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High Current Lead Acid Battery Charger Circuit

This high current lead acid battery charger circuit can be used for charging high current lead acid batteries in the order of 100 to 200 AH, the design is perfectly automatic and switches of the power to the battery and also itself, once the battery gets fully charged.

Looking at the shown 100 to 200 amp high current battery charger circuit, we can understand the circuit idea through the following simple points:

There are basically three stages in the shown configuration viz: the power supply stage consisting of a transformer and a bridge rectifier network.

A filter capacitor after the bridge network has been ignored for the sake of simplicity, however for better DC output to the battery one can add a 1000uF/25V capacitor across the bridge positive and negative.

The output from the power supply is directly applied to the battery which requires to be charged.

The next stage consists of an opamp 741 IC voltage comparator, which is configured to sense the battery voltage while it is being charged and switch its output at pin #6 with the relevant response.

Pin #3of the IC is rigged with the battery or the supply positive of the circuit via a 10K preset.

The preset is adjusted such that the IC reverts its output at pin #6 when the battery becomes fully charged and reaches about 14 volts which happens to be the transformer voltage at normal conditions.
Pin #2 of the IC is clamped with a fixed reference via a voltage divider network consisting of a 10K resistor and a 6 volt zener diode.

The output from the IC is fed to a relay driver stage where the transistor BC557 forms the main controlling component.

Initially, power to the circuit is initiated by pressing the “start” switch. On doing this, the switch bypasses the contacts of the relay and powers the circuit momentarily.

The IC senses the battery voltage and since it will be low during that stage, the output of the IC responds with a logic low output.

This switches ON the transistor and the relay, the relay instantly latches the power via its relevant contacts such that now even if the “start” switch is released, the circuit remains switched ON and begins charging the connected battery.

Now as the battery charge reaches about 14 volts, the IC senses this and instantly reverts its output to a high logic level.

The transistor BC557 responds to this high pulse and switches OFF the relay which in turn switches of the power to the circuit, breaking the latch.

The circuit gets completely switched OFF until the start button is pressed once again and the connected battery has a charge that’s under the set 14 volt mark.

How to set up the proposed high current battery charger circuit.

It’s very easy.

Do not connect any battery to the circuit.

Switch ON power by pressing the start button and keep it depressed manually, simultaneously adjust the preset such that the relay just trips or switches OFF at the given rated transformer voltage which should be around 14 volts.

The setting is complete, now connect a semi discharged battery to the shown points in the circuit and press the “start” switch.

Due to the discharged battery, now the voltage to the circuit will drop under 14 volts and the circuit will instantly latch, initiating the procedure as explained in the above section.

High Current 100 to 200 Amp Automatic Lead Acid Battery Circuit Diagram is shown below


  1. the relay keep turning off and on. turn off when reaching the cut off but turns on again after about 2 secs. what shall I do?

    • Connect a discharged battery and then check, and the transformer current must be rated at around 1/10th of the battery AH.
      Without a discharged battery the circuit will keep fluctuating.

  2. the relay turn off and on. turn off when reaching the cut off but turns on again immediately. what is the solution?

  3. the relay turn off and on. turn off when reaching the cut off but turns on again immediately. what should I do?

    • There are some simple software that can design PCB like Circuit Wizard or PCB Wizard. Easy to use. Just input Sir Swagatam's diagrams and it will design the pcb. Just make little rearrangement afterwards to make the design neat. Practicing it will enhance your knowledge.


  4. The circuit for 10 to 20 amps battery charger is not clear and it is too small. Can you please send me an enlarged circuit diagram. It would be most useful.



  5. I was wondering about a couple things on this schematic. Is the N/O under the start a switch or relay? Also, the 12v Relay, is it a N/C or N/O and how do you make the connections. I am using ExpressPCB to make the schematic and then transfer it to a pcb for printing. I am unsure about those two items in particular. Any help, preferably detailed and maybe pictures, would be greatly appreciated as I'm still a little bit new to all this. Thanks.

    • The N/O is for the relay contacts. An SPDT Relay will always come with both the contacts in one package, here we have used an spdt relay, however only N/O has been indicated, the other contact is obviously is the N/C.

      I would rather advise you to first test the circuit over a general purpose PCB and then go for making the final PCB layout.

      The circuit shown at the bottom of this article would be perhaps a better option

    • I was talking about the one at the bottom of the article. It shows the N/0 but then it shows a relay to the left of that with a ground coming out the left side and a diode looping from the left side(ground side) to the input from the transistor (BC 557). So I'm assuming that is the rest of the pin out hookup for the 12v relay after hooking up the N/O pins to the switch circuit? Sorry to ask so many questions but I'm rather new to this.

