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    Here is a 12 volt lead acid automatic battery charger that shut off the charging process once the battery attains full charge. This prevents overcharging of the battery so that, the charger can be left unattended.

    If the terminal voltage of the battery reduces below the set level, say 13.5 volts, the circuit automatically turns on to the charge mode.

    Charging current as well as the power to the circuit is obtained from a 0-18 volt 2 Ampere step-down transformer. The low voltage AC is rectified by the bridge rectifier comprising D1 through D4 and made ripple free by the smoothing capacitor C1. For charging purpose, 18 volt DC is used while to power the circuit, 9 volt regulated DC from IC1 is used.

    Schematic of the Automatic Battery Charger Circuit

    automatic battery charger circuit schematic

    IC2 (CA3140) is used as a simple voltage comparator to drive the relay. Its inverting input gets 4.7 volt reference voltage from the Zener ZD, while the non inverting input gets an adjustable voltage through the POT VR1.So normally, the inverting input pin 2 gets higher voltage from the Zener (as adjusted by VR1) and output of IC2 remains low. T1 then remains off keeping the relay off. The charging current passes to the battery through the NC (Normally Connected) contacts of the relay.

    When the terminal voltage of the battery increases to 13.5 volts, pin 3 of IC2 gets higher voltage than pin2 and the output of IC2 becomes high. This activates the relay and the contacts break. Charging current to the battery cut off and the relay remains as such since the battery voltage(13.5V or more) keeps the voltage at pin3 of IC2 is higher than that of pin 2.

    Charger Settings

    Before connecting the battery, set the input voltage to IC2 using a fully charged battery or variable power supply. Turn the switch S1 to the off position and switch on the power. Then connect a fully charged battery/ variable power supply to test points TP observing polarity. Measure the input voltage to pin 3 of IC2.

    Slowly adjust VR1 till the input voltage to pin 3 of IC2 raises to 5 volts. At this point, relay should energize and Red LED turns on. Then connect the battery for charging and switch on S1. If the battery takes charge, current to pin 3 of IC2 will be low since most of the current drain occurs into the battery. This keeps the relay off. When the battery voltage increases above 13.5 volts, no more current passes into the battery, so that the voltage at pin3 of IC2 rises and relay turns on.

    attentionThe author D Mohankumar is not an active member anymore. Please take into consideration that the presented information might not be correct.
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    173 Responses to "Automatic Battery Charger"

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    1. BHavesh Lakhani says: on September 21, 2010 at 4:11 pm

      Dear Mr. D.Mohankumar,

      Can you please give me the PCB layout of this circuit, as it is very interesting crt for me. Thanky for your earlier reply.

      Regards.
      Bhavesh.

      • D Mohankumar D.Mohankumar says: on September 22, 2010 at 4:46 am

        Dear Bhavesh
        I haven’t made the PCB layout. I made the circuit in dot type common PCB. it is working well
        Regards
        D.Mohankumar

      • dear sir
        we need for circuit diagarm 24-0-24 5A FULLWAWAVE brgde rectified pls send my mail.

        tahnking you your faith fully
        chandrashekar g

      • i have HA17741 CAN I USE THIS INSTEAD OF CA 3140

      • sir ,

        i want to make a RECHARGEABLE BATTERY CHARGER which people can use in traveling or when they don’t get anything to charge their cell phones .. i want it for sell in Indian market can u plz give me some information about it …like circuit diagram or some LAYOUTS of PCB … which type of battery i have to use .and all ..i own a company YOUTHBIZ PVT.LTD ..plz sir i have no idea of this but i want to do this …

      • We have some interesting circuitry but find your website still under developement do get in touch vide our website we could exchange ideas.

      • SIR IF U HAVE HAVE ANY CIRCUIT TO RELATED ELECTRONICS THEN FWRD ME

      • kannadasan says: on October 23, 2012 at 3:40 pm

        Dear sir

        Can i use 0-12v 0.5amps transformer for the same circuit to charge 12v 100ah battery.

        Regards
        Kannadasan

      • Jim Keith Jim Keith says: on October 23, 2012 at 5:15 pm

        Should work OK, but charge time will be very long for such a large battery.

      • hi sir my name sudharshan. iwant a circuit diagram with fallowing.
        1. Battery terminal voltage at 11.5v input acpower on
        2. when it rises to 14.5v auto matically input off
        thanks inadvance

      • dear sir,

        Can you please give me the circuits for automatic cut off battery charger for 24VDC

      • please can u cut this circuit in to at least four blocks for me? please i love the circuit very much but in cant form a block with it.

