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    This battery charger circuit can be used to charge one or more batteries with the total nominal voltage of 12 V, meaning ten NiCd battery or six 2 V lead acid. The circuit is pretty small and can be built in a housing network adapter. The incorect usage is impossible: connecting the batteries with reverse polarity, shortcircuit of the output terminals or power loss have no impact on the charger or battery.

    We can use a transformer with 18 V on the secondary and then using a diode bridge to rectify the 18V ac voltage we get 22V dc on C1.

    The completely discharged batteries are charged at the begining with a 6 mA current thru R2-D2 and R4-R6-D1. One the bat. have reached 0.3 – 0.5 V, the base-emitter voltage of T1 is high enough to bring the transistor in conduction.

    Green LED D4 is used as an charging indicator and opens T1.
    There is a 60 mA current flowing thru R5-R6, this means that the charging of a 500 mAh NiCd battery will take 12 hours.

    If the battery is connected with reversed polarity or there is a shortcircuit, the power transistor T1 remains blocked and the charging current can not exceed 6 – 12 mA. The current draw at maximum load is around 80 mA.

    Battery charger circuit schematic

    batteries charger circuit diagram

    Battery charger PCB Layout

    12V battery charger pcb with components

    12 volt batteries charger pcb layout

    Components List

    R1 = R2 = 10K
    R3 = 1K
    R4 = 5.6K
    R5 = R6 = 12Ω

    C1 = 1nF
    C2 = 220µF / 35V

    D1 = 1N4001
    D2 = D3 = 1N4148
    D4 = green LED

    T1 = BD140
    T2 = BC546

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    19 Responses to "12V Battery Charger Circuit"

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    1. elfaki Yousif says: on June 6, 2011 at 5:28 pm

      thank you for this circuit itis very good.

    2. where is the D8 in this circuit?

    3. hi im saeid my job is ship fitter i have a question ? how trubble shooting and repair battery charger modell mass 50/24
      tanxxxx

    4. hi can i ask if this circuit would work if you will charge less than twelve volts nominal voltage..thank you!

      • alexpmgr8 says: on February 23, 2012 at 3:37 am

        yep, but i’m not that mean. I’ll let you in on a lil secret staring us all in the face, it is made to charge 12 volts. Put 12volts into a 9v battery and it will kill the battery fairly quickly. Tryfinding a circuit that uses an adjustable lm317t regulator circuit .

    5. can you give me more details about this circuit???

    6. Does this circuit have over charging protection?

    7. Mosfetti says: on June 29, 2012 at 8:23 am

      If you rectify 18 Vac and smooth it to DC, how do get 22 Vdc? Multiply 18 x 1.414 gives 25.5 Vdc

    8. Please make the PCD layouts also large as the circuit diagram. That way it is easy to take a print of the whole article

      -Shibu

    9. T1=BD140 is NPN transistor, not PNP as shown in scheme.

      • You must have used some strange datasheet if you say that BD140 is NPN… It is PNP and has been like this from its birth, when the silicone met the plastic case for the first time.

    10. saideep says: on July 15, 2013 at 6:01 pm

      can you please tell me the necessity of two transistors t1,t2

    11. what will be the output voltage after the rectifier diodes and its output voltage in the circuit if the transformer secondary winding is 12V??

    12. While might be good for charging NiCd batteries (that I don’t Know), this circuit is useless for 12V Lead Acid Batteries(that I do know well). A completely discharged 12v Lead acid Battery has to be charged on 3 stages.1 – Bulk charge (constant current 4A to 10A or more), depending on the battery size,2 – Topping Charge, and 3 – Float charge. To maintain a battery you can use a Trickle 13.2V up to 500mA, a Battery Tender with Hysteresis Threshold 12.6V – 14.5 V up to 1.5A, and a Smart Battery charger up to 20A, with equalizing and battery reconditioning feature.
      Buy at Freight Harbor Tools, a Battery Float Charger, Automatic on sale for $9.99 or ($6.00 with coupon). The factory 13.2V is only a promise. Open the regulator, replace the 56 Ohm resistor marked as VR1, with a 100 Ohm trim pot, via two tiny wires. Now you have a Voltage regulated battery trickle, from 12.5 V to 14.25 V. Float charging a battery is like dancing on a needle. At 11.4 v the car battery is discharged and at 12.9V is fully charged. Increasing the voltage above 2.26V per element or > 13.5V, the battery start boiling. Tiny current as low as 20mA, for long period of time oxidize the positive elements. I set the regulator at 13.25V on the car and forget. I have more than one car, and while not in drive I trickle the battery to keep at 12.9 V on REST (without charging element). This is only the first AID. Periodically you have to equalize the elements of Battery, This can be done increasing the charging voltage, periodically, to 14.5 V for 2 hours. While the weaker cells are charging the strongest cell are boiling. The goal is to equalize the voltage 2.26V per each cell. Periodically check electrolyte level and top it with distilled water on mark. If decide to maintain the battery, do not buy sealed maintenance free batteries. To be able to equalize you need a Battery tender with Hysteresis Threshold, that start charging at 12.6V and stop charging at 14.5V, giving the battery a chance to rest or relax.

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