Estimating Battery State of Charge (SoC) Using the Ampere-Hour Integral Method with Arduino

Estimating the State of Charge (SoC) of a battery using the Ampere-Hour (Ah) integral method involves measuring the current flowing into or out of the battery over time. The core idea is to integrate the current over time to determine how much charge has been added or removed from the battery.

Why Estimate Battery SoC?

Knowing the SoC is essential for managing battery health, optimizing power consumption, and extending the battery's lifespan. The ampere-hour integral method is particularly useful for this purpose.

Components Needed

Arduino board (e.g., Arduino Uno) Current sensor (e.g., INA219, ACS712) Battery (Optional) real-time clock (RTC) module for more accurate time tracking

Basic Concept

The process involves three main steps:

Current Measurement: Use a current sensor to measure the current flowing into or out of the battery. Time Tracking: Keep track of time to integrate the current over time. SoC Calculation: Use the formula to determine the SoC.

SoC Calculation

The formula for calculating SoC is:

(text{SoC} text{SoC}_{text{initial}} times left(frac{text{Current (A)} times text{Time (h)}}{text{Battery Capacity (Ah)}}right) times 100)

Here, SoC_initial is the initial state of charge percentage.

Sample Arduino Code

Below is an example of how to implement the ampere-hour integral method in an Arduino sketch:

paste batch #include // Include your current sensor library as needed, // For example if using INA219 #include Adafruit_INA219 ina219; const float batteryCapacityAh 10.0; // Example: 10 Ah battery capacity float soc 100.0; // Start with full charge unsigned long lastTime; float current 0.0; // Current in Amperes void setup() { (9600); lastTime millis(); } void loop() { // Read current from the sensor current _mA() / 1000.0; // Convert mA to A // Calculate elapsed time in hours unsigned long currentTime millis(); float elapsedTime (currentTime - lastTime) / 3600000.0; // Convert ms to hours lastTime currentTime; // Update SoC soc (current * elapsedTime / batteryCapacityAh) * 100; // Constrain SoC to 0-100 if (soc > 100.0) { soc 100.0; } if (soc

This code provides a basic framework for estimating SoC using the Ah integral method. You can expand upon it by adding features such as averaging current readings, logging data, or integrating a real-time clock for better time tracking.

Explanation of the Code

Libraries: Depending on your current sensor, you may need to include specific libraries, e.g., Adafruit INA219 library. Initialization: The current sensor is initialized, and the initial SoC is set to 100. Loop: In the main loop: The current is read from the sensor. The elapsed time since the last reading is calculated. The SoC is updated based on the current and elapsed time. The SoC is constrained to remain between 0 and 100. The current and SoC values are printed to the Serial Monitor.

Important Considerations

Calibration: Ensure that your current sensor is calibrated for accurate readings. Initial SoC: You’ll need to know the initial state of charge of the battery to start with. Battery Characteristics: Different battery chemistries (e.g., Li-ion, NiMH) may need specific considerations for accurate SoC estimation. Error Handling: Consider implementing error handling for sensor failures or extreme conditions.