Arduino Controlled 12V battery charger circuit

Arduino is an open-source that is designed for artists or for those who do not have an electronic background. Here, in this article, we are going to show you the method of making a battery charger circuit controlled using an Arduino uno board. The project Arduino Controlled 12V battery charger circuit is an advanced version of the previous posted project “12V, 7Ah Smart Battery Charger with PCB Diagram”. This charger also has the features of bulk stage charging and float stage charging as in the previous circuit.

Silent features of Arduino Controlled 12V battery charger circuit

Charge the battery in different stages i.e. bulk stage charging and float stage charging.
16×2 LCD for better visual indication of charging status of the battery and fully charged.
The simple circuit is thus understandable to everyone.
Automatic charging voltage and current according to the battery status.
The high output current of about 5 Amp. Max.

Components Required for Arduino Controlled 12V battery charger circuit

Resistor (all ¼-watt, ± 5% Carbon Unless Stated Otherwise) Ω µF

R₁ = 0.2 Ω/ 5W (Wire wound)

R₂ = 1.5 KΩ

R₃ = 470 Ω

R₄, R₁₃ = 1 KΩ

R₅, R₇, R₉, R₁₁ = 3.3KΩ

R₆ = 330 Ω

R₈ = 4.7 KΩ

R₁₀ = 2.2 KΩ

R₁₂= 22 KΩ

VR₁ = 2 KΩ POT.

VR₂ = 10 KΩ POT.

Capacitors

C₁, C₂, C₄ = 10 µF, 35V or 63V (Electrolytic Capacitor)

C₃ = 2000 µF, 35V or 63V (Electrolytic Capacitor)

C₅ = 100 µF, 24V (Electrolytic Capacitor)

Semiconductors

IC₁ = LM338

IC₂ = LM7812

T₁, T₂ = BC547

D₁, D₂, D₇ = 1N5408

D₃, D₄. D₆, D₈ = 1N4007

Arduino UNO Board

Miscellaneous

LCD₁ = 16×2 Alphanumeric LCD

SW₁ = Push-to-on Switch

Jumpers for connectors

LED₁ = 5mm any color LED

Heat Sink for IC₁ and IC₂

X₁ = 220V AC Primary to 15V-0-15V, 3A Secondary Transformer

Circuit Description of Arduino Controlled 12V battery charger circuit

The circuit is shown in figure 1 and made using Proteous. For circuit description and working of Arduino Controlled 12V battery charger circuit we are dividing the entire section into 4 parts.

Voltage Stepdown and Rectifier Unit | Arduino Controlled 12V battery charger circuit

The stepdown and rectifier is built around 220V AC primary to the 15V-0-15V secondary transformer, two high-power rectifier diode, and a filter capacitor (C₃ = 2000 µF). This arrangement is a full-wave rectifier with a filter circuit. Transformer X₁ step down the AC input voltage to 30V AC which is rectified using two diodes D₁ and D₁ and filtered using capacitor C₃. This DC output contains ripple and the magnitude of DC volt is about 28.5V (30V-0.7V-0.7V = 28.5V). Approximate 1.5V is the voltage drop across diode D₁ and D₂ combined.

Battery Charger Circuit | Arduino Controlled 12V battery charger circuit

The charger circuit is designed around an adjustable voltage regulator IC (LM338). Filtered DC voltage is given to the input pin of IC₁ (LM338). This IC can provide a regulated voltage of about 1.2V to 32V at excess of 5A current. Diode D₃ and D₄ are protection diodes and hence protect from reverse polarity voltage sources.

Transistor T₁ and T₂ control the voltage at output i.e. when the battery is fully charged then output is set to float charging state and when the battery is in charging state the then the output is set to bulk charging.

Figure 2: Adjustable Voltage Regulator with Rectifier

Working of the adjustable voltage regulator

The output voltage (V_0ut) of the adjustable voltage regulator is described by the following equation

$V_{OUT} = V_{REF} \times (1 + \dfrac{R_2}{R_1}) + I_{ADJ} \times R_2$

Where R₂ = VR₁ + R₅ + R₆ i.e. combination of these three resistors.

