10 solar charger for 6V battery

This is a solar charger based on LM317 regulator IC. The charger is similar to the 6V charger project but made simpler. When battery has reached is full charge voltage (Bat voltage is higher than VDz + 0.7), the charger automatically cuts the charging to protect the battery form damage. The led light will indicate the full charge state in the battery. This charger will work only when the voltage from the solar panel is much higher than the battery voltage, unlike the solar charger with regulator and controller that can charge regardless the solar voltage.
charger schematic diagram
Part List:
Solar - 12V solar cells array
C1 - 470uF electrolytic capacitor rated 25V
D1, D2 - 1N5400 or any rectifier diode rated 2A minimum
Dz - 1N5235B or any 6.8V zener diode
R1 - 3 kilo ohms 1/4W
R2 - 330 ohms 1/4W
R3 - 560 ohms 1/4W
R4 - 2 kilo ohms 1/4W
LED -3mm or 5mm  Red or any low power LED
Q1 - 2N2222, CS9013, or similar NPN transistor
Bat - 6V lead acid battery
LM317 pins
2N2222, CS9013 pins

Note: You can convert the charger into 12V by replacing the solar panel with higher voltage ; zener diode DZ; and values of R2 and R1.


  1. sir, i would lik to do this project i am searching many circuits bt all the circuits has that output is always lesser than the input how to desing the circuit with 6.7v as a input and 5v,500ma ouput with auto cutoff sorry for my poor english

  2. reply me as soon as possible ... plz ...

  3. Hi,
    What values of zener diode DZ,R2 and R1 , do I need to change if I need to convert the above circuit to charge 12V lead acid battery ?

    your update will be much appreciated.

    Thank you,

  4. For 12V charger version:
    Keep R1 as 3k, new R2 = 270 ohms and zener DZ = 12.7V zener rated 1W

  5. Thanks for the update on 12V charger circuit. In the above circuit the R1 value is already 3K ohm 1/4 Watt , should it be same or be changed ?
    Because , in the "Note" its mentioned as we need to change R1,R2 and Dz value.

  6. keep R1 3K just change R2 and D2 with the values above

  7. I tried making a 6 Volts charger with the above schematic exactly ,
    I used 3 Watt panel which gives 9V output as a source and it showed 6.7V as as an output , but connecting to battery (6v 4.5Ah) , it is getting discharged rather than charging, any tips to trouble shoot ?
    Battery had 5.5 Volt before connecting charger but now its dropped to 4.8 V (connected approximately for 4 Hrs during peak Sun light)

    Thank you,

  8. can you share the original circuit diagram? luis.sevillano@yahoo.com
    also, can i combine this circuit to the LED driver circuit (High current LED driver using FET)?
    if not, do you have a circuit design wherein LED driver + battery charger + solar power?
    am hoping for your positive and quick response.

    God Bless,

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