Knowledge Point 1: The Difference Between AC Charging and DC Charging
EV charging is primarily divided into two modes: AC (Alternating Current) charging and DC (Direct Current) charging. During AC charging, the alternating current from the power grid must be converted into direct current by the On-Board Charger (OBC) before charging the battery. The power typically ranges from 1.5 to 22 kW, with a full charge taking 5–12 hours, making it suitable for overnight home charging. During DC charging, the AC-to-DC conversion is completed inside the charging pile, which directly outputs DC power to the battery. The power can reach 30–600 kW or above, enabling an 80% charge in approximately 30 minutes, making it ideal for public fast-charging scenarios.
Knowledge Point 2: Major Global Charging Connector Standards
The major global charging connector standards include: China's GB/T national standard (AC and DC), Europe's Type 2 and CCS2, North America's NACS (North American Charging Standard, originally Tesla-exclusive, adopted as the SAE industry standard J3400 in 2024), and Japan's CHAdeMO. Global charging standards are currently converging from diversity toward unification. NACS is rapidly gaining adoption in North America thanks to its compact design and high-power advantages, while China is advancing the more universally compatible Chaoji standard.
Knowledge Point 3: Liquid-Cooled Charging Gun Technology
As charging power continues to increase, traditional air-cooled charging guns require increasingly thick and heavy cables that are difficult to handle. Liquid-cooled charging guns address this by incorporating a dedicated coolant circulation channel (typically using an ethylene glycol-water solution) between the cable and the gun head, efficiently dissipating heat generated during charging. This technology reduces cable volume by over 40% while supporting stable current output above 600A. Liquid-cooled high-power DC fast-charging products can charge a vehicle to 80% in approximately 10 minutes. The liquid-cooled charging gun accounts for roughly 21% of the total charging pile cost, making it the second-largest cost component after the charging module.
Knowledge Point 4: CC-CV Charging Strategy and the Principle Behind "Slowing Down After 80%"
EV fast charging employs the classic CC-CV (Constant Current–Constant Voltage) charging strategy. CC Phase (Constant Current): The current is held at the maximum allowable value while voltage gradually increases as charging progresses, causing the battery SOC to rise rapidly. This is the most efficient phase of charging. CV Phase (Constant Voltage): Once any individual cell reaches its voltage cutoff limit, the voltage is held constant while the current gradually decreases, resulting in a noticeably slower charging speed. This is the fundamental reason why "fast charging slows down after 80%" - at high SOC levels, the lithium-ion "vacancies" inside the cells become increasingly scarce, and continuing to charge at high current would lead to safety risks such as cell overvoltage, lithium plating, and excessive temperature rise. Therefore, the BMS must proactively reduce the current.