About: I am an Electrical Engineer. I love to harvest Solar Energy and make things by recycling old stuff. I believe, IF YOU TRY YOU MIGHT, IF YOU DON'T YOU WON'T.

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One year ago, I began building my own solar system to provide power for my village house.Initially I made a LM317 based charge controller and an Energy meter for monitoring the system.Finally I made PWM charge controller.In April-2014 I posted my PWM solar charge controller designs on the web,it became very popular. Lots of people all over the world have built their own. So many students have made it for their college project by taking help from me.I got several mails every day from people with questions regarding hardware and software modification for different rated solar panel and battery. A very large percentage of the emails are regarding the modification of charge controller for a 12Volt solar system.

You can find all of my projects on :

You can see my other version charge controllers


To solve this problem I made this new version charge controller so that any one can use it without changing the hardware and software. I combine both the energy meter and charge controller in this design.

Specification of version-2 charge controller :

1.Charge controller as well energy meter

2. Automatic Battery Voltage Selection (6V/12V)

3.PWM charging algorithm with auto charge set point according to the battery voltage

4.LED indication for the state of charge and load status

5. 20x4 character LCD display for displaying voltages,current,power,energy and temperature.

6.Lightning protection

7.Reverse current flow protection

8.Short Circuit and Over load protection

9. Temperature Compensation for Charging

Electrical specifications :

1.Rated Voltage= 6v /12V

2.Maximum current = 10A

3.Maximum load current =10A

4.Open Circuit Voltage = 8-11V for 6V system /15 -25V for 12V system

Step 1: Parts and Tools Required :


1.Arduino Nano (Amazon / eBay)

2.P-MOSFET ( Amazon / IRF 9540 x2 )

3.Power diode ( Amazon / MBR 2045 for 10A and IN5402 for 2A)

4.Buck Converter ( Amazon / eBay) or Voltage Regulator (LM7805)

5.Temperature Sensor( Amazon / LM35)

6.Current Sensor ( Amazon / ACS712)

7.TVS diode ( Amazon / P6KE36CA)

8.Transistors ( 2N3904 or 2N2222)

9.Resistors( 100k x 2, 20k x 2,10k x 2,1k x 2, 330ohm x 5)

10.Ceramic Capacitors (0.1uF x 2)

11.Electrolytic Capacitors ( 100uF and 10uF)

12. 20x4 I2C LCD ( Amazon / eBay)

13.RGB LED ( Amazon / ebay)

14.Bi Color LED ( Amazon )

15.Jumper Wires/Wires(eBay)

16.Header Pins (Male,Female and right angle)

17.Heat Sink ( Amazon / eBay)

18.Fuse Holder and fuses ( Amazon / eBay)

19.Push Button ( Amazon )

20.Perforated Board (Amazon / eBay)

21.Project Enclosure

22.Screw terminals ( 3x 2pin and 1x6 pin)


24.Plastic Base

Tools :

1.Soldering Iron ( Amazon )

2.Wire Cutter and Stripper ( Amazon )

3.Screw Driver ( Amazon )

4.Cordless Drill ( Amazon )

5.Dremel ( Amazon )

6.Glue Gun ( Amazon )

7.Hobby Knife ( Amazon )

Step 2: How the Charge Controller Works :

The heart of of the charge controller is Arduino nano board.The arduino MCU senses the solar panel and battery voltages.According to this voltages it decides how to charge the battery and control the load.

The amount of charging current is determined by difference between battery voltage and charge set point voltages. The controller uses two stages charging algorithm.According to the charging algorithm it gives a fixed frequency PWM signal to the solar panel side p-MOSFET. The frequency of PWM signal is 490.20Hz(default frequency for pin-3). The duty cycle 0-100% is adjusted by the error signal.

The controller gives HIGH or LOW command to the load side p-MOSFET according to the dusk/dawn and battery voltage.

The full schematic is attached bellow.

Step 3: Main Functions of Solar Charge Controller:

The charge controller is designed by taking care of the following points.

1.Prevent Battery Overcharge: To limit the energy supplied to the battery by the solar panel when the battery becomes fully charged.This is implemented in charge_cycle() of my code.

