Where does AC become DC?
The technician opens the door of DC charger 1. Behind it: stacked power electronics, fans, thick copper bars.
Inside the AC charge point next to the hotel there is little more than a switch, protection and a meter.
The questionWhat does it take to turn grid current into the current a battery accepts?
Alternating current arrives at 400 volts on three phases, through the site's connection and its protection.
Select each step to see what it does.
230 V × 16 A, a simple wallbox or a household socket
√3 × 400 V × 16 A, the most common wallbox
√3 × 400 V × 32 A, the top of AC charging
800 V × 375 A, a fast charger at full output
Computed from voltage and current. With AC, the onboard charger of the car can cap the power below what the connection offers.
| Current | Equipment | Converter | |
|---|---|---|---|
| Mode 2household or industrial socket | AC | cable with control box | in the car |
| Mode 3wallbox or public AC charge point | AC | fixed charge point | in the car |
| Mode 4DC fast charger | DC | fixed charger | in the charger |
The modes are defined in IEC 61851-1, which applies to charging equipment up to 1,000 V AC and 1,500 V DC. The control and protection box in a Mode 2 cable has its own standard, IEC 62752.
Why the charger asks before it switches
A DC charger connects its output to the battery directly, at several hundred volts. That is why nothing flows at first: car and charger exchange their limits, the charger checks the connection, and only then do the close.
During charging, the car keeps asking for new values and the follows. The battery decides, the charger delivers. How that shapes the power over a session is shown in the charging curve.
Check your understanding
3 questions. Answer all of them to complete this stop. Each answer explains itself.
What does the DC/DC converter in a fast charger do?
Turning AC into DC is the rectifier's job, measuring is the meter's. The DC/DC stage matches the battery.
Which charging mode is a DC fast charger?
Mode 3 is AC from a fixed charge point, Mode 2 AC from a socket with a control box in the cable. DC charging is Mode 4.
What power does a three-phase connection at 400 V and 16 A provide?
√3 × 400 V × 16 A is about 11 kW. At 32 A it is about 22 kW, on one phase at 16 A about 3.7 kW.
- Contactor An electrically operated switch for high currents; in a DC charger it connects the output to the car only after both have checked the connection and matched the voltage. EV charging fundamentals, stop 04 Glossary
- DC/DC converter The stage of a DC charger that turns its internal DC voltage into the voltage and current the car asks for, moment by moment. Glossary
- IEC: IEC 61851-1:2017, Electric vehicle conductive charging system, Part 1: General requirements. https://webstore.iec.ch/en/publication/33644. Checked 09 Oct 2026.
- IEC: IEC 62752:2024, In-cable control and protection device for mode 2 charging of electric road vehicles. https://webstore.iec.ch/publication/59658. Checked 09 Oct 2026.