About: a MAD man who fancies himself a genius

Hello friends

Today I am back with another project called DIY AUTOMATIC SOLAR CHARGE CONTROLLER.

It’s an automatic switching circuit that used to control the charging of a battery from solar panels or any other source. It’s a 555 based simple circuits the charge the battery when the battery charge goes below the lower limits, and stop charging when the battery reaches it's upper limit voltage

Step 1: My Goal

“To make a cheap and efficient solar charge controller”

Step 2: Circuit

This is the driving circuit of the DIY AUTOMATIC SOLAR CHARGE CONTROLLER.

To make this circuit you need

1. NE555 IC with IC holder

2. One 2N2222 or PN222a Transistor

3. Three 1K Ohm resistors

4. One 330 Ohm & 100 Ohm resistors

5. Two 330 Ohm 1/5 w resistors(optional)

6. Two 10K variable resistor

7. Two LEDs (green & red)

8. 1N4007 Diode

9. 5V SPDT relay

10. two, 3-Pin PCB connector

11. Wires

12. PCB

13. LM7805 (TO-220 type)

14. Two capacitors(i am using .1uF,you can use any)


This is the finished circuit (Fig)

The 5v relay is the main component of this circuit; it’s an SPDT (Single Pole Double Throw) relay. It have one common (pole) terminal and 2 contacts in 2 different configurations. One is N.O (Normally Open) and other one is N.C (Normally closed)

In our case we connect the +ve of the solar panel to the pole of the relay and +ve of the battery to N.O when the battery is connected to the SCC (solar charge controller) the circuit check the battery voltage the voltage is less than or equal to lower limit the current is flows to the battery and battery start charging. When the battery voltage reaches the upper limit, the rely is activated and the current is redirect to N.C for dumping

Step 3: Calibration

After finishing the circuit you need to set the upper and lower limits. Batter calibration is required to avoid the overcharging and over discharging of the battery. I am using 12v as lower lower limit and 14.9v as upper limits. that means when the battery charge reaches the 12v battery start charging.wen the battery voltage reaches the upper limit or 14.9 volt .the relay is activated and circuit start dumping

To set the limits you will need a multimeter and a variable power supply or two power supplies. one with 12v and other one with 15v.first you will need to set the lower limit. for that set the voltage to 12v and connect it to the circuit. connect the ground weir to the conmen of the multimeter and touch the testing probe to the pin 2 of the 555 IC. Adjust the voltage by adjusting the VR to get 1.66 volte. Then set the voltage to 14.9v and touch the probe to the pin 6 of the 555 IC. adjust the voltage to 3.33v.check once aging .now over SCC is ready for use

Step 4: Wiring

The Fig show the wiring diagram of the SSC

First connect the +ve from the solar panel to the centre pole of the relay then connect a red wire from battery to N.O of the relay. connect the –ve wire from the solar panel to the -ve of the circuit then connect the battery’s–ve to the circuit.

Step 5: Working

when the battery voltage is less than 14.9 v the it start charging by passing current through N.O of the relay. when the batteries voltage reached 14 volt its automatically switch the relay to N.C.if you are using solar panel you don't need an dummy load to dump the excess power. you can add an extra battery to the N.C to harvest the excess power

Step 6: Moment of Truth

this is a quick video of the DIY AUTOMATIC SOLAR CHARGE CONTROLLER

Step 7: Thank You

I will give thanks to you Mr. Mike Davis. this DIY AUTOMATIC SOLAR CHARGE CONTROLLER is based on the his design. I just modified it a bit to make it more compact. I will give all credit to Mr. Mike Davis

A New Solar / Wind Charge Controller Based on the 555 Chip

Solar Contest 2016

Third Prize in the
Solar Contest 2016

2 People Made This Project!


  • Tape Contest

    Tape Contest
  • Trash to Treasure

    Trash to Treasure
  • Arduino Contest 2019

    Arduino Contest 2019

135 Discussions


22 days ago

Hi there, it's a neat little project, has been keeping me busy for a bit now. I have one question about the output circuitry for the 555: what was the purpose of using an npn transistor and the mosfet? Would it not have been simpler to use only the mosfet, or is there something that I am missing?

Kym Tan

Question 4 weeks ago

Hi Sir, can I know how you conduct the calibration and to adjust the upper and lower of battery voltage?

Shruthi George

Question 3 months ago on Step 2

what is the use of P.B in the circuit
What type of P.B must be used


4 months ago

What is the output current and voltage values of this charge controller and which type it belongs to? whether mppt,pwm....?


Question 4 months ago

I tride this circuit but it is not working, Please share complete details..


10 months ago

Why didn't you tell us up front that this is a Premium instructable? :(

I started gathering the components, tried to understand the schematic and saw that not everything was mapped on there... and then I saw other people struggling with this instructable, because to see all information you have to have a Premium account.

1 reply

Question 6 months ago

what is the use of push buttons


Question 7 months ago

How it will maintain the constant voltage?


Question 8 months ago

The output of your 7805 is shorted to ground and the negative side of your 330r connected to batt+ in this schematic this is obviously a mistake, right?


Question 9 months ago on Step 2

Hi guys i have made this circuit twice and it works well as mentioned, but i have a question, i have 1kw 18v solar panels and requires a controller that can handle about 70amps so i used 2x 40amp relays connected in parallel to the circuit, this works but the controller fails after a few days showing that it cant handle such amperage. What should i change or add to the circuit so that it can handle 70amps?


1 year ago

Can i know how u got 1.66 volts for pin 2 and 3.33 volts for pin 6.

1 reply

Reply 10 months ago

Just multi meter the pins on the 555 chip :)


Question 10 months ago

Hi - Great system, but how do I reduce the maximum charge voltage to 12V and set the lower limit to 10v - Thanks :)


Question 11 months ago on Step 7

Hey man. I sound like a complete amateur right now but I'm just getting started with engineering and all the electronic stuff. I can't read the circuit diagram so if you can make the wiring on a breadboard on a program or something I can follow easily. It's quite a bit to ask for but Im a noob at this stuff, please help me.


12 months ago

sir as shown above where should i connect load directly, at dump load what type of load can be connect.


Question 1 year ago on Step 2

What are the tolerances? Does it matter? As I'm looking for parts, a lot of the parts need a tolerance with them. i.e. 2N222 .05%, .1%, .5%.

1 answer

Question 1 year ago on Step 5

Sir where to connect solar panel and for what NO and NC terminals r used? I need the bottom view of the circuit of pcb please