I have a project where I need to use arduino to turn on/off all 10 parallel connected fans at the same time. I have bought a 24V relay. Is there anything else I need to buy?
The fans run at 220V AC 0.05A or 24V DC 0.05A.
Thank you in advance. Cheers
What determines the fans on and off events ?
Button, time, doggy door ?
AC or DC? Is it capable of switching 10 Amps?
Can you confirm these numbers?
I'm planning to run on a 24V 5A DC adapter. The fan takes up 24V 0.05A each. In parallel total would be 24V and 0.5A.
There will be three buttons (start, stop and reset) as of now. The buttons act as on/off buttons only
Sorry, I can't see the terminal labels on that picture. Incorrectly connecting a 24V relay to your 5V Arduino could be disastrous so I'll pass.
No, that's a 5V relay with only 3 control terminals instead of the 4 in your first picture.
Maybe I'll send another one when I receive the item. Thank you in advance
I'll be watching. Good luck. 
This is an example 12v DC relay with the terminals. I ordered a 24V DC. Hope this will help.
Connect 24V+ (positive) to DC+, 24V- (negative) to DC-, Arduino 5V to VREF, Arduino output pin to CH1. Relay should activate when output pin is LOW.
Thank you for your detailed explanation. Appreciate it. Will try when the relay arrives this weekend 
I have bought 2 relays. One is 5V and another one is 24V. I have connected the 5V relay and apparently it works. The seller advised me to use a 5V relay as the Arduino can only output maximum 5V to the relay in order to turn it on and off. Is there still a need to change to 24V relay?
This is my code for reference.
#include <LiquidCrystal.h>
const int relayPin = 6; // Relay pin to control the fan
const int buttonPin = 4; // Button pin
const int greenLedPin = 3; // Green LED pin
const int redLedPin = 5; // Red LED pin
const int piezoPin = 2; // Piezo pin
bool deviceOn = false; // State of the device
unsigned long startTime; // Start time for the fan
unsigned long runTime = 10000; // 30 minutes in milliseconds
// Initialize the library with the numbers of the interface pins
LiquidCrystal lcd(8, 9, 10, 11, 12, 13);
void setup() {
Serial.begin(9600); // Start the Serial communication
pinMode(relayPin, OUTPUT);
pinMode(buttonPin, INPUT_PULLUP); // Use internal pull-up resistor
pinMode(greenLedPin, OUTPUT);
pinMode(redLedPin, OUTPUT);
pinMode(piezoPin, OUTPUT);
// Set up the LCD's number of columns and rows
lcd.begin(16, 2);
lcd.print("Press button to");
lcd.setCursor(0, 1);
lcd.print("turn on device");
// Ensure the fan and LEDs are off initially
digitalWrite(relayPin, LOW);
digitalWrite(greenLedPin, LOW);
digitalWrite(redLedPin, HIGH);
}
void loop() {
// Check if the button is pressed
if (digitalRead(buttonPin) == LOW) {
delay(50); // Debounce delay
while (digitalRead(buttonPin) == LOW); // Wait for button release
deviceOn = !deviceOn; // Toggle device state
if (deviceOn) {
lcd.clear();
lcd.print("Device is ON");
delay(1000); // Display message for 1 second
lcd.clear();
lcd.print("Fan is running");
// Turn on the fan and green LED, turn off the red LED
digitalWrite(relayPin, HIGH);
digitalWrite(greenLedPin, HIGH);
digitalWrite(redLedPin, LOW);
// Record the start time
startTime = millis();
} else {
// Emergency stop
lcd.clear();
lcd.print("Emergency Stop");
delay(1000); // Display message for 1 second
lcd.clear();
lcd.print("Press button to");
lcd.setCursor(0, 1);
lcd.print("turn on device");
// Turn off the fan and green LED, turn on the red LED
digitalWrite(relayPin, LOW);
digitalWrite(greenLedPin, LOW);
digitalWrite(redLedPin, HIGH);
// Ensure no sound notification
digitalWrite(piezoPin, LOW);
}
}
// If the device is on, calculate the remaining time
if (deviceOn) {
unsigned long elapsedTime = millis() - startTime;
unsigned long remainingTime = runTime - elapsedTime;
// Update the LCD display with the remaining time
lcd.setCursor(0, 1); // Move to the second line
lcd.print("Time left: ");
lcd.print(remainingTime / 60000); // Display minutes
lcd.print(" m");
// Check if the time is up or emergency stop
if (elapsedTime >= runTime || !deviceOn) {
// Turn off the fan and green LED, turn on the red LED
digitalWrite(relayPin, LOW);
digitalWrite(greenLedPin, LOW);
digitalWrite(redLedPin, HIGH);
// Notify with the piezo if the time is up
if (elapsedTime >= runTime) {
lcd.clear();
lcd.print("Process complete");
for (int i = 0; i < 5; i++) {
digitalWrite(piezoPin, HIGH);
delay(500);
digitalWrite(piezoPin, LOW);
delay(500);
}
}
// Update the device state
deviceOn = false;
lcd.clear();
lcd.print("Press button to");
lcd.setCursor(0, 1);
lcd.print("turn on device");
}
}
}
If your project works OK with the 5V relay, I see no need to change it.
Thank you for your help.
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