Car battery charger

john April 7, 2010 52 Comments

Description.
Given below, is a very simple circuit that can be used for charging car batteries. In this circuit there is facility for monitoring the charging current and voltage.

The circuit is based on the IC MC78T12ABT from Freescale.The IC is nothing but a 7812 in TO-3 package with 3A capacity. The transformer T1 steps down the mains voltage and diodes D1&D2 does the job of rectification. Capacitor C1 does the filtering and C2 acts as a decoupling capacitor. The ground terminal of IC1 is lifted to 2.1V using the diodes D3 , D4 and D5 . So the output from the IC1 will be a regulated 14.1V (12+2.1).The battery is charged via diode D6.The D6 blocks reverse flow of current from battery to charging circuit when the mains power is not available. Meter M1 shows the charging current and M2 shows the charging voltage.

Circuit diagram with Parts list.

car-battery-charger-circuit

Notes.

  • The transformer T1 can be a 230V primary; 15-0-15V, 3A secondary step down transformer.
  • The meter M1 can be a 3A FSD  ammeter.
  • Meter M2 can be a 20V FSD  volt meter.
  • Fuse F1 can be a 1A fuse.
Comments
  • RICKY THE ELECTROGEEK
    September 16, 2017

    This is a Cheap And Easy To Build Circuit!!! Experimentation is NOT a Waste Of Time!!!!! ( I sometimes Detect Some Negativity In The Comments!!! LOL!!! LOL!!!) Thank You To The Designer…Yee-Ha!!!

  • Colin Mitchell
    September 2, 2017

    You will never be able to charge a 12v battery with a 12v regulator. A battery rises to 13.6v to 15v when being charged and you need a special type of transformer. This circuit is just a waste of time.

  • msdava
    July 19, 2016

    bu devre 72a otomobil bataryasınışarz edebilirmi

  • August 10, 2014

    Sir,How long the car battery has to be charged?

  • August 10, 2014

    Sir,What is the time of charging?

  • Fly
    July 9, 2014

    sir, what is the time of charging ????

  • sooraj ps
    June 5, 2014

    Sir,
    Can we use 12-0-12 transformer insted of 15-0-15 transformer.because my transformer is 12-0-12.

    • seetharaman
      July 4, 2014

      If you have only a 12 volt transformer use a rectifier and 2.5 ohms 10 watts resistance in series with the battery to be charged as a current limiting resistance, no filter capacitor is also required.

  • sonickay
    November 11, 2013

    Hello, I find this circuit and its explanation very interesting and explanatory in its entirety. However, you didn’t say the function of the LED1 in the circuit. also I will like to see a video of building this circuit if available because I dont undastand the windings/coils in T1. what do they symboolise? A video will be helpful please. My email is sonickaybid@yahoo.com

  • SJK
    November 5, 2013

    sir, i have a car battery of 12v,(not sure of how many amps it supply),and a 14v 4amps transformer ,can i make use of this circuit to charge the battery? also how will i come to know when the battery is fully charged? please do reply….thanx

    • Seetharaman
      November 7, 2013

      You can use. Once the battery terminal reaches around 13.6 Volt, the charger will only start trickling, hence no problem.

  • roomi
    June 10, 2013

    hi, what part i need to tweak in this circuit in order to charge battery on 5 amp

  • Seetharaman
    April 4, 2013

    Hi Rene you can use
    Hi Sara Paul that depends on the battery condition. A flat battery may consume 3Amps. A fully charged battery around 30 to 50mA.

  • robinho
    April 3, 2013

    hi sir ..i am student and i want to design a battery charger as my project,i don’t have much knowledge about battery charger,pls i need help and suggestions from you regarding this project

  • Sara Paul
    January 7, 2013

    sir,what will be the approximate reading of M1..

  • Rene
    December 30, 2012

    What if i don’t have a 230V AC but 127 V AC (because this is the most common voltage for electrical circuits in my country) can I get this circuit to work with a 127V to 15-0-15 V 3A transformer?

  • angad singh
    November 26, 2012

    how to covert this battery charger so that it can also charge flat batteries upto 40A/h ???

