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Battery voltage and current draw monitor

For this project the goal was to keep track of backup batteries during float and active states - and also to save a few $$$. Total cost for this setup was about $20 CAD in parts. This monitor helps to ensure the trickle (solar) charger is still functioning, and when in a power outage, how much current is being drawn from the system and how much capacity is left.  The system can be used to shut the inverter down remotely if it appears the batteries are at critical low voltage. An email alert is also sent when the voltage goes below 11 volts.

Wiring: 

voltage_current_relay.jpg

parts:

20240703_181704.jpg

The current sensor is  just a transformer coil wrapped around the AC cable which comes out of the inverter.  It is much easier in my experience than dealing with shunts that produce unreliable readings.  This simple coil provides readings with a 99% accuracy range over a wide range of currents ranging from 10 watts to 1800 watts (15 amps@120volts). 

20240717_210620.jpg

20240717_210645.jpg I set a "fudge" in the code to get accurate readings by comparing the real-time  readings compared to an outlet wall meter which I knew to be accurate. The readings simply needed to be boosted by a tiny fraction ( X 0.0000444 ) to get near 100% accuracy. 

Online view of realtime data:

2024-07-03_18-24.png

code:

#include <WiFi.h>
#include <HTTPClient.h>
#include <Wire.h>
#include <Adafruit_ADS1X15.h>
#include <LiquidCrystal_I2C.h>
#include <EEPROM.h>


// last updated July 1, 2024

//////////////////////////////
// EDIT THIS SECTION


int activeConnection = 1;

// cottage 1
const String ssid1 = "rewa";
const String password1 = "gfggf";

// cottage 2
const String ssid2 = "fdsa";
const String password2 = "rreter";

const String voltateUrl = "http://batterymonitor.uytr.ca/set_current_voltage.php?data=";

// end edit section
////////////////////


#define EEPROM_SIZE 8
int eepromActiveConnectionAddress = 0;
int eepromPingsAddress = 2;
float totalServerPings = 0;
int eepromFailedPingsAddress = 1;
float totalServerPingFails = 0;
int eepromActiveConnection = 1;

String prevWattagePerHourText = "";
String prevWattageVoltageText = "";
String prevConnectivityText1 = "";
String prevConnectivityText2 = "";

const int potPin = 34;
const int buttonPin = 14;
int buttonState = 0;
int displayMode = 1;  // 1: watts, watts per hours, voltage   2: internet

int ACDCVoltage = 120;

const float criticalVoltage = 11.8;  // this is considered the critical point for deep cycle sla batteries

const float deadBatteryVoltage = 9;  //  set to 9

const float potOffset = 880;            // offset accounts for base reading on pot value -  should be zero in theory but in reality it is not
const float voltageMultiplier = 0.025;  // adjust for non-linear increase in pot value vs actual voltage
const float voltageDividerRatio = 4;    // 10K / 2.5k voltage divider
const int pulseRate = 1000;             // loop runs once per second

const int serverSendInterval = 15;                      // 15 minutes between sending a voltage update to the server
const int samplesPerReading = 60 * serverSendInterval;  // every x minutes send a sample to the server

float averagePotValue = 0;
float potValue = 0;
float accumulatedPotValues = 0;
int voltageLoopCount = 0;

int lcdBacklightOnCounter = 0;

float accumulatedAmps = 0;
float averageCurrentValue = 0;
float averageWattage = 0;

float wattsPerHour = 0;
float ampHoursPerDay = 0;

long secondsOfHour = 0;

const int secondsPerHour = 3600;  // set to 60 for debugging
int houryAmpsArrayCurrentIndex = 0;
int dailyAmpsArrayCurrentIndex = 0;

float houryAmpsArray[secondsPerHour];

const int hoursPerDay = 24;
float dailyAmpsArray[hoursPerDay];

float voltage;

bool connectingToWifi = false;
bool wifiConnected = false;
bool wifiPaused = false;
int wifiPausedTick = 0;
bool wifiSleeping = false;
bool debug = false;  // when true server does not update
bool serverFailed = false;
int wifiConnectionAttempts = 0;

HTTPClient http;