      • Jim Keith Jim Keith says: on December 17, 2012 at 1:32 pm

        Block 1: Transformer Isolated Power Supply
        transformer, rectifier bridge (D1-4)
        input filter capacitor C1

        Block 2: 9V Regulator
        7809 (IC1), C2

        Block 3: Voltage Comparator
        3140 Op Amp (IC2), R2, VR1, R3, ZD

        Block 4: Relay Driver & Relay
        R4, T1, D5, RL, R5, LED (Red)

        Block 5: Output Control
        relay contacts, S1, R1, LED (Green)

        Block 6: Battery Under Charge
        Test Points (TP)

        These blocks can now be renumbered and rearranged for best visual clarity, showing interconnecting lines & arrows etc.

        Share with your classmate Abraham

      • Raphael says: on May 14, 2014 at 4:56 pm

        I have produced this circuit on PCB and seems to work fine, except for the relay which chatters when either cutting in or out. How can I solve this problem?

        Ralph

    2. The guide line of M.F battery (any kind of Maintenance Free Battery) is the between 14.4volt and 15.0 volt.
      So, the transformer needs to change from 18volt to 15volt.
      Do you think so?

      • D Mohankumar D.Mohankumar says: on September 23, 2010 at 5:33 am

        12 V Lead Acid battery attains full charge at 13.8 volts while in Tubulular batterty, it is 14.8V. It is better to give a higher voltage ( 3 or 4 volts) excess than this, because there will be a drop in voltage through the circuit and also the LED takes around 2 volts.

      • Can you please give me the circuits for automatic cut off battery charger 150AH.OR 100AH.PLEASE HELP ME

      • I do not understand why the LED takes around 2 volts, isn’t it in parallel?

      • Hello Sir,

        is it possible to get 5V & 0.8V multiple output through USB port? the input is 230V, 50Hz AC supply.

        If yes.. Then please tell me how it is possible.

        Thank you.

        Regards,
        RONAK

    3. Hello Mohan sir,
      How are you ? This is an excellent modification of this diagram ! Now it is really rated circuit !!

      And- I have found you there …… http://dmohankumar.wordpress.com/
      But still you have not post this circuit there .

      • D Mohankumar D.Mohankumar says: on September 27, 2010 at 5:54 am

        Hello Neon
        Thanks for the feedback. I am not posting the same circuits in electroschematics and in my blog dmohankumar.wordpress.com. It is an Academic Blog in which I am posting Theory and Articles

      • i need 7.5ah battery charger with automatic cut off, please send the circuit diagram

    4. Sanjoy chakraborty says: on September 24, 2010 at 3:50 pm

      This is an excellent modification of this diagram

    5. hai fnd u r idea is good and the explanation is clear.can u send me the topics for my final year project.i did a hobby kit on power saving using micro controller and street lights if u want i can send it to u

    6. vinay saini says: on September 28, 2010 at 5:24 pm

      sir i have intrasted for electronics circuit layout
      plz sir give me other information in electronics projects.bcz i m related in computer hardware networking field. but i m intrasted i hardware projects. because i m a computer hardware faculty.

    7. in this case if i decide to use this design for home ups and connect the battery terminal to my external battery i believe it should work for auto switching but what thing that baffle me most now is that the home ups battery is like 60Amphere so can that work for this design becoz you specify 2A

      • D Mohankumar D.Mohankumar says: on October 2, 2010 at 4:30 pm

        If the battery is 12 volt, you can use the circuit.Current rating is not a problem. If the battery is good, it will take less than 1 Amps current

      • 1)Thank you sir for the quick reply but what if the battery is 12v but the amper is more than 2A..
        2)what is i want to use the circuit as a customize home ups monitor , just to monitor the charging of the home ups and when its fully charged it should automatically cutoff the charging and when the battery drops the monitor should automatically reply on the charging

    8. mohankumar.r says: on October 2, 2010 at 12:34 pm

      thank u for ur information

    9. venkatesan says: on October 3, 2010 at 9:55 am

      Hello Mohankumar,
      I would like to know some details of this circuit.
      1.The usage of the Green LED
      2.The PIN connections for the COIl and Pole,N/C and N/O for the Relay
      3.The wattage for the Resistors
      4.Can we use any comparator like LM339 instead of CA3140
      5.Can this circuit be used to charge an Inverter battery(12V 100AH) without getting heated up.

      Thanks,
      Venkatesan

    10. D Mohankumar D.Mohankumar says: on October 3, 2010 at 4:21 pm

      Hello Venkatesan
      1.Green LED is indicates whether current is flowing or not through the relay contacts to the battery.
      2. Pin connection of Relay depends on the type. Generally two contacts for coil, one common contact, one NC and one NO. Use common and NC contacts.
      3. All 1/4 or 1/2 watt
      4.CA 3140 is the better choice as its switching is very fast. You can use a comparator, provided its output should be exactly Zero in the off state( CA3140/3130 has this advantage).
      5.You can use the circuit for Inverter battery.Use high gauge wires for connecting the battery and use an Industrial type Relay with sufficient contact rating.