  • eby
    November 14, 2012

    Hello sir, I need a charger for 12 V 65 Amps car battery, can I use this circuit by upgrading 15-0-15v 5Amps and by changing diodes to 6A4 kindly advice

  • Wasiu
    October 6, 2012

    Pls which diod can we use to represent dat BY127 if is not available and can we use voltmeter for both M1 and M2

    • seetharaman
      October 8, 2012

      you can use 1N5404. M1 is ammeter 0 to 3amps scale. M2 is voltmeter 0 to 15Volt DC

  • ahmad
    May 12, 2012

    plz admin help i cannot get d terminals 2 connect wit d battery in d circuit

  • seetharaman
    April 28, 2012

    Hi Fredz it can charge only one partially discharged 12 volt 40AH battery and not for even a flat battery.

  • April 26, 2012

    can this charge 3 12v car batteries connected in series?

  • Seetharaman
    March 30, 2012

    Hi Vikram yes partially discharged ones but not a flat battery. for a flat battery of 35AH you require 10amps.

  • Vikram
    March 30, 2012

    Thank you Seetharaman,

    so is this circuit compatible to charge 12v 35Ah car battery?

  • Seetharaman
    March 24, 2012

    Hi Vikram you can charge partially discharged 40AH battery over night. For 100AH battery you require atleast 20amps peak current capability charger. this charger cannot handle your requirement.

  • Vikram
    March 24, 2012

    Hi Seetharaman,

    Can i charge my 12V 100Ah battery on this ckt?

    And what is charging time for 12v 100ah battery?

    Thanx in advance

  • hari
    November 12, 2011

    Tanks

  • seetharaman
    November 5, 2011

    Hi Binesh see my reply to Hari. the same will hold good for you also.

  • binish
    November 3, 2011

    hai i have 12-0-12, 4a , can i use that in this circuit..

  • seetharaman
    October 30, 2011

    Hi Hari 4nos BY127 as bridge is ok but 12 volt may not be sufficient, you require 0-15 volt transformer. you can use 12 volt transformer with 4 BY127s in bridge and connect the output of the bridge rectifer through 2 ohm 20 watts wire wound resistance in series with positive lead to battery to be chargerd is just sufficient, no need for any IC etc.

  • hari
    October 29, 2011

    Hai Seetharaman,
    I have a 0-12v 3Amp step down transformer.I think,In this case ckt will change with Arranging BY127 as bridge order… is’t ok…?

  • seetharaman
    October 29, 2011

    Hi Nidesh C2 & C3 are ceramic disc capacitors with working voltage of 40volts or above.

  • Nidesh k g
    October 29, 2011

    sir,in this circuit, if the capactors c2,c3 are ceramic or polyster? and what is the voltage rating of c2,c3. sir its very urgent Pls reply thanks.

  • February 4, 2011

    Hello peter we appreciate all the schooling and guidance but how do we get in touch with u for practical and theory lessons and can somebody study on line and get a certificate or diploma maybe even degree in the electrical and radio telecommunication? If yes please give us more details about this.

  • Seetharaman
    October 14, 2010

    Hi Abhi the DC voltage will become low and as the battery voltage builds up your charging current will become too low and the battery may not get fullt topped up.
    If you have only 12-0-12 2A on hand then use 2nos 1N5404 and a 2.2 ohms 10watts resistance and charge no other electronics is required. This will be the simplest charger watch for the terminal voltage once it reaches 14 volts terminate the charge, as the peak DC voltage can reach 12 X rt2(1.414). (appoximately 17 volts).

  • Abhi
    October 13, 2010

    Can I use a 12-0-12 (2A) step down transformer instead of 15-0-15(3A) step down transformer? Please tell me.

  • patrick vaz
    September 8, 2010

    HI seetharaman,
    Still waiting for a reply!!!

  • patrick vaz
    September 3, 2010

    Hi Seetharaman awaiting eagerly for a sketch!!!

