from chemistry to pack
Do electric vehicles expose their occupants to electromagnetic fields? Yes, to low-frequency magnetic fields, and the published measurements put most readings below the public reference levels, with a few that need a closer look. This post sets out what the measurements show, then treats it as a design topic: the field comes from current loops … Read more
The GB 38031 page sets out what the 2025 edition of China’s traction battery safety standard requires. This post asks two different questions: how would an engineering team actually go about passing it, and what have the big battery makers said publicly about where they stand? It deliberately does not repeat the test descriptions, so … Read more
When one cell goes into thermal runaway, whether you end up with a contained event or a pack fire depends on what its neighbours experience, thermally and electrically. This post sets out the heat paths that published test work identifies, what that work does and does not quantify, and the electrical effects, which get less … Read more
Current Sensor Drift and SOC Estimation Error Propagation This is a worked example accompanying Failure Mode and Effects Analysis (FMEA) in Battery Design. It is the System FMEA example in the set, and deliberately chosen because it shows something the cell-level and pack-level examples cannot: a failure that originates in one subsystem (a sensor) and … Read more
Busbar Joint Failure Modes and Contact Resistance This is a worked example accompanying Failure Mode and Effects Analysis (FMEA) in Battery Design. It works through a pack-level DFMEA line on a bolted busbar joint, a component that is mechanically simple but disproportionately responsible for field failures because it sits at the intersection of high current, … Read more
Separator Failure Modes and Internal Short Circuit This is a worked example accompanying Failure Mode and Effects Analysis (FMEA) in Battery Design. It walks through a single DFMEA line at cell level in full, from failure mode to recommended action, using the separator as the subject. The separator is a good first example because it … Read more
Why Certification Alone Won’t Save Us Introduction Lithium-ion batteries power modern life, from the phone in your pocket to the electric vehicle in your driveway to the grid-scale energy storage facility humming at the edge of town. With this ubiquity comes an uncomfortable truth: these systems store enormous energy in compact volumes, and when they … Read more
Virtual temperature sensors (also referred to as “soft sensors” or “sensorless estimators”) are software-based algorithms that estimate the temperature of battery cells without relying on a direct, physical hardware sensor at the measurement location [2]. Instead of measuring heat directly, these virtual sensors act as real-time state reconstruction algorithms running within the Battery Management System … Read more
The exact number of temperature sensors you need depends on the size of your battery pack, its physical configuration, rate of charge/discharge (C-rate), and the required level of thermal observability. In commercial Battery Management Systems (BMS), it is common practice to use one temperature sensor for every 4 to 20 cells, depending on the specific … Read more
When a lithium-ion battery cell experiences thermal runaway (due to mechanical intrusion, defects, or electrical abuse), it releases a superheated, highly pressurized gas plume containing vaporized electrolyte and carbon particles. This gas behaves as an electrically conductive fluid. In conventional battery packs, if this gas vents randomly into the pack cavity, the blasting hot airflow … Read more