AC charging speed

A wallbox can say 11 kW on the label, yet your car sits around 7 kW night after night. Then you pull up to a 350 kW fast charger and the number on the screen still does not match the headline. Most of the time, nothing is wrong. AC and DC fast charging convert power in different places, so the bottleneck moves.     What “charger” means here People use “charger” for the wallbox, the cable, or the whole station. In AC charging, the wallbox is usually EVSE hardware that supplies AC power safely and controls the session. On AC, the AC-to-DC converter is in the car (the on-board charger). On DC fast charging, the station does the AC-to-DC conversion and sends DC to the car.     The two power paths AC charging power pathGrid → EVSE/wallbox → vehicle inlet → on-board charger (AC→DC) → battery   DC fast charging power pathGrid → DC fast charger cabinet (AC→DC) → DC connector/cable → vehicle inlet → battery (BMS controls the requested current)     Home charging (AC): what caps your everyday kW Two things usually cap AC charging: the car and the circuit.   The car-side limit: OBC ratingThe OBC has a maximum AC input it can convert. If the charging power rises and then sits at a steady number every session, and it never approaches the wallbox rating, it’s often the OBC limit.   The home-side limit: circuit capacity and EVSE settingsA wallbox rating assumes the circuit can supply it and the EVSE is configured to allow it. Breaker size, wiring, run length, and voltage under load all affect what the EVSE can actually deliver.     Single-phase vs three-phase: why the same wallbox can look “faster” in one place than anotherIn many regions, AC charging power depends on whether the car and the site support single-phase or three-phase input. A vehicle that supports three-phase AC can often charge at 11 kW or 22 kW with the right supply and EVSE, while a single-phase-only setup may cap closer to the car’s current limit even if the wallbox label looks similar. This is why checking both the vehicle’s AC input details and your site wiring matters as much as the EVSE rating.   DC fast charging: why the number starts high and then drops DC power usually ramps up, hits a peak, then tapers. Your car draws high power only when the battery can accept it safely. As state of charge rises, most vehicles reduce power. Battery temperature matters as well; a cold or heat-soaked pack often limits power early. The site can cap it too—shared power, or the charger throttling to keep cables and equipment within temperature limits.     A simple example Example vehicle specs: AC (home): OBC rated at 7.4 kW DC (fast): up to about 150 kW when conditions are right   At home, you install an 11 kW-capable wallbox. You still see about 7 kW because the OBC sets the ceiling.   On the road, you charge at a 350 kW station. With a low SOC and a battery in a good temperature range, it can climb near the car’s limit (around 150 kW in this example). As the battery fills or warms up, the car tapers the power down.   On AC, you’re usually limited by the OBC or the circuit. On DC, you’re limited by the car’s charge curve and battery conditions—even if the station is rated higher.     On-board vs off-board, side by side Topic On-board charger (OBC) Off-board charger (DC fast charger) Location Inside the car Inside the charging station cabinet What it does Converts AC to DC for the battery Converts grid power to DC and sends DC to the car When it matters AC charging (home/work) DC fast charging (public stations) What usually limits power OBC kW rating, AC phase/current support, home circuit Car’s acceptance curve, battery temperature, SOC, plus site limits What to check in specs Max AC charging power (OBC kW) Max DC charging power; 10–80% time if listed       Find your real limit in the spec sheet Vehicle side OBC power (kW) or max AC charging power AC details (single-phase vs three-phase, max AC current) Max DC charging power (kW) Inlet type used in your region (compatibility, not “extra kW”)   Home side Breaker rating and continuous-load assumptions EVSE current setting (some units are adjustable) Cable run length and installation quality (long runs can reduce voltage under load)   What to do with what you find OBC is the limit → a larger wallbox will not make AC charging faster Circuit is the limit → wiring/breaker/panel work can increase AC charging speed DC acceptance or conditions are the limit → focus on battery temperature, SOC range, and choosing stations that match your car’s capability     A short note on DC handles and thick cablesDC fast charging runs much higher current and heat than AC charging, so cables are heavier and connectors need robust temperature monitoring. If you are specifying DC hardware, prioritize stable contact design, reliable temperature sensing, and consistent thermal performance, because heat is the real constraint at high current. For teams sourcing components, options like Workersbee DC charging connectors can be evaluated against those thermal and sensing requirements.     FAQ Is the wallbox the charger, or is the charger in the car?In AC charging, the wallbox is usually EVSE that supplies and controls AC power. The car’s on-board charger typically performs the AC-to-DC conversion for the battery.   Does DC fast charging use the on-board charger?In most cases, no. DC fast charging sends DC from the station to the vehicle, and the OBC is largely bypassed.   Why do two cars charge differently on the same home EVSE?They can have different OBC ratings and different AC input limits. The EVSE can supply the same AC power, but each car converts and accepts it differently.   Peak kW vs 10–80% time: what should I compare?Peak kW is a brief moment under ideal conditions. 10–80% time is usually a better planning metric because it reflects taper under real charging behavior.   Can adapters increase charging speed?Adapters can change physical compatibility. They do not increase the car’s OBC rating or its DC acceptance limits.   Can you upgrade an on-board charger?For most vehicles, it is not a practical upgrade because it is integrated into the vehicle’s power electronics and thermal design.   What does bidirectional on-board charging mean in practice?It means the car can also send power back out, not just charge. Whether it works depends on your model and the equipment you pair with it.