Now a days the most advance solar charge controller are Maximum Power Point Tracking (MPPT). These controllers are more expensive than the PWM charge controllers, but it has several advantages in compare to. The MPPT charge controllers are used for extracting the maximum available power from solar panels for charging battery under certain conditions.
Of corse, you can buy one because to build one require some basic knowledge of electronics.
MPPT circuit is based around a synchronous buck converter circuit.
I shall not insist upon it. There are lot of knowledge on this site. A good job was made by Julian Ilett, who put a lot of youtube tutorials waiting for you.

First you can try one of that kind of converters and after a little encouragement and success you cant start an new project if you don`t keep reading the last one of these:

– Tim Nolan web archive page, with folowing link

Arduino powered solar battery charger

Arduino solar charge controller

Arduino based MPPT solar charger controller

I thanks to all of them for sharing their knowledge. The first one is Tim Nolan who initiated this adventure. And I think you will not be the last who will try.
Now I can not tell you “Abandon all hope, ye who enter here.” but will not be so easy and you may try that just one more time in your life.
All of these enthusiasts was inspired me to build one, and finish this project.

In this page deba168 wrote on 29.07.2016: ā€œI am no more working on this project due to some issues. This controller is not working.ā€

I think you wrong. Your project is living. Look at here. I have nothing to complain. I just made some little changes, et voila…

schema-electrica-ppt1

In the next image are the waveforms of input signals for the MOSFET`s and the output signal :

oscilloscope

The waveforms are for 5V/div amplitude and 5 us/div timebase.

And this is the image of my functional MPPT Solar Charger powered by an Mono Crystalline Silicon PV Module, with a maximum power of 50W (maximum 21,5V / 3,5A) , for charging a 12 V lead acid battery:

The Arduino code is from from MPPT solar charger build around Tim Nolans open source MPPT solar prototype project updated by Debiasish Dutta in his website, that I made a couple of changes:

Arduino code:


//ARDUINO MPPT SOLAR CHARGE CONTROLLER (Version-3)
//Author: Debasish Dutta/deba168
//          www.opengreenenergy.in
// This code was wrote for an arduino Nano based Solar MPPT charge controller.
// This code is a modified version of sample code from www.timnolan.com
// updated 06/07/2015
// Adapted for Arduino Pro mini on my project on 11/2016

#include "TimerOne.h"
#include "LiquidCrystal_I2C.h"
#include "Wire.h"  

// A0 - Voltage divider (solar)
// A1 - ACS 712 Out
// A2 - Voltage divider (battery)
// A4 - LCD SDA
// A5 - LCD SCL
// D5 - LCD back control button
// D6 - Load Control
// D8 - 2104 MOSFET driver SD
// D9 - 2104 MOSFET driver IN
// D11- Green LED
// D12- Blue LED
// D13- Red LED

#define LOAD_ALGORITHM 0
#define SOL_VOLTS_CHAN 0
#define BAT_VOLTS_CHAN 1
#define SOL_AMPS_CHAN 2
#define AVG_NUM 8
#define SOL_VOLTS_SCALE 0.024900275
#define BAT_VOLTS_SCALE 0.024926075
#define SOL_AMPS_SCALE  0.024506081
#define PWM_PIN 9
#define PWM_ENABLE_PIN 8
#define PWM_FULL 1023
#define PWM_MAX 100
#define PWM_MIN 60
#define PWM_START 90
#define PWM_INC 1
#define TRUE 1
#define FALSE 0
#define ON TRUE
#define OFF FALSE
#define TURN_ON_MOSFETS digitalWrite(PWM_ENABLE_PIN, HIGH)
#define TURN_OFF_MOSFETS digitalWrite(PWM_ENABLE_PIN, LOW)
#define ONE_SECOND 50000
#define LOW_SOL_WATTS 5.00
#define MIN_SOL_WATTS 1.00
#define MIN_BAT_VOLTS 11.00
#define MAX_BAT_VOLTS 14.10
#define BATT_FLOAT 13.60
#define HIGH_BAT_VOLTS 13.00
#define LVD 11.5
#define OFF_NUM 9
#define LED_GREEN 11
#define LED_BLUE 12
#define LED_RED 13
#define LOAD_PIN 6
#define BACK_LIGHT_PIN 5       

