LM317 Lead acid battery charger | 6V, 12V, 24V

I am going to show you LM317 lead-acid battery charger circuit. I like this type of battery because of so cheap. You too, right?

This lead-acid battery charger project for 6V, 12V, and 24V battery. Although there are many methods to choose from. But you may be missing If not read this post to the end.

4 Lead acid battery charging circuit using LM317

Often I like to use LM317 power supply. Because it is so easy to use, with a few parts. And important cheap, too.

Why use LM317?

If your main goal is to use the battery for a long time. You have enough backup batteries. For your work without interruption.

Did you know we can recharge batteries almost five hundred times? But must be recharged with the correct method.

It is easy.

Manufacturers always print the appropriate voltage and current for charging the battery.

The important thing is heat while charging the battery.

It is natural for electronic parts. If it is hot. It has a short life. The battery, too.

And the heat is caused by the voltage and current levels are too high

Most problem is too high a voltage level. Should not normally exceed 14V.

When we use LM317 to maintain a constant voltage. So, It is great.

Of course, these circuits below is not an instant circuit. Perhaps great ideas may be the best ways for you to improve your electronics skills.

Note: Though this project is good. But it may difficult to build and expensive. I love these projects better: Simple auto cut off 12V battery charger

Here are 4 circuit ideas. Ready to get started?

Note: Very important, friends should choose a good quality LM317.

Check out the LM317 on Amazon

6V-12V Lead Acid battery charger using LM317

Imagine you have both batteries 12V and 6V. You may be interested in this lead acid battery charger circuit.


It can charge both 6V and 12V two in one by choosing of S2-switch.

Look: in the circuit below.

At output current max 1.5A as limiting current of LM317K.

6V or 12V Lead Acid battery charger using LM317

Recommended: Recycle Free Li-ion battery from E-waste

How it works

When you see the circuit. It looks like a DC voltage-regulated power supply using LM317. Some love this circuit. any circuit requires energy.

In the first section, T1, S1, D1-D4, C1, and C2 are unregulated power supplies. Do you know about them? I guess you will understand. And you may read it more.

They will reduce AC main voltage down to 21V DC.

Have you ever wondered about the value of these parts?

Yes, the designer has an interesting concept. I like 2 things.

Transformer—when we use 1.5A output current. So should 2A transformer. And the output voltage is about 15VDC (approximately).
So, the input voltage of LM317 should be about 17V to 22V DC. Because if over-voltage it is easy to hot. But too low is not keep a constant voltage well.

Filter Capacitor—We need full output power and low ripple voltage. According to basic principles, we should use the capacitance of C1 and C2. The 2,200uF per 1A input. So, the filter capacitor is 4,400uF(2,200uF+2,200uF).

Then, see in LM317 Regulator section. We know to change R3 and R2 to set the output voltage. Which control with S2.

  • Closed switch S2 for 6V battery charger. —See R2 and R3 connect together in parallel. It makes the output voltage is about 7 volts.
  • Opened switch S2 for 12V battery. In contrast, R2 runs only is high resistance than two. So, output voltage is about 14 volts.

Are you understand?

Recommended: Simple Li-ion Battery Charger Circuit with Automatic Cut-Off

The diode D3 and D4 help protect a reverse voltage from an output load. It will over-current up until the fuse is blown. And protect charging with the wrong polarity.

Parts you will need

IC1: LM317K Variable voltage regulator TO-3
D1-D4: 1N5402, 3A 200V Diodes
D5,D6: MBR1545 Schottky Diodes & Rectifiers 16A
C1,C2: 2,200uF 35V Electrolytics
C3: 47uF 25V electrolytic.
0.25W Resistors, 5% tolerance
R1: 220 ohms
R2: 2.2k
R3: 1.8K
S2: Toggle SPST Switch
S1: ON-OFF SPST switch
F1: Fuse 0.5A or 1A
F2: Fuse 2A
T1: 117V/230V AC primary to 15V,2A secondary transformer

See: LM317K pinout

12V lead acid battery charger using LM317K

Suppose that you have Dry cell lead-acid battery, 12V 7.5hA sizes. And you need a battery charger, simple and economize. Also, you have 18V unregulated power supply.

I recommend the circuit diagram below. It uses LM317K as main too.

This circuit has the principle is simple. And can keep a stable voltage at 13.5 volts. By setting of R2 and R2.

12V lead acid battery charger using lm317k

Which you may use current 1A to take time charging about 8 hours or 10 hours. Then, It will have full electric energy.

Also, above circuit, it has D1 protect a reverse voltage from an output load. With Furse blow to cut off the circuit.