R₁ = 470-ohm

V_REF = 1.25V

I_ADJ = 45 uA

Therefore the above equation can be re-written as:

$V_{OUT} = 1.25 \times (1 + \dfrac{R_2}{470}) + 45\mu \times R_2$

Mathematical Calculation of theoretical value of R₂

The maximum voltage at which we can charge the 12V battery is about 14.2V. So, let us assume V_OUT = 14.2V and calculate the value of variable resistance VR₁.

$14.2 = 1.25 \times (1 + \dfrac{R_2}{470}) + 45\times 10^{-6} \times R_2$

$11.36 = (1 + \dfrac{R_2}{470}) + 36\times 10^{-6} \times R_2$

$10.36 = \dfrac{R_2}{470} + 36\times 10^{-6} \times R_2$

$10.36 = 2.1636 \times 10^{-3} \times R_2$

Therefore,

$R_2 = 4788.18 \Omega$

Now, Calculate the value of variable resistor VR₁

$R_2 = VR_1 + R_5 + R_6$

$4788.18 = VR_1 + 3300\Omega + 330 \Omega$

Therefore, theoretical value of variable resistor VR₁ is

$VR_1 = 1158 \Omega$

So, adjust the wiper of the variable resistor in between.

Now let’s see the working of the automatic charger stage in three different cases.

CASE 1: When Both the transistor is OFF i.e. both the digital pin D8 and D9 of the Arduino board is low.

$R_1 = 470 \Omega$

Value of resistor R₂ is a combination of all three resistor VR₁, R_5, and R₆ because this two transistor is off and does not conduct any voltage i.e. R₂ = 4788-ohm

So, the voltage output can be calculated as

$V_{OUT} = 1.25 \times (1 + \dfrac{4788}{470}) + 45\times 10^{-6} \times 4788$

$V_{OUT} = 13.98V + 0.215V$

Therefore

$V_{OUT} = 14.195V \approx 14.2V$

Thus, battery Charge at bulk stage

CASE 2: When the Transistor T₁ (Charger OFF Transistor) is off and transistor T₂ (charge low transistor) is ON. In this case resistor, R₆ does not contribute any resistance to adjustable resistance because conducting transistor T₂ heavily conducts and passes all the voltage to the ground from the endpoint of R₅. Thus, equivalent resistance (R₂) = 4788 – 330 = 4458-ohm.

$R_1 = 470\Omega$

$R_2 = 4458\Omega$

Therefore, output voltage V_OUT

$V_OUT = 1.25 \times (1 + \dfrac{4458}{470}) + 0.215$

$V_{OUT} = 13.32V$

Thus, in this case, the charger circuit maintains only a float charging state i.e. battery charger supply 13.2 voltage to the battery at a constant rate. As we all know that batteries have some internal resistance and start to self-discharge at a constant rate and to solve this issue we used here float charging concept.

CASE 3: When both the transistor is on, in this case, no resistor (i.e. VR₁, R_5, and R₆) contributes in R2 i.e. R₂ becomes zero because transistor T₂ starts to conduct and all the voltage is passed from collector to emitter to ground. So, the output voltage can be calculated as

$V_{OUT} = 1.25 \times (1 + 0) + 0$

$V_{OUT} = 1.25V$

Fixed Voltage Regulator | Arduino Controlled 12V battery charger circuit

Fix voltage regulator 7812 (IC₂) is used to power the Arduino uno board and also used to calculate the power consumption to find whether the battery is good or not. Two diodes D₅ and D₆ are used for protection as in the above circuit. A voltage divider network is made using two resistors R₈ and R₁₀ which are used to measure the voltage difference. One output between these two resistors is given to analog pin A1 of Arduino uno board as shown in the circuit diagram.

Figure 3: Fixed Voltage Regulator Circuit

Display Unit | Arduino Controlled 12V battery charger circuit

The display unit is built around a 16×2 alphanumeric LCD and Arduino board. As this LCD is based on Hitachi so for contrast we don’t need a variable resistor. A fixed value resistor is connected to the V_DD pin (pin 3) of LCD to the ground as shown in the circuit diagram. The higher data pin of LCD (D4, D5, D6, and D7) is connected to Arduino uno digital pin (D5, D4, D3, and D2) respectively. Where enable (E) and Reset/Set (RS) pin of LCD is connected to D6 and D7 respectively as shown in the circuit diagram. LED+ and LED- (pin 15 and pin 16) of LCD is connected to +Vcc (5V of Arduino) through current limiting resistor R13 and GND respectively. If you are new to Arduino and LCD interfacing then please watch this video before interfacing: Interfacing of 16×2 LCD to Arduino UNO Board.

