sagar saini
Published © GPL3+

1.5V Alkaline Battery SOC Measurement Technique

A simple yet effective method to measure the SOC of non rechargable batteries.

BeginnerFull instructions provided2 hours139
1.5V Alkaline Battery SOC Measurement Technique

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Code

Code

Arduino
/**************************************************
 * Alkaline Battery SoC Estimation
 * Method 1: I between 9.7 & 22
 * Method 2: Voltage-SoC LUT (with calibration)
 **************************************************/

#define ADC_PIN        A0
#define MOSFET_LOW     6     // 9.7 load
#define MOSFET_HIGH    7     // 22 load

#define R_LOW   9.7
#define R_HIGH  22.0

#define ADC_REF       4.83
#define ADC_RES       1023.0
#define DIVIDER_RATIO 1.0

// ---------- USER CALIBRATION ----------
#define VOLTAGE_GAIN   1.000   // slope calibration
#define VOLTAGE_OFFSET 0.000   // offset calibration (Volts)

// ---------- ADC SETTINGS ----------
#define ADC_SAMPLES   12

// ---------- TIMING (ms) ----------
#define LOAD_PULSE_MS 20
#define RECOVERY_MS   300

// ---------- I THRESHOLDS ----------
#define DI_MAX  81.0   // mA  100%
#define DI_MIN  61.0   // mA  0%

// ---------- VOLTAGESOC LUT ----------
#define VSOC_POINTS 11

const float voltLUT[VSOC_POINTS] = {
  1.60, 1.55, 1.50, 1.45, 1.40,
  1.35, 1.30, 1.25, 1.20, 1.10, 1.00
};

const float socLUT[VSOC_POINTS] = {
  100, 90, 80, 70, 60,
  50, 40, 30, 20, 10, 0
};

// -------------------------------------------------
// ADC voltage read with averaging
// -------------------------------------------------
float readBatteryVoltage()
{
  long sum = 0;
  for (int i = 0; i < ADC_SAMPLES; i++) {
    sum += analogRead(ADC_PIN);
    delay(2);
  }
  float adc = sum / (float)ADC_SAMPLES;
  return (adc * ADC_REF / ADC_RES) * DIVIDER_RATIO;
}

// -------------------------------------------------
// Voltage  SoC using LUT + interpolation
// -------------------------------------------------
float voltageToSoC(float V)
{
  if (V >= voltLUT[0]) return 100.0;
  if (V <= voltLUT[VSOC_POINTS - 1]) return 0.0;

  for (int i = 0; i < VSOC_POINTS - 1; i++) {
    if (V <= voltLUT[i] && V >= voltLUT[i + 1]) {
      float t = (V - voltLUT[i + 1]) /
                (voltLUT[i] - voltLUT[i + 1]);
      return socLUT[i + 1] +
             t * (socLUT[i] - socLUT[i + 1]);
    }
  }
  return 0.0;
}

// -------------------------------------------------
// I  SoC conversion
// -------------------------------------------------
float deltaIToSoC(float deltaI_mA)
{
  if (deltaI_mA >= DI_MAX) return 100.0;
  if (deltaI_mA <= DI_MIN) return 0.0;

  return 100.0 * (deltaI_mA - DI_MIN) / (DI_MAX - DI_MIN);
}

// -------------------------------------------------
// Full battery measurement
// -------------------------------------------------
void measureBattery()
{
  float Voc_raw, Voc_cal;
  float V_low, V_high;
  float I_low, I_high;
  float deltaI_mA;
  float soc_deltaI, soc_voltage;

  // ---- Open-circuit voltage ----
  Voc_raw = readBatteryVoltage();
  Voc_cal = (Voc_raw * VOLTAGE_GAIN) + VOLTAGE_OFFSET;

  soc_voltage = voltageToSoC(Voc_cal);

  // ---- 22 load ----
  digitalWrite(MOSFET_HIGH, HIGH);
  delay(LOAD_PULSE_MS);
  V_high = readBatteryVoltage();
  digitalWrite(MOSFET_HIGH, LOW);

  delay(RECOVERY_MS);

  // ---- 9.7 load ----
  digitalWrite(MOSFET_LOW, HIGH);
  delay(LOAD_PULSE_MS);
  V_low = readBatteryVoltage();
  digitalWrite(MOSFET_LOW, LOW);

  // ---- Currents ----
  I_high = V_high / R_HIGH;
  I_low  = V_low  / R_LOW;

  deltaI_mA = (I_low - I_high) * 1000.0;
  soc_deltaI = deltaIToSoC(deltaI_mA);

  // ---- Print ----
  Serial.println("===== Battery Measurement =====");

  Serial.print("Voc (raw): ");
  Serial.print(Voc_raw, 4);
  Serial.println(" V");

  Serial.print("Voc (cal): ");
  Serial.print(Voc_cal, 4);
  Serial.println(" V");

  Serial.print("SoC (Voltage): ");
  Serial.print(soc_voltage, 1);
  Serial.println(" %");

  Serial.print("V(22): ");
  Serial.print(V_high, 4);
  Serial.println(" V");

  Serial.print("I(22): ");
  Serial.print(I_high * 1000.0, 1);
  Serial.println(" mA");

  Serial.print("V(9.7): ");
  Serial.print(V_low, 4);
  Serial.println(" V");

  Serial.print("I(9.7): ");
  Serial.print(I_low * 1000.0, 1);
  Serial.println(" mA");

  Serial.print("I: ");
  Serial.print(deltaI_mA, 1);
  Serial.println(" mA");

  Serial.print("SoC (I): ");
  Serial.print(soc_deltaI, 1);
  Serial.println(" %");

  Serial.println("================================");
}

// -------------------------------------------------
// Setup & loop
// -------------------------------------------------
void setup()
{
  Serial.begin(9600);

  pinMode(MOSFET_LOW, OUTPUT);
  pinMode(MOSFET_HIGH, OUTPUT);

  digitalWrite(MOSFET_LOW, LOW);
  digitalWrite(MOSFET_HIGH, LOW);

  Serial.println("Alkaline Battery SoC Meter (Voltage + I)");
}

void loop()
{
  measureBattery();
  delay(5000);
}

Credits

sagar saini
98 projects • 103 followers
I am Sagar Saini an electronic hardware enthusiast

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