    11. D Mohankumar D.Mohankumar says: on October 3, 2010 at 4:21 pm

      Hello Venkatesan
      1.Green LED is indicates whether current is flowing or not through the relay contacts to the battery.
      2. Pin connection of Relay depends on the type. Generally two contacts for coil, one common contact, one NC and one NO. Use common and NC contacts.
      3. All 1/4 or 1/2 watt
      4.CA 3140 is the better choice as its switching is very fast. You can use a comparator, provided its output should be exactly Zero in the off state( CA3140/3130 has this advantage).
      5.You can use the circuit for Inverter battery.Use high gauge wires for connecting the battery and use an Industrial type Relay with sufficient contact rating

      • 1. hi sir i am comfuss with the relay ( NC ) how in the way the relay place in the diagram (Relay Contacts Comm)next to D2 and D4, i dont know how to connect those pins .. please help me out thanks..

    12. G.mohanakumar says: on October 15, 2010 at 6:46 am

      Hello Mr D.mohanakumar,
      Please send me a circuit of 12v-5a battery charger
      thank you

    13. Dear Mr D,, are you over whelmed yet? nice circuit alot of response and questions hugh?

    14. hello Mr D,i find your circuit very interesting.in fact,there is a project i’m working on and i would like if you could help.i want to know how i could charge 2 of 1.5V batteries with a solar panel and the charging automatically stops when they are fully charged?pliz help…

    15. can i use this circuit to charge 12V 200ah deepcycle battery

      • D Mohankumar D.Mohankumar says: on December 13, 2010 at 6:41 pm

        Dear Peter
        The charging current will be around 2 Amps.You can use the same circuit.

      • JUNCOBE says: on March 24, 2012 at 7:05 am

        i used opto coupler for isolation circuit my input is 5 v connected to led and ouput is transistor is 48v if is input 50khz in transistor are the same yes or no?

    16. m.aqeel khan says: on January 28, 2011 at 9:09 am

      hello sir,
      this really an excellent modification in this ckt,i want to ask that i’am using “150ah” car battery in my home inverter(800va) ,well it needs atleast “15amps” of cgarging current to get fully cgarged in 10hrs,so i’want to ask that if i replace 2mps transformer with 15amps for this ckt.will it be able to cutoff charging automatically when the batterry’s terminal voltage reaches 13.8 ? or i need some modifications. (please reply).
      thanks

      • D Mohankumar D.Mohankumar says: on January 29, 2011 at 3:36 pm

        Hello M.Aqeel Khan
        Irrespective of the battery capacity, the charging current depends on the current requirements of the battery. Initially, the battery will consume more current which reduces to 500 ma or less during the remaining period. 15 Amps current is not necessary. 2-5 amps is sufficient.15 Amps transformer cannot be used for this circuit due to high current.

      • Hello Sir,

        May I know the value of R3 470R?

        Thank you

      • Hello Sir,

        May I know the value of R3 470R?

        Thanks

      • IC CA3140 is not available in any of the store in my place. Is there a substitute that can be used in battery charger circuit?

        Thanks.

    17. Hi Sir Mohankumar,
      Thanks a lot for your circuit design. I just wonder if it is alright to use a transformer that is 18 volt but 3 amperes instead of 2 amps. I cant find a 2amp in the store.
      Thanks a lot for your response.

    18. Kishore says: on June 14, 2011 at 6:04 pm

      Dear Mohankumar,
      I am looking for a 12 Volts, 4.5Amps (DC lead acidbattery charger, which will do the following.
      1) In the absence of electric supply, our embedded system should be able to derive power from 12V,4.5AmpsHr battery.
      2) If electric supply is there, our embedded system should derive power from electric supply only and not from battery.
      3) At any circumstances, if the voltage level of the battery is less than or equal to the lower thresold, then battery should be automatically recharged.
      4) If battery voltage level is equal or exceeds the upper thresold, then battery charger circuit should be disconnected i.e battery should not be charged.
      Can you please send me the schematic?

      Thanks,
      -Kishore

      • gyan singh says: on November 7, 2011 at 11:20 am

        dear kishore,
        I am looking for a 12 Volts, 1.2Amps (DC lead acidbattery charger, which will do the following.
        1) In the absence of electric supply, our embedded system should be able to derive power from 12V,1.2AmpsHr battery.
        2) If electric supply is there, our embedded system should derive power from electric supply only and not from battery.
        3) At any circumstances, if the voltage level of the battery is less than or equal to the lower thresold, then battery should be automatically recharged.
        4) If battery voltage level is equal or exceeds the upper thresold, then battery charger circuit should be disconnected i.e battery should not be charged.
        Can you please send me the schematic?Thanks,
        regard:gyan

    19. hey,
      Can you give me the link to the new 12V 5A automatic battery charger. Suppose if we have to increase the current in the above circuit what are the modifications needed.