byte battery_icons[6][8]=
{{
  0b01110,
  0b11011,
  0b10001,
  0b10001,
  0b10001,
  0b10001,
  0b11111,
  0b00000,
},
{
  0b01110,
  0b11011,
  0b10001,
  0b10001,
  0b10001,
  0b11111,
  0b11111,
  0b00000,
},
{
  0b01110,
  0b11011,
  0b10001,
  0b10001,
  0b11111,
  0b11111,
  0b11111,
  0b00000,
},
{
  0b01110,
  0b11011,
  0b11111,
  0b11111,
  0b11111,
  0b11111,
  0b11111,
  0b00000,
},
{
  0b01110,
  0b11111,
  0b11111,
  0b11111,
  0b11111,
  0b11111,
  0b11111,
  0b00000,
},
{
  0b01110,
  0b11111,
  0b11111,
  0b11111,
  0b11111,
  0b11111,
  0b11111,
  0b00000,
}};
#define SOLAR_ICON 6
byte solar_icon[8] =
{
  0b11111,
  0b10101,
  0b11111,
  0b10101,
  0b11111,
  0b10101,
  0b11111,
  0b00000
};
#define PWM_ICON 7
byte _PWM_icon[8]=
{
  0b11101,
  0b10101,
  0b10101,
  0b10101,
  0b10101,
  0b10101,
  0b10111,
  0b00000,
};
byte backslash_char[8]=
{
  0b10000,
  0b10000,
  0b01000,
  0b01000,
  0b00100,
  0b00100,
  0b00010,
  0b00000,
};
float sol_amps;
float sol_volts;
float bat_volts;
float sol_watts;
float old_sol_watts = 0;
unsigned int seconds = 0;
unsigned int prev_seconds = 0;
unsigned int interrupt_counter = 0;
unsigned long time = 0;
int delta = PWM_INC;
int pwm = 0;
int back_light_pin_State = 0;
boolean load_status = false;
enum charger_mode {off, on, bulk, bat_float} charger_state;
LiquidCrystal_I2C lcd(0x27, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE);  

void setup()
{
  pinMode(PWM_ENABLE_PIN, OUTPUT);
  TURN_OFF_MOSFETS;
  charger_state = off;
  lcd.begin(20,4);
  lcd.backlight();
  for (int batchar = 0; batchar < 6; ++batchar)
  {
    lcd.createChar(batchar, battery_icons[batchar]);
  }
  lcd.createChar(PWM_ICON,_PWM_icon);
  lcd.createChar(SOLAR_ICON,solar_icon);
  lcd.createChar('\\', backslash_char);
  pinMode(LED_RED, OUTPUT);
  pinMode(LED_GREEN, OUTPUT);
  pinMode(LED_BLUE, OUTPUT);
  Timer1.initialize(20);
  Timer1.pwm(PWM_PIN, 0);
  Timer1.attachInterrupt(callback);
  Serial.begin(9600);
  pwm = PWM_START;
  pinMode(BACK_LIGHT_PIN, INPUT);
  pinMode(LOAD_PIN,OUTPUT);
  digitalWrite(LOAD_PIN,LOW);
  digitalWrite(BACK_LIGHT_PIN,LOW);
  lcd.setCursor(0, 0);
  lcd.print("SOL");
  lcd.setCursor(4, 0);
  lcd.write(SOLAR_ICON);
  lcd.setCursor(8, 0);
  lcd.print("BAT");
}

void loop()
{
  read_data();
  run_charger();
 // print_data();
  load_control();
  led_output();
  lcd_display();
}

int read_adc(int channel)
{
  int sum = 0;
  int temp;
  int i;

