Automotive BMS Validation with a Four-Channel DC Power Supply

Introduction

The surge in electric vehicles has increased demand for LiFePO4 batteries, in turn driving the need for battery management systems (BMS).

Manufacturers must thoroughly test BMS features before installing them in vehicles. BMS testing aims to simulate real-world conditions, such as cell balancing, overvoltage protection, and undervoltage, to ensure that these features work as intended to protect the battery pack.

The BMS testing includes the following:

• Voltage imbalance simulation to evaluate the BMS cell balancing function.
• Overvoltage protection simulation to verify the BMS response to cells exceeding safe voltage thresholds.
• Undervoltage protection simulation to ensure that the BMS can detect and respond to low-voltage conditions.

This application note outlines the testing methodology, tools, and detailed results of the BMS condition simulations conducted with a 400 W four-channel DC power supply.

The four-channel DC power supply used is part of the Keysight Smart Bench Essentials Plus suite of instruments. This elevated set of basic instruments — power supply, waveform generator, digital multimeter, and oscilloscope — comes with proven pro-level measurement technologies that deliver precision and reliability. The instruments include with large color screen displays and graphical interfaces to visualize, analyze, and share test results quickly.

Battery Management System

The BMS ensures the safety, reliability, and longevity of battery packs by monitoring and managing the state of charge (SOC), state of health, and temperature of individual cells. It usually includes features such as cell balancing, overvoltage protection, and undervoltage protection to prevent damage and optimize performance.

The terms 3S, 4S, and 5S indicate the number of cells connected in series in a battery pack, where the “S” stands for series. Cells in series increase the total voltage of the pack while maintaining the current capacity. For example, a 3S configuration (three cells) with 3.6 V LiFePO4 produces a nominal voltage of 10.8 V. In comparison, a 4S (four cells) results in 14.4 V.

These series configurations are crucial for determining the overall pack voltage, ensuring compatibility with system requirements, and enabling proper monitoring and balancing by the BMS. Figure 1 shows that the sampling cable has five wires, although it is a 4S BMS, consisting of one black and four red wires. The black wire is the ground, while the red wires are for sampling and monitoring each cell.

The test setup uses the DC power supply to simulate four LiFePO₄ cells in series (4S configuration). Engineers connect each channel of the power supply to mimic individual cells, allowing them to control and vary voltages independently.

It is important to validate the BMS’s auto-balancing feature. Over time, slight variations among cells can lead to imbalance, affecting performance and safety. The application note describes how to simulate voltage differences and monitor BMS responses using the power supply’s LIST mode and data logger. It explains both passive and active balancing mechanisms and highlights how the tested BMS uses passive balancing.

Further, it details methods to simulate overvoltage and undervoltage conditions, showing how the BMS responds by disabling charging or discharging when thresholds are exceeded. These tests ensure the BMS correctly protects cells from dangerous voltage levels.

By simulating real-world scenarios in a controlled environment, this approach enables thorough BMS validation, helping manufacturers build safer, more efficient battery systems for electric vehicles and other high-reliability applications.