Problem in Computing the Energy in Energy Meter using ESP32

Question

So me and my groupmates are been working on with our thesis project about energy meter. In our project, the esp32 is the main board we are using. We also have voltage sensor (ZMPT101B) and current sensor (SCT013 100V:50mA) connected to our main board.

here is the link for the ZMPT101B... https://www.autobotic.com.my/ac-voltage-sensor-module-zmpt101b-single-phase

and here is the link for the SCT013... https://innovatorsguru.com/sct-013-000/

I am also using the Emon library from https://www.arduino.cc/reference/en/libraries/emonlib/ to read the value thrown by the current and voltage sensor.

To get the power, i will multiply the current and voltage values.

Then to get the value of the energy i will be needing the time because Energy = Power x time. I saw formula online, it uses millis () function to get the time... but to be honest i dont know how millis works.

 last_time = current_time;
 current_time = millis();
 Wh = Wh + power *(( current_time -last_time) /3600000.0) ; 

The value of the energy will be send to the database, in our case our database is the firebase realtime database. Using this code...

  Firebase.setDouble(firebaseData, path , KWh);

If the electricity cuts off , ESP32 will also be dead and will stop working. So we decided to add this line of codes...

Firebase.getInt(firebaseData, path);
totalEnergyDB = (firebaseData.intData());
preKWh = totalEnergyDB;

.... once the esp32 is turned on again, this code is used to get the data from the firebase... wherein the data got from the firebase will be used as a pre-kwh.

I used this lines of code to add the current readings from the pre-kwh.

KWh = (Wh/1000) + preKWh;

I set the calibration for the voltage and current sensor high so the changes will be easy to be seen.

My problem is that i was able to get the value from the database but it seems the energy formula is not working properly.

this is the result from the serial monitor... (171 KWH is the initial value from the database) enter image description here

i wasn't able to show you the result of the power but it say in the lcd that it is around 3000W! But still Energy reading is not changing even its been turned on for over an hour:(

Here is the complete code for our project...

#include "EmonLib.h"  
#define VOLT_CAL 52.5000
#define CURRENT_CAL 10.07
#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x27, 20, 4);

EnergyMonitor emon1;
int i;

// Wifi
#include <WiFi.h>
#include "FirebaseESP32.h"
   
#define FIREBASE_HOST "#!@#!@[email protected]" 
#define FIREBASE_AUTH "RRw3u$!@%!@#%@#%$@%^#$^oI8LpQyVo0AWBC"
#define WIFI_SSID "WIFI"
#define WIFI_PASSWORD "PASSWORD"

// Define Firebase Data object
FirebaseData firebaseData;

// Root Path
String path = "/USER INFO/jdc/totalEnergy";

unsigned long last_time =0;
unsigned long current_time =0;
int Wh = 0;  
int preKWh;
int KWh;
int totalEnergyDB;

void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  initWifi();
  lcd.init();
  lcd.backlight();
  lcd.begin(4, 20);
  
  lcd.clear();
  lcd.setCursor(1,4);
  lcd.print("LOADING...");
  Serial.print("LOADING...");
  emon1.voltage(32, VOLT_CAL, 1.7);  // Voltage: input pin, calibration, phase_shift
  emon1.current(33, CURRENT_CAL); 
  for ( i = 0; i < 5; i++ ) {
  emon1.calcVI(20,2000); 
  float currentDraw            = emon1.Irms;  
  float supplyVoltage          = emon1.Vrms; 
      
  }
delay(1); 
  Firebase.getInt(firebaseData, path);
  totalEnergyDB = (firebaseData.intData()); 
  preKWh = totalEnergyDB;
   
}

void loop() {
  emon1.calcVI(20,2000);
  float currentDraw     = emon1.Irms;             //extract Irms into Variable
  float supplyVoltage   = emon1.Vrms;
  float power = currentDraw * supplyVoltage;
  last_time = current_time;
  current_time = millis();
  Wh = Wh + power *(( current_time -last_time) /3600000.0) ; 
  KWh = (Wh/1000) + preKWh;

  lcd.clear();
  lcd.setCursor(0,0);
  lcd.print("VOLTAGE: ");
  lcd.print(supplyVoltage);
  lcd.print(" V");
  lcd.setCursor(0,1);
  lcd.print("CURRENT: ");
  lcd.print(currentDraw);
  lcd.print(" A");
  lcd.setCursor(0,2);
  lcd.print("POWER: ");
  lcd.print(power);
  lcd.print(" W");
  lcd.setCursor(0,3);
  lcd.print("ENERGY: ");
  lcd.print(KWh);
  lcd.print(" KWh");
  
  delay(100);  

    if (isnan(Wh)) {                       // if Wh is Not A Number
    Serial.println(F("Error reading Energy!"));
  }
  else {
    Serial.print(F("preKWh: "));
    Serial.print(preKWh);
    Serial.println(F("KWH"));
    Serial.print(F("Energy: "));
    Serial.print(KWh);
    Serial.println(F("KWH"));
    Firebase.setDouble(firebaseData, path , KWh);
    
    delay(100);
  }
    
    }
  

void initWifi(){
  WiFi.begin(WIFI_SSID, WIFI_PASSWORD);
  Serial.print("Connecting to Wi-Fi");
  while (WiFi.status() != WL_CONNECTED)
  {
    Serial.print(".");
    delay(300);
  }
  Serial.println();
  Serial.print("Connected with IP: ");
  Serial.println(WiFi.localIP());
  Serial.println();

  Firebase.begin(FIREBASE_HOST, FIREBASE_AUTH);
  Firebase.reconnectWiFi(true);
  
  //Set database read timeout to 1 minute (max 15 minutes)
  Firebase.setReadTimeout(firebaseData, 1000 * 60);
  //tiny, small, medium, large and unlimited.
  //Size and its write timeout e.g. tiny (1s), small (10s), medium (30s) and large (60s).
  Firebase.setwriteSizeLimit(firebaseData, "tiny");
}

Can anyone help me with the code. What changes should be done?

Answer 1

Looking at your data types, you are storing Wh and KWh as an integer, and you are adding likely very small floats to them (imagine (current_time - last_time) being 1000 (1 second), then Wh would become Wh + power * 2.78e-5, which will result in rounding errors unless your power consumption is enormous. To solve this, you should not round to integers, and keep Wh and KWh as floats.