Purdue Prototypes New EV Fast-charge Cable
The patent-pending charging station cable uses a novel cooling method to enable EV battery recharging in under five minutes.
A new charging station cable designed by a Purdue University research team could enable an electric vehicle (EV) battery to be recharged in under five minutes, comparable to filling an average passenger vehicle’s fuel tank at a gas station. The patent-pending technology “addresses a better thermal management scheme for EV charging cables based on the principles of sub-cooled flow boiling. This would enable ultra-fast charging of EVs by the safe passage of much higher electrical currents through the cable,” said V.S. Devahdhanush, a Purdue University Ph.D. candidate and research project team member.
The Purdue team’s prototype charging station cable is designed to dissipate heat as electrical current flows through the cable. In comparison to the cable used by Tesla on its Supercharger V3 – currently considered the fastest charger in the U.S. market – the prototype cable delivers 4.68 times the current, according to Devahdhanush. The Tesla V3 supercharging architecture supports peak charging rates up to 250 kW per car.
To achieve a faster charge rate, a cable needs to enable higher electrical current flow. “We’ve been able to demonstrate experimentally the safe, steady passage of 2,438-amp current through a 0.25-in wire,” Devahdhanush said, noting higher values are theoretically possible. With a 10-foot long (3-m) cable containing two high-direct current wires, equivalent to a single 20-foot wire, 24.22 kW of heat is removed via the cooler cable providing 2,438-A current.
Purdue Ph.D. candidate V.S. Devahdhanush monitors system pressure within the cable and the flow rate of a dielectric heat transfer fluid via a Rotameter flow meter. (Jared Pike)
Most of today’s charging stations can deliver current up to approximately 520 A. However, DC fast chargers typically deliver less than 150 A. Charging times vary from approximately 20 minutes to several hours, depending on whether a Level 1 (120 V), Level 2 (240 V) or Level 3 (DC fast) charger is used. The main influencers for charging times are the EV battery’s power input rating, the power supply’s output rating, and the charging cable. A sub-five-minute charge time would require that the power ratings and charging cable be rated at 2,500 A.
Commercially available charging station cables are liquid cooled, using the principle of forced convection heat transfer, noted Devahdhanush. In this conventional cooling technique, fluid absorbs heat from the cable. After the heat is dissipated to the external surroundings, the fluid temperature falls and the cooling cycle continues.
The Purdue cable design incorporates a liquid-to-vapor cooling process. A dielectric heat transfer fluid flows within the cable conduit that surrounds the wires. When the wires’ surface temperature becomes greater than the fluid’s boiling point, the liquid starts boiling at the wire surface and small vapor bubbles are produced.
“These vapor bubbles slowly condense back to liquid after departing the surface because the bulk liquid temperature is so low,” Devahdhanush explained. “Any remaining vapor at the exit of the cable is condensed back to liquid, and the overall coolant temperature is lowered in a condenser at the charging station.” A cool cable is required at charge stations for safety reasons. An overheated cable isn’t safe for humans to handle, and at highly elevated temperatures “the wires would burn out and cause a fire,” Devahdhanush said.
Purdue University’s charging station cable R&D team, led by mechanical engineering professor Dr. Issam Mudawar, regularly communicates with a team of Ford Motor Co. researchers to review findings and provide feedback on various focus areas. Michael Degner, senior technical leader at Ford Research and Advanced Engineering, noted that this research alliance has the potential to make EV and commercial fleet ownership considerably more appealing and accessible.
The next steps in the project include testing the innovative charging station cable on EVs. “We are now negotiating with several cable, coupler, pump, and heat exchanger vendors as part of our just-announced Research Center for Electric Vehicle Charging and Thermal Management to determine how to commence such testing,” Devahdhanush said.
2022 will see more battery-electric vehicle introductions, including the Ford F-150 Lightning Pro truck that targets commercial fleet customers. “This cable would be useful for all EVs, including light-duty passenger vehicles, Class 8 trucks and other commercial vehicles,” said Devahdhanush. He believes that a commercialized version of the prototype charging station cable would be especially relevant to Class 8 and other heavy-duty trucks. “Those vehicles are equipped with large high-capacity battery packs that need enormous electrical power to get fully charged,” he said.