  for (i=0; i<AVG_NUM; i++) { temp = analogRead(channel); sum += temp; delayMicroseconds(50); } return(sum / AVG_NUM); } void read_data(void) { sol_amps = (read_adc(SOL_AMPS_CHAN) * SOL_AMPS_SCALE -13.51); sol_volts = read_adc(SOL_VOLTS_CHAN) * SOL_VOLTS_SCALE; bat_volts = read_adc(BAT_VOLTS_CHAN) * BAT_VOLTS_SCALE; sol_watts = sol_amps * sol_volts ; } void callback() { if (interrupt_counter++ > ONE_SECOND)
  {
    interrupt_counter = 0;
    seconds++;
  }
}

void set_pwm_duty(void)
{

  if (pwm > PWM_MAX)
  {
    pwm = PWM_MAX;
  }
  else if (pwm < PWM_MIN)
  {
    pwm = PWM_MIN;
  }
  if (pwm < PWM_MAX)
  {
    Timer1.pwm(PWM_PIN,(PWM_FULL * (long)pwm / 100), 20);
  }
  else if (pwm == PWM_MAX)
  {
    Timer1.pwm(PWM_PIN,(PWM_FULL - 1), 20);
}
}	

void run_charger(void)
{
  static int off_count = OFF_NUM;
  switch (charger_state)
  {
    case on:
      if (sol_watts < MIN_SOL_WATTS) { charger_state = off; off_count = OFF_NUM; TURN_OFF_MOSFETS; } else if (bat_volts > (BATT_FLOAT - 0.1))
      {
        charger_state = bat_float;
      }
      else if (sol_watts < LOW_SOL_WATTS)
      {
        pwm = PWM_MAX;
        set_pwm_duty();
      }
      else
      {
        pwm = ((bat_volts * 10) / (sol_volts / 10)) + 5;
        charger_state = bulk;
      }
      break;

    case bulk:
      if (sol_watts < MIN_SOL_WATTS) { charger_state = off; off_count = OFF_NUM; TURN_OFF_MOSFETS; } else if (bat_volts > BATT_FLOAT)
      {
        charger_state = bat_float;
      }
      else if (sol_watts < LOW_SOL_WATTS) { charger_state = on; TURN_ON_MOSFETS; } else { if (old_sol_watts >= sol_watts)
        {
          delta = -delta;
        }
        pwm += delta;
        old_sol_watts = sol_watts;
        set_pwm_duty();
      }
      break;

    case bat_float:
      if (sol_watts < MIN_SOL_WATTS) { charger_state = off; off_count = OFF_NUM; TURN_OFF_MOSFETS; set_pwm_duty(); } else if (bat_volts > BATT_FLOAT)
      {
        TURN_OFF_MOSFETS;
        pwm = PWM_MAX;
        set_pwm_duty();
      }
      else if (bat_volts < BATT_FLOAT)
      {
        pwm = PWM_MAX;
        set_pwm_duty();
        TURN_ON_MOSFETS;
        if (bat_volts < (BATT_FLOAT - 0.1)) { charger_state = bulk; } } break; case off: TURN_OFF_MOSFETS; if (off_count > 0)
      {
        off_count--;
      }
      else if ((bat_volts > BATT_FLOAT) && (sol_volts > bat_volts))
      {
        charger_state = bat_float;
        TURN_ON_MOSFETS;
      }
      else if ((bat_volts > MIN_BAT_VOLTS) && (bat_volts < BATT_FLOAT) && (sol_volts > bat_volts))
      {
        charger_state = bulk;
        TURN_ON_MOSFETS;
      }
      break;
    default:
      TURN_OFF_MOSFETS;
      break;
  }
}

void load_control()
{
#if LOAD_ALGORITHM == 0
  load_on(sol_watts < MIN_SOL_WATTS && bat_volts > LVD);
#else
  load_on(sol_watts > MIN_SOL_WATTS && bat_volts > BATT_FLOAT);
#endif
}

void load_on(boolean new_status)
{
  if (load_status != new_status)
  {
    load_status = new_status;
    digitalWrite(LOAD_PIN, new_status ? HIGH : LOW);
  }
}

void print_data(void)  // you can skip this part)
{
  Serial.print(seconds,DEC);
  Serial.print("      ");
  Serial.print("Charging = ");
  if (charger_state == on) Serial.print("on   ");
  else if (charger_state == off) Serial.print("off  ");
  else if (charger_state == bulk) Serial.print("bulk ");
  else if (charger_state == bat_float) Serial.print("float");
  Serial.print("      ");

