55 Soteria e-bike project | EVD safety standards with, for example, bills presented to both parts of the US Congress (the Senate and the House of Representatives), which, if passed, will require a nationwide battery safety standard to be put in place. Further, the Society of Automotive Engineers (SAE) has formed a micromobility standards committee to address the issue. “Active participation is needed to make sure the bills pass, and that the committees put in place standards with all of the necessary features that will produce a very safe battery pack,” Morin says. While getting these bills through Congress is important, he argues that the fastest way to achieve the industry’s safety goals is through voluntary adoption of the Soteria standard, and using markings to identify to consumers that enhanced safety features are in place. Interim precautions Until such a standard governs the production and testing of e-bike batteries, the owners, riders and operators will remain obliged to handle and maintain them in a manner that minimises risk. This, Morin argues, involves taking a conservative (and somewhat expensive) attitude towards service life, particularly of cheaper batteries. “I wouldn’t use an e-bike battery pack beyond about 250 charges. After this, the cells can start to age, and not knowing the quality of the battery pack manufacturer, it is safer to replace it with another high-quality pack.” (It is possible to have a service centre check the battery’s state of health, even if its BMS doesn’t report it to the user.) Morin also advises against further use of any battery with more than cosmetic surface damage to the pack casing, and only ever to use a charger recommended by the battery’s manufacturer, and always to charge it in a cool, dry place, well away from flammable materials. Another non-obvious risk is that conventional alarms are not good at detecting the smoke and gases from lithium-ion battery fires. Such alarms are designed to detect the smoke from burning wood, plastic, paper and other common domestic materials, which range in size from a few microns to tens of microns, and their effectiveness drops significantly for particles smaller than 1 micron. Unfortunately, the smoke from a lithium-ion battery is mostly composed of particles smaller than 0.1 microns. To solve this problem, Soteria is developing a dedicated detector that is sensitive to the emissions given off by lithium-ion battery fires, including hydrogen, carbon dioxide and volatile organic compounds (VOCs). As many batteries are designed to vent gases before the cells reach a temperature at which they will ignite, Soteria’s alarm can sound an alert up to 15 minutes before a fire starts. In one set of tests, the organisation says, a single cell going into thermal runaway brought the hydrogen level from below 1 ppm (ambient) to over 500 ppm. Morin says the system is expected to be available in the autumn. Progress and future plans Since Soteria reported its interim results last summer, it has continued to push its work forward. This has included the disassembly of more battery packs, including used ones to build an understanding of how usage affects their condition, and interviews with e-bike manufacturers. The consortium has run a workshop with more than 20 participating organisations, and it was this event that defined the minimum feature set required to make a very safe battery. The results of this workshop also informed the draft of the Soteria E-bike Battery Safety Standard, which has been refined and is now supported by an audit checklist that battery developers can use to ensure their products conform to the standard. Going forward, the consortium’s efforts are focused on getting the safety standard published and working with industry to help them implement it. “We will work with the supply chain to ensure companies can produce components of the quality required, and with battery pack manufacturers to help them design packs and get them certified to the standard,” Morin emphasises. “We also plan to run a communication campaign to help e-bike riders understand the difference in battery pack design and how it affects their safety.” Soteria has issued an open invitation for anyone interested in advancing e-bike battery safety to get in touch. E-Mobility Engineering | July/August 2024 Once cells start to age after about 250 charges, Soteria recommends replacing the pack with a new one from a reputable manufacturer (Image courtesy of Bosch)
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