Adafruit_ADS1115 ads;

LiquidCrystal_I2C lcd_i2c(0x27, 16, 2);

const float FACTOR = 20;                  //20A/1V from the CT
const float hallSensorFudge = 0.0000472;  // fudge for inaccuracy in the hall sensor


void setup() {


  // We sometimes run into brownouts due to main hydro line voltage drops. For this situation set BOD to 3 volts
  // WRITE_PERI_REG(RTC_CNTL_BROWN_OUT_REG, 0);  //disable brownout detector
  WRITE_PERI_REG(RTC_CNTL_BROWN_OUT_REG, 0x03);  // 3 volts
  //WRITE_PERI_REG(RTC_CNTL_BROWN_OUT_REG, 0x04); // set brownout detector to 3.2 volts
  // WRITE_PERI_REG(RTC_CNTL_BROWN_OUT_REG, 0x07); // Set 3.3V as BOD level

  Serial.begin(115200);  // this needs to match the value in the serial monitor

  //Init EEPROM
  EEPROM.begin(EEPROM_SIZE);

  pinMode(buttonPin, INPUT);

  for (int i = 0; i < secondsPerHour; i++) {
    houryAmpsArray[i] = -1;
  }

  for (int i = 0; i < hoursPerDay; i++) {
    dailyAmpsArray[i] = -1;
  }

  delay(2000);

  EEPROM.begin(EEPROM_SIZE);

  activeConnection = EEPROM.read(eepromActiveConnectionAddress);

  Serial.print("eepromActiveConnection :");
  Serial.println(activeConnection);

  if (isnan(activeConnection)) {
    activeConnection = 1;
  }

  if (activeConnection == 0) {
    activeConnection = 1;
  }

  if (activeConnection > 2) {
    activeConnection = 2;
  }
  Serial.print("activeConnection: ");
  Serial.println(activeConnection);


  if (!connectToWiFi()) {
    delay(2000);
    WiFi.disconnect();
    delay(1000);
    if (activeConnection == 1) {
      activeConnection = 2;
    } else {
      activeConnection = 1;
    }
    connectToWiFi();
  }

  // in case we did a reboot allow remote server a moment
  delay(5000);

  // if wifi connect failed again just reboot
  if (WiFi.status() != WL_CONNECTED) {
    ESP.restart();
  }

  if (!ads.begin()) {
    Serial.println("Failed to initialize ADS.");
    while (1)
      ;
  }

  ads.setGain(GAIN_FOUR);


  lcd_i2c.init();
  lcd_i2c.backlight();
}

void loop() {

  secondsOfHour++;

  // after 24 hours reset this integer
  if (secondsOfHour > 86400) {
    secondsOfHour = 1;
    // Serial.println("restarting :");
    ESP.restart();
  }

  if (lcdBacklightOnCounter == 0) {
    //lcd_i2c.noBacklight();
    lcdBacklightOnCounter++;
    displayMode = 1;
  } else {
    // if lcb backlight counter is over zero it is active so increment
    lcdBacklightOnCounter++;

    Serial.print("lcdBacklightOnCounter: ");
    Serial.println(lcdBacklightOnCounter);

    // turn off backlight after 5 mintes of inactivity
    if (lcdBacklightOnCounter % 150 == 0) {

      Serial.println("backlight off");

      displayMode = 2;  // ensure when clicking for light we see temp again
      lcd_i2c.noBacklight();
      lcdBacklightOnCounter = 1;
    }
  }


  buttonState = digitalRead(buttonPin);

  Serial.println("buttonState: ");
  Serial.println(buttonState);

  if (buttonState == LOW) {
    lcd_i2c.clear();
    lcd_i2c.backlight();
    lcdBacklightOnCounter = 1;
    displayMode++;
    if (displayMode > 2) {
      displayMode = 1;
    }
  }



  ////////////////////////////
  // CURRENT AND VOLTAGE

  // CURRENT

  float amps = getAmps();
  accumulatedAmps += amps;

  cycleHourlyAmpsArray(amps);

  float ampsPerHour = getAverageAmps(houryAmpsArray, secondsPerHour);

