Many electronics circuits and projects for learning in simple ways.

Two Automatic battery charger circuits

A lead-acid battery charger circuit  is most popular though it will very large size than others battery type. But them have advantage are : cheap, easy to buy and long life if correctly uses.

The charging is best importance.
When I had 10 year old ago. My father bought it to me in first time of my life. In 6volts size for that era motorcycle.
When power outage will charge at shop near the house. Which is quick charger with high current. While charging will Air bubbles inside the battery and high temperature. Which technician tell me no problem it high power.
But can be application 2-3 time only it is failed.

Which as usually this battery type if correctly charges wil can use for 4-5 years
Battery do not like hot!
At all time do not use or store them in too heat area. OR If while use may short circuit or high current use them will too hot.
An importance while charging do not quick charge with high current and high voltage.


1.  Simple Automatic battery charger circuit 

Principle working

This is an automatic battery charger circuit,  Which normally producer will tell at battery as follows:

Must charge with DC voltage only.

And neat voltage level not should more than 15-volts or 1.5 times of a battery voltage.
Most importance should use charger current 10 % of battery current for example 2.5Ah size use time for 10-12 hour.

In my site we suggest many battery charger circuit. You will love it, because use simple circuit,cheap so easy to build.

simple aciti battery charger which I use idea from…

First of all, I think “When…Charge? And When stop?”
Normally we should charge battery when voltage lower than 12.4 volts and voltage maximum of most battery is 14.4volts but someone guru tell me voltage saving of 13.8 or 13-volts approximately.

Secondly,Thus we need to use comparator circuit which in first times I often use IC-op-amp such as LM339,LM311,LM324,LM301 but sometimes we cannot buy them. And This our working is simple stye only.
When begin we learn basic principle of electronic parts, I like use Diode, Zener diode, which they are both valves for electrical currents. The Current will flow one way. But the zener diode is connected backwards. It then blocks current until the voltage exceeds a certain level.

I try to test them with the zener diode 12-volts the current will flow through it when voltage higher than 12V.
Therefore I use Zener diode for detects voltage over than 13V to control stop charger system.

Then, I use relay to control current to a battery. Because cheap and used easily.

Next, I use a SCR for uses as quick control switch.


As Figure 1 is perfect circuit diagram.

You can watch video below I test it. This projects will always cut off battery when voltage drop across it is 13.6V up. Then LED2 (yellow) glow brightly. While relay will pulls out from contact NC-C. Which no current to battery and voltage lower down.

Then you can charge again with pressing SW2 to reset, recharge them again.

Though This projects will easy technology but very useful for all.
Importance it cheaper! I love it.


If you want to read more: how it works,parts list and look full size circuit image.

You like my sites want to support me by buy this E-book.


2. Automatic OFF 12V Battery Charger by power SCR

This stop current give battery, when Voltage of battery tall arrive at the level that load with full speed already ahead for protect something charger too much poor distilled dry water. This circuit can is usable very wide can use with battery many model. By choose diode and SCR at can durable the trend loads topmost follow to want. Fining decorates while initial lead battery at charger until with full speed ahead already come to build reach at a pole for charger. Fine R1 – 500Ohm until Amp Meter begin be down be O as a result fully be usable already.

Automatic OFF 12V Battery Charger by power SCR

Note : above circuit is just basic ideal only we lets to see really uses below.

Auto dry battery charger using SCR

This projects is automatic dry battery charger that can use for many size such as 6V, 9V and 12V Depending on the changes, some devices only.

How this circuit works

As circuit below. To begin with an AC220V will flow to a transformer to transform to 15 volts, then flow to bridge diode to rectifier AC to DC is 15V. The LED1 is power indicator of the circuit.

dry battery charger circuit

Beginning SCR1 is working, because the 15V flow to R3, to limit the current to decrease, and flow through to diode D5 to To prevent the reverse voltage, Before bias to lead G of SCR1.

While SCR1 conduct, to make the 15V flow from lead K will feed to the positive battery terminal. Ideally SCR1 will conduct current and stop current alternately very fast with frequency of 100 Hz.

Since the 15V voltage from the bridge diode is full wave rectifier so output frequency of 50+50 Hz. The feature of current will be continuous positive half sine wave.

Which will differ with the voltage from capacitor filter that is smooth as a straight line. So will see that SCR1 do not conduct current all time. When have positive voltage to bias at lead G. Since waveform of voltage Not smooth enough in a straight line.

Theoretical of SCR, it will stop conducting current when disconnect the power supply output. Which in this circuit is do not have positive side of the power supply range. And when have positive voltage waveform new SCR1, it starts to currents again, this was reversed with a frequency 100 Hz.

