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!


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5 Questions


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

Sorry for my dumb question. I've got confused with the relay icon here. It's written NO, but the contact is closed. I really don't get it.

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.

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%.


i used 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


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.

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

1 reply

Just multi meter the pins on the 555 chip :)

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

sir I have to connect inverter to this charge controller so should I connect it directly to battery or to the dump terminal ?

1 reply

connect the inverter to battery

Why the MOSFET? I thought it was PWM or something, is it? If its just to switch a relay, any regular General Purpose transistor could achieve that, or is the MOSFET doing anything else of high relevance? Good Tutorial...I love..

1 reply

i use mosfet because i have lots of them at that time. a 2n222a can do the work :)

Why its done so complicated? 7805 can be eliminated if 12 volts relay used here. 7805 regulator drain lots of battery power.

3 replies

Yes ,but that LM7805 is not for the relay it's use to power the 555 IC with a constant 5V, a 555 need Vcc 4.5 to 15. a 12 v solar panel is not have a study 12v out put every time, sumtimes it's go high upto 18v (Open circuit voltage up to 20V)this type of changes may course problems to IC.thats whey i use a voltage regulator in this circuit ig you want to use 12v relay use this circuit (not safe)


Yes I agree with your logic, but IC is always powered from Battery right not from Solar source.

Btw I've question, how we got 1.66 volts for pin 2 and 3.33 volts for pin 6. Please let me know how to calculate it so that I can apply same logic after removing 7805.

not directly,but at the time of charging the battery is connected to solar panels this is the reason for the 5v regulator.a battery is not a constant voltage source. if are using 12v battery, the voltage change from 11.9 to 13.9 changing voltage may interfere with precision of the circuit

but i will conceder your request and find a solution soon

Wow! I really liked the way you place and solder all the components. It's so neat, just as the way I do ;)

3 replies

i have only one rule at soldering, its an art not a job;)

From one of my projects! :)

No automatic alt text available.

yea i like that....same rule as mine

currently around 10 amps you need big relay to increase the current

Please tell me regarding the use of MOSFETs instead of relays in higher currents. Thanks in advance

This is almost exactly what I'm looking for, thank you. The only change I need is to handle 30V (and 15A but I'll use a bigger relay for 15A). What components in the circuit would need to change for 30V capability?