Abstract
The open wire detection function plays a crucial role in the safe and reliable operation of the battery management systems (BMS). Due to its critical importance, it is recommended for those interested in BMS or involved in BMS design to take the time to understand this function. Taking Analog Devices’ cell monitor as an example, this article discusses in detail how BMS circuits can accurately identify almost all instances of open wire connections when interfacing with external cells using algorithms. The discussion on open wire detection algorithms aims to provide readers with a deeper understanding of this function within BMS. The pseudocode provided in this article for open wire detection is intended to serve as a design reference for BMS designers.
Introduction
In the battery management systems (BMS), there are extensive wiring connections between individual cells and cell monitor circuits. These wiring connections are essential for enabling reliable monitoring of cell parameters, including voltage, current, temperature, and others by the cell monitors. Additionally, these wiring connections may serve as the current path for cell passive balancing discharge or the transmission path for relay control signals. The number of cells to be managed in BMS is typically very large, necessitating the use of a significant amount of wiring connections. These wiring connections are numerous, some even lengthy, as they often need to span between different printed circuit boards (PCBs) and between PCBs and battery packs (comprising numerous individual cells). They also require many connecting components to be used in conjunction. The occur- rence of open wires in the BMS is to be vigorously avoided. After all, if a cell experiences open wires, it means that effective monitoring of its state will be weakened or lost, and unmonitored cells will pose a hidden safety hazard to the entire BMS, with the threat of becoming fatal to the system at any unknown time. When open wires do occur, the primary task is to quickly, accurately, and effi- ciently determine the location of the open wires and provide timely notifications. An effective and accurate open wire detection algorithm will greatly enhance the reliability of the BMS and facilitate troubleshooting for both the BMS and battery pack. Accurate fault localization by the algorithm can effectively reduce many unnecessary repetitive checks, as well as disassembly and assembly work, during manual troubleshooting processes.
Open Wire Detection in the C Pin of a BMS
Due to the critical importance of open wire detection in a BMS, most of ADI’s cell monitors are equipped with open wire detection commands and their respective implementation methods. The open wire detection methods used in different models of ADI cell monitors may vary, such as those used in the ADBMS6830B differing from those used in the LTC6813 (the latter of which is the focus of this article). The open wire detection method employed by the LTC6813 is also a common method used in various models of ADI cell monitors, possesses generality, and is based on the ADOW (open wire check) command.
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