    • OK got it….the box which shows "Relay 12V" is the relay coil, the wires coming from the transistor and the positive goes to the relay coil….where as the symbol at the left of the box are the contacts of the relay with the N/O and the N/C contacts.

      Yes the supply needs to go through the relay contact such that the system shuts OFF completely once the battery charges fully and the relay trips.

    • Thanks, yes you may use this circuit for charging 50AH battery, just make sure that the diode connected at the positive of the battery should be rated at 1/10th of the battery AH, means 50/10 = 5amp to 6 amp diode.

  6. hey…..How can i make it fully automatic????…..like i wanna replace that switch so that i dont need to press it for charging….n it should detect BAttery Voltage n automatically start……

    • Connect power directly to transformer, eliminate the switch.

      Wire up the N/O contact with the battery to be charged.

      Connect a variable resistor of around 470K across pin#6 and the preset center pin. This must be adjusted for setting the low voltage threshold.

      That's all…. Now when the circuit is powered with a battery connected, the relay will activate, the battery will start charging charging via N/O of the relay, once it's full, the relay will disconnect and stay in that position until the battery voltage reaches the lower threshold….the cycle will repeat as long as the battery remains connected, charged and used up…

  7. hii Swagatam,
    good ckt.

    actually am looking for a solar charge controller to charge 150 AH 12V battery. solar panel is 12v/225-250W/ and around 15amps current.

    so can i use this circuit by replacing the power supply ckt (transformer,brdige ckt and filter capacitor) with the out put of solar panel?

    if yes, what are the necessary changes which i have to do? is there any regulator ckt needs to regulate the voltage to the battery from solar panel?. because the out put voltage of the solar panel will vary up to 20V.

    one more doubt,what is the value of potentiometer which is connected to 3rd pin of IC 741.
    thanking you ,

    • Hi Mahroof,

      The circuit will work with all types of solar panels provided the max voltage does not exceed 20V (if the IC is 741) and 30V if the IC is 1/4 LM324).

      Yes you may connect the panel supply at the input of the bridge.

      It's a 10K preset.

    • thank you.

      the solar panel open ckt voltage(Voc) is more than 20v as per specification.so any voltage regulator ckt i need to use?

      if the voltage is below 20V,we don't want to use any voltage regulator for 12v battery? i mean for 12V battery if we charge by 19V, the battery will not damage?

      as the voltage comes from solar panel it self 'dc' i need to use bridge ckt again?

      thank fully,

    • A voltage regulator will be required for controlling the output voltage to around 14V, so anything above 14V will require a voltage regulator for 12V batteries.

  8. hello sir,
    i have build this circuit but my problem is the switch can i connect the circuit directly to the battery without using the switch or how do i do it.

    secondly i connect circuit to 10v dc battery the relay is not energies but immediately wen i connect it to anything 12v dc or above it energies the relay
    and am told to charge 12V 200AH battery with 13.5V supply so the relay energies even b4 the battery attain full charge so how do i overcome this problem

    becouse normally 12V 200AH reaches i think about 14-14.5V b4 its fully charge

    • You will have to read the whole article for understanding the operations.

      Without switch the system will not cut of after the battery is fully charged.

      The preset needs to be adjusted for setting the desired cut off voltage level.

  9. hello Sir,
    Are the 10k's all a variable resistor?
    I want to use it to charge two 12v 200AH batteries connected in parallel.
    what if I want to use it for 24v 200AH or 2V 400AH.


    • hello sir,
      Thanks for the reply.
      would the circuit be suitable to charge 12v 400AH battery.
      I want to charge four 6v 200AH batteries in series parallel, thus two of the 6v 200AH IN series making 12v 200AH.
      Two of the 12v 200AH in parallel, thus making total of 12v 400AH. I am using it to connect to an inverter, keeping it connected permanently. Thus charging the batteries when battery discharges and using the batteries when power outages occurs.
      Would leaving it connected to the inverter damage the inventer?
      Your responses are highly welcome.

    • Hello PK,

      Yes you can charge them, just make sure the relay contacts are rated accordingly.

      This circuit will not initiate automatically, you will have to press the switch for initiating the charging process.

      If the battery is connected to the inverter via a cut off relay then it's fine.

  10. Hello,
    I want to make a car lead acid battery charger for a 72Ah and a 100Ah lead acid battery, could it be possible to use this charger circuit with to different settings for the current that loads the battery. And wich kind of diodes should I use to regulate these currents

    best regards

    • yes the above circuit can be used for your need.

