Charging

Charging refills the EV battery. Learn AC charging (onboard charger, levels 1/2, single/three-phase), DC fast charging, connector standards (CCS, CHAdeMO, NACS, GB/T), CC–CV profiles and tapering, charging-time calculation, charging power limits and smart/bidirectional charging.

Most EV charging happens at home or work on AC at 3–22 kW, taking hours. Road trips rely on DC fast chargers delivering 50–350 kW, adding hundreds of kilometres in 20–30 minutes.

Charging speed depends on the charger, cable, vehicle electronics and — above all — what the battery can accept at its current temperature and SOC.

An analogy

Charging is like filling a glass from a tap: it goes fast at first, then you slow down near the top to avoid overflow — that's the CC–CV taper.

AC vs DC

AC charging: the grid's AC goes to the car's on-board charger, which converts it to DC — limited by the OBC (typically 7–11 kW, some 22 kW). DC fast charging: the station contains the converter and feeds DC directly to the battery at 50–350 kW.

Connectors and protocols

CCS1/CCS2 (combined AC + DC), NACS/SAE J3400 (North America), CHAdeMO (Japan), GB/T (China). Communication (PLC with ISO 15118/DIN 70121) negotiates voltage/current limits; Plug & Charge authenticates automatically with certificates.

Charging curves

The battery charges at constant current until cell voltage reaches its limit, then at constant voltage while current tapers. DC fast charging is fastest from ≈ 10–60 % SOC and slows sharply above ≈ 80 %. Battery temperature strongly limits power — pre-conditioning is key.

Grid integration and bidirectional charging

Smart charging shifts load to cheap/green hours; demand charges and grid capacity limit fast-charging hubs (often with on-site storage). V2L/V2H/V2G use bidirectional chargers to power devices, homes or the grid. Megawatt charging (MCS) targets heavy trucks; 800 V architectures halve current for the same power.

Formulas

• Charging time: t = E_added / (P_avg · η)
• Energy added: E = E_usable × (SOC_end − SOC_start)
• Current: I = P / V
• AC power: P = V · I (1-phase), √3 V_LL I (3-phase)

Worked example: Home AC charging time

Given: 60 kWh usable, 20 → 80 %; 7.4 kW single-phase, η = 0.9

Find: Time.

• E = 60 × 0.6 = 36 kWh
• t = 36/(7.4 × 0.9) = 5.4 h

Answer: ≈ 5.4 h (overnight)

Worked example: DC fast charging

Given: Same 36 kWh; Average 100 kW over the session

Find: Time; current at 350 kW on 800 V.

• t = 36/100 h = 21.6 min
• I = 350 000/800 = 437.5 A (liquid-cooled cable)

Answer: ≈ 22 min; ≈ 440 A

Common mistakes

• Wrong: Expecting peak kW for the whole session. — Right: Use average power; above 80 % charging slows a lot.
• Wrong: Fast charging a cold battery. — Right: Pre-condition while driving to the charger for full power.

Applications

• Home & workplace: Wallboxes with smart scheduling and solar integration.
• Highway corridors: 150–350 kW fast chargers for road trips.
• Fleets & heavy trucks: Depot charging and megawatt charging systems.

Key takeaways

• AC via on-board charger; DC direct to battery.
• t = E/(P_avg η); use average, not peak, power.
• CC–CV: fastest 10–80 %.
• Temperature and SOC limit charging power.

Going further

• Battery swapping: Replaces packs in minutes — used by some two-wheeler and Chinese car networks.
• Wireless charging: Inductive pads (SAE J2954) at 3.7–11 kW, dynamic charging research.
• V2G economics: Frequency regulation and peak shaving revenues vs battery wear.