12v Battery Charger Circuit with Auto Cut off

This is a simple DIY charge controller schematic posted in response to a request by one of our readers on our facebook page. The main component of this auto battery charger circuit is a 555 timer which compares the voltage in the battery. It turns ON the charger if the battery voltage is below the variable preset voltage (12 volt chosen here) and turns OFF the charger if the voltage reaches 13.8 volt. The battery charging voltage of the charger can be varied by adjusting the variable resistor.
Recommented for you:

To understand the working of this 12 volt battery charge controller circuit you must have an idea of the internal diagram of 555. You can refer the pin out section at the bottom. You must also check charge controller using LM324 IC where you can find video demonstration too.

Automatic battery charger circuit diagram

Automatic battery charge controller circuit using 555 timerClick on the image for enlarged view

Components Required

  1. IC 555
  2. Transistor BC 548
  3. Diode (6A4 x5 ,1N4007)
  4. Zener diode (5.1V)
  5. LED (red, green)
  6. Capacitor 4700uF,25V
  7. Resistor (1K x 3,820,2x10E 10W)
  8. Variable resistor 10K
  9. Relay 12V,10A
  10. Transformer 230V/0-15,5A

Working

  • Positive terminal of the upper comparator of 555 is connected with reference voltage in order to turn OFF the charger if the battery charges above 13.8V.
  • Reference voltage is obtained by connecting a zener dide in series with a resistor.
  • If the battery voltage is below the preset voltage (set by us), lower comparator will reset the flip flop. This turns ON the transistor and the relay will switch to charge the battery.
  • The recharge voltage (preset voltage) can set by varying the variable resistor.
  • Power ON is indicated by a red LED and charger ON status is indicated by a green LED.

Components pin out


229 thoughts on “12v Battery Charger Circuit with Auto Cut off

    • Hi,
      Please connect a diode in series as diagram, and connect battery and set the voltage level by rotating the pot, that you wants turn on the charger.

      • please give a circuit diagram of emergency light with automatic battery saver means that it works on a pwersupply charging stopped when batter’s charge full and start again charging when batter’s volt is low

    • You follow this procedure
      1)Disconnect the AC supply from the source .
      2)Connect a variable DC power supply from the output of the circuit.
      3)Set the variable DC power supply at 13.8v then varie the preset until the LED goes off
      4)Then read the circuit description again…
      ME bhanu

    • in this circuit you can expect that the red LED will always glow bcause it is connected direcly from the transformers DC outputs. Only the green LED will do the on and off during charging. If on charge mode green LED glow and when fuylly charge greenLED turns off.

    • Caloy
      Your comment is awaiting moderation.
      November 23, 2014 at 2:16 am

      actually in my opinion i will not connect directly the TH to 12v from the relay, connect it to the output terminal of the VR which is the other terminals of the VR one is connected directly to +12v from the relay and the other connected to GND. And for the trigger terminal of ic555 use 33ohm 1/4w resistor connect to GND. Adjust the VR until you can reach the voltage of 13.8v. Also use capacitor 100uf/16v filter it to the relays coil terminals. Just try, hope it can help.

  1. I have a small UPS & a 12v 75ah car battery can I use the UPS as my inverter? and will the UPS be able to charge the 12v 75ah car battery? because the normal battery in the UPS is 12v 7.0 ah.

    • You can use UPS as inverter but it will take more time for charging of the battery. You have to use separate battery charger to charge 75ah battery.

  2. what is the charging current of this charger.how many 12V batteries can it charge at a time.
    is this charger able to charge deep cycle batteries used for inverters.

    • It is highly recommended to use your name while commenting for better response from us.

      1) Charging current depends on the transformer used, here we are using 5A transformer, so the charging current is a little bit less than 5A(some loss due to the series resistance).

      2) You can use any number of batteries but charging time will increase.