  // to get average wattage get the last 10 reading divided by 10

  float wattsAverage = getLastXWattReadings(5) * ACDCVoltage;
  float wattsPerHour = ampsPerHour * ACDCVoltage;

  float ampHoursPerDay = getAverageAmps(dailyAmpsArray, hoursPerDay);

  if (secondsOfHour % secondsPerHour == 0) {
    cycleDailyAmpsArray(ampsPerHour);
  }

  float dailyAmpHours = getDailyAmpHours();

  float wattagePerDay = dailyAmpHours * ACDCVoltage;

  // VOLTAGE
  potValue = analogRead(potPin);
  accumulatedPotValues += potValue;

  Serial.print("pot value:");
  Serial.println(potValue);

  voltage = (potValue / (potOffset + (potValue * voltageMultiplier)) * voltageDividerRatio);

  Serial.print("volts");
  Serial.println(voltage);

  String wattsAverageString = String(wattsAverage, 0);
  wattsAverageString.trim();

  String wattsPerHourString = String(wattsPerHour, 0);
  wattsPerHourString.trim();

  String wattsPerDayString = String(wattagePerDay, 0);
  wattsPerDayString.trim();

  String wattagePerHourText = wattsPerHourString + "WH " + wattsPerDayString + "DWH ";
  String wattageVoltageText = wattsAverageString + "W BV:" + String(voltage, 1);

  // keep the noise down
  if (voltageLoopCount % 10 == 0) {
    averagePotValue = accumulatedPotValues / voltageLoopCount;
    voltage = (averagePotValue / (potOffset + (averagePotValue * voltageMultiplier)) * voltageDividerRatio);
    float currentVoltage = (potValue / (potOffset + (potValue * voltageMultiplier)) * voltageDividerRatio);
  }

  averagePotValue = accumulatedPotValues / voltageLoopCount;
  voltage = (averagePotValue / (potOffset + (averagePotValue * voltageMultiplier)) * voltageDividerRatio);

  averageWattage = (accumulatedAmps / voltageLoopCount) * ACDCVoltage;

  /////////////////////
  // SERVER RELAY


  // if voltage is below 9 the batteries are basically dead!
  if (!debug && (voltageLoopCount >= samplesPerReading && voltage >= deadBatteryVoltage) || serverFailed) {

    accumulatedPotValues = 0;
    accumulatedAmps = 0;
    voltageLoopCount = 0;

    setWifiSleepMode(false);

    String recordedAverageVoltage = String(voltage, 2);
    String recordedAverageWattage = String(averageWattage, 0);

    recordedAverageVoltage.trim();
    recordedAverageWattage.trim();

    http.begin(voltateUrl + recordedAverageVoltage + "," + recordedAverageWattage);
    int httpCode = http.GET();
    if (httpCode > 0) {
      String payload = http.getString();
      Serial.println("HTTP Response: " + payload);
      recordPingSucces();
    } else {
      Serial.println("HTTP Request failed with error code: " + String(httpCode));
      recordPingFailure();
    }
    http.end();


    setWifiSleepMode(true);
  }

  voltageLoopCount++;


  ////////////////////////////
  // LCD DISPLAY

  switch (displayMode) {
    case 1:
      wattagePerHourText.trim();
      wattageVoltageText.trim();

      if (prevWattagePerHourText != wattagePerHourText || prevWattageVoltageText != wattageVoltageText) {
        lcd_i2c.clear();
      }

      prevWattagePerHourText = wattagePerHourText;
      prevWattageVoltageText = wattageVoltageText;

      lcd_i2c.setCursor(0, 0);
      lcd_i2c.print(wattagePerHourText);
      lcd_i2c.setCursor(0, 1);
      lcd_i2c.print(wattageVoltageText);

      break;

    case 2:
      String connectivityText1 = "";
      if (wifiConnected) {
        connectivityText1 += "WF ON";
      }
      if (wifiConnected && !serverFailed) {
        connectivityText1 += " SERVER ON";
      }

      String serverPings = String(totalServerPings, 0);
      serverPings.trim();

      String serverPingFails = String(totalServerPingFails, 0);
      serverPingFails.trim();