      72ah and 100 ah would almost require identical current levels for getting charged, so an added current regulator circuit wouldn't be required.

      you may incorporate a 12V 10 ampere transformer for charging both the batteries with the above circuit.

      be sure to use a 6800uF/50V capacitor across the bridge positive/negative terminals

    • but doenst a 72Ah need to be loaded with 7,2A and a 100Ah with 10A? And about the potentiometer which resistance and which power should this component need?


    • ideally it should be done in that way, you may add a LM196 circuit stage for that, it's not critical though.

      The main thing is to switch OFF the charger when battery voltage reaches 15% more than its rated value….charging at slightly increased current rate won't harm the battery if it's switched OFF when fully charged.

  11. Sir,
    what do i need to change in this circuit if i use for charging of a 150 Ah lead acid deep cycle battery? would you pls guide me.

    Thank you


    • Hi Maung,

      just use a 20amp rated transformer, rest everything will remain as it is.
      also be sure to select the diodes rated at 25 amps and the relay contacts also at 25amps

  12. hi Swagatam,

    a very promising circuits youve always share, actually Im always visit your blog coz im also electronics hobbyist from the philippines… i have read many your posted electronics designs especially on battery charging circuits 🙂 its very simple and yet reliable and efficient circuits, building those circuits using your designs works great and thank you so much swagatam! but until, i was thinking an solidstate automatic dual battery charging isolator for deep cycle agm 100ah batteries, i am using some of your design charging circuits and delay and relay techniques, but unfortunately, always got me an error… what should I do sir?. can you guide me with my issues? thanks so much.

    here is the step of how the circuit may do…

    1. before starting, the two agm batteries 1&2 will combine in parallel connections to use for starting the engine to provide more smooth and more power to start.
    2.then, once the engine is started, the battery 1 will automatically disconnect and relay for automatic fast charging and to float mode ( dpdt relays to be used?)
    3.while the battery 2 is connected,a voltage low level cut-off monitoring is standby for 11.5v,
    4.so when the low volt reach as 11.5v the circuit will automatically trigger the relay of the fully charged battery 1 in parallel connection.
    5. after the battery 1 connected in parallel, a delay relay cut-off circuits of battery 2 will engage for automatic fast charging and to float mode.
    6.a continuation cycle of relays, monitor, charging. thats it.

    I hope you understand of what i mean.

    hoping to hear from your sir. i hope you can help me with this circuits to make.

    Thank you so much and more power to you sir!

  13. I haven't built this circuit, but may do so. Can I make a couple of comments.
    It can be confusing for some of you readers to mix "ampere hours" with amps, as in you title and elsewhere.
    With a very slow change of battery voltage the 741 circuit makes a poor comparator. Especially as constructors will have a variety of relays. Relays are notoriously slow at releasing and the 741 will behave unpredictably when the inputs are close to equal. Best practice surely would be to add a touch of hysteresis by adding a resistance between the output (pin 6) and the + input (pin 3). this would cause the 741 to snap quickly and give the relay a chance to close properly. I am no circuit designer might try 470K to start with.
    Also please explain the purpose of the 100uf capacitor on the output. Wouldn't that add to the problem.
    Finally, I think the circuit would work much more reliably if the relay (perhaps a stand automotive relay) were connected between the battery + and the comparator circuit, rather than on the mains input side.

    • Thanks, I appreciate your attempt, here are more precise answers:

      AH signifies the charge or the discharge rate of the battery. ideally it indicates the full charge or full discharge rate of the battery in an hours period.

      Opamps are excellent comparators and they work very well in battery charge cut off applications.

      hysteresis is surely needed so that the relay doesn't keep switching ON/OFF at the thresholds due to the extreme accuracy and sensitivity of the opamp.

      Hysteresis delays the relay actions and makes the response slower so that it doesn't chatter…… without hysteresis the relay would snap rapidly producing rapid switching at the thresholds.

      A hysteresis can be added in the above diagram to avoid the same.

      In the above diagram the position of the relay switches OFF power completely, right from the transformer, so it becomes much safer and reiable.

    • Sir,
      Thank you once again.
      would it be possible to add a charging current controller?
      would you please kindly explain us what type of component need to be use ?

      Thank you and with best regards

      Maung Pru

    • Hi Maung,

      can you specify your current requirement, if it's upto 10 amps then it can be simply done using ICs like 338, 196 etc, otherwise it would become sightly complicated.

  14. Sir,
    Thank you very much for your quick reply. 10 amps would be enough for me , would you be able guide us for using ICs like 338, 196 etc on this circuit ? it would be very useful for you.

    Thank you once again sir

    With best regards

    Maung Pru

  15. Sir, I need this circuit to be automatic turn on, not manually with the push button. Can you help me with that subcircuit please? Thanks in advance.

