Battery packs for electric vehicles consist of large modules, which in turn are composed of several smaller batteries.Teledyne FLIR
Thermal runaways can make electric vehicles hit the headlines. But how can such an event be predicted? Thermal imaging cameras can help with this. What scenarios are there and what are the results.
The battery packs used to power electric vehicles are large modules made up of several smaller batteries. These modules are built into a rigid frame and connected to each other to form a larger, complete battery set. Improper mechanical connections between modules can cause high resistance, which can lead to power loss or even a battery fire.
However, inspecting the mechanical connections between the battery modules can be difficult. Inspection systems with visible cameras can check the components for correct position and alignment, but they cannot test and confirm the current flow of the connections. Furthermore, the surfaces of the connectors are reflective, leading to issues with lighting and camera placement.
Manufacturers of battery modules for electric vehicles often need to keep historical records of the performance of each validation and end-of-line test. To do this, they must use precise and repeatable measuring instruments so that the resulting test data can be quickly compared to determine trends and potential issues. This data could also be used in legal disputes if faulty connections lead to a fire.
FLIR A70 thermal imaging camera monitoring a battery pack. The camera can identify faulty connections based on temperature rise.Teledyne FLIR
How thermal imaging cameras inspect connections in EV batteries
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Manufacturers have long used thermal imaging cameras for inspecting electrical systems. These cameras can be used to detect temperature increases caused by increased resistance due to poor or loose electrical connections. They can also help identify other potential issues, such as unstable loads, overloaded electrical circuits, and damage to insulation or cables.
Fixed thermal imaging cameras like the FLIR A-Series Smart Sensor can be easily integrated into the numerous automated processes in electric vehicle manufacturing. Connectivity to existing infrastructure or CMMS software with the FLIR Bridge Pro provides additional benefits and enhances user-friendliness. Thermal imaging cameras can not only detect hotspots but also provide accurate temperature data for each pixel in the image. This ensures flexibility in the size and type of connections that the end user can monitor. Depending on the physical size of the battery pack, the positions of the connections, and where the camera can be mounted, multiple connections can be checked simultaneously with a single camera.
The use of thermal imaging cameras in manufacturing and testing processes for electric vehicle batteries can increase confidence in the integrity of battery packs and cable connections. Fixed models like the A70 can identify a higher number of potentially loose connections and reduce the number of end-of-line failures of the battery system. With FLIR Bridge, an edge gateway for the industrial Internet of Things (IIoT) that collects thermal and sensor data in a hub, manufacturers can further optimise the transfer of thermal data into their preferred software. Bridge helps integrate thermal data with other sensor data and serial number information, so that problem connections can be flagged for assessment and possible repair. All this ensures fewer overlooked connections, more information, and safer batteries in our vehicles.
FLIR A50 and A70 cameras with Smart Sensor are ideal for users who want integrated, in-camera analysis and alarm functions for condition monitoring and early fire detection.Teledyne FLIR
Monitoring partially charged battery cells
Most manufacturers of EV battery modules and packs use battery cells that have a certain state of charge during assembly, as it is generally assumed that a fully discharged lithium-ion battery is more dangerous than a fully charged one. When the individual battery modules are connected, current begins to flow between the components. This current flow often leads to a temperature increase in the cells and/or modules. As the temperature rises, the voltage in the system decreases, leading to an increase in current, which further increases the temperature. This cycle of temperature increase is known as 'thermal runaway' and, if not detected, can lead to damage to the batteries and even fires in the facility.
The battery management system (BMS) monitors the temperatures and checks the battery for loose connections and internal short circuits. However, the BMS is usually only installed in the system later in the assembly process. Therefore, the monitoring of the temperatures of cells and modules during initial assembly is carried out with portable IR temperature guns, which only provide temperature information in a small area, or it is not measured at all.
Thermal imaging cameras offer battery system manufacturers the ability to monitor the entire battery assembly for elevated temperatures and potentially dangerous situations due to thermal runaway. Since battery configurations can vary greatly from assembly line to assembly line, the ability of thermal cameras to measure temperatures at thousands of different points helps ensure that no critical hotspot is overlooked.
The FLIR Advanced Smart Sensor cameras of the A-series can be installed to monitor each exhaust vent of the battery assembly. Through the online camera control interface, multiple areas of interest can be created, with upper limits for temperature alarms defined for each ROI. Alarm signals can be sent to an industrial PLC via EtherNet/IP for data logging and control of an alarm display when a critical temperature threshold is exceeded. This configuration allows for the recording of temperature data history, a visual display for workers when dangerous conditions occur. Furthermore, it eliminates the potential for human error when using a portable temperature measuring device.
The use of A-series cameras like the A70 offers a significant improvement over the use of handheld measuring devices by individual operators, as the repeatability and reliability of temperature measurements for detecting thermal runaway significantly increase. The automated and enhanced thermal monitoring provides a level of assurance that potential hazards are quickly detected, contributing to the reduction of risks for both plant personnel and the facilities.
The article is based on material from Teledyne FLIR.
