about the possibility of modifying this circuit so we can control charging current (like a pot. instead of R2), also kindly to explain to me why should sealed lead acid charging voltage be 13.6 not 15 volts as it is the cycle voltage written on it, and why max current is 700 mah not 2 amps as written also.
    Thanks a lot

    • Seetharaman

      Hi Najeeb 13.6v is for normal cycle use charge voltage limitation. for boost charge 15.2 volt can be used. For rapid charge you can use 30% of the capacity of Lead Acid Batteries as the max current limit with 13.6 volt(for a fully exhausted battery not for partially discharged battery)but for a over night charge it is better to limit it to 10% of the rated capacity of the battery to avoid heating of the battery which will reduce it cycle life..

  41. hi
    i am looking for a circuit for converting 110vac to 4-20ma,please send me
    schematic of this circuit.and more,it can programmed by computer.
    the best regards
    thank you

  42. I want to make 24V 60A battery charger with regulator for 135W solar cell
    please help me

  43. Hi Sir, can I use NI-MH battery 9v 250 mAh battery or 1Ah? Pls reply.. Thanks Sir

  44. mohammad sajid

    very good .
    sir i have a battery charger 24 volt 50 ampere but it not automatic. if you have any circuit diagram which i connect it please send me .ill be very thank full to you.


    please can you help to build a solar charger capable to charger a 12v, 60AH Battery.with overcharge protector,

  46. hi sir as i have got to do miniproject to design an experiment for an apllication involving minimum of 1 digital and analog unit it .i am full too confused please help me

  47. novice 29

    Hi Seetharaman
    thanks a lot for this information and prompt reply. this is the circuit i was looking for my 24v SLA 14 AH battery . i will change R2 to .5 ohms.
    can i use 2n3904 transistor instead of BC547 ?

  48. novice 29

    can a 12V lead acid battery have 5 or 7 cells?
    will this charger switch off when battery fully charged ?

    • Seetharaman

      Hi it will have 6 cells of 2 volts each. as the charge voltage reaches end point, the battery will be tricle charged with low current to just top up the battery against self discharge.

  49. Hi.
    I’ve constructed this charger for a set of 2x12V/2Ah batteries changing R2 to 0.47 ohm. I tried to insert a second BC547 as suggested (base of 2nd BC547 to base of 1st and emitter to the other emitter and collector to a led and a 2.7K resistor to C1 positive) to indicate full charge with no luck whatsoever!
    Am I doing something wrong?

  50. thanks sir for this circuit. Pls can u send me the circuit diagram containing the charging indicator(green and red).pls send it to my email.

  51. 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

  52. Anshumaan Dey

    may i use 24V output tansformer????Pls reply soon

    • Seetharaman

      Hi Dey you can use if the transformer is good quality low loss type (may be a torroidal)if not the regulation will be poor, charging time will become longer and may not charge a flat battery
      Hi Gangadhar you can but ensure the output voltage is adjusted to 14.2 volts without load with pot R4.

  53. gangadhar sapkota

    is this possible to make 12v, 7AH SLA
    battery with rectified input of 18v via transformer and bridge…… using same circuit?

  54. Seetharaman

    Hi Gangadhar BC547 to limit the maximum charge current(limiting max current level) to 700 to 750mA, the requirement of the type of battery selected

  55. gangadhar sapkota

    what is the use of transister(BC547) in this circuit?
    please reply me soon im doing this as minor project of making inverter.

  56. Can u explain Phase detection and phase reversal relay

  57. Kiseka Mike

    hi, i built this circuit and its working thank you, please i request you to help me with the design of 12v 100Ah and 12v 1560Ah thank you brother waiting to hear from you.

  58. hi,

    i need to charge 4 x 12v 33Ah sealed Pb maintenance batteries.

    request a charger circuit with indicator lights and option of slow and fast charging. should have auto cutoff and trickle charge facility.


