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 and maximum charging is limited by a 13.8V zener diode on the fifth terminal of 555 IC.
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.

Automatic battery charger circuit diagram

 

                                                                Click on the image for enlarged view

Components Required

  1. IC 555 
  2. Transistor BC 548 
  3. Diode (6A4 x5 ,1N4007) 
  4. Zener diode (13.8V) 
  5. LED (red, green) 
  6. Capacitor 4700uF,25V 
  7. Resistor (1K x 3,820,5E 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 13.8V in order to turn OFF the charger if the battery charges above 13.8V.
  • 13.8V is obtained by connecting a 13.8V zener 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



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26 comments:

  1. AnonymousJuly 10, 2013

    wt u mean 5E 10W

    ReplyDelete
  2. Hiii
    howmuch prize of this circuit?

    ReplyDelete
    Replies
    1. Hi Gaurav,
      To know the price of circuits, please visit our online circuit store Buy from our store

      Delete
  3. AnonymousJuly 23, 2013

    both the leds glow...
    10k pot has no effect on output voltage
    what to do???

    ReplyDelete
    Replies
    1. 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.

      Delete
    2. Please Clarify which diode you are talking about?
      is it shown in the above drawing?

      Delete
  4. 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.

    ReplyDelete
    Replies
    1. 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.

      Delete
  5. 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.

    ReplyDelete
    Replies
    1. 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 (Tubular batteries) are using constant current charging. This circuit is for constant voltage charging, so if this circuit is used for that it will take more time.

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

    ReplyDelete
  7. 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.

    ReplyDelete
    Replies
    1. Hi Mike,
      Your question is not clear

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

    ReplyDelete
    Replies
    1. Shaded part indicates negative terminal.

      Delete
  9. 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

    ReplyDelete
    Replies
    1. You cannot use this for 6 volt battery.

      Delete
  10. Hi! Is it works if i will use BC 546, BC 547 or BC 549 instead of BC 548? Are they the same specifications? What are the differences?

    ReplyDelete
    Replies
    1. They vary in the collector current (Ic). For BC 548 Ic=500mA, others are 100mA. So they may not be able to drive the relay.

      Delete
  11. Hi,
    Thanks for your lecture. Will the external charger be connected in parallel with the ups in-built charger or separate?

    ReplyDelete
    Replies
    1. Why do you need the external when you have in-built?

      Delete
  12. I need external charger because of your advice on August 7 to an anonymous fellow.

    ReplyDelete
    Replies
    1. Hi Marvellous,
      You cannot connect it parallel. You have to charge it separate by using (if it's a car battery) High current adjustable power supply circuit by setting it's output voltage to 14V.

      Delete
  13. Thanks for your response. l want to use the ups as an inverter and the battery for longer period of time. What can l do then?

    ReplyDelete
    Replies
    1. 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.

      Note:If you have no exact idea then don't go for this as it may damage your UPS and it may harm your health.

      Delete

 

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