Critical to the operation of any electric vehicle (EV) is the energy stored in its battery, which determines the distance it can travel. The amount of charge stored in the battery is measured in coulombs or ampere-hours, with the total energy usually measured in watt hours. Determining the amount of energy available in a battery is a complex task because battery age, discharge current, and temperature all impact battery capacity. To accommodate this energy measurement complexity, EVs employ a sophisticated battery management system (BMS) to continuously monitor battery condition.

A BMS must be able to predict accurately the state of the battery system. These predictive capabilities are only as accurate as the information on which they are based. Accurate current measurement is a necessary function of any BMS. Hall Effect devices have been used for current measurement, but they are prone to errors caused by neighboring electronic systems.

Measuring current with a conventional resistive shunt is not affected by their environment but can produce measurement errors. A shunt with a high resistance can measure small currents, but can overheat and consume significant energy when dealing with high currents. If the shunt has a low resistance, it may be able to measure high currents accurately, but may not be able to distinguish signal from noise in smaller currents. In addition, when measuring microvolt level signals, you must compensate for the thermoelectric potential differences in contacts (i.e., the Seebeck effect).

Sendyne’s SFP200MOD battery current and voltage sensing module consists of Sendyne’s low-resistance current shunt and the SFP200 high-precision sensing IC (Fig. 1). This module addresses the unique requirements of electrical energy storage and monitoring of EV batteries. The SFP200 is a digitally assisted analog data acquisition IC with unique circuits tailored specifically to a wide range of current measurements. The IC simultaneously measures bi-directional dc current across a resistive shunt, voltage, and shunt temperature. This IC uses algorithms that compensate for many micro phenomena that affect measurement accuracy. The SFP200 is rated for the –40° C to +125° C automotive temperature range.
Read more: EV Battery Sensing Module Yields Critical Measurement Data