      3)Inverter batteries (

      • so tell us how we can achive the 1/10 rate of charging current …sir you know that car lead acid must be charged by 1/10 of thier current for example a 22 amper per hour must be charged by a 2.2amper per hour
        how we can achieve this using your design …555 is common chip and easy to find your design will be so popular if it can satsfy the golden current charging rate of 1/10 ..thanks

      • Then to charge a Car batery 50ah we use transformer with 10 ampere rating?
        And 1 more question ouput of this circuit is 12v or 14v?

    • To set my preset value where do i connect my multi testing meter and should my charger be turned on while adjusting the preset value.

  3. My name is Friday, I have assembled the circuit, both LEDs glow, battery is @ 7.14V, how do I set my low battery level?

  4. Am mike, sir, pls help me i dont understand hw to connect diode in serie to d circuit, and d output volt drop to battery voltage when connect wit battery. hw do i solve dis isseu thanks.

  5. What does the shaded part of the capacitor means ?
    I have the polarity problem..
    Is Upper side of capacitor is positive ?

  6. Dear sir,

    I made this circuit for 6 volt 4 ah battery. Taking relay connection I'm facing some problem and properly not work (auto cutoff when battery full charged).

    Pls solve it for my doing the needful.

    Awntg yours
    Brgds – Main

    • I cannot give any answer without seeing your UPS board. Here is my suggestion, charge the UPS battery with the external charger independently when charging is required. After charging reconnect battery to the ups board.

      If you can identify the charging components of the UPS board,then you can connect external charger in paralle with the battery without removing UPS connection.
      <

  7. Could you please show me a design in which you use the above circuit (12V Battery charger with auto cut off) but with a Wind Turbine DC generator motor. Thanks

    • Hi FOUAD
      To increase the current replace transformer with higher current type, also replace 10watt resistors with short circuit.

    • Replace larger amp value of transformer, use also larger diode amp capacity and no need to use 10ohm/10w resistor just connect directly from the b+

  8. Hi!

    I have a question about the current, this charger only work with battery of 75ah? can i charge another kind of battery?(45ah, 55ah,etc.)
    Thank for your time!

    • Hi Cristian
      It work with all 12V battery .by increasing the capacity, time taken for charging will increase,to reduce time you have to increas the current of transformer.

    • Hi Hafeez Ashraf
      You can, but you should increase the current of the transformer used to reduce charging time…also replace the zener with 5.1V .

    • Yes you can replace transistor bc 548 to 2sc1815 but make sure to locate the proper transistor terminals. For bc 548 (1=emiter 2=base 3=collector), for c1815 (1=emiter 2=collector 3=base) C1815 is much better than bc548 because its (collector current) is Ic=150mA, while bc548 Ic=100mA.

  9. Sir thanks for your innovative works, sir can this circuit work for 12v,200ah? sir if not, what are the things to replace.Thanks.

  10. Please can I use 12.6v,4A battery charger to charge a battery of a 12v,5A while the normal charger for the battery is 14.5v,5a

  11. There’s an errors on the actual diagram to what has been explained on this project. It says the circuit will stop charging when the battery’s voltage reached 13.8 but the zener used in the diagram was only 5.1. Zener should be between 13v to 14v, I used a series of 3v and 12v in series also with 150 ohms to achieve 13.83v on 15v 3amps power supply.

    • hi i have design and construct 12v 30A battery charger but i fine difficult to design the cut off circuit plz can you help with an easy and simple circuit diagram plz

  12. hello Yaseen I want to use this circuit with 0 -20 5Amp TXR so plz help me and what you mean .Resistor (1K x 3,820,) plz relpy me thanks.

  13. 1. i connected this circuit with transformer 3 amper 24 volt DC
    timer was very hot , and output voltage 6.7 dc volt
    i changed resistor many times but no change
    and it’s still very hot

  14. thanks for your answer
    yeah timer damaged but i replaced it with another one
    the circuit working but it didn’t cutoff and the relay alway on
    thanks in advanced

  15. hi sir: I connect 14 v to the circuit two LED came on but the relay keep clicking , is the relay keep click on when circuit working

  16. voltage at Control voltage is 5.1 (as zener diode is used) fixed . and also battery positive (12 V)terminal is directly connected to Thrshold so Thr > 5.1 , this will show that battery is full . please give me solution what will be done here. thanks

    • actually in my opinion i will not connect directly the TH to 12v from the relay, connect it to the output terminal of the VR which is the other terminals of the VR one is connected directly to +12v from the relay and the other connected to GND. And for the trigger terminal of ic555 use 33ohm 1/4w resistor connect to GND. Adjust the VR until you can reach the voltage of 13.8v. Hope it can help.