      Thankyou

    20. Dear Sir,

      I am a follower of your acdemic blog as well as electroschematics and can you explain the advantages and disadvantages of Trickle and Regular charging of lead acid batteries and also I am very much thankful if a charger circuit incoporating both functions are posted in one of your blogs.
      Further to get 13.8V dc a Transformer of 12V ac secondary is sufficient or better to have 18Vac secondary to get 13.8V dc after rectfication and smoothing.

      Finally if possible kindly include some theoretical and practical notes on SCR and Triac’s etc.. and some battery chargers circuits with SCR/Triacs/Diacs also lateron.

      Thank you,

      Ananda

    21. good day sir.
      .can i use this ckt to charge 8 1.5V battery in series?? what would be the max.current?is it the individual current rating or the total current rating of the 8 batteries??
      please reply as soon as you have read this.
      thank you so much..

    22. Hello Mr D.mohanakumar,
      Please send me a circuit of 12v-100ah battery charger 3 state.
      thank you

      • gyan singh says: on November 7, 2011 at 11:16 am

        sir,tell me where from i will get 12v,1.2AH,AUTOMATIC BATTERY CHARGER CKT
        PLZZZZZZZZZZZZZ REPLY OR IF POSSIBLE SEND ONE CKT
        REGARD:
        GYAN

    23. ola gostaria de saber a potência dos resistores

    24. hello Mr D
      if relay contact close,voltage trans case pin + opamp >pin – opamp then relay off then again relay on then loop start again?

    25. Sir Can You Plz tell me how can i use it to show on a 7 seven display the time it takes to charge?

    26. its posible to change this circuit for 24 volts battery

    27. gyan singh says: on November 7, 2011 at 11:12 am

      hello mr. mohan sir,

      sir, i have 1A.,12v transfer+bridge rect+filter,
      sir i have to charge 12v/1.2AH battery+1 mobile (4.2v) with that.
      condition when battery gets full charge charger must cut off…………. sir plz help me out in that,send me 1 circuit regarding that plzzzzzzz.
      regard:
      gyan singh

    28. AbdulHuck says: on November 16, 2011 at 2:26 pm

      Dear Sir,

      It’s a nice circuit which I would like to implement in a solar charging circuit. Can we replace the 6V relay with a switching transistor? I would love to see a schematic with this modification.

      Thanks,
      Abdul

    29. dear sir,

      can i use this cicuit for Li-ion battery?
      plz suggest me.

      thanks
      arun

    30. hi sir iam new to building electronic circuits actualy i wnt to ask u dat what is need of relay

    31. Actually I need the block diagram,advantages and disadvantages of automatic battery charger circuit.Please send us.

    32. sir
      if we are using a dead battery for charging den it ill affect a low voltage so the circuit ill charge continuously . so how can we maintain dat. can u pls reply abt it

    33. Upinder Cheema says: on January 11, 2012 at 12:41 pm

      Hi, Mohan ji
      There are two relays in this ckt. What is the function of 2nd relay and what the red LED indicates

    34. Bhaaskar.R says: on January 17, 2012 at 4:16 pm

      Dear sir,
      Thanks for sharing circuits.I need a circuit to show the charging status (Two LEDs or more to show the status while charging the battery like in UPS). Please send the circuit.

    35. Dear Sir Can you tell me a circuit of 1.45V DC 3.0 mili Amp power supply from 220V AC. The 1.45V should be constant.

    36. Dear sir D. Mohankumar!
      Plz tell me. How can i 12 voltages to 5 voltages drop for a battery charge and i want make an automatic switch off circuit when battery is full charge… And i want make a remote control circuit of 3.5 channels of radio control for fly micro or small circuit….plz plz reply me as soos as with a circuit diagram. From pakistan..
      Regards

    37. stakilobishut says: on February 8, 2012 at 10:18 am

      Is the output volts of the transformer according to the voltage of the battery or higher or lesser? Pls. tell me. I’m new at electronics

    38. Omorodion Odigie says: on February 9, 2012 at 2:46 pm

      sir,
      please can u help me with an smart SLA Battery charger for 2 X 200A battery in parallel

    39. i want to build a fully automatic charger for 200 ah battery..please help me to build it well.thanks

    40. hello sir can t please give me the detailed description of this project. what is the use of red led.

    41. hello sir,
      can u pls give me details and ckt diagram of simple automatic mobile charger for 3.7 volt battery..

    42. Sir i have to charge a 12V 66AH lead acetate battery the battery must give 4 hours backup and the load on battery is about 11AH. the battery must be charged at the same time while in use which circuit do u recommend for this because i need to charge the battery fully in about 6 hours please reply soon sir

    43. hello sir,
      can u please give me the detailed description of this project. and also what is the use of the LED.
      sir please post the answer in this page. i was unable to view your blog in my mobile. so please post the answer right here sir.

