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.
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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 timer1 12v Battery Charger Circuit with Auto Cut off
                                                                Click 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


  • 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

555+timer+internal+diagram+and+pin+out 12v Battery Charger Circuit with Auto Cut off
BC+548+pin+out 12v Battery Charger Circuit with Auto Cut off

101 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.

    • 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

  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 (

    • 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.

  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 .

  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.

  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

  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

  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?


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

  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.


  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

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