Figure 4: Display Unit for Arduino Battery Charger

Battery Status | Arduino Controlled 12V battery charger circuit

For checking battery status press the switch SW₁ for a few moments. Arduino board gets power from the battery and it measures the voltage from the voltage divider network formed using resistor R₁₂ and variable resistor VR₂. The jumper is used for calibration of the circuit for battery testing.

Figure 5: Battery Status Circuit

Software Code | Arduino Controlled 12V battery charger circuit

The software code for Arduino controlled 12V battery charger circuit is written in Arduino programming language and compiled using Arduino IDE.

#include <LiquidCrystal.h>

//               RS  E  D4 D5  D6 D7
LiquidCrystal lcd(7, 6, 5, 4, 3, 2);

int ADC_PIN = A0;
int PWR_PIN = A1;
int CHRG_OFF_PIN = 8;
int CHRG_LOW_PIN = 9;
int CALIBRATION_PIN = 10;
int LED_IND  = 13; 
int ADC_VAL = 0;  
int PWR_VAL = 0;
int VOLTS = 0;
int isCalibrate=0;
int loopno=0;

void setup() 
{
  pinMode(LED_IND, OUTPUT); 
  pinMode(CHRG_OFF_PIN, OUTPUT); 
  pinMode(CHRG_LOW_PIN, OUTPUT); 
  pinMode(CALIBRATION_PIN, INPUT);
  digitalWrite(CHRG_OFF_PIN, HIGH);   
  digitalWrite(CHRG_LOW_PIN, HIGH);
  delay(2000);
  lcd.begin(16, 2);
  lcd.setCursor(0, 0);
  lcd.print ("Arduino controld" );
  lcd.setCursor(0, 1);
  lcd.print("12V battery chrgr");
  delay(1000);
  lcd.clear();
}

void loop() 
{
  START:
  loopno++;
  isCalibrate = digitalRead ( CALIBRATION_PIN );
  digitalWrite(LED_IND, HIGH); 
  if ( isCalibrate == HIGH )
  {
    digitalWrite(CHRG_OFF_PIN, LOW);
    digitalWrite(CHRG_LOW_PIN, LOW);
  }
  else
  {
    digitalWrite(CHRG_OFF_PIN, HIGH);
    digitalWrite(CHRG_LOW_PIN, HIGH);
  }
  delay(20);
  PWR_VAL = analogRead (PWR_PIN);
  delay(20);
  ADC_VAL = analogRead(ADC_PIN);
  VOLTS = (ADC_VAL+2) / 4;
  
  lcd.setCursor(0, 0);  
  lcd.print (VOLTS/10);   
  lcd.print (".");   
  lcd.print (VOLTS%10);   
  lcd.print (" V   ");
   
  if ( isCalibrate == HIGH )
  {
    lcd.setCursor(0, 1);  //lcd.print ("STATUS:" ); 
    lcd.print ("CALIBRATION.....");
    lcd.setCursor(7, 0);  
    lcd.print ("A0 = " );   
    lcd.print (ADC_VAL); 
    lcd.print ( "   " );
    delay(500); 
    goto START;
  }
 