      String connectivityText2 = serverPings + "/" + serverPingFails + " PINGS";

      connectivityText1.trim();
      connectivityText2.trim();

      if (prevConnectivityText1 != connectivityText1 || prevConnectivityText2 != connectivityText2) {
        lcd_i2c.clear();
      }

      prevConnectivityText1 = connectivityText1;
      prevConnectivityText2 = connectivityText2;

      lcd_i2c.setCursor(0, 0);
      lcd_i2c.print(connectivityText1);
      lcd_i2c.setCursor(0, 1);
      lcd_i2c.print(connectivityText2);
      break;
  }


  delay(pulseRate);
}

bool connectToWiFi() {

  if (connectingToWifi || wifiConnected) {
    return true;
  }

  connectingToWifi = true;

  String activeSsid = "";
  String activePassword = "";

  if (activeConnection == 1) {
    activeSsid = ssid1;
    activePassword = password1;
  } else if (activeConnection == 2) {
    activeSsid = ssid2;
    activePassword = password2;
  }

  Serial.print("Connecting to WiFi: ");
  Serial.println(activeSsid);

  WiFi.begin(activeSsid, activePassword);

  while (WiFi.status() != WL_CONNECTED && wifiConnectionAttempts < 20) {
    delay(500);
    Serial.print(".");
    wifiConnectionAttempts++;
  }

  wifiConnectionAttempts = 0;

  if (WiFi.status() == WL_CONNECTED) {
    Serial.println("\nConnected to WiFi");
    Serial.print("IP Address: ");
    Serial.println(WiFi.localIP());

    EEPROM.write(eepromActiveConnectionAddress, activeConnection);
    EEPROM.commit();

    Serial.print("set activeConnection to : ");
    Serial.print(activeConnection);

    wifiConnected = true;
    connectingToWifi = false;
    return true;

  } else {
    Serial.print("Connection to ");
    Serial.print(activeSsid);
    Serial.println(" failed. Trying alternative");

    wifiConnected = false;
    connectingToWifi = false;

    return false;
  }
}


/**
 * set wifi sleep mode between data relays to conserve energy
 * @param sleepMode - if true set wifi card to sleep to conserve energy
 */
void setWifiSleepMode(bool sleepMode) {

  wifiSleeping = sleepMode;

  if (sleepMode) {
    WiFi.disconnect();
    WiFi.setSleep(true);
    wifiConnected = false;
    delay(1000);
    Serial.print("sleep wifi status: ");
    Serial.println(wl_status_to_string(WiFi.status()));
  } else {
    WiFi.setSleep(false);
    WiFi.reconnect();
    delay(2000);
    Serial.print("awaken wifi status: ");
    Serial.println(wl_status_to_string(WiFi.status()));
    // Check if the connection is still active. if not trigger wait for it to come back online
    if (WiFi.status() != WL_CONNECTED && !wifiPaused) {
      Serial.println("Connection lost. Attempting to reconnect in 1 minute ...");
      WiFi.disconnect();
      wifiPaused = true;
      wifiConnected = false;
      connectToWiFi();
    }
  }
}

/**
 * record server ping success in long term memory
 */
void recordPingSucces() {
  totalServerPings++;
  EEPROM.begin(EEPROM_SIZE);
  EEPROM.writeFloat(eepromPingsAddress, totalServerPings);
  EEPROM.commit();
  EEPROM.end();
  wifiConnected = true;
  serverFailed = false;
}

/**
 * record server ping fails in long term memory
 */
void recordPingFailure() {
  totalServerPingFails++;
  EEPROM.begin(EEPROM_SIZE);
  EEPROM.writeFloat(eepromFailedPingsAddress, totalServerPingFails);
  EEPROM.commit();
  EEPROM.end();
  wifiConnected = false;
  serverFailed = true;
}

/**
 * ESP32 wifi card statuses
 * @param status
 * @return string
 */
String wl_status_to_string(wl_status_t status) {

