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Over Current Cut-off Power Supply Using Arduino

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In this post I will show how to construct a battery eliminator / DC variable power supply which will automatically cut-off the supply, if the current flow through the load exceeds the preset threshold level.

Table of Contents

By Girish Radhakrishanan

Main Technical Features

The proposed over current cut-off power supply circuit using Arduino has 16 X 2 LCD display, which is used to show case the voltage, current, power consumption and preset threshold current limit in real time.

Being an electronics enthusiast, we test our prototypes on a variable voltage power supply. Most of us own a cheap variable power supply which might don’t sport neither voltage measuring / current measuring feature nor short circuit or over current protection built in.

That’s because power supply with these mentioned features can bomb on your wallet and will be overkilled for hobby usage.

Short circuit and over current flow is a problem for beginners to professionals and beginners are prone to this more often because of their inexperience, they might reverse the power supply’s polarity or connect the components in wrong way, etc.

These things can cause the current flow through the circuit unusually high, resulting in thermal runaway in semiconductor and passive components which results in destruction of valuable electronic components. In these cases ohm’s law turns into an enemy.

If you never made a short circuit or fried circuit, then congrats! You are one of few people who are perfect in electronics or you never try something new in electronics.

The proposed power supply project can protect the electronic components from such frying destruction, which will be cheap enough for an average electronics hobbyist and easy enough to construct one for who is slightly above beginner level.

The Design

The power supply has 3 potentiometers: one for adjusting the LCD display contrast, one for adjusting the output voltage ranging from 1.2 V to 15V and the last potentiometer is used for setting the current limit ranging from 0 to 2000 mA or 2 Ampere.

The LCD display will update you with four parameters every second: the voltage, current consumption, pre-set current limit and power consuming by the load.

The current consumption via load will be displayed in milliamps; the pre-set current limit will be displayed in milliamps and the power consumption will be displayed in milli-watts.

The circuit is divided into 3 parts: the power electronics, the LCD display connection and power measuring circuit.

These 3 stage may help the readers to understand the circuit better. Now let’s see the power electronics section which controls the output voltage.

Schematic diagram:

warning message: electricity is dangerous, proceed with caution
power supply circuit for Arduino

The 12v-0-12v / 3A transformer will be utilized for stepping down the voltage, the 6A4 diodes will convert the AC into DC voltage and the 2000uF capacitor will smooth out the choppy DC supply from diodes.

The LM 7809 fixed 9V regulator will convert the unregulated DC to regulated 9V DC supply.

The 9V supply will power the Arduino and relay. Try to use a DC jack for arduino’s input supply.

Don’t skip those 0.1uF ceramic capacitors which provide good stability for output voltage.

The LM 317 provides variable output voltage for the load which is to be connected.

You can adjust the output voltage by rotating the 4.7K ohm potentiometer.

That concludes the power section.

Now let’s see the display connection:

Connection Details

Arduino connected with LCD disaply

There is nothing to explain here much, just wire up the Arduino and LCD display as per the circuit diagram. Adjust the 10K potentiometer for better viewing contrast.

The above display shows the sample readings for the four parameters mentioned.

Power Measuring Stage

Now, let’s see the power measurement circuit in detail.

The power measuring circuit comprises of voltmeter and ammeter.

The Arduino can measure voltage and current simultaneously by connecting the network of resistors as per the circuit diagram.

resistor network for Over Current Cut-off Power Supply Using Arduino

Relay Connection Details for the above Design:

Arduino relay connection details

The four 10 ohm resistors in parallel which forms 2.5 ohm shunt resistor which will be utilized for measuring the current flow through the load.

The resistors should be at least 2 watt each.

The 10k ohm and 100k ohm resistors helps the Arduino to measure voltage at the load. These resistor can be one with normal wattage rating.

If you want to know more about the working of Arduino based ammeter and voltmeter check out these two links:

Voltmeter: https://www.homemade-circuits.com/2016/09/how-to-make-dc-voltmeter-using-arduino.html

Ammeter: https://www.homemade-circuits.com/2017/08/arduino-dc-digital-ammeter.html

The 10K ohm potentiometer is provided for adjusting the maximum current level at the output.

If the current flow through the load exceeds the pre-set current the output supply will be disconnected.

You can see the preset level in the display it will be mentioned as “LT” (Limit).

Say for example: if you set the limit as 200, it will gives out current till 199mA. If the current consumption gets equal to 200 mA or above the output will be immediately cut-off.

The output is turned on and off by the Arduino pin #7.