  if ( VOLTS>130 )
  {
    digitalWrite(CHRG_OFF_PIN, LOW);   
    digitalWrite(CHRG_LOW_PIN, HIGH);
    lcd.setCursor(7, 0); 
    lcd.print ("CHRG.FULL" ); 
    lcd.setCursor(0,1);  
    if(PWR_VAL<600) 
    lcd.print( " CHARGER IS OFF " ); 
    else 
    lcd.print ("FLOAT CHARGING. " );
  }
  else if ( VOLTS<=15 )
  {
    digitalWrite(CHRG_OFF_PIN, HIGH);   
    digitalWrite(CHRG_LOW_PIN, HIGH);
    lcd.setCursor(7, 0); 
    lcd.print ("NO BATTRY" ); 
    lcd.setCursor(0,1);   
    if(PWR_VAL<600) 
    lcd.print( " CHARGER IS OFF " ); 
    else  
    lcd.print ("  NOT CHARGING. " );
  }
 else if ( VOLTS<80 )
  {
    lcd.setCursor(7, 0); 
    lcd.print ("BATT:DEAD" ); 
    lcd.setCursor(0,1);   
    if(PWR_VAL<600) 
    lcd.print( " CHARGER IS OFF " ); 
    else  
    lcd.print (" SLOW CHARGING. " );
    delay(1000); 
    digitalWrite(CHRG_OFF_PIN, LOW);   
    digitalWrite(CHRG_LOW_PIN, HIGH);
  }
  else if ( VOLTS<110 )
  {
    digitalWrite(CHRG_OFF_PIN, LOW);   
    digitalWrite(CHRG_LOW_PIN, LOW);
    lcd.setCursor(7, 0); 
    lcd.print ("BATT:WEAK" ); 
    lcd.setCursor(0,1);    
    if(PWR_VAL<600) 
    lcd.print( " CHARGER IS OFF " ); 
    else  
    lcd.print (" FAST CHARGING. " );
  }
  else
  {
    digitalWrite(CHRG_OFF_PIN, LOW);   
    digitalWrite(CHRG_LOW_PIN, LOW);
    lcd.setCursor(7, 0); 
    lcd.print ("BATT:GOOD" ); 
    lcd.setCursor(0,1);   
    if(PWR_VAL<600) 
    lcd.print( " CHARGER IS OFF " ); 
    else  
    lcd.print (" FAST CHARGING. " );
  }
  
  
  if ( loopno%2 )
  {
    lcd.setCursor(15,1);
    lcd.print ( '.' );
  }

  if(loopno>1000)
    loopno = 0;
  digitalWrite(LED_IND, LOW);
  delay(2000); 
}

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#include <LiquidCrystal.h>

// RS E D4 D5 D6 D7

LiquidCrystal lcd(7, 6, 5, 4, 3, 2);

int ADC_PIN = A0;

int PWR_PIN = A1;

int CHRG_OFF_PIN = 8;

int CHRG_LOW_PIN = 9;

int CALIBRATION_PIN = 10;

int LED_IND = 13;

int ADC_VAL = 0;

int PWR_VAL = 0;

int VOLTS = 0;

int isCalibrate=0;

int loopno=0;

void setup()

{

pinMode(LED_IND, OUTPUT);

pinMode(CHRG_OFF_PIN, OUTPUT);

pinMode(CHRG_LOW_PIN, OUTPUT);

pinMode(CALIBRATION_PIN, INPUT);

digitalWrite(CHRG_OFF_PIN, HIGH);

digitalWrite(CHRG_LOW_PIN, HIGH);

delay(2000);

lcd.begin(16, 2);

lcd.setCursor(0, 0);

lcd.print ("Arduino controld" );

lcd.setCursor(0, 1);

lcd.print("12V battery chrgr");

delay(1000);

lcd.clear();

}

void loop()

{

START:

loopno++;

isCalibrate = digitalRead ( CALIBRATION_PIN );

digitalWrite(LED_IND, HIGH);

if ( isCalibrate == HIGH )

{

digitalWrite(CHRG_OFF_PIN, LOW);

digitalWrite(CHRG_LOW_PIN, LOW);

}

else

{

digitalWrite(CHRG_OFF_PIN, HIGH);

digitalWrite(CHRG_LOW_PIN, HIGH);

}

delay(20);

PWR_VAL = analogRead (PWR_PIN);

delay(20);

ADC_VAL = analogRead(ADC_PIN);

VOLTS = (ADC_VAL+2) / 4;

lcd.setCursor(0, 0);

lcd.print (VOLTS/10);

lcd.print (".");

lcd.print (VOLTS%10);

lcd.print (" V ");

if ( isCalibrate == HIGH )

{

lcd.setCursor(0, 1); //lcd.print ("STATUS:" );

lcd.print ("CALIBRATION.....");

lcd.setCursor(7, 0);

lcd.print ("A0 = " );

lcd.print (ADC_VAL);

lcd.print ( " " );

delay(500);

goto START;