Battery level monitoring

This circuit will get voltage from the battery positive through R2 to reduce current, and have C1 to filter current to smoothly. Then will flow through VR1 to divide voltage to feed to a zener diode ZD1 before send to bias lead G of SCR2.
A adjust level of VR1 will must make in full battery, adjust VR1 until voltage at negative of ZD1 have level more than 6.8V or about 7.3V.

Which will cause ZD1 to saturation voltage collapse flow through to ZD1 to feed lead G of SCR2, cause SCR2 conducting current by R4 is helper to SCR2 extraordinary stable work. When SCR2 work will cause negative voltage flow to lead K to A result to LED2 glow. And the same time SCR1 will stop conducting current.

Since lead G of SCR1 get negative voltage from SCR2 there. In the case of battery is lower voltage, cause voltage at negative of ZD1 have lower than 6.8V, makes lead G of SCR2 not get positive voltage but can get only negative voltage through R4 result SCR2 don’t conduct current.

The parts list
Resistors ½W 5%
R1, R5_____________2K
R3_____________560 ohm
VR1_____________10K Potentiometer
C1_____________100uF 25V Electrolytic capacitor
ZD1_____________6.8V 1W
LED1, LED2________5M LED as you want
PCB,and other, etc.

How to make and setting

After preparation equipment is ready, then we soldered it successfully on PCB as Figure , next checked again. For example The device has a positive – negative. Are they correct polarity?

the component layout of dry battery charger
The component layout of dry battery charger

soldering point of dry battery charger
Soldering point of dry battery charger

Complete assembly on PCB
Complete assembly all parts on PCB

Fully 12v battery 2.5Ah

To Safety, customization first step, to find full battery voltage fit, be connected to the circuit to correct polarity. Then apply AC220V , next adjust VR1 clockwise until LED2 go out. Then to rotate VR1 clockwise slowly until LED2 light up, then stop immediately, do not too much spin is strictly prohibited. The principles, LED2 will light when battery voltage until full. So the battery will be adapted for the first circuit has to be really full voltage.

Please watch video below to increase understand this projects.

Circuit modification

This saving dry the battery circuit, can charge voltage 3 size are 6V, 9V, 12V. We can change each value parts as neat charged battery.
For this circuit we use with 12V battery Look at the chassis battery is stated as 12V 20AH, mean, Battery voltage 12V currents supply 20 amps per hour. When you know voltage at the battery is charged, Now I have to choose the transformer to be used. currents transformers used can be selected from 3-5 A.

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The table below shows the change in each device. To fit the battery charger.

Battery Voltage

Transformers Voltage

Zener Diode voltage

R3 and R5

6 volts

9 volts

12 volts

9 volts

12 volts

15 volts

3.3 volts

4.7 volts

6.8 volts




We recommend:

Best 12V battery charger circuit using LM311

6V or 12V lead acid battery charger using LM317

This Post Has 61 Comments

  1. sir,can u plz tell me what is the function of LED1

  2. if i want to o/p 12vdc and 10 amp current then what should i do???????

  3. Sir, how can we make a auto cuttoff charger for 6v 4.5 ah battery using solar panel

  4. sir, how can I make a auto cut-off 24V lead acid battery charger using same circuit? what parts will I change?

  5. Hi,Ramdas
    Thanks for your feedback.
    Yes, you can use 6v battery but 6v relay
    and change others parts.

    now I cannot sure value parts.
    I am sorry,

  6. Hi,Mattcarlo
    Thanks for your feedback,
    Yes, you can but now I cannot show you how to find value of parts.
    I am sorry.

  7. So the relay engages when the charge level has exceeded 13.6 volts?

    That seems to be evident by the way it is drawn with the common (armature) contact connected to the NC contact of the relay when it is off.

    Normally relays are drawn in their non-powered state in schematic drawings, and I am assuming that is the case here.

    – Techowl –

  8. Hi,Techowl
    Thanks for your feedback.
    As this article, the relay not pull in when voltage at battey exceeded 13.6V.
    At the same, the contact C to NC is opened. so no current to the battery.

  9. Thanks for the reply, but your comment contradicts itself.

    I realize that your native language is not English, and I appreciate you trying to get your point across to me in a foreign language, so I’ll ask the question another way.

    #1 Where is the contact C connected when the battery is being charged? (NC or NO)

    #2 Is the relay energized (pulled in) when the battery is being charged? (Yes or No)

    – Techowl –

  10. Hi,Techowl
    Thanks for understand my English.

    #1 when the battery is charging C and NC connect together, until battery full.
    #2 No, because voltage at battery lower than 13.6V
    SCR1 not works.

