China Aims New EV Coolant Regulation at Battery Safety

SAE Standards “running fast” in the race to standardize a much-needed product.

October 29, 2024

Lindsay Brooke

Car technician checking electric vehicle system problems with a wireless scan tool. (Shutterstock/BLK Studio)

A new regulation from China’s central government aims to reduce the electrical conductivity of fluids that help heat and cool EV propulsion systems. Document GB 29743.2, currently in draft form, defines a maximum dielectric requirement for EV thermal-management liquids that maintain battery, motor and power electronics operating temperatures, a critical factor in EV thermal safety. Release timing for the proposed regulation (considered a “standard” within China’s motor industry) is expected by mid-2026 at latest, according to reports.

A liquid cooling pipe of a modern electric car. (Shutterstock/Asharkyu)

All EVs sold in China must comply with the new GB regulation, which has potential implications for coolant fluid formulation, service life, and EV maintenance regimes, according to experts interviewed by SAE Media.

“Moving forward, it’s going to require a service life for EV coolants, as opposed to being in the vehicle indefinitely,” said Brian Engle, chair of the SAE International Battery Standards Steering Committee and director of business development at Amphenol, a supplier of EV propulsion system sensors and connectivity solutions. “It’s going to change the makeup of the coolants.”

The regulatory prefix GB stands for Guo Biao, or “Chinese national standard.” GB regs are issued by the Standardization Administration of the People’s Republic of China. What differentiates the upcoming GB 29743.2 from the ASTM D3306 standard (the general minimum requirement for ICE coolants), is primarily a focus on reducing EV fluids’ electrical conductivity, said Tom Corrigan, director of EV Technology at coolant supplier Prestone Products Corp.

“What we’re seeing from not only this Chinese GB but also from the OEMs and the ASTM’s proposed EV standards [for fluids] is a convergence around 100 microsiemens per centimeter,” he noted. “That’s a pretty safe value if there was an accident that involves fluid contact with the high-voltage electronics.” Microsiemens, abbreviated μS, is a multiple of siemens (SI), a unit used to measure electrical conductance. By comparison, an ICE coolant would be rated at 2000-5000 μS/cm.

The GB reg is expected to include an aging factor that sets a maximum 300 μS/cm limit. “Compared with today’s water/glycol blends, any water in future coolant would have to be pretty minimal,” Engle said. “And the constituents that reduce breakdown cannot drive it into a higher conductivity. This is based on testing of external short-circuiting of battery systems conducted during the past year.”

SAE Standards “running fast”

EV thermal management is a booming area for industry engineers and scientists. In China, a spate of highly publicized EV-related fires in city parking garages has caused some hotel and property managers there to ban all EVs, including cars, vans, scooters and e-bikes, from their underground garages. Those lithium-fueled conflagrations likely influenced the central government’s action.

“They’re tired of batteries catching fire when there’s a collision event or a leaking coolant line,” Engle said. He added that the resulting GB regulation, supported by the major battery manufacturers, had to include a conductivity threshold under which the batteries, when directly exposed to coolant, would not develop an external short circuit that could lead to thermal runaway.

SAE’s Battery Standards Steering Committee has some 750 engineers and scientists in 32 subcommittees crafting the SAE J-documents. “We’re running fast to keep pace with China’s EV industry; they’re leading the way in many of these technologies,” Engle stated. “Their development of GB 29743.2 kicked off less than a year ago.”

SAE Battery Standards Committee chair Brian Engle, sees major changes in EV thermal management fluid formulation aimed at increasing EV battery safety. (Brian Engle)

The SAE Standards teams are creating an EV fluids-focused standard document covering “everything from how to measure, to how to turn the China GB test procedures being used into international test procedures for the materials, for material compatibility – and how we tie it into our SAE Thermal Management Committee,” Engle said. He said EV manufacturers are increasingly looking for “significant dielectric reductions in terms of very electrically non-conductive material for immersion-based cooling systems.”

One SAE initiative is working with seven different coolant manufacturers, many based in China, to drive test protocols for EV coolant fluids and determine degradation mechanisms and material constraints. “We now have identified a family of materials, not all the same, that can be used,” Engle said. “Hyundai and some 17 OEMs in China are using some form of dialectric coolant in their EV cooling packages. They’re already moving in that direction to be compliant.”

Agnostic standard needed

Will there be an SAE standard for the EV coolant sold in gallon jugs at Pep Boys, per the SAE standards for motor oil? “That’s what we would hope,” Engle said. “The objective is to create a global standard.” Engle is also technical advisor on the Global Technical Regulations for EV Safety’s GTR20, a group aimed at aligning the FMVSS 305, the [EU battery safety test] R100, and the China GB regs.

“Ultimately, we want to have something that is an agnostic industry standard that allows for translating what China is doing into something that looks like a rating system, to allow customers to order application-specific coolants for EV service. We need a material spec for those coolants. You can’t rely on brands because they change over time. And consumers don’t want to mix coolants that would have a material compatibility problem that leads to degradation of the cooling system that could hazard the pack.

“SAE Standards is running so fast that sometimes we’re lacing our shoes up as we’re running!”