2.Prevent Battery Over discharge: To disconnect the battery from electrical loads when the battery reaches low state of charge.This is implemented in load_control() of my code.

3.Provide Load Control Functions: To automatically connect and disconnect an electrical load at a specified time. The load will ON when sunset and OFF when sunrise.This is implemented in load_control() of my code.

4.Monitoring Power and Energy : To monitor the load power and energy and display it.

5.Protect from abnormal Condition: To protect the circuit from different abnormal situation like lightening,over voltage,over current and short circuit etc.

6.Indicating and Displaying: To indicate and display the various parameters

7.Serial Communication: To print various parameters in serial monitor

Step 4: Sensing Voltages,Current and Temperature :

1.Voltage Sensor:

The voltage sensors are used to sense the voltage of solar panel and battery.It is implemented by using two voltage divider circuits.It consists of two resistors R1=100k and R2=20k for sensing the solar panel voltage ans similarly R3=100k and R4=20k for battery voltage.The out put from the R1and R2 is connected to arduino analog pin A0 and out put from the R3 and R4 is connected to arduino analog pin A1.

2.Current Sensor :

The current sensor is used for measuring the load current.later this current is used to calculate the load power and energy.I used a hall effect current sensor (ACS712-20A)

3.Temperature Sensor :

The temperature sensor is used to sense the room temperature. I used LM35 temperature sensor which is rated for −55°C to +150°C Range.

Why Temperature monitoring is Required ?

The battery’s chemical reactions change with temperature.As the battery gets warmer, the gassing increases. As the battery gets colder,it becomes more resistant to charging. Depending on how much the battery temperature varies, it is important to adjust the charging for temperature changes.So it is important to adjust charging to account for the temperature effects. The temperature sensor will measure the battery temperature, and the Solar Charge Controller uses this input to adjust the charge set point as required.The compensation value is - 5mv /degC/cell for lead acid type batteries.(–30mV/ºC for 12V and 15mV/ºC for 6V battery).The negative sign of temperature compensation indicates,increase in temperature require a reduction in charge set point.

For more details on Understanding and Optimizing Battery Temperature Compensation

Step 5: Sensors Callibration

Voltage Sensors :

5V = ADC count 1024

1 ADC count = (5/1024)Volt= 0.0048828Volt


Vin = Vout*(R1+R2)/R2 R1=100 and R2=20

Vin= ADC count*0.00488*(120/20) Volt

Current Sensor:

As per seller information for ACS 712 current sensor

Sensitivity is =100mV / A =0.100V/A

No test current through the output voltage is VCC / 2= 2.5

ADC count= 1024/5*Vin and Vin=2.5+0.100*I (where I=current)

ADC count= 204.8(2.5+0.1*I) =512+20.48*I

=> 20.48*I = (ADC count-512)

=> I =(ADC count/20.48)- 512/20.48

Current (I) =0.04882*ADC -25

More details on ACS712

Temperature Sensor :

As per data sheet of LM35

Sensitivity=10 mV/°C

Temp in deg C =(5/1024)*ADC count*100

Note : The sensors are calibrated by assuming the arduino Vcc= 5V reference.But in practical it is not 5V always.So there may be chance of getting wrong value from the actual value.It can be solved by following way.

Measure the voltage between arduino 5V and GND by a multimeter.Use this voltage instead of 5V for Vcc in your code.Hit and try to edit this value until it matches the actual value.

Example: I got 4.47V instead of 5V.So the change should be 4.47/1024=0.0043652 instead of 0.0048828.

Step 6: Charging Algorithm

1.Bulk :At this mode, a preset maximum constant amount of current (amps) is fed into the battery as no PWM is present. As the battery is being charged up , the voltage of the battery increases gradually

2. Absorption: When the battery reaches the bulk charge set voltage, the PWM begins to hold the voltage constant. This is to avoid over-heating and over-gassing the battery. The current will taper down to safe levels as the battery becomes more fully charged.
3. Float: When the battery is fully recharged, the charging voltage is reduced to prevent further heating or gassing of the battery

This is the ideal charging procedure.

The present charge cycle block of code is not implements 3 stages charging.I use a easier logic in 2 stages.It works good.