  17. hi sir

    how did you come up with the values of these resistors and caps, i want to build one for the batteries at my work place, what was your ripple current (Idc)

  18. gud evening sir…can i use this ciruit as monitoring the battery voltage? bcoz last time i use battery alternator check to monitor the battery voltage. Then i add a timer to switch off the trasformer, when the battery down at 12.5v the transformer on again…when the battery reach at 13.8v the timer on again to cut off the trasformer..

  19. i wana ask that how it sense that voltage in the battery is greater than 12v, plz answer in detail i have many confusion regarding this ?

  20. dear sir i want to charge 12v 45ah batt.
    1. can i use ups transformer for this?
    2.the component required is written that 5 ohm and circuit shows 10 ohm 10w why so?
    3. what will be the zener , diodes and other resistor values for my requirement?
    thank you.

  21. Hi. I have a question. Can i use a 12v 5 amp SMPS as input of the circuit replacing the 15v 5amp transformer
    Thanks in advance.

  22. Sir, i want to know if it can be possible to recharge an inverter battery using same source generated from the inverter through external battery charger. Please i want know if that canbe possible. Thanks. Reply.

  23. I cant find the 5ohm 10 watt resistor in the diagram … i can see is 2 pcs 10ohm 10 watt resistor…. pls need help…tnx

      • I want to make a led bulb consisting 10 nos of LED of 4v DC each in parallel.can you please refer me a circuit diagram using stepdown transformer to get 4v DC supply from 220v/230v (generally available in india).The circuit should have sufficient longevity,cost efficient. What will be the rated watt of the Bulb?
        Please kindly reply me.Thanking You.

  24. my UPS battery rechargable voltage is 82V but i required 110V for charging so tell me whom components are repairable

  25. Where should I put my multimeter red & black Prob when I am setting The recharge voltage (preset voltage). Should I set the voltage when the battery connected or disconnected. pls reply soon. I am waiting for your reeply

  26. Hi Yaseem,

    Can we ignore the 10ohm,10 watt resistor, if we ignore do the circuit have any impact on output?

    Thanks

  27. Dear Sir,
    Good day.
    Can you suggest how to modify the circuit adaptable to a 48 VDC charger.
    Thanks,
    Nestor

  28. Hi Sir,

    I have designed this circuit and i could see both the red and green LED are glowing. Please tell me is this normal.

    also i just tried tuning the pot but no effect on the circuit still both the LED is glowing. Please help me sir. Thanks

    • for admin:
      WHY YOU DO NOT ANSWER THIS QUESTION. Both LEDs Glow even if you vary the POT. Nothing happen honestly. I know i have a correct connection no doubt.

      I HAVE READ THE ABOVE COMMENTS. YOU DIDNT ANSWER ANY THIS KIND OF QUESTION. I RUIN MY PROJECT BECAUSE I TRUST YOUR DIAGRAM. WE NEED YOUR HELP…. THANK YOU!

      • in this circuit you can expect that the red LED will always glow bcause it is connected direcly from the transformers DC outputs. Only the green LED will do the on and off during charging. If on charge mode green LED glow and when fuylly charge greenLED turns off.

        • Try this changes: Do not connect directly the TH to 12v from the relay instead connect it to the output terminal of the VR which is the other terminals of the VR is connected directly to +12v from the relay and the other connected to GND. And for the trigger terminal of ic555 use 33ohm 1/4w resistor series it to GND. Adjust the VR until you can reach the voltage of 13.8v. Hope it can help.

      • Try this changes: connect directly the TH to 12v from the relay, connect it to the output terminal of the VR which is the other terminals of the VR one is connected directly to +12v from the relay and the other connected to GND. And for the trigger terminal of ic555 use 33ohm 1/4w resistor connect to GND. Adjust the VR until you can reach the voltage of 13.8v. Hope it can help.