    44. i want to build a fully automatic charger for 150 ah battery..please help me to build it well.thanks

    45. sir i m asking for u this battery charger use genset ya ATS Pannal.plz send ma circuit diagram use the pannal and genset battery charg.I m wait you,r replay for mail

    46. This is the worst battery charger circuit I have seen.
      The transformer is either 16v or 18v RMS and this will convert to at least 20v after rectification.
      The battery voltage is about 14v when charging and this means the difference in voltage is 6v.
      There is no dropper resistor to drop the 6v and this means the transformer will deliver more than 2 amp and it will burn out in less than an hour.
      You simply cannot connect a transformer to a battery without some form of current-limiting.

      The author of the circuit has absolutely no idea how to design any type of circuit.
      DO NOT BUILD THIS CIRCUIT.

      Colin Mitchell
      talking@tpg.com.au

    47. 1N4007 diodes are 1 amp and they will also fail after about 10 minutes.

      • Eliminator says: on March 19, 2013 at 8:49 am

        Colin Mitchel has very little knowledge of electronics, he only boasts in front of hobbyists who are new and inexperienced, just check out the below given link to see how he was SHOWN THE DOORS when he tried to impose his limited knowledge over the experts:

        www(dot)forum(dot)allaboutcircuits(dot)com/showthread.php?t=62887

    48. sir how can i use this circuit for charging a 3.7 volt LIB ? looking forward for your reply…. Thanks for Posting Such Interesting circuit….

    49. SHAUKAT says: on March 22, 2012 at 9:40 am

      WHY UPS/INVERTER BATTERY DAMAGE BEFORE 1 YEAR AND NEED TO REPLACED PLEASE REPLY

    50. Dear sir
      Thanks for ckt diagram, can u tall me it posible to auto cut ac of this ckt and how posible to use this circuit to charge 24v battery.
      Thanks
      Salim

    51. dear sir,

      as per the your diagram, i assembled the same circuit,in that my application i required cut-off between 13V,how can i change it, plz guide me.

    52. Sir
      I want to switch on the circuit when the voltage drops to 12.5 v after fully charging the battery.(i.e 13.5 v). I have assembled the circuit and the relay keep chattering since the circut is going for charging mode when voltage drops to even 13.4 v.

    53. maikbless says: on April 10, 2012 at 10:51 pm

      Dear sir
      i humbly request to know how i can simulate a ‘battery charger circuit using SCR’ with a ‘battery indicator circuit’.thanks and regards

    54. maikbless says: on April 11, 2012 at 3:14 pm

      Dear sir, mr. D. Muhankumar,i humbly reguest to for explanationg as to how i can simulate a ‘battery charger circuit using SCR’ with a ‘battery indicator circuit’ to get a battery charger/indicator circuit

    55. asad al hakeem says: on April 16, 2012 at 5:13 pm

      Dear all,
      i made the circuit and the result as i’ve expected
      1. the control part is working very good
      the green led lights and when calibrating the voltage of input no. 3 of the ic2 the red led lights up
      2. the fault of this circuit is the battery and the contacts are built inside the circuit and because the transformer is 18v it gives 24v dc so the current flowing the circuit board is very high so it burns the board.
      3. the circuit needs to be modified so that the battery charging path does not go through the board

      thank
      regards

    56. hai sir
      i need some more electronic project circuit pls help m e sir

    57. Hello Mr. D.Mohankumar,

      I need your help, Here is a 6V 4.5 AH battery charger circuit which is able to charge 6V 4.5 AH lead acid batteries. The schematic is very simple and using only few components. IC LM317T is the heart of the circuit. The circuit is automatic so when the battery will become full charge it will stop charging. So, tell me were I put LED connection for Charging Indication or when full battery then show Full Indication LED auto ON. you can see circuit diagram on this link. http://www.circuitdiagram.org/6v-4.5ah-battery-charger-circuit.html

      awaiting your prompt reply.

      Tahir

    58. DEAR sir;
      i want automatic charging circuit for 12volt lead acid battery(80amp hour.
      thanks

    59. sir, how can i cannect my circut to this circuit.? i want my system to work in ac but when no power it should work through battery. pls help me out sir

    60. muktesh says: on May 19, 2012 at 7:03 pm

      Dear sir,

      I have 2 dry 12 V , 26 AH batteries

      I want to make automatic charger for it, please provide circuit diagram and components details as well.

      It will be very helpful to us for completion of our project and it will be added advantage of our project

      In our project we are using this batteries, but we doesn’t have any charger – after each full use of batteries we need to charge it from outside agencies.

    61. pls i need 10A BATTERY charger circuit diagram for 100AH Deep cycle battery

    62. Sir, How Will i Relay connect???

    63. Sir,
      Can i use 220V-12V 3A transformer???

    64. Syed Ashraf Yousuf says: on June 1, 2012 at 10:56 pm

      I have tried some schematics of Mr. Mohankumar on IR. I have found them simple, easy and good-working. There are many schematics on the Web, but most of them are not perfect. Till now I have not tried “Automatic Battery Charger” , but am sure it will also work like IR.