I am trying the following logic for implementing the 3 stages charging.

Future Planning for Charging Cycle :

The bulk charge begins when solar panel voltage is larger than battery voltage. When the battery voltage reaches 14.4V, absorption charge will be entered. The charging current will be regulated by PWM signal to maintain the battery voltage at 14.4V for one hour. Float charge will then enter after one hour. The float stage generates a trickle charge to keep the battery voltage at 13.6V. When the battery voltage falls below 13.6V for 10mins, the charging cycle will be repeated.

I request community members to help me for writing the piece of code to implement the above logic.

Step 7: Load Control

To automatically connect and disconnect the load by monitoring dusk/dawn and battery voltage,load control is used.

The primary purpose of load control is to disconnect the load from battery to protect it from deep discharging. Deep discharging could damage the battery.

The DC load terminal is designed for low power DC load such as street light.

The PV panel itself is used as the light sensor.

Assuming solar panel voltage >5V means dawn and when < 5V dusk.

ON Condition:

In the evening, when the PV voltage level falls bellow 5V and battery voltage is higher than LVD setting, the controller will turn on the load and the load green led will glow.

OFF Condition:

The load will cut off in the following two condition.

1.In the morning when the PV voltage is larger than 5v,

2.When the battery voltage is lower than the LVD setting

The load red led ON indicates that load is cut off.

LVD is refers to Low Voltage Disconnect

Step 8: Power and Energy

Power :

Power is product of voltage (volt) and current (Amp)


Unit of power is Watt or KW


Energy is product of power (watt) and time (Hour)

E= Pxt

Unit of Energy is Watt Hour or Kilowatt Hour (kWh)

To monitor the load power and energy above logic is implemented in software and the parameters are displayed in a 20x4 char LCD.

Step 9: Protection

1.Reverse polarity protection for solar panel

2. Overcharge protection

3. Deep discharge protection

4. Short circuit and Overload protection

5.Reverse current protection at night

6.Over voltage protection at solar panel input

For reverse polarity and reverse current flow protection I used a power diode (MBR2045).Power diode is used to handle large amount of current.In my earlier design I used a normal diode(IN4007).

Overcharge and Deep discharge protection is implemented by the software.

Over current and overload protection is implemented by using two fuses ( one at the solar panel side and other at load side).

Temporary over voltages occur in power systems for a variety of reasons, but lightning causes the most severe over voltages. This is particularly true with PV systems due to the exposed locations and system connecting cables.In this new design I used a 600 watt bidirectional TVS diode (P6KE36CA ) to suppress the lightning and over voltage at the PV terminals.In my earlier design I used a zeener diode.You can also use a similar TVS diode on the load side.

For selection guide of TVS diode click here

For choosing a right part no for TVS diode click here

Step 10: LED Indication

Battery State Of Charge (SOC) LED:

One important parameter that defines the energy content of the battery is the State of Charge (SOC). This parameter indicates how much charge is available in the battery

A RGB LED is used to indicate the battery state of charge.For connection refer the above schematic

Battery LED ------------>Battery Status

RED --------------------> Voltage is LOW

GREEN --------------------> Voltage is Healthy

BLUE --------------------> Fully Charged

Load LED :

A bi color (red/green) led is used for load status indication.Refer the above schematic for connection.

Load LED --------------------->Load Status

GREEN -------------------------> Connected (ON)

RED ---------------------------> Disconnected (OFF)

I include a third led for indicating the solar panel status.

Step 11: LCD Display

To display the voltage,current,power,energy and temperature a 20x4 I2C LCD is used.If you do not want to display the parameter then disable the lcd_display() from the void loop() function.After disable you have indication led to monitor the battery and load status.

You can refer this instructable for I2C LCD

Download the LiquidCrystal _I2C library from here

Note : In code you have to change the I2C module address.You can use the address scanner code given in the link.

Step 12: Bread Board Testing

It is always a good idea to test your circuit on a breadboard before soldering it together.

After connecting everything upload the code.The code is attached bellow.

The entire software is broken into small functional block for flexibility.Suppose the user is not interested to use a lcd display and happy with the led indication .Then just disable the lcd_display() from the void loop().Thats all.

