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Constant Current Charger Circuit for Lead Acid Battery

Constant Current Charger Circuit for Lead Acid Battery

Are you looking for a constant current charger circuit to facilitate a safe and automatic charging of your lead acid battery? A simple circuit presented here using the IC L200 will simply show you how to build a constant current lead acid battery charger unit.

Why a Constant Current Charger

A constant current charger is highly recommended as far as maintaining safety and long battery life is concerned. Using the IC L200, a simple yet a very useful and powerful lead-acid battery charger providing constant current output can be built.

I have already discussed many useful battery charger circuits through my previous articles, some being too accurate and some much simpler in design.

Although the main criteria involved with charging batteries largely depends on the type of the battery, but broadly it’s the voltage and the current which particularly needs appropriate dimensioning to ensure an effective and safe charging of any battery.

In this article we discuss a battery charger circuit suitable for charging lead acid batteries equipped with visual reverse polarity and full-charge indicators.

The circuit incorporates the versatile but not so popular voltage regulator IC L200 along with a few external complementing passive components to form a full fledged lead acid battery charger circuit.

Let’s learn more about this constant current charger circuit.

constant current battery charger Circuit Diagram


Circuit Operation

The IC L200 produces a good voltage regulation and therefore ensures a safe and a constant current charging, a must for any kind of chargeable battery.

Referring to the figure, the input supply is acquired from a standard transformer/bridge configuration, C1 forms the main filter capacitor and C2 being responsible for grounding any left residual AC.

The charging voltage is set by adjusting the variable resistor VR1, with no load connected at the output.

The circuit includes a reverse polarity indicator using LED LD1.

Once the connected battery becomes fully charged i.e. when its voltage becomes to the set voltage, the IC restricts the charging current and stops the battery from over charging.

The above situation also reduces the positive biasing of T1 and creates a potential difference of above -0.6 volts, so that it starts conducting and switches LD2 ON, indicating that the battery has reached its full charge and may be removed from the charger.

The resistors Rx and Ry are the current limiting resistors required to fix or determine the maximum charging current or the rate at which the battery needs to be charged. It is calculated using the formula:

I = 0.45 (Rx + Ry) / Rx.Ry.

The IC L200 may be mounted on a suitable heatsink to facilitate consistent charging of the battery; however the built-in protection circuitry of the IC virtually never allows the IC to get damaged. It typically includes built-in thermal run away, output short circuit and over load protections.

Diode D5 ensures that the IC doesn’t get damaged in case the battery accidentally gets wrongly connected with reverse polarities at the output.

Diode D7 is included to restrict the connected battery from getting discharged through the IC in case the system is switched OFF without disconnecting the battery.

You may quite easily modify this constant current charger circuit to make it compatible with the charging of a 6 Volt battery by doing the simple changes in the value of a few resistors. Please refer the parts list to get the required info.


Parts list for the proposed constant current lead acid battery charger circuit.

R1 = 1K

R2 =100E,

R3 = 47E,

R4 = 1K

R5 = 2K2,

VR1 = 1K,

D1—D4 AND D7 = 1N5408,

D5, D6 = 1N4148,

LEDS = RED 5mm,

C1 = 2200uF/ 25V,

C2 = 1uF/25V,

T1 = 8550,

IC1 = L200 (TO-3 Package)

A = Ammeter, 0-5amp,

FSDV =Voltmeter, 0-12Volt FSD

TR1 = 0 - 24V, current = 1/10 of the battery AH

How to Set up the CC Charger Circuit

The circuit is set up in the following manner:

Connect a variable power supply to the circuit.

Set the voltage close to the upper threshold volt level.

Adjust the preset so that the relay remains activated at this voltage.

Now raise the voltage slightly more to upper threshold volt level and again adjust the preset such that the relay just trips off.

The circuit is set, and can be used normally using a fixed 48 volts input for charging the desired battery.

A request from one of my followers:

Hi Swagatam,

I got your email from a website www.brighthub.com where you shared your expertise with regards to construction of a battery charger.

Please i have a little problem that i hope you could help me out:

I am just a layman with no much knowledge of electronics.

I have been using a 3000w inverter and recently i discovered it doesnt charge the battery (but inverts). We have no much experts around here and for fear of further damaging it, i decided to get a separate charger to charge the battery.

My question is: the charger i got has an output of 12volts 6Amps will that charge my dry-cell battery with 200ahs capacity? If yes, how long will it take to full and if no, what charger capacity do i get to serve that purpose? I have had experience in the past where a charger damaged my battery and i dont want to risk that this time.

Many thanks.

Habu Maks

My Answer to Mr. Habu

Hi Habu,

The charging current of a charger should be ideally rated at 1/10 of the battery AH. That means for your 200AH battery the charger must be rated at around 20 Amps.
At this rate the battery will take around 10 to 12 hours for getting fully charged.
With a 6 amp charger it may take ages for your battery to get charged, or simply the charging process might fail to initiate.

Thanks and Regards.


About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!

14 thoughts on “Constant Current Charger Circuit for Lead Acid Battery”

  1. Howdy, Friend! Interested to Learn Circuit Designing? Let's Start Discussing below!
  2. would this design work with a 25amp max,variable voltage(3-15v)power supply to provide an adjustable cconstant current density output for aluminium anodising using the low current density method as explained on caswell forums?any help greatly appreciated

  3. Hi Swagatam,

    Thank you for your kind suggestion for LM338. Can you please advise the formula for calculating the R6 (the Current Sensor in your LM338 – How to Make an Automatic 12 volt Battery Charger Circuit Using IC LM 338).
    Thank you for your kind help.

    • Hi Rajneesh,

      It's same as explained earlier:

      R = 0.6/charging current….charging current should be around AH/10 or mAh/10 of battery

  4. Hi Swagatam, Request kindly advise the value of Rx and Ry for delivering a constant current of 500ma to batteries. Thank you

    • Hi Swagatam, Thank you for your kind reply and the help. Request kindly advise if I can use one resistor of 1E rather than Rx & Ry.

      Additionally, please be kind to advise the advantage of using two (Rx & Ry) instead of one resistor. Thank you.

    • Hi Rajneesh,
      It's as per the datasheet of the IC, I don't have much idea why they have used two resistors.
      If you are having problems calculating the above circuit, you can try building an LM338 current controlled circuit which is much better and easier than the above design.

  5. Hi Swagatam,

    I am looking for a 24VDC 500ma Constant current charger with trickle charge of 24VDC 85ma for NiMH Batteries. Please advise.

    • Hi Rajneesh,
      You can try the following circuit:


      Replace the 2k preset with 10k and adjust it to get 24V output, and replace R3 with two calculated resistors which can be selected with a switch for getting 500mA and 85mA.
      Formula for R3 is given in the diagram.

    • Hi Swagatam, Thank you for your kind and swift response. Request kindly advise, if it is possible to switch between 500mA and 85mA automatically, i.e. when the battery is fully charged, then the circuit switches to 85mA.

      For your kind and ready information, In our case, the 500mA output and 85mA output need not be on the same line. These can be two separate outputs.

      Thank you for your kind help.

    • Hi Swagatam, For the formula – R3 = 0.7/Chg. Current. Kindly advise if the R3 is in Ohms and Chg. Current is in Amps.


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