  • patrick vaz
    September 3, 2010

    Hi Seetharaman, what ur saying is I could have a slide switch, if slide switch is moved toward ther 12 volt indication, than with the 2 rectifiers and 1to 2 ohms as current limiting resistance, would be able to charge the 12 volts battery.
    when slide switch is moved towards 6 volts then after full wave rectification followed by a thyristor and zener, transistor i would be able to charge the 6 volts battery, pls if u would add a circuit for the above would really appreciate, thanks for the help

  • patrick vaz
    September 2, 2010

    Hi Seetharaman, what ur saying is I could have a slide switch, if slide switch is moved toward ther 12 volt indication, than with the 2 rectifiers and 1to 2 ohms as current limiting resistance, would be able to charge the 12 volts battery.
    when slide switch is moved towards 6 volts then after full wave rectification followed by a thyristor and zener, transistor i would be able to charge the 6 volts battery, pls if u would add a circuit for the above would really appreciate, thanks for the help
    my email id is patrickvaz2002@yahoo.com

  • seetharaman
    September 2, 2010

    Hi Patrick With a 12 0 12 transformer you can charge a 12volt car battery with just 2 rectofiers and one 1 to 2 ohms current limitting resistance. To charge a 6 volt battery you have to add one thyristor after the full wave rectification with zener and transistor to limit charging voltage at 6.9 volts. Current limitting can also be achieved by limitting charging current at 30% of the rated capacity of the battery.
    Hi Sanjay you chage any chargeable battery with appropriate external charger.

  • sanjay
    September 1, 2010

    is there any kind of external battery charger device?

  • patrick vaz
    September 1, 2010

    Hi Seetharaman, I have a 12-0-12 2Amps Transformer, will there be any modifications required to the circuit,I want to induce toggle switches/Sliding switch to have 6 and 12 volts and slow & fast charging, Pls reply thanks

  • patrick vaz
    September 1, 2010

    Hi Seetharaman, I have a 12-0-12 2Amps Transformer, will there be any modifications required to the circuit,I want to induce toggle switches/Sliding switch to have 6 and 12 volts and slow & fast charging, Pls reply!!!

  • patrick vaz
    August 31, 2010

    HI Seetharaman, IS there a possibility of adding a toggle switch for 6 and 12 volts charging and toggle switch for slow and fast charging in this circuit.
    thanks a lot

  • Seetharaman
    February 18, 2010

    hi mr peter the above circuit is most suited for your application requirement. by replacing D3 D4 and D5 with a link and also D6 with a link.

  • Seetharaman
    February 18, 2010

    Hi since this is regulated voltage charger with a flat battery at the start of charging the current will be at 3amps, gradually decrease and once the terminal voltage reaches the rated voltage the current will reduce to minimum and it will be just doing the topping up function, hence no additional circuit is required. regarding the charge indication, replace the link between C2 and D5 connect a 0.22 ohms 5 watt resistance. a BC 547 transistor emitter to C2 & 0.22 ohm junction, base through 100 ohms resistance to 0.22 ohm & D5 junction and collector through LED and series with 2.2Kohm resistance to IC1 ‘in’. The LED will glow brighty to start with and slowly it will dim down as the battery is nearing its rated charge limit.

    • usman
      July 3, 2014

      kindly i need to design 30 amps charger some one should help me with the circuit, thanks.

  • faradaY
    February 18, 2010

    PLS. HOW CAN I MAKE THE CIRCUIT SHUT DOWN WHEN THE BATTERY IS FULLY CHARGED AND VICE VERSA . ALSO INCLUDING INDICATING LEDS. PLS.REPLY ME. 1000 THANKS.

  • MARRIJ ALI
    December 23, 2009

    GREETINGS,
    THIS MARRIJ.SIR I NEED A CIRCUIT THAT CONVERTS 12VDC TO 35VDC FOR A AMPLIFIER.
    PLZZZZZZZZZZZZZZZZZZ HELP ME

  • Peter Steenkamp
    October 27, 2009

    I need to build my own power supply for 220 volt ac to 12 volt dc around 30 watt is ok,it must be reliable for LED signage,,can I be assisted? Thanks

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