Currently, charging times for electric vehicles can vary from 20 minutes to several hours, and long waiting times are cited as a major source of anxiety for people considering buying an electric vehicle. But now, engineers at Purdue University in Indiana have invented a new charging station cable that’s capable of fully recharging certain EVs in less than five minutes – roughly the same time as it takes to fill a petrol-powered car.
The speed at which an EV’s battery can be charged using a conventional cable is limited by the danger of overheating. Faster charging requires sending a higher current through the charging cable, which leads to higher temperatures than the chargers’ cooling system can deal with.
These cooling systems use liquid to remove heat, so increasing the current through a charging cable would require both larger conductive wires and more liquid coolant. Together, these would make the cable heavier and hence more difficult for users to operate.
‘My lab specialises in coming up with solutions for situations where the amounts of heat that are produced are way beyond the capabilities of today’s technologies to remove,’ said Issam Mudawar, Purdue’s Betty Ruth and Milton B. Hollander Family professor of mechanical engineering.
Mudawar has spent the past 37 years developing ways to more efficiently cool electronics by taking advantage of the fact that liquid captures heat when it boils and becomes a vapour. Such liquid-to-vapour cooling systems can remove at least ten times more heat than simple liquid-cooling systems.
‘The industry has a gap in knowledge and expertise needed to switch from pure liquid cooling to liquid-phase-change cooling,’ Mudawar said. ‘How do you design the system? What type of equations do you use to optimise it? But we do have this knowledge through our extensive research.’
The prototype created by the engineers mimics the traits of a real-world charging station, with a pump, a tube with the same diameter as an existing charging cable, the same controls and instrumentation. Although it hasn’t been tested on an EV yet, Mudawar and his students have demonstrated in the lab that it can accommodate a current of more than 2,400 amperes – far more than the 1,400-ampere minimum that would be needed to reduce charging times for large commercial EVs to five minutes. Currently, the most advanced chargers only deliver currents up to 520 amperes, and most consumer chargers support currents of less than 150 amperes.
‘The industry doesn’t really need EVs to charge faster than five minutes, but we think we can increase the current even more by modifying both the state of the incoming liquid and the design of the cooling space around the conductor wires in the charging cable,’ Mudawar said.
The team hasfiled a patent application for the charging cable and is looking for additional industry partners (it’s already working with Ford) to continue the technology’s development, hoping to be able to test the prototype on EVs within the next two years.
The research has been published in the International Journal of Heat and Mass Transfer.