  11. Thanks, now I understand.

    I’ll let you know the result when I finish building the project.

    – Techowl –

  12. Hi, techowl
    Happy you understand my English.

  13. hello , thank you for your free circuit and for your
    helpfull , I wonder if I replace the transformer T1
    with adapter 13.8v 750mA >

  14. I meant replacing trans, bridge and capC1 with adapter

  15. Hi, wal kadoor
    Thanks for your feedback.
    OK, you can use it but you may reduce voltage zd3 to 3v or lower, to reduce vz from 13.6v to 13v
    When battery is full about 13v. The scr will runs.

  16. thanks alot

  17. Hi, wal kadoor
    Thanks for your feedback.

  18. I built this circuit. But it is not working. Full charge indicator LED is always on. When I press the reset button, that LED suddenly goes off and on again. Can’t charge a battery. Can anyone help me please.

  19. Thanks For your help…
    it help me lot to understand the circuit 🙂

    -Pritam Pyare

  20. Although it is good idea to cut off charging at a particular voltage, the problem is the circuit will shut-off as soon as it reaches this voltage and the battery will not be fully charged. It needs to go to “trickle-charge.”

  21. what a model the component SCR use?

  22. Hi syuk,
    Thanks for your feedback.
    The SCR is small size low current switching.

  23. Hi Colin Mitchell,
    Thanks for your comment.

  24. Sir,
    You are intelligent. But to effectively convey your ideas to others globally, you must definitely improve your English grammar.

  25. definitely nidhin must improve his knowledge of circuitry and definitely must drop the smarty pants style. Is that comment all he can definitely post?

  26. I have 12 Volt, 7 ah dry Battery, which charger would be best, can 12 volt 1.5 charge?, why AC charger could not be used?, How can we know that our battery if charged fully

  27. Hello sir,
    I need to knows some thing from you.
    I have a 18-0-18 transformer. I want to use it on
    this ckt. How Can I do it (mens how can I convart
    it’s voltage in 15 or 12 volt?

    Best Regards,

  28. 12vto 10 amp

  29. Hello Sir,
    Thanks for your circuit , I m loving it but Their is only one problem which dont know why SCR cuts off the circuit and the green led glows but when I wany to recharge its not going back . Also by pressing the button green led glows but not going back on charge mode . I connected anode and kathode with button. What is the right connection please state .

  30. hi,
    how could I get to know that the battery is fully charged?
    please give suggestions to add an indicator


  32. Please for those interested in the second charger: The Automatic cut-off 12V Battery Charger using SCR:

    Below is the detailed explanation of how it works.

    When the rectified input dc voltage to the charger circuit is supplied, the LED D1 glows.

    After the voltage input is supplied, current flows through R3 and diode D3 to bias the gate terminal (G) of SCR1. The SCR1 then conducts, allowing the outward voltage flow from its cathode (K) to the positive terminal of the battery to be charged. SCR1 conducts and stops current alternately with very fast frequency of about 100Hz. It will stop conducting current when power supply is disconnected. The current from the positive terminal of the battery being charged, then flows through R2 and get filtered by the capacitor C1. The variable resistor VR1 together with R2 divide the battery voltage for the zener diode ZD1. The current then flows to bias the gate (G) of SCR2.
    When the battery voltage is low (i.e. below 13.6v), the zener diode (ZD1) voltage is below 6.8V (due to the voltage division), and because this voltage is below the zener breakdown voltage, positive current (clock pulse) is applied at the gate of the SCR2 and it starts conduction in a forward bias.
    When the battery charge voltage is 13.6v and above, the SCR2 receives a negative pulse from the zener diode (ZD1) and it will not conduct. The gate G of SCR1 also gets negative voltage from SCR2 and will cease to conduct current to the battery being charged. Hence terminates the charging process of the battery. When this happen, a negative voltage from SCR2 will complete the circuit of LED2 and as a result, it glows.
    The value of VR1 and the voltage value of the zener diode are used to determine the voltage limit of the battery to be charged. When VR1 is adjusted until voltage at negative of ZD1 is 6.8V, it means the battery to be charged will be cut off at 13.6v.

    Important Definitions:
    • A Silicon-Controlled Rectifier, or SCR, is essentially a Shockley diode with an extra terminal added. This extra terminal is called the gate, and it is used to trigger the device into conduction by the application of a small voltage.
    • A Zener diode is a diode which allows current to flow in the forward direction in the same manner as an ideal diode, but also permits it to flow in the reverse direction when the voltage is above a certain value known as the breakdown voltage

    [email protected]

  33. Hi,

    Great site and a lot of good information, thank you


    1. I am interested in how efficient this charger is. I am looking for the lowest possible efficiency with the largest electron emission, into the surrounding environment, from the charging circuit to the battery itself.