  29. Hi
    I would like to know the formula for calculate the voltage that I want to start charging the battery.
    At pin 2, the voltage is around 2.5 volt and the pot can change this value so, what voltage I must
    have if I want to start charging at 11.5 volt for example. There is probably a formula to calculate this,
    I would like to know this formula.

    Thanks to share

  30. Hi sir!

    What changes should be made to controll an Input current of 7-10 Amp and 18 volts PV. Basicaly i have Solar panel of 150 Watts. Waiting for your reply

  31. Hi sir,I have read all d coments bt u didn’t reply them dat has d problem of both leds coming up while d voltage refuses to vary.pls correct it for us I face d same problem.

    • in this circuit you can expect that the red LED will always glow bcause it is connected direcly from the transformers DC outputs. Only the green LED will do the on and off during charging. During charge mode green LED glow and when fuylly charge greenLED turns off. Try this changes: connect directly the TH to 12v from the relay, connect it to the output terminal of the VR which is the other terminals of the VR one is connected directly to +12v from the relay and the other connected to GND. And for the trigger terminal of ic555 use 33ohm 1/4w resistor connect to GND. Adjust the VR until you can reach the voltage of 13.8v. Hope it can help.

      • good day sir. I want to ask can I use 1k variable resistor on this circuit f not which part affected and need to replace, I ask this because in my area barely hard to find electronic items like this. that’s why I need replacement only

  32. You have 230 VAC input in my case i have 110VAC. WOuld this circuit still work for me the way it is or would i have to change some components?

  33. Hi,
    It posible relay use to cut ac. I mean this ckt cut battery positive terminal, but I think cut ac power supply by using relay tx primary side.

  34. Hi,
    This circuit will be applicable for 12 volt 30 AH Battery (Auto battery) ?

    I have 5 Amp Transformer, Can I use this circuit ?

  35. hi sir my trans4mer is 15-0-15 v then i put the 6A4 diode at 0-15 v and i filter with 4700uF /25v cap. then i put 1 more 6A4 diode at + but when i test it the output voltage is 22.3v. and the 10E 10w resistor is very hot and also my ic555..

    plzz help me..

  36. Sir I made it as given above schematics on PBC, I have some problems please help me.
    I am using 15-0-15 transformer (2A). I got only 5V on pin number 4 of 555, 5.2 on pin # 3 of 555 and 4.9 at the input of relay. means 12v DC relay not operate on that voltage. kindly reply me what i do and how to solve this problem???

  37. hai sir, evething is 5n….how i can made the pcb. As per schematic /comments u given the changes know…….pls let me know design is over, i need to make a pcb pls confirm it sir. Which type of relay i wnt to buy i have little bit confusion if u have the image means pls send me sir with connection……..i am awaiting ur reply

  38. Thanks for this. A couple of questions though.
    My reference voltage on pin 5 is reading 18.2V and my 12V battery is obviously overcharging. Supply is 15V 3A. Across the zener it’s reading 5.1V. Any idea on what could be wrong?
    Also when the battery has a very low voltage or is not connected the relay oscillates. Any advice on how to disable the circuit in this situation?

  39. Sir, i have made this circuit and work properly……….but i can’t understand the working of 555 timer and its connection………sir, please kindly elaborate…

  40. Hi my friend. I have a 24V 2A transformer which i can reduce to 17V through an LM317 which will give i think 1.5A. I do not nee the red led and can therefore remove and the resistor. Can i place tactile switch before the Transistor to reset if required? As i am only using 1.5Amp and not 5Amp transformer, I think the two 5E 10w resistors will be to big, what size do they now need to be with the lower current? Finaly in the diagram is the picture showing the relay normaly open or normaly closed? Many thanks

  41. Sir, i want to make adjustable voltage and current battery charger with auto cut off after full charge, like if i want to charge 6v battery ,then for this i want to set charging voltage and cut off, same for 12v battery.

    plz help me soon…
    Thank You..