Similarly according to the user requirement he can enable and disable the various functionality.

Download the code from my GitHub Account


Step 13: Power Supply and Terminals :

Terminals :

Add 3 screw terminals for solar input,battery and load terminal connections.Then solder it.I used the middle screw terminal for battery connection,left to it is for solar panel and the right one is for load.

Power Supply:

In my previous version the power supply for arduino was provided by a 9V battery.In this version the power is taken from the charging battery itself.The battery voltage is step down to 5V by a voltage regulator(LM7805).

Solder LM7805 voltage regulator near to the battery terminal.Then solder the electrolytic capacitors as per schematic.At this stage connect the battery to the screw terminal and check the voltage between pin 2 and 3 of LM7805.It should be near to 5V.

When I used a 6V battery the LM7805 works perfectly.But for 12V battery it heated up after some time.So I request to use a heat sink for it.

Efficient Power supply :

After few testing I found that the voltage regulator LM7805 is not the best way to power the arduino as it waste lots of power in the form heat.So I decide to change it by a DC DC buck converter which is highly efficient.If you plan to make this controller, I advice to use a buck converter rather than LM7805 voltage regulator.

Buck Converter Connection:

IN+ -------> BAT+

IN- --------> BAT-

OUT+ -----> 5V

OUT- -----> GND

Refer the above pictures.

You can buy it from eBay

Step 14: Mount the Arduino :

Cut 2 female header strips of 15 pins each.Place the nano board for reference.Insert the two headers according to the nano pin.Check it whether the nano board is perfect to fit into it.Then solder it back side.

Insert two rows of male header on both sides of nano borad for external connections.Then join the solder points between arduino pin and header pins.See the above picture.

Initially I forgot to add Vcc and GND headers.At this stage you can put headers with 4 to 5 pins for Vcc and GND.

As you can see I connected the voltage regulator 5V and GND to the nano 5V and GND by red and black wire.Later I removed it and soldered at the back side for better look of the board.

Step 15: Solder the Components

Before soldering the components make holes at corners for mounting.

Solder all the components as per schematic.

Apply heat sink to two MOSFETs as well as power diode.

Note: The power diode MBR2045 have two anode and one cathode.So short the two anode.

I used thick wire for power lines and ground and thin wires for signal.signal. Thick wire is mandatory as the controller is designed for higher current.

Step 16: Connect the Current Sensor

After connecting all the components solder two thick wire to the load mosfet's drain and upper terminal of load side fuse holder.Then connect these wires to the screw terminal provided in current sensor( ACS 712).

Step 17: Make the Indication and Temperature Sensor Panel

I have shown two led in my schematic.But I added a third led(bi color) for indicating the solar panel status in future.

Prepare small size perforated board as shown.Then make two holes (3.5mm) by drill on left and right( for mounting).

Insert the leds and solder it to the back side of the board.

Insert a 3 pins female header for temperature sensor and then solder it.

Solder 10 pins right angle header for external connection.

Now connect the RGB led anode terminal to the temperature sensor Vcc(pin-1).

Solder the cathode terminals of two bi color led.

Then join the solder points the leds terminal to the headers.You can paste a sticker with pin name for easy identifications.

Step 18: ​Connections for Charge Controller

Connect the Charge Controller to the Battery first, because this allows the Charge Controller to get calibrated to whether it is 6V or 12V system. Connect the negative terminal first and then positive. Connect the solar panel(negative first and then positive) At last connect the load.

The charge controller load terminal is suitable for only DC load.

How to run an AC Load ?

If you want to run AC appliances then you must need an inverter. Connect the inverter directly to the battery.See the above picture.

Step 19: Final Testing :

After making the main board and indication board connect the header with jumper wires(female-female)

Refer the schematic during this connection.Wrong connection may damage the circuits.So be care full in this stage.

Plug the usb cable to the arduino and then upload the code.Remove the usb cable.If you want to see the serial monitor then keep it connected.

Fuse Rating: In demo I have put a 5A fuse in the fuse holder.But in practical use, put a fuse with 120 to 125% of short circuit current.