  59. Mahmood Alam

    i read on( 24 v lead acid battery charger circuit .i found a mistake in circuit details description (para 2) D1 is used for rectifier and D2 is prevent reverse flow of current from battery.kindly let it correct.
    Mahmood Alam (MSc Electronics) from karachi ,Pakistan

  60. I have a 22 volt 15 amp transformer connected. I also tried connecting a 35 volt transformer. For some reason I only get 8.5 volts out. Why such a large voltage drop????

  61. dr ashish

    hi, i built this circuit and its working well ,on testing.
    i have few queries.
    1) i got a 40 volts 5 amp transformer , is this suitable for charging two 12 v sla batteries, can a high amp damage the batteries.

    2) how much time will it require for the batteries to be fully charged.can the charging time be reduced.

  62. Jan

    collector conneted to the led and 2.7k resistor to c1 pos. base connected to 100ohm resistor after r2. emitter connected before R2. same a Q1, just the collector is different.

  63. Please advise what is the modification for charging 4 x 12V-7AH (total 48V-7AH). Thank you.

  64. Hi

    As the charge indicator is mandatory you can connect Q2 BC547 similar to Q1 with collector connected through an LED and a 2.7K ohm 1/4 Watt resistance to C1 positive. When the drop across R2 is greater than 0.65volt the LED will start glowing.”
    Q2 collector connect to C1 ok. Where are connect to Q2 B and E?

  65. seetharaman

    Hi Jan it is suitable for 24volt 7AH capacity. (can be 2nos of 12volt 7AH in series)

  66. It would appear that the circuit requested by P. R. Srinivas is exactly what I need for a charger for the battery pack for an APC Smart UPS 1500 — two 12v 18Ah sealed lead acid batteries connected in series. Would you please either post the modified circuit diagram or send the diagram and parts listing to my e-mail address which I have sent to you separately?

    Thank you for your assistance.

  67. dr ashish

    hi, i have a electric bike whose charger got damaged,this circuit fills in for the charger.

  68. Sir,

    I can’t design and simulate a circuit to be able to charge battery of 12 to drive a small power dc motor of 9V to 12V wirelessly. with airgap transformer or two isolated induction coils.

  69. Hello Sir, I’m having a BLDC motor now(speci:0.25hp,24vdc,3000rpm).gng to do a project on EV with that motor.First part of it is to design a battery charger..pls guide me what type of battery will be good and also suggest me some circuit to design a good charger for it.. if u mail me I’ll be more thankful to u.. if any details is missing please mail me or post here.. Please help.. my mail id

  70. Hello Sir, I’m having a BLDC motor now(speci:0.25hp,24vdc,3000rpm).gng to do a project on EV with that motor.First part of it is to design a battery charger..pls guide me what type of battery will be good and also suggest me some circuit to design a good charger for it.. if u mail me I’ll be more thankful to u.. if any details is missing please mail me or post here.. Please help.. my mail id is:

  71. seetharaman

    Hi CJ you are correct, Mr SOD requires 5 units to be charged that is 5 X 7.2 volts that is 36volts. Drop across LM338n is 5 volt drop across diode in the output circuit is 0.7. hence DC requirement at LM338 input is 41.7 volt at rated load current. Hence a 30Volt RMS at rated load is sufficient.

  72. hi there,
    Why we need to use a 35V,3A transformer?
    charging voltage is 27.6V,
    peak voltage input for the lm317 is 35×1.414=~49V
    49-27.6-0.7=20.7V drop across the lm317?
    ~14w drop on the lm317?

    Can we use 30V transformer?

    Correct me if i am wrong.

  73. seetharaman

    Hi Soo the above circuit will do only the open load out put voltage to be adjusted by 10K pot to 35volts before connecting the battery.

  74. I need to charge 5 units x 6V 12AH SLA batteries for backup. What modifications need to be done in the circuit ? Thanks.

