The eMobility market is an emerging one and growing rapidly. With requirements and specifications still evolving, it is difficult for manufacturers to design processes and set test limits for EV components that will ensure the delivery of a high-quality product. At the same time, stringent leak testing is an important component of EV battery production and safety in the field.
Many of the components in an electric vehicle battery, including battery packs, trays, and covers, are susceptible to leaks. These components must be leak tight to avoid customer inconvenience and even catastrophic failure. In off-roading vehicles especially, battery pack designers must be especially sensitive to water and dust ingress that could lead to potential performance and safety issues.
Unique Challenges of Leak Testing EV Battery Packs
Battery packs present a particular set of challenges in leak testing—while lacking a clear industry standard across manufacturers.
Part size is a common issue as it is more difficult to reliably test large volumes. Variation in temperature and atmospheric pressure can also result in variation of the test results. Some assemblies also need to meet IP67 or IP69K standards, which puts more pressure on today’s engineers to discuss robust leak testing processes.
Electric vehicle battery packs are also prone to part expansion at unpredictable rates. Ballooning parts and flexible components create a significant challenge in leak testing and can compromise results unless the proper test method and equipment is chosen to address the unique challenges of the application.
The goal with designing effective leak test solutions for battery pack final assembly trays and covers is cost-effectiveness, maximized cycle time, and a reliable, repeatable test with low gage R&R.
At CTS, we have the solutions and services you need to solve leak test problems and EV test goals and requirements. The most common test methods we will suggest are pressure decay and tracer gas testing, as discussed below.
Pressure Decay Leak Testing for EV Battery Pack Final Assembly
In simple terms, a pressure decay test fills a pressure vessel with air until it reaches its target pressure. Then it cuts the air source to isolate the pressure and measures the decay (loss) of that pressure over a set period of time. A pressure loss greater than a predetermined setting indicates a leak.
A few keys to testing EV battery packs using pressure decay technology is using high flow valves and precision regulator systems that can bring a part up to a repeatable pressure and to exhaust large parts quickly. Repeatably testing very large parts is of the utmost importance but is also be very challenging.
Most tests can be performed rather quickly, with highly accurate results, but the larger the part, the longer the cycle time that is required to achieve an accurate test result.
A manufacturer can typically test 30-35 scc/m* or higher dependent on the battery pack size and leak paths. For example, if a part has robust seals designed inside, good weld and adhesive joints, then you might test at higher leak rates.
CTS Examples: Battery Pack Enclosure Test Systems
Above are both examples of CTS leak test stations built for EV battery pack enclosure testing. The first (Fig 1, left) is a pressure decay and differential pressure decay station (using the Sentinel I28). The TracerMate II is also used in this operation. The part is first leak tested using pressure decay. If a leak is detected, it is then backfilled with trace gas and a sniffer leak location test is conducted to identify the specific location of the leak for repair.
The second station (Fig 1, right) uses the Sentinel 3520. This instrument is suggested for leak testing extremely large battery packs, due to its electronic regulator and atmospheric pressure measurement capabilities to offset any changes in atmospheric pressure. This pressure could become an issue with such a large battery and its potential for expansion and contraction. This instrument allows you to cut out that noise to give your test a more repeatable measurement.
An additional option for large battery pack leak testing is utilizing the Sentinel I28 with ambient pressure correction that comes with the Expanded Pressure Decay option on this instrument. Both the Sentinel 3520 and Sentinel I28 utilize a secondary pressure sensor to apply a correction value to each test result based on part volume changes affected by atmospheric pressure fluctuations during the test cycle.
Tracer Gas Leak Testing for EV Battery Pack Final Assembly
When using a tracer gas leak test method for EV battery pack components, leaks are found by first pressurizing the outside of the part with trace gas. Then, you’ll measure the concentration of the same gas inside the part. If there is a leak, the trace gas concentration inside the part will increase. The bigger the leak, the faster the concentration increases.
Trace gas leak testing is utilized to reduce test cycle time and test at lower reject leak rate levels/limits; roughly < 15 scc/m* for EV battery pack enclosures and < 5 scc/m* for EV battery trays and covers.
*However, do note that these specification ranges can vary widely. Enclosures could be tested 4 scc/m all the way to 60 scc/m. There is a diverse range of specification requirements. It comes down to the construction of the part and the specifics of the process. For example, if there’s a process that could create heat in the part upstream of the leak test (like a weld operation or battery charge and discharge functional measurement), testing with air could become problematic, even if your specifications are broad enough to use an air test under normal circumstances. It’s important to consider all aspects of the process when designing your test.
CTS Examples: Battery Tray Test Systems & Tracer Gas Accumulation Systems
CTS designs and delivers battery tray test systems built for your specific needs. We deliver many variations, including manual load or automated options, as well as smaller designs for a more compact footprint on the plant floor, to accommodate different tooling, etc.
The below examples all utilize tracer gas leak testing. In the below example (Fig 3), the manufacturer places extremely large trays on the belt and is able to load/unload on either side while one is in test cycle for improved cycle time and efficiency. When the tray is in place, the tracer gas chamber moves down around the part (Fig 3, right). The test cycle begins, pressurizing the outside of tray and measuring trace gas as it leaks into the system. This chamber can also identify certain zones for leak location after the test cycle.
There are also smaller and manual loading variations of machine design for EV battery pack leak testing (Fig 4). In the below example (Fig 4, right), the manufacturer slides the loaded battery pack under tooling to reduce the height required to move a chamber over a part. At CTS, efficiencies and technologies are integrated into your test design based on part sizes, required cycle time, tooling motions, and more.
CTS Leak Test Solutions for EV Battery Pack Final Assembly Trays and Covers
Cincinnati Test Systems is a go-to for manufacturers when facing challenges related to leak testing new components for EV and the eMobility industry. These challenges are not new to us—we’ve been supplying testing solutions to manufacturing companies for over 40 years. Now, we’re applying that experience and success into consulting with manufacturers in the EV market and delivering leak test services and instruments that help you understand, define, and address EV battery leak testing standards and requirements.
Our team has been supporting eMobility testing from the very beginning, helping companies move from R&D prototype testing to production testing. With every new product comes a range of challenges that CTS has helped other companies address for leak testing their components, sub-assemblies, and final assemblies.
Need help with your EV leak testing applications? Our leak test specialists would be happy to assist you to ensure an accurate test every time.
You can also watch our on-demand webinar, Leak Testing for Water-tight EV Components, and learn how to choose the correct technology for production leak testing of various water-tight EV components.
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