  Serial.print("pwm = ");
  if(charger_state == off)
  Serial.print(0,DEC);
  else
  Serial.print(pwm,DEC);
  Serial.print("      ");

  Serial.print("Current (panel) = ");
  Serial.print(sol_amps);
  Serial.print("      ");

  Serial.print("Voltage (panel) = ");
  Serial.print(sol_volts);
  Serial.print("      ");

  Serial.print("Power (panel) = ");
  Serial.print(sol_volts);
  Serial.print("      ");

  Serial.print("Battery Voltage = ");
  Serial.print(bat_volts);
  Serial.print("      ");

  Serial.print("\n\r");
  //delay(1000);
}

void light_led(char pin)
{
  static char last_lit;
  if (last_lit == pin)
      return;
  if (last_lit != 0)
      digitalWrite(last_lit, HIGH);
  digitalWrite(pin, LOW);
  last_lit = pin;
}

void led_output(void)
{
  static char last_lit;
  if(bat_volts > 14.1 )
      light_led(LED_BLUE);
  else if(bat_volts > 11.9)
      light_led(LED_GREEN);
  else
      light_led(LED_RED);
}
void lcd_display()
{
  static bool current_backlight_state = -1;
  back_light_pin_State = digitalRead(BACK_LIGHT_PIN);
  if (current_backlight_state != back_light_pin_State)
  {
    current_backlight_state = back_light_pin_State;
    if (back_light_pin_State == HIGH)
      lcd.backlight();
    else
      lcd.noBacklight();
  }

  if (back_light_pin_State == HIGH)
  {
    time = millis();
  }

 lcd.setCursor(0, 1);
 lcd.print(sol_volts);
 lcd.print("V ");
 lcd.setCursor(0, 2);
 lcd.print(sol_amps);
 lcd.print("A");
 lcd.setCursor(0, 3);
 lcd.print(sol_watts);
 lcd.print("W ");
 lcd.setCursor(8, 1);
 lcd.print(bat_volts);
 lcd.setCursor(8,2);

 if (charger_state == on)
 lcd.print("on   ");
 else if (charger_state == off)
 lcd.print("off  ");
 else if (charger_state == bulk)
 lcd.print("bulk ");
 else if (charger_state == bat_float)
 {
 lcd.print("     ");
 lcd.setCursor(8,2);
 lcd.print("float");
 }

 int pct = 100.0*(bat_volts - 11.3)/(12.7 - 11.3);
 if (pct < 0) pct = 0; else if (pct > 100)
     pct = 100;

 lcd.setCursor(12,0);
 lcd.print((char)(pct*5/100));

 lcd.setCursor(8,3);
 pct = pct - (pct%10);
 lcd.print(pct);
 lcd.print("%  ");

 lcd.setCursor(15,0);
 lcd.print("PWM");
 lcd.setCursor(19,0);
 lcd.write(PWM_ICON);
 lcd.setCursor(15,1);
 lcd.print("   ");
 lcd.setCursor(15,1);
 if( charger_state == off)
 lcd.print(0);
 else
 lcd.print(pwm);
 lcd.print("% ");

 lcd.setCursor(15,2);
 lcd.print("Load");
 lcd.setCursor(15,3);
 if (load_status)
 {
    lcd.print("On  ");
 }
 else
 {
   lcd.print("Off ");
 }
 spinner();
 backLight_timer();
}

void backLight_timer()
{
  if((millis() - time) <= 15000)
      lcd.backlight();
  else
      lcd.noBacklight();
}
void spinner(void)
{
  static int cspinner;
  static char spinner_chars[] = { '*','*', '*', ' ', ' '};
  cspinner++;
  lcd.print(spinner_chars[cspinner%sizeof(spinner_chars)]);
}

And this is the final project image:

final

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