  75. seetharaman

    Hi Issac for 12 volt LA battery the maximum allowed terminal voltage is 14.2 , and the maximum initial current is 25% of the rated capacity. design a constant voltage charger with 14.2 volt regulated supply capable of supplying a maximum current limit of 25Amps. Supply this through a relay contact the relay should be an under voltage relay to open at 10.8 volts. the relay can be 12 volt @ 50 to 100mA coil with a contact rating of 30Amps DC. The UV switching circuit can be with a comparator
    IC 741 with a transistor to switch the relay you can use any comparator circuit appeared earlier in Circuitstoday.

  76. I built an inverter of 500w capacity that is using 12VDC/100AH Battery, but Iam faced with the problem of battery overdrain/overcharging. Pls, help me with a battery protection circuit that can disconnect a system at 10.8 and 15.0VDC. Thanks.

  77. Seetharaman

    Hi Ocsee 10 batteries in series and 1.5AH each. Since you have already regulated 140DC it is just 1 volt higher than the required voltage. only current limiting is required. When battery is discharged fully terminal voltage will be around 10.8, that is 108 volts 140-108 @400mA 32 / 0.4 80 ohms 20 watt resistance is required. or you can use a MOSFET series current limiter for 400mA. Thyristor or triac cannot be used as you have already regulated 140Volt DC.

  78. Hi,

    i need to charge 10 batteries connected in series

    Battery specs are: 12 Vdc 1.5 Ah

    So, to charge 10 batteries connected in series i need 120 Vdc

    I have already regulated 140 Vdc.

    Can you Help with basic Schematic including Traic control


  79. Just wondering if anyone has a charge with dump load circuit for my 24v system.I’m running 2 sets of 8v 4 cell lead acid 170ah batteries linked 3 in series then parralell.Just built an alternator from Fisher&Paykel motor,split the windings into 2 sections for vawt low speed winds.It puts out up to 100v rectified @ 2000rpm 40v @ 100rpm(unsure what amperage).Any help would be greatly apreciated.

  80. Seetharaman

    Hi Kushlendr first reduce the transformer sec voltage to 15volt RMS AC. without connecting the output to battery set the output voltage to 13.8volts with R4 pot. reduce R5 to 0.5 ohms 2 watts connect to battery and charge it for 12 hrs.

  81. kushlendr

    sir, plz tell me how can i charge 12V 7AH lead acid battery..

  82. stefan brown

    hey thanks for the reply much appreciated ,could anyone point me somewhere else to meet wot i need to do thanks .

  83. Seetharaman

    Hi Stefan for charging 430AH 30V lead acid battery. you require a constant voltage source of 34.5 volts and maximum charging current limited to 30%, that is 130Amps. For boost charging 35.5 volt again limited to 100Amps. This requirement cannot be fulfilled by the above circuit.

  84. stefan brown

    gday there everybody was just looking at this circuit and i need to build a charger to charge a 430ah 30volt lead acid battery ,can anybody tell me if this circuit could be adapted to do so and what i would need to change .

  85. Hi
    Can you please give a circuit to charge 4x12v33ah batteries in series? or can I use the above posted circuit in series to charge this battery size ?
    Please reply.

  86. moh_gouda

    dear sirs,
    can i used this circuit to charge 2X12 volt 60 AH batteries by using a transformer with 24 volt /10 amp.
    pls reply with the modification required

  87. Seetharaman

    Hi Srinivas sorry for the delay in replying. Change to LM338, transformer to 35 volt 5 amps. Bridge rectifier 7 amps or 6A4 X 4 for the bridge, reduce R5 to 0.125 ohms that is use 4nos 0.5 ohms 5 watts in parallel, Chenge D2 to 6A4 and fuse to 5 amps. since the current pulled by Q1 still low even with 120 ohms for R3 and 5 K for pot, BC547 can be still used 100 ohms is to limit base current during short circuit of the out put leads, i prefer a 470 ohms or 1K so that the base current is limitted to less than 20mA during just a short circuit. you can go ahead. you can send your further queations to my email id

  88. Hi every body,
    I want to make a charger for 02 nos 12v lead acid batteries in series with each rating of 200AHs. Can any body help me to give a circuit. BAttery are for diesel genset and charger required for standby chargig. Please with detail..