  16. Hi Swagatam am just so proud of you i also made this circuit at the bottom.i did not have BC 557 I used 2N2907, 6.8 Zener and for preset i used a 50k. when i connect it to my supply, the relay trips. the problem is in setting the cut off voltage.i tried adjusting but still it was on pliz help me thanx

    • Thanks very much, you can do the following things:

      Connect an LED in series with the transistor base 10k (anode to base, cathode to 10k) for indication.

      Keep the transformer disconnected, and apply an external power supply of 14.4v across IC supply pins.

      Now flick the preset to and fro until you find a point where the LED toggles ON/OFF, adjust this point to just switch ON the LED.

      Your circuit is all set now.

      Now carry on with its normal operations through the trafo.

      While adjusting the preset do not connect the battery.

  17. Hi Swagatam,

    I wish I had seen your blog earlier. In my set up, I need my charger, connected to the 220 Volts AC mains to start automatically to charge the battery when the voltage drops to 11 and stop the charger when the battery is charged to 14 volts.

    Your advise and guidance would be of immense value.


  18. Hi Swagatam,

    Thanks for your prompt and positive response.

    I just read, – Hire me for Designing Circuits – Circuit Ideas, Inventions for Sale – in your blog.

    I have a special requirement for my set up, the details I will send to your email ids you have mentioned, would you be kind enough to reply whether there is any scope for making them and your charges as well?


  19. Mr,Swagatam i like your good work you been doing so far but one thing i don't understand is you answer to some people questions but you don't reply to me why sir or they are your family? ok please and again as soon as you received this message please i am burgin you to reply me allow me to be one of the your friend cos i am a electronic Hobie i do like your project.my firs quotation is this 12v battery charger circuit i build it but when i power the the circuit relay switch correctly but the problem is out put is 11v and if i calibrate 10k preset to left side it switch on the relay and it give 11v out put if i calibrate to right side it switch off the relay and give me 13v out put why sir any help? i will be glad for your assistance, looking foreword to hear from you thank you.

    • Mr Anonymous, I reply to each and every comment and rarely miss any, may one in a million, or as long as it does not have an outbound link.
      Anyway, did you make the circuit as it is shown in the diagram, with the start button or did you do any other modifications?
      The DC input to the circuit should be 14V DC and the connections to the relay should also be exactly done, and the input current should be rated at 1/10th of the battery
      Also did you follow all the instructions mentioned in the article??
      It's just about setting up the opamp correctly that's all….the functioning is very starightforward

  20. thank you for the replayed sir,no i did not make any modifications but one thing is that i use 1n5399 for the 4 diode showing there and also i used In540(16A4) the one that connect to the battery positive is it 6A or 6.4A? sir i build one of your circuit How to Make a Simplest 200 VA Uninterrupted Power Supply UPS Circuit i build only the charger it work very well but i don't think it can charge 24vDC battery two 12v battery? if it can chard what can i do sir help me with the circuit thank you jah guide you and hop to hear from you soon..

  21. I have a modified pc smps that gives 14v and 20A
    so I want a circuit that charges a 12v 100ah battery automatically ie it should turn off the smps when battery is full and turn on the smps when the battery is low

  22. Hi Swagatam,

    I need to change 50-64 amp car battery. Can I use this circuit? How much amp transformer I would be required. And also is there any other changes with capacitors and diode are need to be done here?

    • Hi Nabeel, yes definitely you can use this circuit for charging a 50AH 0r 60AH battery, the transformer current rating should not be more than 8 amps.

      the bridge rectifier diodes must be rated at 10amps each…or a single 10amp bridge module will also work at the indicated position

  23. hello sir.. still, the relay did not tripped after the battery is fully charged.. i also put and LED in series with the transistor base. there is no changes in the led too after the battery is fully charged. thank you for your response sir…

    • when you connect the discharged battery pin3 voltage is supposed to be lower than the pin2 voltage and when battery is fully charged pin3 should become higher than pin2….please confirm whether this is happening or not

  24. Hi…I am confused that how are u producing dc output just after the bridge because u said in a comment that u can remove 100u capacitor.although if we continue with this capacitor I think it will discharge very quickly and produce huge ripples at output

    • Hi, 100% pure DC is not essential for charging a battery, however in the other comment my recommendation about removing the filter capacitor in order to eliminate the relay chattering might not be correct.

      the correct remedy to prevent relay chattering at the cut-off threshold is to add 100K hysteresis resistor across pin#6 and pin#3. This will latch the opamp at the cut off levels and enable a quick and complete switch OFF of the relay and the entire system.