Example :A 100W solar panel having Isc=6.32A needs a fuse 6.32x1.25 = 7.9 or 8A

How to test ?

I used a buck boost converter and black cloth to test the controller.The converter input terminals are connected to battery and the output is connected to the charge controller battery terminal.

Battery status :

Rotate the converter potentiometer by a screw driver to simulate different battery voltages.As the battery voltages change the corresponding led will turn off and turn on.

Note: During this process Solar panel should be disconnected or covered with a black cloth or card board.

Dawn/Dusk : To simulate dawn and dusk use a black cloth.

Night : Cover the solar panel entirely.

Day: Remove the cloth from the solar panel.

Transition : slow the remove or cover the cloth to adjust different solar panel voltages.

Load Control : According to the battery condition and dawn/dusk situation the load will turn on and off.

Temperature Compensation :

Hold the temperature sensor to increase the temperature and place any cold things like ice to decrease the temp.It will be immediately displayed on the LCD.

The compensated charge set point value can be seen on the serial monitor.

In the next step onward I will describe the making of enclosure for this charge controller.

Step 20: Mounting the Main Board:

Place the main board inside the enclosure.Mark the hole position by a pencil.

Then apply hot glue to the marking position.

Place the plastic base over the glue.

Then place the board over the base and screw the nuts.

Step 21: Make Space for LCD:

Mark the LCD size on the front cover of the enclosure.

Cut out the marked portion by using a dremel or any other cutting tool.After cutting finish it by using a hobby knife.

Step 22: Drill Holes:

Drill holes for mounting the LCD,Led indication panel,Reset button and external terminals

Step 23: Mount Everything:

After making holes mount the panels, 6 pin screw terminal and reset button.

Step 24: Connect the External 6 Pin Terminal :

For connecting the solar panel,battery and load a external 6pin screw terminal is used.

Connect the external terminal to the corresponding terminal of the main board.

Step 25: Connect the LCD, Indicator Panel and Reset Button :

Connect the indicator panel and LCD to the main board as per schematic.(Use female-female jumper wires)

One terminal of the reset button goes to RST of Arduino and other goes to GND.

After all connections.Close the front cover and screw it.

Step 26: Ideas and Planning

How to plot real time graphs ?

It is very interesting, if you can plot the serial monitor parameters (like battery and solar voltages) on a graph on your laptop screen.It can be done very easily, if you know little bit on Processing.

To know more you can refer Arduino and Processing ( Graph Example ).

How to save that data ?

This can be done easily by using SD card but this include more complexity and cost.To solve this I searched through internet and found a easy solution.You can save data in Excel sheets.

For details you can refer seeing-sensors-how-to-visualize-and-save-arduino-sensed-data

The above pictures downloaded from web.I attached to understand what I want to do and what you can do.

Future Planning :

1. Remote data logging via Ethernet or WiFi.

2. More powerful charging algorithm and load control

3.Adding a USB charging point for smart phone/tablets

Hope you enjoy my instructables.

Please suggest any improvements.Raise a comments if any mistakes or errors.

Follow me for more updates and new interesting projects.

Thanks :)

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752 Discussions


Question 6 weeks ago

Im going to this proyect pal. Im going to use 12V 40W solar panel, is it ok to use the same components or should i change a bit? i have TMP36, can i use it for this proyect?


6 answers

Answer 21 days ago

Hi RyuKim, A 12V 40W panel should be fine without any component changes.
I believe you should be able to use a TMP36 as a direct replacement for the LM35.


Reply 1 day ago

Hi again, sadly we don't own 12V40W solar panel, we have 20V40W solar panel, is a risk to connect the panel to the circuit? We are going to power up everything with a 12 volts battery. And for powering the arduino, can we use the voltage regulator (7805)? We should use Vout and the GND of the 7805 to power up the arduino?