  89. i need a charger to charge a car battery of 12v and 88Ah


    Dear Mr. Seetharamanan,
    ” Greetings from FSMS Pvt. Ltd., Chennai “.
    Thank you for the Charger Circuit (shown below) and explanations given. We would like to make a Charger to charge two 12V, 17Ah Lead Acid batteries connected in series.
    I think that,
     The Transformer 35V/3A to be replaced with “Transformer 35V/5A”.
     The 3A bridge rectifier to replaced with “7A bridge”.
     Regulator LM317 to be replaced by “LM388”.
     BC547(Q1) to be replaced by “2N2955 power transistor”.
     100Ω (R1) to be replaced by “6.8 Ω”.
     0.85Ω/2W (R2) to be replaced by “0.1 Ω/5W”.

    We would request you to provide me the Circuit for “Charger to charge two 12V, 17Ah Lead Acid batteries connected in series (24V, 17Ah)” (with explanation), with features of
    o Automatic shutting down of charging voltage, when Battery charge is full, and vice versa.
    o Charging indicator, charge-full indicator.
    Awaiting for your earliest response.

    Thanks and Regards

    P. R. Srinivas
    Sr. Manager – Technical Support,
    HQ, Faber Sindoori Management Services Pvt. Ltd,
    Paras Plaza, 20/31 Cathedral Garden Lane,
    Nungambakam, Chennai-600034
    Tel: 044-42649403/04 Extn: 120
    Fax: 044-42649405
    Mob: 095512 69912

  91. from where can i get a good wheelchair driver circuit for 180 W motors

  92. i need a charger circuit for a wheelchair. my amp hr rating is higher(24 V 18Ah) …what modifications should i make in the above circuit ?

  93. Dear Mr.Seetharaman,
    This circuit is really nice and i would request if you could send me a circuit diagram showing a RED LED while charging and a green LED when the battery is full. Rest everythng is ok with me.
    Thanks in advance.

  94. Seetharaman

    Hi Preeti Batteries cannot be charged in parallel as their present charecter will be different so better to charge the lead acid batteries in series. to charge them in parallel you require individual charging circuit for each battery from the charger

  95. Seetharaman

    Hi Preeti all the 6 batteries you have charge in series. hence the current will be still 1.3 / 10 = 130mA and a maximum of 400mA. The voltage has to be 13.8 X 6 = 82.8volt.

    Hi Seng Siong Lithium batteries require different type of charger with protection etc., this cannot be used.

  96. hello, i want to charge 6 lead acid batteries( each 12v/1.3 amp hour ). what will be the current requirement of the charging circuit? please help me if suitable circuit for charging batteries in parallel configuration is available.

  97. seng siong

    is this circuit compatible with 24V lithium polymer battery pack?

  98. seetharaman

    Hi Anthony to charge sealed lead acid battery you should have aregulated power supply with 13.6 volts out put and the maximum initial charge current shoild not be greater than 30% of the rated capacity of the battery.

  99. Thanx Seetharaman, next Q. If I go for 2N2955 option, how will the circuit change – can you send me a new diagram? I have read about charging SLA batteries, will this constant current charger decrease the life of SLA batteries-alternatively do you have a circuit to charge 24V 17Ah sealed lead acid battery?

  100. seetharaman

    Hi Anthony your idea correct, you have to change the transformer to 5 amp rating with the same voltage ofcourse a 7amp bridge LM388 or same 317 with 2N2955 (PNP power transistor with 6.8 ohms) to increase the current rating. 0.1 ohm 5 watts will do.(0.5 / 0.47 ohms 1 watt 5nos in parellel will also suit)

  101. Hi Seetharaman, If I want to step up to enable me to charge 2x 12V 17Ah batteries in series can I use the same circuit as the 2x13Ah or would I have to change the following:
    T1 30-35V 5A transformer, 7A Bridge rectifier, IC LM337 (?)- would I need to go for a 5A Voltage regulator and as I only know of Positive 3 terminal like LM338 I would need to change circuit? Lastly R2 to 0.1 ohm 10W . Alternatively step down to LM317 to drive 2N3055 transistors ?

