Join us as we delve into what the recent changes to UL 2271 mean for light electric vehicle (LEV) markets, specifically in the design phase of product development for developing safe & reliable battery systems that meet & exceed these new safety measures.
Contact: Betsy Barry
Communication Manager
706.206.7271
betsy.barry@acculonenergy.com
There are several consequential changes to UL 2271’s 3rd edition released in September of 2023–changes that mean some OEMs and micromobility players will have to undergo UL testing as a requisite for bringing products with lithium batteries to market. This, in turn, could mean substantial redesigns to ensure compliance for a range of applications, from all-terrain vehicles to UAVs and from golf cars to e-bikes.
Why now?
A hearing by the Consumer Product Safety Commission in the summer of 2023 convened to tackle the safety issues surrounding micromobility products that employ lithium-ion batteries. This hearing focused specifically on the micromobility sector, prompting regulatory agencies to revisit prevailing industry standards surrounding LEVs. The result, in part, is an update to UL standards governing these products, namely UL 2271.
UL 2271 is a standard that outlines requirements for the safety and performance of electrical energy storage assemblies (EESAs). This safety standard covers light electric vehicles (LEVs), like e-bikes, e-scooters, golf cars, ATVs, lawnmowers, and like-applications that fall under the LEV umbrella. Additionally, UAVs now fall under UL 2271 as well. The UL 2271 certification standard evaluates the entire battery system, from its components to its overall architecture. For example, there are rigorous tests that evaluate the battery enclosure’s resistance to environmental factors like impact, heat, flame, and water. Other tests and evaluations ensure the battery’s wiring is properly designed to withstand strain and unintentional shorting through a series of electrical tests. Finally, there are multiple mechanical tests to check the battery’s physical endurance during intense vibration, and being shocked, dropped, and crushed.
The 2nd edition of UL 2271 was released in 2018, but there are some standout updates to the 3rd edition, released just a few months ago in the fall of 2023.
What are some of the significant changes to UL 2271 and how do they impact battery design?
Manual Disconnect: One addition to this standard to enhance safety measures is that an Electrical Energy Storage Assembly (EESA) must be equipped with a manual disconnect. This feature is essential to prevent unintentional access to hazardous voltage components both during servicing and in the event of a collision.
A manual disconnect was not in the previous edition of 2271, so this is a new requirement and reasonably straightforward. However, the installation of a manual disconnect may pose challenges to some smaller LEV applications where volume and weight are limiting factors.
This new requirement could be difficult for battery systems that are designed for multiple applications, as this switch has to be accessible before any exposed conductors. Also, in most applications, the switch will have to be exposed on the exterior of the pack, making this feature inclusion difficult without significant modifications to the end product to accommodate the space constraints. For non-OEM products placed into the aftermarket, the design implications for a smaller battery with the same energy may become a challenge. Let’s not forget this is a safety component that has to be listed on the critical components list thereby requiring UL-approved switches only. All in all, the installation of a manual disconnect represents an impactful change that will send product designers back to the drawing board.
High-Rate Charge Test: These latest updates also include the addition of a high-rate charge test that will evaluate the safety of the batteries when the charging rate is higher than the application specification levels. Importantly, unless the BMS has been evaluated as meeting the functional safety requirements under a single-fault failure (see below), OEMs will have to adhere to a charge rate 20% higher than their specifications.
This update will inform BMS design to either rate limit, or completely shut down during charging if the charge currents exceeding the maximum-allowed value are detected. This update is a bit tricky from a design perspective because two use cases must be handled. 1) Where communication and control of the charger must be accommodated, and 2) where a “dumb” charger (as opposed to a “smart” charger) is hooked up to charge the battery. In the first scenario, the BMS must be designed to rate-limit to protect the battery. In the second scenario, the design could facilitate opening contactors altogether in the event that a “dumb” charger with no communication with the BMS is connected. Ultimately, this change encourages optimally sizing the system by using software to protect the battery, instead of oversizing the components to handle a 20% overcharge current.
The significant changes to UL 2271 could have major impacts on many players in light electric vehicle (LEV) markets, in some cases
even requiring substantial product redesigns to ensure compliance.
Taking the necessary steps to design products with these standards at the forefront can help products not only meet but exceed these new safety measures.
Overload Under Discharge Testing: Another important addition to 2271 is the overload under discharge test, which will replace the “soft short” in the short circuit test. Now you have to run the test at 90% of the current by which the BMS would activate its protection devices. These tests are designed to stress the system by maximizing current to see if the system can handle it and if backup systems come into play.
This update will require an intelligently designed BMS, which will facilitate optimal testing conditions because the system can be constrained to never experience 150% of the max allowed discharge current. Therefore, designers can optimize component sizing instead of oversizing to meet the specifications, which will save cost, volume, and weight.
Single-Fault Failure Testing: Perhaps the biggest update of this standard is the addition of a single-cell failure test for any battery over 1Kwh: a threshold that will likely impact approximately 95% of applications that fall under the LEV category. This single-fault failure is identical to the test outlined in UL 2580 with the stipulation of no explosion or fire outside of the device under test (DUT) for up to one hour after the test.
This update is critical to the overall design process because it may require starting from the ground up to design a pack that can withstand a single cell going into thermal runaway. This update will no doubt privilege battery modules that already have this designed into the system. Other battery modules and packs that have not been designed to this specification already will struggle to apply a “band-aid fix to their current system, which could cost valuable time and money.
The impact of this new requirement cannot be overstated, as it influences everything from cell selection to material selection. This update impacts the entire mechanical design of the pack, including aspects like case thickness and venting, as well as cell spacing and the use of propagation mitigation materials like foam and other intumescent materials.
Sodium-Ion Batteries: Finally, sodium-ion battery modules and packs now fall under the UL 2271 umbrella, meaning these batteries will have to undergo the same testing requirements as their lithium counterparts.
These changes come as law and policymakers grapple with increasing safety concerns surrounding lithium-ion batteries in LEV applications–concerns that are resulting in local governments and municipalities taking up the charge of safety in mobility products and passing laws that ultimately seek more stringent safety standards for these products. Cities like New York City are passing laws requiring all lithium-ion batteries for mobility devices to be certified to UL 2271 after seeing a dramatic increase in fires related to lithium-ion batteries in e-bikes and e-scooters. These sweeping changes are poised to inspire significant changes to battery design and product development in these markets.
Acculon’s David Ginder, Director of Engineering, was a key contributor to the additions and revisions in the 3rd edition, having decades of safety standard affiliations worldwide. If you are interested in a more in-depth discussion about the scope and breadth of the 2023 UL 2271 updates and the implications for LEV battery systems, please reach out to us for a more in-depth discussion!