  String response = "";

  switch (status) {
    case WL_NO_SHIELD:
      response = "WL_NO_SHIELD";
      break;
    case WL_IDLE_STATUS:
      response = "WL_IDLE_STATUS";
      break;
    case WL_NO_SSID_AVAIL:
      response = "WL_NO_SSID_AVAIL";
      break;
    case WL_SCAN_COMPLETED:
      response = "WL_SCAN_COMPLETED";
      break;
    case WL_CONNECTED:
      response = "WL_CONNECTED";
      break;
    case WL_CONNECT_FAILED:
      response = "WL_CONNECT_FAILED";
      break;
    case WL_CONNECTION_LOST:
      response = "WL_CONNECTION_LOST";
      break;
    case WL_DISCONNECTED:
      response = "WL_DISCONNECTED";
      break;
  }

  return response;
}

/**
 * Get the current in amps coming from the hall sensor
 * @return float
 */
float getAmps() {
  float hallSensorVoltage;
  float current;
  float sum = 0;
  long time_check = millis();
  int counter = 0;

  while (millis() - time_check < 1000) {
    hallSensorVoltage = ads.readADC_Differential_0_1() * hallSensorFudge;  // get voltage from hall sensor with fugdge
    current = hallSensorVoltage * FACTOR;                                  // 1 volt = 20 amps with current sensor

    sum += sq(current);
    counter = counter + 1;
  }


  current = sqrt(sum / counter);
  return (current);
}


/**
 * read the accumulated amps divided by readings
 */
float getAverageAmps(float array[], int size) {

  float accumulatedValues = 0;
  int ampCounts = 0;

  for (int i = 0; i < size - 1; i++) {
    if (array[i] >= 0) {
      ampCounts++;
      accumulatedValues += array[i];
    }
  }

  return accumulatedValues / ampCounts;
}


/**
 * read the total amp over a 24 hour periods
 */
float getDailyAmpHours() {

  float accumulatedValues = 0;
  for (int i = 0; i < hoursPerDay - 1; i++) {
    if (dailyAmpsArray[i] >= 0) {
      accumulatedValues += dailyAmpsArray[i];
    }
  }

  return accumulatedValues;
}


/**
 * get average wattage from samples
 * @param int sampleCount
 * @return float
 */
float getLastXWattReadings(int sampleCount) {

  float accumulatedValues = 0;

  int countedValues = 0;

  for (int i = secondsPerHour; i > 0; i--) {
    if (houryAmpsArray[i - 1] >= 0) {
      accumulatedValues += houryAmpsArray[i - 1];
      countedValues++;
    }
    if (countedValues >= sampleCount) {
      break;
    }
  }

  return accumulatedValues / sampleCount;
}



/**
 * remove first item from array, shift all value to left and add new value to end.
 */
void cycleHourlyAmpsArray(float newValue) {

  // this means we the array if full so we can begin shifting
  if (houryAmpsArray[secondsPerHour - 1] >= 0) {
    for (int i = 0; i < secondsPerHour - 1; i++) {
      houryAmpsArray[i] = houryAmpsArray[i + 1];
    }
    houryAmpsArray[secondsPerHour - 1] = newValue;

  } else {
    // allow the array to initialize with real values
    houryAmpsArray[houryAmpsArrayCurrentIndex] = newValue;
    houryAmpsArrayCurrentIndex++;
    if (houryAmpsArrayCurrentIndex > secondsPerHour) {
      houryAmpsArrayCurrentIndex = secondsPerHour - 1;
    }
  }
}



/**
 * remove first item from array, shift all value to left and add new value to end.
 */
void cycleDailyAmpsArray(float newValue) {

  // this means we the array if full so we can begin shifting
  if (dailyAmpsArray[hoursPerDay - 1] >= 0) {
    for (int i = 0; i < hoursPerDay - 1; i++) {
      dailyAmpsArray[i] = dailyAmpsArray[i + 1];
    }
    dailyAmpsArray[hoursPerDay - 1] = newValue;

  } else {
    // allow the array to initialize with real values
    dailyAmpsArray[dailyAmpsArrayCurrentIndex] = newValue;
    dailyAmpsArrayCurrentIndex++;
    if (dailyAmpsArrayCurrentIndex > hoursPerDay) {
      dailyAmpsArrayCurrentIndex = hoursPerDay - 1;
    }
  }
}

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