Introduction: ARDUINO SOLAR CHARGE CONTROLLER ( Version 2.0)

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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696 Discussions

aim getting following error while uploading the code to Arduino nano

Arduino: 1.8.5 (Mac OS X), Board: "Arduino Nano, ATmega328P"

V2_Deba_168:91: error: 'POSITIVE' was not declared in this scope

LiquidCrystal_I2C lcd(0x27, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE); // Set the LCD I2C address // In my case 0x27


/Users/paaker/Documents/Arduino/V2_Deba_168/V2_Deba_168.ino: In function 'void setup()':

V2_Deba_168:106: error: no matching function for call to 'LiquidCrystal_I2C::begin(int, int)'

lcd.begin(20, 4); // initialize the lcd for 16 chars 2 lines, turn on backlight


/Users/paaker/Documents/Arduino/V2_Deba_168/V2_Deba_168.ino:106:18: note: candidate is:

In file included from /Users/paaker/Documents/Arduino/V2_Deba_168/V2_Deba_168.ino:8:0:

/Users/paaker/Documents/Arduino/libraries/Arduino-LiquidCrystal-I2C-library-master/LiquidCrystal_I2C.h:76:7: note: void LiquidCrystal_I2C::begin()

void begin();


/Users/paaker/Documents/Arduino/libraries/Arduino-LiquidCrystal-I2C-library-master/LiquidCrystal_I2C.h:76:7: note: candidate expects 0 arguments, 2 provided

exit status 1

'POSITIVE' was not declared in this scope

avrdude: stk500_recv(): programmer is not responding

avrdude: stk500_getsync() attempt 7 of 10: not in sync: resp=0x00

avrdude: stk500_recv(): programmer is not responding

avrdude: stk500_getsync() attempt 8 of 10: not in sync: resp=0x00

avrdude: stk500_recv(): programmer is not responding

avrdude: stk500_getsync() attempt 9 of 10: not in sync: resp=0x00

avrdude: stk500_recv(): programmer is not responding

avrdude: stk500_getsync() attempt 10 of 10: not in sync: resp=0x00

Problem uploading to board. See for suggestions.

Invalid library found in /Users/paaker/Documents/Arduino/libraries/LiquidCrystal_I2C: /Users/paaker/Documents/Arduino/libraries/LiquidCrystal_I2C

Invalid library found in /Users/paaker/Documents/Arduino/libraries/LiquidCrystal_I2C: /Users/paaker/Documents/Arduino/libraries/LiquidCrystal_I2C

This report would have more information with

"Show verbose output during compilation"

option enabled in File -> Preferences.


I have 3 more questions.

in the diagram there are two points showing I+. I- this is for ACS 712?

P6KE36CA diode not available here. what is the substitute for it?

ACS712 it has 3pin out 5V, analog in, Ground, these connections has to connect for this circuit or Arduino or just leave it?



Question 25 days ago

if i want to add another source like windmill (PV panel and Windmill), what component should i add? or just plug the source in paralel? thank you

17 more answers

Hi AdhiN4, You cannot (or should not) just connect the windmill and PV panel in parallel.

Nor do you need to duplicate the entire charger.

Currently the input from the solar panel is connected to a transient surge suppressor, a voltage divider for voltage measurement, then through a power diode MBR2045.

Your windmill input should have a duplicate set of those components. The cathodes of the two MBR2045 diodes will be connected together.

This is to prevent the PV panel from taking current from the windmill when it is dark, and the to prevent the windmill from taking current from the PV panel when the wind is not blowing.

You will also need to make corresponding changes to the software to take the higher of the two input voltages (PV and wind).


Hi AdhiN4, I think the current fuse (in series with the solar panel) is in the wrong place. If a solar panel is short circuited it will generate current not much higher than its maximum power point current and there will be no damage to any component.

In this design, it would be better to put the fuse in series with the battery, which can generate very high and potentially damaging currents if it is short circuited.

As for whether your windmill needs a fuse, that depends on its design. It is probably a good safety practice to put in a fuse if you are not sure.


Hi farmerkeith, i was wondering could you tell me why this code is used in this program? what is the use of this average number?

int read_adc(int adc_parameter)


int sum = 0;

int sample ;

for (int i=0; i<AVG_NUM; i++)

{ // loop untuk membaca nilai kasar dari adc

sample = analogRead(adc_parameter);

sum += sample;



return(sum / AVG_NUM);



Hi AdhiN4,

You obviously have a different version of the software from me. Google Translate tells me that the comment that is in your code is Indonesian and they translate it as "loop to read the rough value of adc". The version in this Instructable, written by deba168 and which I am looking at, has comments in English and more of them. The corresponding comment in that code says

{ // loop through reading raw adc values AVG_NUM number of times

which I think is a bit more informative than the English translation of the Indonesian comment.

The purpose of this code is to smooth out any noise that my be getting into the voltage readings. If you look in the preamble section, you will see that AVG_NUM is defined as 10. So this bit of code makes 10 measurements of whichever pin it is told to look at, adds all the measurements together, and divides the total by 10, thus getting the average of the readings rounded down to the nearest integer, which it returns as its result.

If you need more clarification, or explanation, don't hesitate to ask again.


Hi farmerkieth,

i'm sorry that was me who wrote that, i'm indonesian so i was trying to translate it to indonesian so that i can understand it better, but it fails, that is why i ask you that question. i've the same version of the software as you do. thank you for your explanation.

i have another problem that i just realized, so when i attach the PV and when it reaches ~20V and higher, the lcd display is blinking back and forth showing only 2 value i.e the solar voltage going back and forth between 15V and 20V and the battery status display charge and discharge. not only that, during that condition the battery is bubbling up and i heard some kind of beeping sound coming from the lcd(or other component). is the voltage to high? or something wrong with the program? i just cannot figure this one out.

