Analysis of Thermal-Induced Shunt Current Sensor Errors in a Low-Cost Battery Management System

Lithium-Ion batteries are becoming a standard solution for automotive applications. These batteries must be equipped with a Battery Management System that monitors and controls the battery avoiding hazardous situations. The battery current measurement is crucial for both safety and control tasks. Shunt-based current sensors are widely used in automotive applications, thanks to the affordability and linearity of the measurement. This article discusses an unexpected current measurement error occurred during the test of a prototypal Battery Management System for a 12 V cranking battery. The current error only shows up during the cell balancing procedure, pointing to a thermal related effect. A theoretical assessment of the problem suggests the thermoelectric effect as the best candidate to explain the error. The thermal simulation of the circuit validated the hypothesis with perfect match. Finally, the guidelines for a correct shunt choice in a Battery Management System are provided.