See LED1 shows correct polarity current connection. And D2 connected in reverse biased to show a wrong battery connecting.

Parts you will need

IC1: LM317K Variable voltage regulator TO-3
D1: MBR1545CT Schottky Diodes & Rectifiers 16A
C1: 2,200uF 35V Electrolytics
C3: 47uF 25V electrolytic
C2: 0.1uF 50V Ceramic capacitor
0.25W Resistors, 5% tolerance
R1: 220 ohms
R2: 43 ohms
R3: 2.2K
R4: 1K
LED1: Green 5mm LED
LED2: Red 5mm LED
F1: 2A Fuse

Automatic battery charger using lm317 circuit

This is a simple automatic battery charger circuit. When the battery voltage is lower than 13.4V, it will start flowing through R3 to charge the battery.

Automatic battery charger using LM317 circuit diagram

And when the battery voltage reaches 13.4V, the current will finally stop flowing. And when we use the battery until the voltage drops below 13.4V, the current will start flowing automatically into the battery again.

Read more: Gel cell battery charger circuit

24V Automatic Charger and Full charged indicator

This is a 24V automatic charger circuit and a fully charged indicator.


Automatic charger and full charged indicator using LM317 TL431

Imagine you have 24V battery, 10Ah. You can also use LM317K to build a 24V lead-acid charger circuit for this battery.

It requires a stable current about 1.5A and 27volts constant voltage.

They are similar to the above circuit.

Here is the step-by-step process.

First, it has DC unregulated power supply, 35VDC at 2A is across C1.

This is a voltage input of LM317K. Which it can withstand voltage up to 40V.

Then, LM317 and other parts keep stable voltage at 27V. We adjust VR1 to set this voltage.

When the battery is fully charged or using current more than 2A. The R6 is a polyswitch. It will cut off the current to the battery.

Full Charged indicator—when full charging the battery voltage up to 27V. The TL431 will recognize this voltage level. Then, turn on LED1 to light up immediately.

Also, above circuit, D5 protect a reversed voltage from the battery.
And, R6 cut off this current too.

IC1 should hold with a large heat sink.

Parts you will need

IC1: LM317K Variable voltage regulator TO-3
IC2: TL431 Precision Shunt Regulator TO-92
D1-D5: 1N5402, 3A 200V Diodes
C1: 2,200uF 50V Electrolytics
C3: 47uF 50V electrolytic
C2: 0.1uF 50V Ceramic capacitor
0.25W Resistors, 5% tolerance
R1: 220 ohms
R2: 4.3K
R3: 1K
R4: 82K
R5: 10K
LED1: Green 5mm LED
R6: 2A Polyswitch
VR1: 1K
VR2: 20K

LM317 Universal battery charger

Here comes a very simple idea is the universal battery charger circuit.
When input power is applied to the circuit.

This is another concept of the
LM317 battery charger. But I haven’t tried it yet. I keep this circuit. For future learning only.

The SCR1 (Silicon controlled rectifier) turns off, then does not has a bias current path to ground.

The LM317 acts as a current regulator, It is connected to the battery thought a one way diode D1, limiting resistor R1, and a bias resistor R2.

The D1 prevents the circuit from battery discharging, when the power out off from this circuit.
As the battery charges, the voltage across A point potentiometer R5 and some point rises, to turn on the SCR1.

Then current from the regulator LM317 can flow to the ground, so now the IC1 is in functions the voltage-regulating mode.
The R6 be used to control the output voltage.

When the SCR1 turn on, it also provides LED1 through R3 with a path to ground.
But when LED1 is on, this circuit is in the voltage-regulating mode, while LED1 is off to be in the current-regulating mode.

You may like these circuits, too.


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39 thoughts on “LM317 Lead acid battery charger | 6V, 12V, 24V”

  1. “The universal battery charger using Lm317”
    Please explain that this charger is automatic or not. By automatic, i just mean that when battery voltage reaches a particular level, this charger will be off. and when the battery voltage reduces to a particular limit charger will starts charging. And 2 LEDs are indicating these two states.

  2. Dear Sir,

    Could you please help me with a circuit for 6v 12v automatic battery charger using 0-15v 5amps transformer, LM338 IC & ammeter and voltmeter etc (like a professional)


  3. Hi there,

    I built “12V lead acid battery charger by LM317K” and it’s working, but can someone explain me what does that GREEN Led, indicates full charged battery?


  4. Please can you explain why a power supply 12.5V DC stabilizer can not be use as batery chargerfor a sealed lead asid type battery?
    Thank you Sarantis

  5. Please can you explain why a 12.5 V dc power supply stabilizer can not be used as a battery charcher for a sealed lead acid type of battery?
    Thanks Sarantis

  6. No sarantis a 12.5 V dc power supply stabilizer can’t be used.That is becase you.ll need more voltage than 12 volts to charge a battery ,about 13,5-14,5 volts.