When this pin is high the transistor energizes the relay which connects the common and normally open pins, which conducts the positive supply for the load.

The diode IN4007 absorbs the high voltage back EMF from the relay coil while switching the relay ON and OFF.

Program Code:

//------------------Program Developed by R.GIRISH------------------//
#include <LiquidCrystal.h>
#define input_1 A0
#define input_2 A1
#define input_3 A2
#define pot A3
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
int Pout = 7;
int AnalogValue = 0;
int potValue = 0;
int PeakVoltage = 0;
int value = 0;
int power = 0;
float AverageVoltage = 0;
float input_A0 = 0;
float input_A1 = 0;
float output = 0;
float Resolution = 0.00488;
float vout = 0.0;
float vin = 0.0;
float R1 = 100000;
float R2 = 10000;
unsigned long sample = 0;
int threshold = 0;
void setup()
{
lcd.begin(16,2);
Serial.begin(9600);
pinMode(input_3, INPUT);
pinMode(Pout, OUTPUT);
pinMode(pot, INPUT);
digitalWrite(Pout, HIGH);
}
void loop()
{
PeakVoltage = 0;
value = analogRead(input_3);
vout = (value * 5.0) / 1024;
vin = vout / (R2/(R1+R2));
if (vin < 0.10)
{
vin = 0.0;
}
for(sample = 0; sample < 5000; sample ++)
{
AnalogValue = analogRead(input_1);
if(PeakVoltage < AnalogValue)
{
PeakVoltage = AnalogValue;
}
else
{
delayMicroseconds(10);
}
}
input_A0 = PeakVoltage * Resolution;
PeakVoltage = 0;
for(sample = 0; sample < 5000; sample ++)
{
AnalogValue = analogRead(input_2);
if(PeakVoltage < AnalogValue)
{
PeakVoltage = AnalogValue;
}
else
{
delayMicroseconds(10);
}
}
potValue = analogRead(pot);
threshold = map(potValue, 0, 1023, 0, 2000);
input_A1 = PeakVoltage * Resolution;
output = (input_A0 - input_A1) * 100;
output = output * 4;
power = output * vin;
while(output >= threshold || analogRead(input_1) >= 1010)
{
digitalWrite(Pout, LOW);
while(true)
{
lcd.clear();
lcd.setCursor(0,0);
lcd.print("Power Supply is");
lcd.setCursor(0,1);
lcd.print("Disconnected.");
delay(1500);
lcd.clear();
lcd.setCursor(0,0);
lcd.print("Press Reset the");
lcd.setCursor(0,1);
lcd.print("Button.");
delay(1500);
}
}
while(output >= threshold || analogRead(input_2) >= 1010)
{
digitalWrite(Pout, LOW);
while(true)
{
lcd.clear();
lcd.setCursor(0,0);
lcd.print("Power Supply is");
lcd.setCursor(0,1);
lcd.print("Disconnected.");
delay(1500);
lcd.clear();
lcd.setCursor(0,0);
lcd.print("Press Reset the");
lcd.setCursor(0,1);
lcd.print("Button.");
delay(1500);
}
}
lcd.clear();
lcd.setCursor(0,0);
lcd.print("V=");
lcd.print(vin);
lcd.setCursor(9,0);
lcd.print("LT=");
lcd.print(threshold);
lcd.setCursor(0,1);
lcd.print("I=");
lcd.print(output);
lcd.setCursor(9,1);
lcd.print("P=");
lcd.print(power);
Serial.print("Volatge Level at A0 = ");
Serial.println(analogRead(input_1));
Serial.print("Volatge Level at A1 = ");
Serial.println(analogRead(input_2));
Serial.print("Voltage Level at A2 = ");
Serial.println(analogRead(input_3));
Serial.println("------------------------------");
}

//------------------Program Developed by R.GIRISH------------------//

By now, you would have gained enough knowledge to construct a power supply which protect you valuable electronic components and modules.

If you have any specific question regarding this over current cut-off power supply circuit using Arduino feel free to ask in comment section, you may receive a quick reply.

Reader Interactions

Comments

  2. GOOD DAY SIR! PLEASE I WOULD LIKE YOU WRITE A CODE FOR AC LOAD MONITORING USING ARDUINO UNO. THE POWER LIMIT OF THE LOAD WILL BE SET USING PUSH BUTTONS. THERE WILL BE WARNING ALARM AS SOON AS THE LIMIT IS REACHED FOR 3 TIMES AFTER WHICH THE LOAD WILL BE SHUTDOWN. THE PROCESSES WILL BE SHUN ON THE LCD THROUGH I2C.