  42. Hi,
    Please help me.
    Ihave a 18-0-18 transformer but for this ckt I needs to convert this transformer in 15-0-15. So how can I convert it? please can you give me a ckt with attache main auto cut of battery ckt or separately…

    Please…

  43. Sir i have a 12v 1amp transformer will it be able to charge up my 12v 7.2ah car battery. if so what time it take?
    if i increase the amp rateing to 2amp or 4amp what will be the effect? will it damage the battery?

  44. Hello sir,
    I need to knows some thing from you.
    I have a 18-0-18 transformer. I want to use it on
    this ckt. How Can I do it (mens how can I convart
    it’s voltage in 15v?)
    one more, On the ckt I can see use 2 registance
    10 ohm 10 watt in parallel (it’s mens maybe, 5
    ohm 20 watt). Can I use another resistance in
    this place?
    What about the lag 1, 7, 8 of IC 555 and relaly’s
    upper lag? It’s not will be use on this ckt?
    please give me solution, it’s urgent… I will waiting
    for you.
    Best Regards,
    Roni

  45. can i use 18V 12A transformer in this circuit
    can this circuit work for 12v,200ah? sir if not, what are the things to replace.

  46. sir….is it possible for me to put another relay between the upper positive terminal of the battery and the junction to 6 pin of ic….which xan be actuated by the 12 v to close and open if there is power failures

  47. Hi Every Body, I would like to inform u that this circuits is propperly for only 12voolts dc battery only attach the supply only dc 12 volts no need to variable then it ll be correct work.
    2nd thing for all persons also mention your email id and skype id

    Thanks.

    Salman waheed
    salmanwaheed2008@gmail.com

    • I have 4 batt each 2 conected in series and each group(2 series batt)conected in parrellel each batt is 12v 110amp and my source 115 ac volt 60hz how can i use this circiut to charge my batteries

  48. The circuit is superb I just want to know that if battery voltage gous down after cout off (full charg)
    Like the charger is connected with battery and also connected an load to battery it will start charging automatically or I have to reset the circuit

  49. Respect sir, I am doing a project in my School in which I am able to generate 12 volt DC, using motors and dynamos.
    Sir my question is, can 12 volt DC input supply charge a 12 volt rechargeable battery ? Please, please, please, reply as soon as soon as possible.

    • You have to increase voltage because current flow from high potential to low potential if battery voltage is grater the moter the it will work as moter but if voltage is lower then moter then dc moter will work as genrater so I will recommend you to use an 6v battery or an dc-dc boost convertor wich will help to increase the voltage and boost convertor also give an stable output voltage

  50. hello sir ,
    a big fan of yours projects i have a question that i have a 18v step down transformer can this will work with that or i have to buy a 15 v transformer i hope you will reply thanks

  51. Hello Sir!

    Can i ask you, how can be increased the cutting-off threshold, because i want the power supply to be cutted-off at 14.4V, but not at 13.8V?

    Thank you!

  52. hi sir,
    I want this circuit on 6v lead acid battery.So sir what changes are apply on the above circuit.
    sir kindly help me…….

  53. Hello Sir,
    I want to use this circuit for supercapacitor charging (2.7V, 10F). The circuit should have capability to provide +/- 10 A. what kind of change I have to made in this circuit or this circuit is fine for that.
    thanking you.

  54. green led continue on. output voltage is 16 v . when set by 10k variac voltage become 11.67. can’t set to 12 volt for charge 12 volt car battery. plz help me.

  55. Is there any way to use an SCR to turn off and on the charge circuit? and not have float charging or trickle charge.
    Would it be possible to let me know by email?

  56. sir this 555 charger will able to charge 12 v 35 amp car battery ? of any replacement of components are require ?please specify.

  57. I made this circuit. What i found are :
    1. All red dan green lamps are
    2. The otomatic cut off n automatic on, both not wirking
    3a. When I turn the variable resistor or pontesion, (max) to one side, the effect is the green lamp is off but the IC is become very hot
    3b. When I turn it (max) to the other side (opposite 3a), the green is on and IC temperarature is normal
    4. The current output is okay around 14.5 Volt (with traffo 5A) so it is still working to recharge the battery.
    5. So the only problem is how to overcome the otomatic cut off and otomatic on to work?