    I would imagine a capacitor change would be part of this equation along with a long distance wire from circuit to battery ?

    Thank you

    Btw…I am certainly willing to help you with editing your text/grammar if you are interested, for free of course


  34. hello. i am iranian. circuit charger battry lead asid to i emailed .
    Thank you very mach

  35. Thank you momename for you onsite on this topic
    I’m currently working on a project that requires charging a 48 volts battery made from 4 x (12 volts 7.5Ah/20HR) SLA batteries.
    Which components of the part list do I need to change ?
    I’ll prefer you build it for me as I do not have all the requirements to make one myself. How much will it cost ?

    [email protected]

  36. how long can a 12v 75ah battery take to be full charged. …and how many batteries can be changed at a go.

  37. Hi. I have a question about battery charger, I’m wondering how they works specially this one, CENTECH model 60431, this one has charging FLOAT and uses thermal overload protection and automatic shut off, and i;m carious about this: if the cables did not connected to the battery poles did not turn on. it has sensors or another circuit ? Is there any way I can have a schematic diagram of this model?. THANK YOU SO MUCH FOR YOUR HELP.

  38. In the battery charger ” Using Auto dry battery charger using SCR” circuit above, wanted to clarify regarding the maximum current which would pass through SCR1. Assuming we are connecting a discharged Lead Acid battery. Then when the circuit is powered ON, the peak AC voltage at the anode of the SCR1 would be 21V (15V rms). This would forward bias the SCR1 since cathode is at zero voltage (as battery output is zero). The Gate of SCR1 is at higher potential than Cathode and hence SCR1 would conduct. At this stage since the internal resistance of a battery is in the range of 20-50 milli ohm. The current which would pass through SCR and battery as per ohm’s law would be approx. 20V/20 milli ohm (assuming 1V drop across SCR in conduction phase). This would be a very large current which could potentially damage the SCR/battery. Is there something I am missing here?

  39. I tried this circuit but the battery was charged for a period and disconnect for a period about 5 – 7 sec …. why?

  40. all respected brothers,
    plz help me out.

    can i charge a 65ah 12v car battery with 1600va 24v double battery inverter plz tell me as soon as possible .
    i am connectting one battery of 12v 180ah and second battery is my cswift car battery (i.e. 12v & 65 ah)
    in series with the 1600va double battery inverter.

    is it right or not, if not then plz tell me the right way ….
    thanking you

  41. Sir I please provide me a diagram for auto cut off battery charger using 12 volts 12 ampere transformer and a LM SCR.

  42. Thanks, but can we use this circuit to charge lead acid battery ( 35A – 100A) sure we must use SCR with high Current.

  43. thanks for the diagrams. I need to convert my 350VAc UPS unit into an Inverter using external 12 V car battery. please advice on the technicalities involved gor this to work.

  44. This battery charger circuit is safety or not?
    And what is the function of POT in the battery circuit using SCR?
    Please reply urgently, thank you.

  45. I need compleate circuit i am not able to make it how to purches it please e mail with price

  46. It’s actually a cool annd helpful piece of information. I’m glad
    that you sikmply shared this useful info witrh us.
    Please sty us up to date like this. Thank you for sharing.

  47. Pl 4v battery charger circuits digram send my email

  48. Thank you for this great information but is there any other components you can use to replace the SCR in the first circuit and it will still work perfectly.

  49. hello sir! i want to build an adapter that automatic cut off the charging when it is battery full for cellphones to prevent damage and overheating. is it possible? the design is like: electrical outlet => adapter => charger => cellphone.

    thanks in advance! can you send me the diagram @ [email protected] if you have solution 🙂

  50. Hi there !
    Unfortunately Your English is really Bad and hard to understand .Could you pls do something about it? Thanks.

  51. Sir it’s useful for me but there is no volume in this video it’s difficult to understand..can you please modify

  52. Iam asking about changing of battery using scr

  53. Vary nice information.i am looking some kind of this website.Thanks

  54. Autocut off 12v charger 20ah to 80ah required -10nos best price quote.

  55. Nice project,finally got what I am looking for please modify to add volume tohourvideo,for proper explanation thank.

  56. Nice project, and very good information…thanks for your proper information…

  57. I want very simple project and simple circuit diagram

  58. Nice circuit !Works great
    thanks for sharing
    Is it possible to regulate the amount of current in a circuit ??
      Do you have an idea?

  59. Why you have not added a regulator

  60. Is there is problem if i use 16 v transformer

  61. Is scr and lm 317 works as op amp

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