    Reply

        • Here’s the complete code.
          ACS712 OUT = connect to A0
          Button1 (Increase) = connect to D2 (Pull-down 10k to GND)
          Button2 (Decrease) = connect to D3 (Pull-down 10k to GND)
          Buzzer = connect to D4
          Relay module IN = connect to D5
          LCD SDA = connect to A4
          LCD SCL = connect to A5
          ACS712 VCC/GND, Relay VCC/GND, Buzzer = Connect to Arduino 5V/GND

          #include
          #include

          #define CURRENT_SENSOR A0
          #define BUTTON_UP 2
          #define BUTTON_DOWN 3
          #define BUZZER 4
          #define RELAY 5

          LiquidCrystal_I2C lcd(0x27, 16, 2);

          float current = 0;
          int limit = 2; // Default current limit in Amps
          int overCount = 0;
          bool loadOn = true;

          unsigned long lastRead = 0;

          void setup() {
          pinMode(BUTTON_UP, INPUT);
          pinMode(BUTTON_DOWN, INPUT);
          pinMode(BUZZER, OUTPUT);
          pinMode(RELAY, OUTPUT);

          digitalWrite(RELAY, HIGH); // Relay ON
          lcd.begin();
          lcd.backlight();
          lcd.setCursor(0,0);
          lcd.print("AC Load Monitor");
          delay(2000);
          lcd.clear();
          }

          void loop() {
          // Button press handling
          if (digitalRead(BUTTON_UP) == HIGH) {
          limit++;
          delay(300);
          }

          if (digitalRead(BUTTON_DOWN) == HIGH) {
          if (limit > 1) limit--;
          delay(300);
          }

          // Read current every 1 second
          if (millis() - lastRead > 1000) {
          lastRead = millis();
          current = readCurrent(); // Measure current

          lcd.clear();
          lcd.setCursor(0, 0);
          lcd.print("I:");
          lcd.print(current, 1);
          lcd.print("A Lim:");
          lcd.print(limit);

          lcd.setCursor(0, 1);
          if (loadOn) {
          lcd.print("Load ON ");
          } else {
          lcd.print("Load OFF");
          }

          // Check overload
          if (current > limit && loadOn) {
          beep();
          overCount++;
          lcd.setCursor(10,1);
          lcd.print("Warn:");
          lcd.print(overCount);

          if (overCount >= 3) {
          loadOn = false;
          digitalWrite(RELAY, LOW); // Turn off load
          lcd.setCursor(0,1);
          lcd.print("Overload Shutdown ");
          }
          }
          }
          }

          // Simulated average current read from ACS712
          float readCurrent() {
          long sum = 0;
          for (int i = 0; i < 150; i++) { sum += analogRead(CURRENT_SENSOR); delay(2); } float voltage = (sum / 150.0) * (5.0 / 1023.0); float current = (voltage - 2.5) / 0.1; // For ACS712-20A (100mV/A) if (current < 0) current = 0; return current; }void beep() { digitalWrite(BUZZER, HIGH); delay(200); digitalWrite(BUZZER, LOW); }

          Reply

      • HELLO SIR! THANK YOU SO MUCH FOR THE CODE AND INSTRUCTIONS YOU SENT TO ME.I APPRECIATE. SIR WHAT I ACTUALLY WANTED IS THE LOAD MONITORING IN WATTAGE. THAT IS WHERE A PARTICULAR LOAD LIMIT WILL BE SET IN WATTAGE. THAT WILL ENABLE ME TO SET A PARTICULAR POWER LIMIT A GIVEN APARTMENT WILL CARRY. SO WHAT MODIFICATIONS CAN BE MADE TO ACHIEVE THAT BASED ON THE CODE YOU SENT TO ME BECAUSE POWER = CURRENTX VOLTAGE. LETS SAY I WANT TO LIMIT THE LOAD AT 500W OR ANYTHING ELSE . AGAIN I INTEND TO THE TYPE OF CURRENT SENSOR TYPICAL OC COMMERCIAL INVERTERS THAT CAN HANDLE UP TO 100A.

        Reply

  3. Hi sir , I have a megger ago meter . which has burnt four resistors connected in series with the voltage connection leads. The reason was I used it to check voltage across diode in a microwave oven. Please can you help find the value of the burnt resistors

    Reply

    • Hi Stephen, sorry I do not have any idea about it, you can perhaps try using 4nos 1M resistors and see how it works.

      Reply

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