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12v charger

Simple 12 Volt Charger

This is the circuit of a simple 12 volt battery charger for Lead Acid battery. It gives 12 volt and 5 Amps current for quick charging of the battery. If the battery is partially discharged, full charge will be attained in one hour.

The circuit uses a 0-14 volt 5 Ampere Step down transformer and a 10 Amps Bridge rectifier module to convert AC to DC. Since pulsed DC is good for Lead Acid battery, a low value smoothing capacitor is used as C1.To monitor the charging status, Ampere meter is provided in the positive rail. LED act as the Charger on status.

Schematic of the Simple 12 Volt Battery Charger Circuit

12v charger

When the output is connected to the battery terminals, the meter shows a higher reading depending on the current flow into the battery. As the battery attains full charge, its terminal voltage rises to 13.8 volts and current through the meter ceases. The meter reading then returns to zero. This indicates the full charge state and the charging can be terminated.

49 Comments

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  • v sambath kumar

    Hi Riyagote,
    yes it will work , Lm3i7 safe working voltage is 35v, to avoid over heating and safe
    operation of the ckt i prefer the in put voltage supplied to the ic is limited to a max
    of 22 volts. with your 18v center tapped transformer you will get around25.4v.what you can do is give the 25.4v to the collector of a 2n3055 npn transistor and connect a 7818 reg ic in put point to the collector of 2n 3055 tr and ground the centre pin of the ic in series with 5 nos of IN4007 diodes , anode of the diode should go to the ic pin and the cathode of the last diode should go to the gnd ie negative, (you can also put a 3v zener ) but putting the IN4007 diodes are more reliable. now connect the out put pin of the ic to the base of the 2n3055 tr and connect the emitter of the transistor to the input of the charger ckt now your in put voltage will be 20.4v.provide heat sink for the transistor.
    V.Sambath kumar.

  • v sambath kumar

    Hi Riyagote,

    Actually i want to post a project for 12v 7ah bat charger ,this is a tested and found working ok circuit.Try this make sure you go for a 15v 2amp transformer.

    PFA

    Regards,

    V Sambath Kumar

  • riyagote

    I’m using centre tap transformer of 18v/2amp and bateery of 12V/7.5amp. Using these equipments will the circuit work?

  • Davey

    There were not very many diagrams. I’m looking for a diagram of a Linwood MP8 battery charger. The wiring on it was like a rat’s nest and it used 3 amp diodes which were running at their limit. The circuit allegedly produces 6 or 12 volts by operating a switch. Another switch gave High or Low output. Its this last bit which is puzzling as I’m not sure whether “Low” was achieved by putting the extra diode in series with the output or by going from full-wave to half-wave. When I took it to pieces it all seemed so simple but its not!

  • davieson

    Sir, I build my own circuit with 15 volts transformer and 4700uf/ 25 volts capacitor . I want to know if is ok, if it has no bad effect on the battery thanks sir in advance.

  • alabi sam

    pls hw may connect ammeter to a battery charger and the substitude if it is not available

  • Momoh

    can I use 15v/2A transformer replace of 14v/5A transformer….

    • Jan Zumwalt

      I am sorry, about the previous answer – misread the /2 as “12”. The 15v is acceptable but it will only charge at 2A which really does not “charge” it is more like “toping” off the battery.

    • Jan Zumwalt

      No you can not.

      When trying to charge a 12v battery, the charging voltage must be greater than the battery or the battery will drain towards the charger (high to low). Also there is some voltage drop across the bridge diodes so the circuit already has a marginal supply voltage. Many similar charging circuits use a 16V transformer supply.

  • sohail

    Please any can help me, i want to do this without using transformer…

  • arximastoras

    I connect an 12volt 4ah battery and the ammeter shows 3 amperes!I don’t think that’s normal.The battery has max input current less than 1,2A

    • arximastoras

      Thanx for the reply.A couple of questions more if you please.How much should the voltage measure at the output without a load? Also,my transformer is 15 volts.What modification is needed to avoid overcharging the battery?

      My battery has these specs:
      12volts
      4Ah
      standby use 13.6-13.8 volts
      cycle use 14.5-15.9
      max initial current less than 1.2A

    • KROKKENOSTER

      Arxomastors hi! The current into your battery is controlled by the state of charge of your battery and the power output and voltage of your charger. A lead acid battery will take what you throw at them (within reason) The charger you need will need a series resistor to limit the current. I fitted a 12 volt 18 watt globe in series and then your will also indicate that you are charging. This is the cheapest and easiest way to limit the current.

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