In AC charging the station delivers protected energy and it is the vehicle's onboard charger that converts it to direct current. In DC charging the conversion is done inside the station and the energy goes straight into the battery, so it reaches much higher power. Charging levels are separated by power and current type, with thresholds that depend on the country.
Short answer
The difference lies in where the energy is converted. In alternating current (AC), the station only delivers protected, communicated energy, and the vehicle’s onboard charger converts it to direct current. In direct current (DC), a power charger inside the station does the conversion and delivers the direct current straight to the battery. That is why DC charging reaches much higher power, but the station is more complex, more expensive and demands more of the electrical installation.
AC charging
The U.S. Department of Energy describes two equipment levels in AC:
- Level 1: a 120 V household outlet, with a power of about 1.9 kW. It is the portable cord that many vehicles come with.
- Level 2: 240 V in homes or 208 V in commercial buildings, with power from about 2.9 to 19.2 kW depending on the equipment.
These figures are those of the U.S. system. Voltages and power thresholds differ in other countries and under other codes. What is common: in AC the vehicle is the one that rectifies. The station, technically an electric vehicle supply equipment (EVSE), monitors the signal dialogue with the vehicle, measures, protects and energizes the connector only when the vehicle is connected and ready. That communication is explained in more detail in charging modes 1, 2, 3 and 4.
AC power is always limited by the lowest of three values: what the station delivers, what the cable withstands and what the vehicle’s onboard charger accepts. A 22 kW charger does not deliver 22 kW to a vehicle whose onboard charger is smaller.
DC charging
In DC, the conversion leaves the vehicle. The station equipment takes AC from the grid, normally three-phase, rectifies it and delivers controlled direct current to the battery. The Department of Energy notes that this equipment delivers up to 500 kW and that the range recovered in 30 minutes goes from about a hundred to more than two hundred miles, depending on the vehicle and its state of charge.
Here the vehicle does not just receive: it negotiates. The battery and its management system indicate what voltage and current they accept at each moment, and the charger follows them. That is why the power in a fast charge is not constant: it tends to be higher with a depleted battery and to fall as it approaches full charge.
Comparison
| Aspect | AC | DC |
|---|---|---|
| Where the energy is converted | In the vehicle, with the onboard charger | In the station, with a power charger |
| Station complexity | Lower: control, metering and protections | Higher: power electronics, cooling and communication with the battery |
| Power | Limited by the onboard charger | Limited by the station, the cable and the battery |
| Typical use | Home, office, parking lot, fleet with overnight charging | Highways, public stations and fleets with short stop times |
| Connector | The one for AC | The one for DC; in many vehicles it is an extension of the AC one |
| Effect on the grid | Continuous load of moderate power | High-power peaks, especially in groups of chargers |
How charging levels are classified
Standards and regulations define charging levels by power and current type. A common pattern distinguishes:
- Level 1: a standard AC outlet, with low power.
- Level 2: an AC station with intermediate power.
- Level 3: fast charging, in AC at high power or in DC.
The thresholds differ by country, and the connector requirements change as well. Typical connector families are SAE J1772 (Type 1), Type 2 and CCS for AC and DC, and CHAdeMO; more on them in Type 1, Type 2, CCS and CHAdeMO connectors. Different rules may use different thresholds for different purposes; when planning a project, state which one applies. The design and the settings are adapted to the local code and to the requirements of the utility.
What it means for the electrical installation
- Slow AC charging: it is usually solved with a dedicated circuit from a panel, adequate protection and, in groups, load management so as not to exceed the service entrance capacity. See electrical installation of a residential charger.
- DC fast charging: it requires a dedicated or enlarged service entrance and transformer, and a study of how the station affects the grid. See sizing a charging station.
- Power quality: DC chargers are power electronics and can contribute harmonics; the effect is set by the equipment and its installation.
When each one makes sense
It is not a competition between technologies, but a split by available time. If the vehicle spends hours parked (home, office, fleet in a depot), AC is enough and costs less. If the stop time is short (corridors, public transport, continuous operation), DC is justified. Many installations combine the two.
An example to fix ideas
Imagine a vehicle whose onboard charger accepts moderate power in AC and whose battery accepts much more power in DC. Connected to a high-power AC station, the vehicle takes only what its onboard charger can convert, even though the station could deliver more. Connected to a DC station, the bottleneck becomes the battery and its state of charge. The same battery, in two different stations, charges at very different rates: not because of the station, but because of where the limit is. When buying a charger, always compare the power of the station with what the vehicle it will serve accepts.
We help with the study of your station
If you are going to install chargers and need to know what capacity they demand from your transformer, your service entrance and your protections, we help with grid connection studies and primary engineering, done remotely. We quote according to your case from the form.
Related guides
- Electric vehicle: battery, onboard charger and motor
- Charging modes 1, 2, 3 and 4 for electric vehicles
- Charging connectors: Type 1, Type 2, CCS and CHAdeMO
- EV charger testing: Metrel A 1532 XA and A 1632
- THD: total harmonic distortion
References
- U.S. Department of Energy, Alternative Fuels Data Center, Electricity Infrastructure: https://afdc.energy.gov/fuels/electricity_infrastructure.html
Frequently asked questions
Why is DC charging faster?
Because the conversion from AC to DC is done in a power unit inside the station, which can be much larger than the charger that fits in the vehicle. The energy goes straight into the battery without passing through the onboard charger. Even so, the vehicle limits the power according to the temperature and state of charge of its battery.
Does an AC charging station need power electronics?
It needs control, communication and protections, but it does not convert the energy: the vehicle's onboard charger does that. That is why an AC station is simpler and cheaper than a DC one.
How are charging levels classified?
By power and by current type, but the thresholds differ by country and by code. A common pattern has a level 1 on a standard AC outlet, a level 2 on dedicated AC equipment and a level 3 for fast charging, in AC at high power or in DC. When planning a project, state which local code and utility requirements apply.