  102. Hey!

    Thanks so much for the circuit, I got it to work great. Just a quick question: What do the capacitors actually do? And how did you come to these values?


  103. Hi Seetharaman, This is a great circuit and near perfect for me, thanks.. I read your reply to Farada about switching on and off, but I cant figure out how to do this with your explanation. Is it possible you can draw this for me. I would like to be able to identify when batterys are charged and when they are charging (ie: with 2 LEDs?). So it will switch off and on sutomatically because my charger will be always connected. Also(!) can you protect from draining batterys if charger is switched off?
    Thank you, Carl

  104. seetharaman

    Hi Dedi 9 volt dry battery or 8 volt lead acid battery or 9.6 volt nicad battery. kindly specify your battery type voltage AH capacity etc.

  105. can i use this circuit for 9 volt battery and what components i must change…

    sorry my english isn’t good

  106. seetharaman

    Hi DYK this charger cannot used for charging 100 amp batteries. This can be used upto maximum capacity of 20AH.
    Hi Estephane can you give you battery’s complete detail and whether you want to charge them together or one at a time.

  107. seetharaman

    Hi Louie The same charger can be used for charging 24volt 4.5AH battery. reduce R2 to 0.47 ohms 2 watts.

  108. estephanie

    Hi,i would like to ask if you could give me a circuit that can charge a battery of a forklift,a 24volts and a 36volts.

  109. what can i do to make this circuit charge 100AMP batteries?

  110. I desire to construct the circuit for an inverter in which can use two car batteries by which one battery to provides the dc input to the inverter and the second battery to be charged at the same time and vice versa without the need of solar power.Please can provide me with a circuit diagram?
    Thank you in advance.

  111. Seetharaman

    Hi for 24 volt 13AH lead acid gel battery the initial charging current (for a flat battery)preferrably sholud be limitted 3.5Amps max. With a regulated power supply of 27.6Volt. can charged for 12hrs to 15hrs max. As the battery terminal voltage increases tofinal level the charging will fall down slowly to trickle level. Hence the resistance value for R2 should be reduced to 0.2 ohms 5watts. Transformer rated at 30 volt 4amps bridge rectifier rated for 5amps and IC as LM337K (T03 casing)

  112. Hi,

    R2 is the current “Ah” limiter. There is a detailed discussion about calculation of the R2 in another battery charger circuit in this website.


  113. What’s about the base of BC547 if I added it for a charge indicator?

  114. Could I charge a 24v / 13amp battery with this circuit?

  115. Seetharaman

    Hi D2 is 1N5403. The transformer can be 30 volt AC at 1 Amp as our out put current is limited to less than 1 amp by Q1. As the charge indicator is mandatory you can connect Q2 BC547 similar to Q1 with collector connected through an LED and a 2.7K ohm 1/4 Watt resistance to C1 positive. When the drop across R2 is greater than 0.65volt the LED will start glowing.

  116. pls. how do make the circuit automatic so that when the battery is fully the circuit shuts down and vice -versa.also wiTH indicating LEDS

  117. sir

    i have a inverter circuit , but for charging we are using relay and the battery not charge fully, i heard abourt the circuit by using bta 12 triac and lm324 no need of relay and capacitor,can you help me

    my requirement is instad of relay i need bta12 for switching for current limitting avoid capacitor

    expecting your reply

    thank you


    • Hi, I have tried the circuit for charging the battery. But the charging current is too low. It reads only 70 milliAmps. I tried several times by adjusting the components but couldn’t get higher current. Does current varies on changing R2? How current varies with R2? How to get higher output current from the circuit. Please reply>

    • Hi, I have tried the circuit for charging the battery. But the charging current is too low. It reads only 70 milliAmps. I tried several times by adjusting the components but couldn’t get higher current. Does current varies on changing R2? How current varies with R2? How to get higher output current from the circuit. Please reply.