Hi AdhiN4, I think you need to take a systematic step-by-step approach to working out the problem.

You at least need a multimeter to measure voltages, and have your computer connected so you can put in some Serial.print() commands to check what the software is doing.

If the battery is connected, but no solar panel, do you get what you expect? Are the voltages from the multimeter consistent with what the software sees. If not you should adjust the calibration factors in the software until they are close.

When this part is right, connect your solar panel and use a shade over the solar panel to control its output. Get its voltage on the multimeter and in the software to be consistent.

The charger behaviour mainly depends on solar_volt and bat_volt and its relationship to bulk_charge_sp and float_charge_sp.

If the battery voltage is less than the float charge set point (ie float_charge_sp) the PWM duty cycle should be high and the solar panel voltage should be only a little bit higher than the battery voltage. and the panel should be producing its full current capability.

If the battery voltage is higher than the bulk charge set point, the PWM duty cycle should be low and the solar panel voltage should be
at close to its open circuit value and several volts higher than the battery voltage with almost no current.

I hope this helps. good luck,


Hi farmerkeith, so i have do what you suggest me to, and it makes no different, when the solar_volt reaches ~20.5 V and over this is when the blinking start to happen again. is the charge set point to high for my battery? i use a 12V 5Ah battery. and i notice that the battery is around 14.4V(i use multimeter to check this too) which is the bulk charge set point. but the display is not stable, it keep blinking back and forth between 14V and 13V just like the solar volt. could you suggest me another way to solve this? or this is a normal thing when the battery reach this point?

Hi AdhhiN4, Can you please post a sample of your serial monitor output at a time when this blinking is happening?


is it save to plug my laptop when the PV is connected when the voltage is that high? if so i'll gladly to show you.

Hi AdhiN4, You will just be connecting the USB from you laptop to the mini-USB connector on the Arduino Nano. I expect it is perfectly safe, but you can double check by measuring the 5V pin on the Nano, before you plug in the laptop. The 5V pin on the nano is connected to t he 5V wire in the USB cable.

So before you plug in the laptop, you should find pretty close to 5V on that nano 5V pin. So long as you find a voltage close to 5, your laptop will be safe.


those are the screenshot of the serial monitor


Hi AdhiN4, It is a bit of a puzzle. It is not clear why the battery voltage seems to be jumping around. I would like you to try the following:

a) in the function called void print_data(void) add 2 new statements just ahead of the first Serial.print statement, as follows:

Serial.print("Time is ");

b) in the function called void charge_cycle(void) add 2 new statements right at the top (before the first test, but after the opening brace:


c) Instead of capturing a screen shot, press the button at the bottom left of the screen to stop it scrolling, and select a couple of screens full of the output, copy to your clipboard (edit copy) and paste it into a posting. That will give a sequence showing the transitions between states on multiple cycles.


i only took those 2 screenshots because that is the only thing that shown on the serial monitor at that time, like i said before the system only show 2 values, it keeps repeating it self. the first screenshot was taken when clouds are covering the sun, the second screenshot is when the sky is clear

I now understand you are saying, that if I label the first (left) screenshot 1, and the top half 1a and the bottom half 1b, then the sequence is 1a 1b 1a 1b 1a 1b ... and so on, when there is not much illumination; and that it changes to 2a 2b 2a 2b 2a 2b ... when there is full sun. Is that correct?

Based on that understanding, the behaviour becomes clear. There is nothing wrong, except possibly your voltage calibration is a bit off, and/or the set points are a bit too high.

In the 1a 1b 1a 1b sequence where the panel is not producing very much, start with the PWM running at 99%, and the battery is already fully charged. The current from the panel is sufficient to raise the battery voltage reading to 13.62V. Since the PWM is nearly 100%, the panel voltage is only a little bit higher than the battery voltage - enough the cover the voltage drop mainly in the series diode. The panel reading is 14.24V, which is 0.62V above battery V, and about right for the diode.

The charge_cycle logic sees that the battery is between float_charge_sp (13.42V) and bulk_charge_sp (14.22V) and changes the PWM to 60%.

The print_data function prints out the panel and battery voltages as above, and the NEW PWM duty cycle.

The change of PWM duty cycle to 60% means that the battery is not being charged as much as before, and so its voltage drops a little bit - by 0.22 volts, to 13.4 V. Because the current is lower, the panel voltage rises also, to 16.73 V.

Because the new battery voltage (13.40V) is lower than the float_charge_sp (13.42V) the charge_cycle logic changes the PWM back to 99%.

And so the sequence goes on, alternating between PWM 60% and 99%.

Exactly the same mechanism is operating in the 2a 2b 2a 2b sequency except that there is enough current from the panel to push the battery voltage above the bulk_charge_sp of 14.22V when the PWM duty cycle is 99%.

What should be done about it? There are several possibilities.

It would be well worth while checking the calibration of the battery and panel voltage measurements, in accordance with my previous suggestions.

The bulk and float set point voltages could be reduced. I think they are currently at the upper limit of the typical range, and will lead to a bit of gassing, so reducing by 0.2 volts or so would be in order or possibly more. Ideally you want the float set point to be just above the battery voltage when it is fully charged and not being charged nor under load.

A further possibility would be to enhance the charging algorithm to provide better battery management capabilities, such as hysteresis (to prevent or at least inhibit the cycling that you observe) and adding a daily boost-charge function to bring the battery to a fully charged state.


so i have add another pair of those component, now if i want to make another condition where the load turn on not only when the voltage is < 5V but also adding a push button to turn the load on, what and where should i put the code.

thank you