      The remarks of Mr. Sivanand and Collin Mitchell is very sad and irresponsible, as it may frustrate the hobbyists. It is true that Mr. Mohankumar uses to place a recipe, and not a prepared dish on the table. It is a guideline for the beginners. If you great Scientists have better idea, then why you are not coming forward. Instead of uttering rough comments it will be better to serve the humanity with your ideas and knowledge.

      Mr. Mohankumar has not posted this schematics to be used in Air crafts or sensitive electronics gadgets, if it can control a 12v7A U.P.S Battery, even then it is too much to learn.

      We must honor noble persons who are engaged in serving the humanity without personal gain. If I would get chance I am willing to salute Mr.D.Mohankumar personally.

      Syed Ashraf Yousuf.
      Chittagong, Bangladesh

      • MR Syed

        Colin knows his electronics and minces no words for circuits that are inefficient. while Sivanand is a newage electronics expert.

        Both are people who have proficient knowledge and practical experience to say what they say.. They are not theorists like Mohan.

        Many of Mohan’s circuits are inefficient and use of unnecessary components. What is professed by Colin and Siva are efficiency and practicality.

        1. There is absolutley criminal wastage in a lot of the theories and circuits floated.
        2. Use of voltage (Input 2 times the output needs to charge a 6V battery he reccomends a 12 volt Solar panel or transformer
        3. In this circuit he uses a 18v input and then uses a 7809 to drop . If you are going to use 9V the voltage after rectification from a 18V would be approx 24 Vdc. this would heat the 7809.
        4. he recommends 4007 which can withstand only 1 Amp for a transformer that is rated 2 amps .
        5. Use of unnecessary components are not reccomended like something difficult to get hold of CA3140.

        Keep things simple and let the amateur enjoy his journey but then Mohan is a lecturer in electronics and need to keep thing complex .

    65. Easwaramoorthi says: on June 12, 2012 at 4:07 pm

      Dear sir,

      I am trying to do the uninterrupted power supply for the simple led light. led should glow with both external power as well as with battery. can i get the circuit diagram for this using relay.

    66. 1. hi sir i am comfuss with the relay ( NC ) how in the way the relay place in the diagram (Relay Contacts Comm)next to D2 and D4, i dont know how to connect those pins .. please help me out thanks..

    67. Jim Keith Jim Keith says: on August 1, 2012 at 1:59 pm

      Experiment with the relay on the bench to determine which pins provide continuity (0 ohms) without the relay energized (normally closed contact). Then apply power to the coil and observe that the circuit opens. These are the pins to connect in the circuit and they can be swapped without causing problems in this application.

    68. hi,Jim Keith thanks for the advise now my problem is for the first relay how many pins relay i should use for the circuit 3,4 or 5 pins? How/where should i connect the point( NC )on the relay,as for the second relay i know is using 6v 5 pins relay correct?i am not sure with the symbol (NC) in the diagram.Please advise,thanks..

    69. Jim Keith Jim Keith says: on August 1, 2012 at 6:03 pm

      NC means “normally closed contact” and this is what it indicates in this drawing.

      NC could also mean “no connection,” so it can really get confusing.

      I think what you are missing is that while the contacts connect to the points shown on the left side of the drawing, the relay is shown on the right side. These are connected even though the lines are now shown. The NO (normally open contact) is not connected in this case.

    70. Hi,Jim Keith thanks for the explaination,
      1:so in the drawing can i say that the (NC) is not symbol of the relay and i could close contact ( NC ) and S1 act as a switch?
      2:Why there are words (Relay Contacts Comm) in the drawing?I shall ignore it?
      3:Please advise,thanks..

      • Jim Keith Jim Keith says: on August 3, 2012 at 2:51 pm

        “S1″ is the mechanical battery disconnect switch–perhaps toggle switch

        “Relay” is the electromechanical switch (same device indicated on both sides of schematic)

        “Comm” is the relay common terminal or the armature (moveable contact in this case)–it moves between the NC contact and the NO contact. These three terminals called “Form C” relay contacts.

        Sometimes “Com” can refer to circuit common, but that is not the case here

    71. HI Jim Keith. ok noted thank for the advise. So in this drawing can i close contact for the NC (means a striaght line from C1 470uf 25v capacitor at + sign to R1 1K resistor) and use S1 the mechanical battery on/off switch whenever i want to charge battery? is it this way, Please advise. Thanks

    72. Hi Jim Keith thank for all the help/answer…I will start the project,will update you if its done,thanks…

    73. Plz tell me how to connect d relay with d switch close to R1 and battery connection more details about dis project hi nid high current and hight voltage for charging at least 18-0-18 5A can hi replace IC1 to LM338 and tell me hi can hi connect R2 and VR1 plz help sir MOHAN

    74. Plz quick response hi am a final student hi nid dis projects

    75. Plz just tell me how to connect d relay close d switch

    76. Plz hi did nt understand d relay connection contacts comm relays Nc….yehh help me JIM KEITH

    77. Dear mohan sir, I am serching for a circuit of 12v-1A with automatic cut off battery charger for handy transceiver, and how to connect relay
      thank you

    78. actually IN4007 the current rating for this diode is 1amp..and this circuits is 2amp ..this will lead to ecess of damage the diode..there is no current limiting for the battery.. 0_18volt 3amp..is ok IN5408 is sufficient for 3amp….