  7. Dear Sir

    I would like to ask you about the DC output current from the battery charger to charge 2 batteries (12v/250 AH )
    the charger 24v-10A enough for this operation

    Ismail Abdallah
    B.S.C electrical engineering

  8. Respected sir, Please tell me the value & power of used component in The universal battery charger using Lm317. I Like this & this is very useful.
    Thank You.

  9. Pls where can I get a detailed video of building these circuits, its not too straight forward for my level. Or can I get a more detailed explanation. Thanks

  10. I have 6v 4.5ah old battery it shows 1.5v in multi meter. can i charge the battery..?
    I have
    out put 10v(10.9v) dc adaptor can i use
    to charge the battery..?
    I have another old
    transformer(from old fm radio 1990) with center tapped it shots 5.5v ac and
    0.02v ac . What do i do to charge the

  11. I want to build the simple 6V or 12V charger for Lead Acid battery that must give an output voltage of 13.75V for charging the 12V battery. My circuit has the LM317K voltage regulator with R1=220 and R2=2.2k and I’m using a 220V/15V, 3A transformer as shown above. The explanation on the LM317T says that Vin must be at least 2.5 volts greater than the required output voltage to power the regulator. Is it possible then for my design to give out 13.75V., since 15V – 13.75V is just 1.25V which is clearly less than 2.5V ? I ask because the rms 15VAC secondary output of the transformer will also give approximately 15VDC from the full bridge rectifier.
    I really want to build a simple but efficient dual purpose 6V or 12V charger, but it seems to me, from my question above, that this charger would be only efficient for 6V but NOT for 12V.
    Pls reply asap.
    Please reply asap.

  12. For the circuit 2 above, 6V or 12V Lead Acid battery charger, what other diode other than the MBR1545 in the circuit can I use? Pls give me similar/equivalent diode to that MBR1545 because I couldn’t get it in my locality. By the way what is the use of those MBR1545 in the circuit 2 above?
    Awaiting ur reply asap.

  13. Hi, Apiece
    Thanks for your feedback.
    I am sorry , I not test this circuit.

    But I think we can use any diode as power current output.
    You can use 1N5402 or 3A 200V diode for output current maximum 3A.

    If have results any please share us.

  14. hi..
    i want to make a charger in automotive application for 12V input and 5V, 1A output please provide me a circuit diagram but that diagram should have protection like, over voltage, short circuit,EMI/EMC, ESD, i/p surge, over load.

  15. I like to know what the green an red led indicator doing by charging the SLA battery , can anyone let know pls ??? its look as reliable charger but the green an the red led are unknown for me what they indicate ,, full charged , floating charged , ???

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  17. It’s very interesting.pls can I use it to charge 24v 200 to 500amp battery and how do I incorporate relay.also what do I use instead of that polyswitch cos of availability

    • Hello, Oladimeji Akinsanya
      Thank you for visiting.
      If you use a high current battery. You should use high current charging too. For example, 24V 200A. You need a current of 20A or 50A for 500Ah battery. So, this circuit cannot be used for them.

    • Hello James Pittman Jr,

      Let me tell you honestly. I have never built this circuit.

      Therefore, I cannot clearly specify the equipment value. If I guess without caution You may be damaged.

      But I believe You have the ability to design this circuit.


  18. I need to construct a SCR based battery charger for charging 30 volt 100 AH lead acid battery and want float DC 30 vdc

      Thanks for your visit. Personally, I feel this circuit is not suitable for a high current battery.
      Because It can charge only 1A current. If you use a 100AH battery, you should use a 10A current.

      However, you may use a transistor use increase the current up and important high current of input, too.

    • Hello Chandhra Mouleeswaran MK,
      Thanks for your visit. In my view, this circuit can use only a low current of the battery, 20Ah below.

      If your battery is 120Ah, I will charge in 10-12 hours. The charging current should be 12A min.

      So, this circuit cannot power to it. It can give only 1A max.

      But, Personally, I feel if used many transistors and LM317 may increase the current to use 12A output.

      It’s just my guess. However, I believe you can.


    • Hi,
      Yes, I agree like you said. My dad said that it has been popular for a very long time, more than 50 years, such as cars, motorcycles, etc. It’s cheap, Provides high electrical energy. But it was so big I couldn’t lift it. But it will continue to be usable. Because it is cheap and very popular in the market. And it can be recycled very easily. We will have more articles about this type of battery in the future, hope you will continue to follow us. 🙂


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