    Appreciating for kind respon for solution.

    Thx
    Kindly as been set,

  58. hii.. what if i use transformer 220v- 12 instead of that you have used in this circuit and what are the changes that i need to do …

  59. Hi sir ,I am sathish , I want circuit diagram for “testing of induction motor using power converters” anyone pls send me to this mail address (satheeshias212@gmail.com)

  60. What is the Aim, Priciple, Applications and Benifits of this charger?
    What battrey will this charger charge? And how doesi it work?

  61. please I need you to help me with the youtube video of the 555 time automatic battery charger operations. I will be pleased to receive it in my mail.

  62. I made this circuit and give 15 AC current to DIODES , when it rectifier it , It becomes 19v in DC , It supplies 17v to the battery and the circuit is getting hotter and hotter , you said it automatically cutoff the relay bt 13.8v in DC but how is it identify when I giving 17v to the battery. ( 12v , 40AH)

  63. Sir 555 timer automatically turnoff charger when battery is fully charged or it will turn off after particular period of time

  64. Hi Sir, I want to make a rechargeable circuit that voltage can be regulated from 3 to 30 V and current is also variable. Plus, need to discharge itself when the device is fully charged to prevent overcharged. Can you please help me with this ? Thanks 🙂

  65. That circuit doesn’t work. If you fixed the pin # 5 in 5,1V, the 555 only will set when the pin # 6 reach 5,1V.
    You must put a pot 22K between pin # 6 and the battery +.Adjust this pot to 5,1V at pin # 6, when the battery voltage goes
    to 13,8V. Then adjust the 10K pot to 2.5V at pin #2 when the battery voltage goes down 11.5V.

  66. please I have as well done the whole project, am supposed to graduate but am stack_the circuit continues to charge the 12V battery even when full no disconnect. I have really run out of time, all connections are perfect and correct but no future.. the relay is only one side.

    Can I use direct DC supply of 17.5V from solar other than a tranaformer?

    pls reply

  67. I have 12v 2A dc adapter.
    When input Mains is present, with the 2A adapter i want to charge the battery(4.5AH) and with the 2A adapter i want to use my wifi router.
    when the AC mains fails the battery will backup my wifi router without interruption.like UPS.
    MY modem is rated as 12V 2.0A. That is why i want to use two 12v dc adapter.

  68. Hi Yaseen. Pls Sir, can i use the Charge controller to charge LiFePo4 12V battery. And i can’t find the updated circuit that indicate battery connections. Pls sir, help me and post the updated cct to my Email

  69. i want to make battery charger controller for three inputs.
    will you help me on this .
    i want to make simple regulator
    in which 3 inputs and on output .

  70. Both the leds glows but relay is not giving output…relay NO contact not closed…across zener diode the voltage is 5.13v …I m using 12v transformer instead of 15v ….what is the reason for relay working.

  71. Hi! I am Shakil Ahmed from Bangladesh. I have read your circuit description of this battery charger. Some questions are arise while reading this article. Can you please help me to solve my question?

    1.What is reference voltage here and which pin of 555 ic is reference voltage pin?
    2.Which pin is upper comparator pin of 555ic?

  72. I have attempted this circuit numerous times and it does not work. the 10K pot smokes up and it just confuses me totally

  73. I want to way connect charging condition betrry negetive point chargar positive tarminal and bettry posisitive tarminal chargars negetive tarminal
    Pliztel me this regan

  74. Dear sir,

    I want know about circuit diagram of 12v-24v auto detect PWM charger

    can u please guide me sir
    thank you

  75. Plss guys hope dis circuit will work well for me if i follow d diagram above…. Because am abt to satrt my project on ds typic…… Pls i need respose…… Am AFEEZ from nigeria

  76. Hi, pls how do I insert the circuit into a 12v inverter, according to your diagram I can see a negative coming out and also two wires coming out from the transformer. thanks

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