}

if ( VOLTS>130 )

{

digitalWrite(CHRG_OFF_PIN, LOW);

digitalWrite(CHRG_LOW_PIN, HIGH);

lcd.setCursor(7, 0);

lcd.print ("CHRG.FULL" );

lcd.setCursor(0,1);

if(PWR_VAL<600)

lcd.print( " CHARGER IS OFF " );

else

lcd.print ("FLOAT CHARGING. " );

}

else if ( VOLTS<=15 )

{

digitalWrite(CHRG_OFF_PIN, HIGH);

digitalWrite(CHRG_LOW_PIN, HIGH);

lcd.setCursor(7, 0);

lcd.print ("NO BATTRY" );

lcd.setCursor(0,1);

if(PWR_VAL<600)

lcd.print( " CHARGER IS OFF " );

else

lcd.print (" NOT CHARGING. " );

}

else if ( VOLTS<80 )

{

lcd.setCursor(7, 0);

lcd.print ("BATT:DEAD" );

lcd.setCursor(0,1);

if(PWR_VAL<600)

lcd.print( " CHARGER IS OFF " );

else

lcd.print (" SLOW CHARGING. " );

delay(1000);

digitalWrite(CHRG_OFF_PIN, LOW);

digitalWrite(CHRG_LOW_PIN, HIGH);

}

else if ( VOLTS<110 )

{

digitalWrite(CHRG_OFF_PIN, LOW);

digitalWrite(CHRG_LOW_PIN, LOW);

lcd.setCursor(7, 0);

lcd.print ("BATT:WEAK" );

lcd.setCursor(0,1);

if(PWR_VAL<600)

lcd.print( " CHARGER IS OFF " );

else

lcd.print (" FAST CHARGING. " );

}

else

{

digitalWrite(CHRG_OFF_PIN, LOW);

digitalWrite(CHRG_LOW_PIN, LOW);

lcd.setCursor(7, 0);

lcd.print ("BATT:GOOD" );

lcd.setCursor(0,1);

if(PWR_VAL<600)

lcd.print( " CHARGER IS OFF " );

else

lcd.print (" FAST CHARGING. " );

}

if ( loopno%2 )

{

lcd.setCursor(15,1);

lcd.print ( '.' );

}

if(loopno>1000)

loopno = 0;

digitalWrite(LED_IND, LOW);

delay(2000);

}

Figure 6: Calibration Circuit

Calibration of Arduino Controlled 12V Battery Charger Circuit

Connect all the circuit components as shown in the circuit diagram.
Upload the code to the Arduino Uno board.
Short the jumper (CON1).
Connect the multimeter in place of the battery, and set the multimeter in DC voltage measurement mode. (V probe of the multimeter is connected to the output of diode D7 and COM probe to GND of the circuit).
Adjust the wiper of VR₁ until the multimeter shows 14.2V reading. If the multimeter reads 14.2V fix the wiper of VR₁.
Adjust the VR₂ until LCD 14.2V and fix the wiper of VR₂.
Now, remove the jumper and multimeter and connect the battery. Your device Arduino-controlled 12V battery charger is ready to use.

2 Thoughts to “Arduino Controlled 12V battery charger circuit”

Dani

August 21, 2023 at 6:57 pm

Hello, I want to use a solar panel instead how can I work on it?

Dani

August 21, 2023 at 6:58 pm

I used a solar panel in place of the panel but the display doesn’t work it just charges the battery. How can I get it to display

Silent features of Arduino Controlled 12V battery charger circuit

Components Required for Arduino Controlled 12V battery charger circuit

Circuit Description of Arduino Controlled 12V battery charger circuit

Voltage Stepdown and Rectifier Unit | Arduino Controlled 12V battery charger circuit

Battery Charger Circuit | Arduino Controlled 12V battery charger circuit

Working of the adjustable voltage regulator

Now let’s see the working of the automatic charger stage in three different cases.

Fixed Voltage Regulator | Arduino Controlled 12V battery charger circuit

Display Unit | Arduino Controlled 12V battery charger circuit

Battery Status | Arduino Controlled 12V battery charger circuit

Software Code | Arduino Controlled 12V battery charger circuit

Calibration of Arduino Controlled 12V Battery Charger Circuit

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