Integrating a liquid coolant system into the cable assembly and connector housing of electric vehicle (EV) charging infrastructure moves coolant around the high-current wires and connectors. The liquid coolant circulates through jackets or channels built into the parts, removing heat from them.
The problem with dc fast chargers
One of the biggest problems with fully adopting EVs is that charging takes a long time at the networks of charging sites being planned worldwide.
Some dc fast chargers, such as CCS and CHAdeMO (Figure 1), have been modified to use single-phase liquid schemes to keep the charging wire cool. However, the fastest commercial chargers can only handle about 500 A of electricity.
Figure 1. The dc fast-charger types: CCS and CHAdeMO. (Image: CALeVIP)
Reducing the heat
There are two general methods for reducing the temperature rise of the charging cable and connectors during high-power dc fast charging. First, increasing the cable diameter to lower its electrical resistance decreases the heat generated by Joule heating. However, this approach can make the cables heavier, and heat dissipation from the connectors is not considered.
The high temperatures at the connector terminals can exceed the temperature limits of the connector body materials, such as plastics, causing deformation or degradation over time.
Second, active cooling methods such as air, water, and oil cooling remove the heat generated in the cable conductors and connectors. Specifically, liquid cooling by circulating a coolant through cooling tubes integrated into the charging cable can also address connectors and remove heat.
How CHAdeMO leveraging liquid cooling
Figure 2 shows how a CHAdeMO charging cable and connector can be integrated with a liquid cooling system to dissipate the excess heat from the system.
Figure 2. An illustration of a liquid-cooling system used in CHAdeMO charging cable and connector. (Image: Fujikura Ltd.)
How it works:
- The charging cable contains multiple coolant cooling tubes and power line conductors. The coolant flows through these tubes to remove heat generated by the high current in the conductors.
- The charging connector has a cooling area near the positive and negative terminals. The coolant tubes from the cable are connected to these cooling areas to circulate coolant and extract heat from the terminals.
- The coolant inlet and charging cable outlet are connected to an external cooling unit that cools and circulates the coolant in a closed-loop system.
- The cooling unit contains a pump to circulate the coolant, a radiator with a fan for forced air cooling of the hot coolant, and a coolant storage tank.
Electrically insulating liquid coolants like deionized water prevent electrical short circuits and ensure safety, as high dc voltage is applied to the conductors and terminals.
Summary
Liquid cooling offers several advantages over air cooling for managing the heat generated in high-power EV charging cables. Heat transmission is substantially higher in liquids than in air. This helps liquid cooling systems remove additional heat from cable conductors and connectors.
Effective liquid cooling reduces the cable conductor size while handling the high currents required for fast charging. Unlike bulky external air cooling components, the liquid cooling lines can be integrated compactly within the charging cable assembly.
References
- Over 150 kW Class CHAdeMO Liquid-Cooled Charging Cable and Connector, Fujikura Ltd.
- Self-driven liquid metal cooling connector for direct current high power charging to electric vehicle, Elsevier
- Experimental investigation of subcooled flow boiling in annuli with reference to thermal management of ultra-fast electric vehicle charging cables, Elsevier
- SCU Provides Ultra Fast Liquid Cooling EV Charger for BMW China Production Site, SCU
Images
Filed Under: Charging, Charging Port, Connectors, FAQs