71 Battery leak testing | Product focus can become complex. Sniffer leak detectors can be used as stand-alone devices, and it is possible to build a system that integrates a vacuum leak detector only, but to create a system optimised for speed, throughput and repeatability takes more complex technology, typically provided by system integrators. In support of this, leak detection suppliers build a variety of digital fieldbus interfaces into their products, including Ethernet, PROFIBUS, as well as analogue interfaces. One supplier says its metal-ion battery leak-test capability is now in its third generation and has developed rapidly, along with the industry. Battery leak testing was first required by r&d departments that wanted to test about 20 parts a day; they now offer detectors that can easily test 200 cells per minute. Calorimetric testing measures the heat released from a substance, which can be used to detect leaks. It can be integrated into existing production lines or quality control labs, so long as there is space and power for the challenge gas generator, booster pump and colour-change media, which can be taped, brushed or sprayed onto the part under test. Battery leak and coolant detection is being integrated into production lines for end-of-line testing, and at quality checkpoints throughout the life of the vehicle for preventive maintenance and repair. At one vehicle OEM, if an EV fails coolant filling on the production line, it goes to the service area for testing to pinpoint the leak, so technicians can make a repair, perform a verification test and release the vehicle back onto the line. The developer eases integration by offering a version with an embedded screen and one with an interface that runs on a PC, and it uses industry standards to guide the application programming interface (API), simplifying communications between the software and hardware components of the detector and the host system. While most leak testers are agnostic to battery chemistry, they tend to be designed for use with liquid electrolyte batteries, although one supplier we asked is developing the capability to test solid-state batteries. Another notes that temperature is important, recommending that testing is carried out in steady state environments where all components are in thermal equilibrium. In operation, batteries in e-mobility applications rely more on the BMS to detect problems that could cause or be caused by leaks, although a growing variety of aftermarket leak testers are available to authorised repairers. These systems don’t have to produce results as quickly as those used in high-volume production and a response time of several seconds is generally acceptable, so the sensors can be simpler and less expensive, making building in dedicated leak sensors more attractive, particularly if they include wireless communications to support remote data collection. Also, leak-check vent valves can support portable pressure testers so long as they are accessible, preferably without having to remove the battery. False positives/negatives Consistently reliable results are essential to all testing systems, and the rate of false positives and false negatives is a crucial measure of that reliability. One innovative way of minimising error in differential pressure decay testing involves cancelling out any background noise that can affect the measurements. Sources of disturbance in factories can include temperature variations caused by opening doors or windows, and the operation of fans, heating, ventilation and air-conditioning systems, while the time of day, sound levels and weather conditions can cause pressure variations, and machine movement, wind, forklifts and even music can cause vibration. A leading supplier of differential pressure decay testers has developed an automated learning process that measures such sources of noise and compensates for them. Even with leak detection systems that have inherently low rates of false positives/negatives, such as mass spectrometry, achieving this requires careful handling of the test gas to minimise the concentrations in the environment around the tester, as well as proper use of the equipment. To achieve this, a leading supplier offers intensive consulting services on how to design the leak testing procedure. With colorimetric testing, a false positive is highly unlikely because of the chemistry of the colour-change E-Mobility Engineering | March/April 2025 The ELT Vmax is a leak tester that directly detects electrolyte, is sensitive enough to warn of leaks down to 5x10-7 mbar·l/s (helium equivalent leak rate) and is suited to automated production lines (Image courtesy of INFICON)
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