State of Charge (SOC) in batteries

The State of Charge (SOC) in batteries is calculated based on input from shunt resistors for currect sensors, voltage sensors in addition to temperature sensors.

The battery management system (BMS) tracks the current flowing into and out of the battery pack, combining that with voltage and temperature data to estimate SOC.

Coulomb counting technique tracks the amount of charge entering and leaving the battery over time to refine SOC calculations. They also have sophisticated models to account for non-linear behaviors of the battery, like aging and temperature effects.

Why Just Tracking Voltage (V) and Current (I) Isn't Enough

1. Voltage Alone Is Not a Reliable Indicator of SOC
2. Current Integration (Coulomb Counting) Alone Has Limitations

How to Improve SOC Estimation

To get an accurate SOC, modern Battery Management Systems (BMS) use:

? Coulomb Counting (Ah tracking) – Tracks charge in/out but corrects drift.

? Voltage-based SOC estimation – Used for calibration at known points.

? Temperature & Aging Models – Adjust SOC to account for capacity fade.

? Kalman Filters & Machine Learning – Advanced algorithms to refine SOC estimation dynamically.

Shunt Resistor for EV Battery Monitoring (Preferred Choice)

Why Shunt Resistors?

• Accuracy: High precision, especially for low and medium current ranges.
• Linear Response: Provides a direct and predictable voltage output proportional to current.
• Cost-Effective: Cheaper than Hall effect sensors for the same level of accuracy.
• Temperature Compensation: Can be calibrated for temperature drift, making it suitable for EV environments.

Challenges

• Heat Dissipation: At very high currents, power loss in shunt resistors becomes an issue.
• Isolation: Requires additional circuitry for isolation if the system demands it.

Examples

• Tesla and other major EV makers use precision shunt resistors in combination with custom BMS chips for accurate coulomb counting.
• Automotive-grade shunt resistors from manufacturers like Vishay or Riedon are common.