      Filter capacitor need not be removed.

    • hello jade, only the transformer, the relay and the diode rating will need to be upgraded as per the battery charging current and voltage specs.

      the charging current rate of a 300AH batt can be around 30 to 40 amps

  25. Dear sir, again my transformer with three terminal produce 14V between the last 2terminal and 7V between any of the last terminal and the center terminal. Is this the type of transformers you recommend?

  26. Hi dear Swagatam thanks a lot with this good battery charger circuit. This circuit is for 10 to 20 ok. There five diodes 4 diodes are rectifier and 5 diode is used between bridge positive and battery positive and all diodes have the same value. Now if I charge a 50 ah or 70 ah batteries. should I change all diodes amp or only the bridge rectifier. Thank you very much with best regards. Rohullah.

  27. Again i noticed that if connect it to battery for charging the battery voltage rises to the transformer voltage as if its fully charged so please i want to ask it the charging voltage or the its fully charged once connected

  28. Please sir how do test the current of my power supply because when i use a clap meter to test the current at the positive line its reading 8. 5A could that be the current of my power supply

  29. Please sir how do test the current of my power supply because when i use a clap meter to test the current at the positive line its reading 8. 5A could that be the current of my power supply

    • Faith, you can connect you DMM prods directly with the trafo wires for a few seconds and check the reading which will inform you regarding the current rating of the trafo.

      make sure the DMM is set at AC 10 amp or 20 amp range.

  30. Wen i put my digital meter across the transformer and at the same time clap it with my clap meter and power it burn of my digital meter but the clap meter read 68A. My question is can this transformer be use to charge a three 12v @200A connected in parallel?

    • I really appreciate your help and fast response please i build and tested the first circuit thishttp://www.homemade-circuits.com/2012/08/make-this-48v-automatic-battery-charger.html during setting when vary the preset the led never turn up, could it the 22k or any component i will remove from the circuit to make it work properly

    • the pin#2 resistor must vary and become higher or lower than pin#3 reference voltage in order to change the output state, while adjusting the preset.

      yes, you can try replacing the 22K with 1K, and remove the 4k7 attached with the pin#2/ground since your supply is not 48V rather 24V only

  31. Sir please I'm having serious challenge after making those changes and connect my power supply at the point were we have the battery connected still the led did not come up when varying, and when i measure, the voltage is not in line with the zener diode at pin#3 i have 13.16v, pin#7 i have 16.2v while pin#2 is 12.6v but when i apply the voltage sample in the opposite side i have at pin#3 4.7v, pin#7 15.18v then when i vary the 10k preset at pin#2 such that i have a voltage higher than that at pin#3 there will be no output at pin#6 but when i vary it such that voltage at pin#3 is greater there will be output at pin#6 which i have to 13.2v

    But in all these varying i noticed that the led is on irrespective of fact that the voltage at pin#2 is changing its remain on
    Then when i measure the voltage at the point were the battery will be it's 19.23v

    Please sir what could possibly be the error and the voltage at the point were the battery will be connected i thought it should be my supply voltage and not less

    If this is going to give me little problem please can you recommend another working 24v automatic battery charger please ur advice is seriously needed
    Thanks and best regards

    • Faith, in the previous link of 48V charger which you are trying, you must feed the voltage from the points where it is mentioned "48V"….you cannot apply from the other side for this design because the mosfet would be blocking the voltage….right??

      therefore if you are applying the voltage from the left hand side then it is correct and your adjustment results also look perfectly correct.

      when pin#2 voltage goes above pin#3 voltage then pin#6 must become zero (cut-off)…that's correct.

      Now as for the LED being illuminated all the time, this could be due to the leakage offset voltage from pin#6 of the IC741. Did you connect the shown zener diode at pin#6 of the IC?? make sure you connect that to solve the LED switching problem.

      And what did you use for the power transistor, is it a mosfet or a BJT, remember if it is a BJT then you will require a resistor at its base, and the LED shifted towards the zener side, and not at the base of the BJT.

      this circuit is the easiest one, and you are almost near….if you are having difficulty with such an easy circuit then just imagine what you might have to face with the other relatively complex ones…actually all opamp designs are extremely straightforward it's just about understanding them patiently.

  32. Hello Swagatam,

    Please, what is the job of the 6A4 diode that is connected to the battery considering the fact that it supports just 6A?

    What if someone wants the charger to charge the battery at 20A?

    Will this 6A4 diode not limit the charging current?

    • Hello Afam, it is employed to prevent reverse battery discharge though the opamp resistors….its rating should be much higher than the specified charging current value….for example if the charging current is 50 amp then the diode must be rated at above 60 amps.

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