Fast Charging Next-Generation EVs and Trucks Is A Major Thermal Challenge
With electric vehicle (EV) onboard chargers and DC fast-charging stations getting ever more powerful, managing heat in charger cables and systems is now the main potential point of failure. The industry has to mobilise resources to solve this bottleneck and scale up EV charging to the megawatt range.
Charging your EV now takes from 20 minutes at the fastest stations to many hours at home charging points. Lengthy charging times are still a major obstacle to mass EV adoption. The industry would like to reduce the charging time to about five minutes, requiring charging points to deliver a current at 1400 amperes. Current fast chargers top out at about 500 amps with 1000 volt for about 350 kilowatt (kW) power. Home chargers get to around 150 amperes for 100 kW. The next-generation fast-charging EVs from Porsche, Kia, Hyundai and others promise 350 kW power in under 20 minutes, if charging infrastructure can keep up.
The cables carrying the power from the charging station to the vehicle are a major bottleneck in the system. Heat developing in the cable via resistive (I2R) loss, even with an ohm or less of resistance, would make cables too hot to handle or even catch fire with the number of amperes that car producers now promise and consumer expect. The higher the current, the more heat has to be removed to keep the cables operational. Doubling or tripling the cooling requires fundamental innovation.
Liquid-cooled cables have been on the market for a few years. Swiss cable supplier Huber+Suhner introduced the first cable to allow continuous charging at 500 amps in 2020. The cables still needed to be backed up by separate cooling units for the power lines that feed them. Huber+Suhner sells it as a “plug and play” system, pre-filled with coolant. LS Cable & System in Korea, where liquid cooling is legally required for hyper-chargers over 400 kW, started mass production of their liquid-cooled hyper-charging cables in 2022.
In Europe other cable suppliers like Aptiv, BRUGG eConnect and Kempower are making their moves. Automotive supplier Leoni, after delisting and restructuring with a new investor and CEO, in April 2023 announced a new business unit Charging & Power Solutions to focus on liquid-cooled High Power Charging (HPC) cables for fast charging systems. The company said that it would use its own advanced simulation and testing department where ‘components are designed virtually and then tested under real conditions in close cooperation with the customers’.
Meanwhile in the US, Ford and Purdue University invented a new patent-pending cooling method for a 2400 amps charging cable, far beyond the 1400 amps required to reduce charging time to about the same it takes to fill up a gas tank. The “subcooled flow boiling” method, involving a coolant phase change from liquid to vapor, was initially developed with NASA. Ford downplayed the collaboration with Purdue in a press release as ‘part of hundreds of strategic alliances the company has with university professors around the world’. Purdue will be testing the prototype cable for the next two years. There won’t be a product on the market any time soon.
For passenger cars 350 kW is currently a sufficient and realistic target, but trucks will need power in megawatts. Tesla has been setting the goals, chasing numbers conjured up in China, announcing a new V4 charging cable in December 2022 for Tesla’s Semi and Cybertruck that will use new immersion cooling technology to deliver charges over a megawatt (mW). The first stalls in the rollout of Tesla’s V4 Supercharger Network in Europe supposedly opened in Harderwijk in the Netherlands in March 2023, but the company did not release details of charging speeds.
Developing a megawatts charging infrastructure for trucks is a huge challenge that will not be solved by one company. In July 2022 leading European commercial vehicle manufacturers Daimler Truck, Traton Group and Volvo Group announced a joint venture to invest 500 million Euros to install and operate at least 1,700 high-performance public charge points in Europe by 2027. Anja van Niersen was recently appointed as CEO and the collaboration has started activities under the name Milence. Quotes in the press releases stressed the importance of collaboration across the supply chains. ‘We call on the entire industry to join in our effort,’ Daimler Truck CEO Martin Daum said.
Industry leaders will discuss Scaling Up Cooling in EV Charging Systems to the Megawatts Range at the Thermal Management Expo conference, 5 to 7 December in Stuttgart.