Reply 1 day ago

Hi RyuKim,
Regarding your panel, please count the solar cells that make up the panel, They are usually clearly visible at the front of the panel, and you can see the connections which are usually silver-coloured strips running down the front. What appears to be a short break between cells is actually the connection going to the back of the previous cell. Each cell will produce about 0.5 volts with full illumination. A panel sold as "12 Volts" usually has 36 cells and generates about 18 V at maximum power, or a bit over 20V when open circuit. If you are measuring 20V on your panel when open circuit, it is almost certainly a "12 Volt" panel.
Irrespective of the above explanation, it will be no problem to use your panel with this solar charger.
Regarding powering the Arduino Nano, yes it is powered from the 7805 regulator with 5V (and a ground connection of course).


Reply 1 day ago

Thanks for the reply, we started to connect everything, and saldy i was getting bad measurement, it was getting wrongs variables. Like, it was showing 20V of batery... And 25 volts on solar panel (we didn't connect it). I don't know why this happen, what do you recommend?


Reply 20 hours ago

Hi RyuKim, Did you count the cells in your solar panel?
Regarding the bad voltage measurements, it is likely to be that the resistors you have used for the voltage dividers used in the measurements are a bit off. You can check the dividers with your multimeter. On the battery side, measure the voltage of the battery, and also at pin A1 on the Arduino. The ratio should be 20/120.
You can do the same thing on the panel side, panel voltage and pin A0 on the Arduino. Again the ratio should be 20/120. So for example if your battery voltage is 13V, A1 should be 2.167 V.
The calibration of these can be adjusted in the software, in the read_data function. You will see the (120/20) in the code, you can alter them to the ratio that you get from your actual readings.
If you are not sure what is happening, please send me your readings and I will try to help you figure it out.


Reply 14 hours ago

Sorry late reply, i found the model on internet KL-2368 Solar panel 40W 465*670*25 18.2V. I'm going to do that, and let's see if can be more stable. I will notify if something going wrong


Question 4 days ago

hi, i wonder if this project work perfectly and there are no issues with it ! ,because i really like it and i want to make it as a model for my final project.
I hope that u will answer me very soon.
Thanks in advance.


Question 4 days ago

Hi, I was wondering if you send a PDF version of this so I can put into my research booklet please?


17 days ago

Hello everyone, where is the code? Please..

1 reply

Question 11 days ago

Hi, I'm wondering if you could clarify two problems?
1. the 100uF capacitor doesn't seem to be connected in the schematic.
2. If I used the buck converter, should I still connect capacitor to ground as the schematic?


7 weeks ago

Hi Keith!. i have completed the PCB design for the circuit. However my load switches on and off at regular intervals and seemingly the project is not working. Also the DC regulated supply through which i am powering the arduino goes into Constant Current Mode when i switch on the supply.i Also when I connect the LCD to the 5V and GND of arduino the arduino stops transmitting and the voltage further drops on the regulated power supply . Does it mean there is a short circuit? I have a 16.4 V 10W panel and 12V 7.2 Ah battery. can you look into the PCB images and help resolving my issue.

Arduino PCB.jpgArduino.jpgLed.jpgLEdpcb.jpgmain.jpgPCB main.jpg
2 replies

Reply 21 days ago

Hi Keith. I was able to resolve the problem. However i am still struggling with the LCD. when i connect the LCD To the arduino and when the USB is connected to arduino the diode behind the arduino burnt off. Also the VCC and the GND of I2C is showing connectivity in multimeter. What could be the problem? Is there a short in the I2C or the LCD?


Reply 21 days ago

Hi YashA56, Sorry about my slow reply to your question.
It is very difficult to do debugging using just photographs. I also wonder if you have found the problem since you posted your question.
If you have not, you should post your questions again including some voltage measurements.


2 months ago

Hi, if instead of a mosfet, you used a pnp , you would be able to create an ideal current source that would charge a battery at the voltage that it is at, and no need for a buck. Also, you could PWM the base voltage to obtain any desired charge current.

2 replies

Reply 6 weeks ago

Hi, i tried to upload the code but it i found an error code. so could u please help in this case


Reply 21 days ago

Hi Jouseph, If you post a copy from your Serial Monitor showing the error code and the preceding text I may be able to make some suggestions.


2 months ago

Hi Keith, thanks once again for quick reply. Just to increase the charging current I want to add more mosfets. Please give your valuable suggestion in this regard.
With regards.
Anupam Dasgupta