    79. Dear Sir Mohan,

      Greetings from Philippines!

      can you please elaborate more on how to calibrate this circuit? i am an not an expert but i am an electronics enthusiast. If you have time please email me the guidelines on how to do it.

      Thank you very much.

      wars

    80. J.K.Srinivasan says: on September 10, 2012 at 5:01 am

      sir,
      this site is very useful. please let me know to charge 12v 150ah tubular battery which ams/volts transformer should i use?
      capacitor charger ups is not charging well.
      is passible any changes to do in that ups?

    81. Sir,

      why such complicated circuit?? if you set the transformer output voltage set to 13.8v using lm317t(if more current then 1 amp is required then use current bypass transistor like 3055 ) then battery will always in float mode and no other relay,transistor op amp etc not required.

    82. senthil nathan says: on September 26, 2012 at 8:53 am

      Dear Mr.D.Mohankumar,
      ur circuits r very useful for electronic students and hobbyist, I have tried out most of ur circuits they r well and good
      can u pls give me the circuit for charging 12v/45Amps lead acid battery with auto cut-off & float charging

      thank u

    83. suhagpa25 suhag patel says: on October 1, 2012 at 2:17 pm

      IS THIS ABOVE CIRCUIT CAN WORK FOR 12V & 7AH BATTERY OF 200VA UPS.
      PLZ REPLY FAST…….

    84. electron_revolution says: on October 8, 2012 at 4:19 pm

      this circuit will automatically charge when it reach 4.7 volts n below. the cheapest way to create a automatic battery charging circuit is thru using a only a regulator. for example 12 volts regulator for 12 volts battery but be sure that the battery voltage is greater than the regulators voltage to avoid overcharging..

    85. dear sir

      can this circuit operating normally if i using to charge lead acid battery 12v – 5Amp ?

      thanks

    86. Can this circuit be used for 15 volt 10 amps transformer by changing the relay and diodes the rest as same please suggest.

    87. Nwaubani Henry says: on December 9, 2012 at 3:03 pm

      Pls mr D.Mohankumar i want an automatic 24v battery charger circuit with cut off at full charge.the battery speffication is given below.two,12v battery connected in series,135A each. include the circuit parts pls.thanks.

    88. Rohitkumar says: on December 10, 2012 at 2:39 pm

      DEAR SIR,

      What is the need of 4A Fuse in the circuit?

      why should we use 4A FUSE only?

    89. You cannot charge a battery from an 18v transformer. The transformer will BURN OUT. Do not build this circuit.
      The transformer must be designed as a BATTERY CHARGING TRANSFORMER and its output voltage must be exactly suitable for the battery.

      • Eliminator says: on April 13, 2013 at 7:17 am

        the above person doesn’t know anything about battery charging….he says a battery needs a “designed transformer”

        actually any ordinary transformer having current rating 1/10th of battery AH and voltage a little higher than the battery specs will work perfectly for charging all lead acid batteries…..that’s as simple as it can be.

    90. suhagpa25 suhagpa25 says: on March 12, 2013 at 9:20 pm

      how can i very the battery charging voltage and give 12V constant to the battery with this circuit pzzzz tell me…..

    91. Nonsco1023 says: on March 30, 2013 at 1:06 pm

      Helo sir, i have 2A, 15V trafo should it work in this circuit, pls sir i need reply thanks

    92. Eliminator says: on March 30, 2013 at 4:51 pm

      Nonsco1023,

      the above circuit does not incorporate a current limiting feature, so you should select a transformer whose current is rated at around 1/10th or 1/5th of battery AH that needs to be charged.

    93. Eliminator says: on April 13, 2013 at 7:11 am

      the above circuit (talking electronics) is a bad circuit, it looks good on paper but practically when you try adjusting the threshold cut off level it would keep on producing different tripping points….don’t believe it, just try it.

    94. Nonsco1023 says: on April 23, 2013 at 1:17 am

      Eliminator had worked the circuit with full detail as described but i got it all wrong as you said the relay kept making noise, when you want to set at threshold point, so i need help to make it work well please. Thanks

    95. reduce the 270R resistor

    96. The circuit (from talking electronics), highlighted above is “cheap”, but not cheerful!

      Practically it is very difficult to “set” the threshold point, and in the documentation, he said “In our circuit, the cut-in voltage was 11.5v with a 270R across the relay” (Ref http://www.talkingelectronics.com/projects/200TrCcts/101-200TrCcts.html#84 ).

      This calls for more explanation from the designer. Finally, adding a resistor across an EMR is unorthodox!

    97. sir i’ve used the above circuit to charge battery with solar panel but problem occurred is that the battery instead of charging is getting discharged. can i get any help please?????

    98. kwame frimpong kwame frimpong says: on May 20, 2013 at 12:16 pm

      sir, please i want a circuit that can detect human beings

    99. Md. Ahsanul Haque Chowdhury says: on June 20, 2013 at 11:46 am

      Sir , If i want to make a battery charger for a mobile battery i.e. 3.7 V battery then what should i do

    100. A Lithium Ion charger is a very complex thing to build. Here is one for $1.50 (post free) on eBay:
      http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=170926767910&ssPageName=ADME:L:OU:AU:3160

    101. “I want switch mode charger”
      WHAT DO YOU THINK THE $1.50 charger is ????????????

    102. Md. Ahsanul Haque Chowdhury says: on June 20, 2013 at 11:44 pm

      i need the circuit diagram. there is no circuit diagram given

    103. sir,
      please i want the connection video or photo of this circuit..i dont know how to connect..please mail me the video link or photo. which type of battery is used in this circuit(auto turn off battery charger)…

    104. sir am an animator, also i like electronics,, i have an idea for making power. i need some electric circuit for that. can u help me?. now i need the above showing circuit with full values.

    105. Me ha interesado mucho este circuito para cargar una batería de auto de 12v 45A. puedo ponerle un transformador de 20v 3.5A solamente este he conseguido

    106. vijayakuamr says: on December 17, 2013 at 10:27 pm

      dear sir… i need 12v/26AH dry battery automatic charger circuit diagram. plz send my email id…

    107. Colin Mitchell Colin Mitchell says: on December 17, 2013 at 11:02 pm

      How many amps is your power supply?

    108. vijayakumar says: on December 18, 2013 at 1:20 pm

      power supply maximum 3 Amps

    109. Colin Mitchell Colin Mitchell says: on December 18, 2013 at 6:11 pm

      How many volts is your power supply

    110. vijayakuamr says: on December 18, 2013 at 10:03 pm

      How to charge 12V/26AH battery from the source of 230v,50HZ power supply.. kindly send automatic charger circuit

    111. i need a circut of a rechargeable bettery of 3.7v using input 5v 1000 mah and 5v 1000 mah

    112. Colin Mitchell Colin Mitchell says: on January 13, 2014 at 8:15 am

      This doesn’t make and sense at all:

      i need a circut of a rechargeable bettery of 3.7v using input 5v 1000 mah and 5v 1000 mah

    113. sir,
      i want a charger to charge my lead acid batteries(12V-26Ah) within 6 hours.any options for do this process. pls comment me

    114. Colin Mitchell Colin Mitchell says: on January 21, 2014 at 6:01 pm

      You will need a 5 amp charger

    115. I just made a charger for a 12v 3-4amp acid battery using this circuit (http://www.electroschematics.com/wp-content/uploads/2010/10/12v-charger.jpg)
      how i can integrate the above circuit in my circuit to make it an automatic charger?
      plz reply coz currently its totally manual with a switch
      i wish i wud hv found this first but now im stuck plz help me
      u can contact me on fb @HaZZanZia

    116. That circuit will not work. Te transformer voltage is wrong. The 100u is not needed and there is no current limiting resistor.

      What current does the ammeter read when charging?

    117. Measure the voltage across a 1 ohm resistor

    118. sir,
      i want a charger to charge my lead acid batteries(12V-26Ah) within 6 hours.charging time must important.how much amount of current characteristics (like:volt, amps) for gives to charge the batteries. pls give the circuit for that.

    119. mantu kumar says: on March 13, 2014 at 6:40 pm

      hello sir ,i want a battery charger to charge lead acid batteries(12v,7ah)within 4-5 hours.how much amount of current characteristics (like:volt, amps) for gives to charge the batteries. pls give the circuit for that.

    120. pls i have 800 AV inverter, the charging circuit is not charging d battery. I’ve taken to repairer but can’t rectify d fault.
      I want to build separate battery charger that can stop automatically when battery is fully charge, please send me d circuit diagram, i’m using deep circle battery of 12v/200AH

    121. ezhilvendan says: on May 3, 2014 at 2:32 pm

      hi,
      i need connect one battery . its used to connect load as-well as its want to charged so anybody help for it

    122. Colin Mitchell Colin Mitchell says: on May 3, 2014 at 9:18 pm

      Just put an isolated charger directly onto the battery.

    123. James Wang says: on May 23, 2014 at 6:08 pm

      where is the NO terminal of relay goes??

    124. James Wang says: on May 24, 2014 at 2:53 am

      can i use this charger for acid car batteries??

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