How Does an Electric Vehicle Charging Station Work? Operating Principle (AC, DC, Safety)

When you connect an electric vehicle to the grid, a complex but quite orderly process actually begins: the vehicle and the station recognise each other, a decision is made about how much current can be drawn, safety checks are carried out, and only then does energy start to flow. In this article we explain the operating principle of an electric vehicle charging station end to end, in a technical but understandable way.

The short answer: an EV charging station is a controlled interface that transfers electricity from the grid to the vehicle safely. The station and the vehicle communicate continuously; the station directs the energy, monitors the protection circuits and manages authorisation. The real 'smart' work, though, lies in how the energy is converted and how it is kept safe.

What is the basic job of a charging station?

A common misconception is that the charger 'fills' the battery directly. In AC (alternating current) charging, the station is essentially a controlled switch and safety unit: it delivers the grid voltage to the vehicle, tells it how much current can be drawn, and cuts the circuit in the event of a problem. The vehicle's internal unit does the actual conversion work. In DC (direct current) fast charging, on the other hand, most of the conversion takes place inside the station.

Therefore an EV charging station has three basic jobs: (1) to establish safe communication with the vehicle, (2) to transfer the correct and safe amount of energy, (3) to handle authorisation and, where needed, remote management.

How do the vehicle and station communicate? (Control Pilot / pilot signal)

Before charging begins, the vehicle and the station 'talk' to each other. In Type 2 and CCS2 sockets, at the centre of this communication is the Control Pilot (CP), that is the pilot signal. Over the pilot line, the station and the vehicle confirm that they are connected to each other and agree on how many amps of current is permitted.

In summary, it works like this: The station sends a signal onto the pilot line. When the vehicle connects, it changes this signal to report states such as 'connected' and 'ready to charge'. Through the form of the signal, the station conveys the maximum current limit to the vehicle; the vehicle, according to its own onboard charger capacity, draws a value below this limit. This way, drawing more current than the cable or station can carry is prevented from the very start.

In DC fast charging, on top of this basic signalling, a more advanced digital communication layer comes into play. The vehicle and station continuously share information such as battery voltage, temperature, target state of charge and instantaneous current demand for seconds on end. Based on this data, the station adjusts its output voltage and current in real time.

Proximity detection and cable recognition

Alongside the pilot signal, most systems also have a proximity signal. Thanks to this line, the station can tell that the cable is actually plugged in and which current limit the cable in use is rated for. For example, a 16A cable and a 32A cable are recognised differently, and the system sets the limit accordingly.

The AC path: conversion happens inside the vehicle (Onboard Charger)

Most wall-mounted chargers (wallboxes) at home and at the workplace do AC charging. The alternating current from the grid is delivered directly to the vehicle over the cable. However, the vehicle battery charges with direct current (DC). This is where the vehicle's internal 'onboard charger' (in-vehicle charging unit) comes in: it converts the incoming AC into DC and feeds the battery at the appropriate voltage.

For this reason, the upper limit of AC charging speed is usually set not by the station but by the vehicle's onboard charger capacity. For example, even if the station can deliver 22 kW, if the vehicle's onboard charger is 11 kW the vehicle charges at 11 kW in practice. In AC charging, power from 7.4 kW up to 22 kW may be possible with a single-phase (one phase) or three-phase (three phases) connection.

Bemis E-V Charge AC Wallbox models (7.4-22 kW, Type 2) and Type 2 charging cables work precisely in this AC path: the station delivers AC energy safely and in a controlled way, while the vehicle handles the conversion.

The DC path: conversion happens inside the station (Fast charging)

In DC fast charging the logic is reversed. To avoid being limited by the onboard charger's restricted power, the conversion work is moved outside the vehicle, into the station. In DC fast-charging units such as CCS2, powerful converters (rectifier/power modules) inside the station convert the grid's AC into high-power DC and deliver this direct current straight to the battery.

Because the onboard charger is bypassed, much higher power can be reached in DC charging; this is why DC stations are called 'fast charging'. Here the vehicle continuously tells the station 'I want this much voltage and current'; the station meets this demand with its own power modules and adjusts the output according to the battery's instantaneous state.

• AC charging: The station delivers AC, and the vehicle's onboard charger does the conversion. The power limit is usually set by the vehicle.
• DC charging: Converters inside the station turn AC into DC and deliver it directly to the battery. Much higher power is possible.
• Type 2: The AC charging standard socket of Türkiye and Europe.
• CCS2: The DC fast-charging standard of Türkiye and Europe; it works via two DC pins added below the Type 2 socket.
• kW is power (speed), kWh is energy (the amount stored/transferred).

In AC charging the conversion is done by the vehicle's onboard charger; in DC charging the conversion is done by the station. The station's real job in every case is to transfer energy safely and in a controlled way.

How is safety ensured? (Protection, earthing, socket lock)

Because high power is involved during charging, safety is the most critical part of an EV charging station. The operating principle includes multiple layers of protection.

Residual current protection instantly cuts the energy when an unwanted leak (for example an insulation fault) is detected in the circuit, preventing the risk of electric shock. Earthing provides a safe path for the leakage current in the event of a fault, preventing surfaces such as the enclosure from becoming live. The station also monitors conditions such as overcurrent and overheating; if an anomaly is detected, it stops charging.

The socket lock is also part of safety: while charging is under way, the plug is locked by the station or the vehicle. This prevents the cable from being accidentally pulled out while energy is flowing; the lock does not open until charging is safely ended. On the physical durability side, the IP65-IP66 protection class shows that the unit is suitable for outdoor conditions against dust and water; the CE mark indicates that the product meets the relevant European conformity requirements.

What does the station continuously monitor during charging?

• That the connection with the vehicle remains sound at all times via the pilot signal
• Whether the current drawn stays within the agreed limit
• Whether there is a residual current, short circuit or earthing fault
• Temperature values (plug, cable, power modules)
• That the socket lock stays closed throughout charging

Authorisation: who starts the charge? (RFID / app / OCPP)

In a home setting, most wallboxes can be used so that charging starts as soon as the vehicle is plugged in. In common areas, workplaces and public stations, however, charging is required to be started by authorised people. The most common methods for this are the RFID card and the mobile app: the user taps their card or starts the session from the app, the station verifies the authorisation, and then permits the flow of energy.

This is where OCPP comes in. OCPP-compatible models allow the station to connect to a central management system (CSMS). This way, functions such as authorisation, remote start/stop, usage tracking and energy metering can be managed centrally. This is particularly important in workplace and fleet scenarios where multiple stations are operated.

If you want to look at OCPP and related concepts in more detail, we also have a separate guide explaining what the protocol does.

The stages of a charging session

The best way to summarise the operating principle is to see how a single charging session progresses from start to finish. A typical session goes through the following stages:

• 1) Connection: The cable is plugged into the vehicle and the station; the connection is detected via the proximity signal.
• 2) Recognition and agreement: The vehicle and station recognise each other via the pilot signal, and the maximum current limit is set.
• 3) Authorisation: If required, the session is authorised with an RFID card or app.
• 4) Locking and control: The socket is locked and the safety checks (residual current, earthing, temperature) are completed.
• 5) Energy transfer: On the AC path the vehicle's onboard charger, and on the DC path the station's converters, charge the battery.
• 6) Management: The station continuously monitors the current; as the battery fills, it gradually reduces the power.
• 7) Termination: When the target is reached or the user stops, the energy is cut, the lock opens, and the cable is safely removed.

Why does the battery slow down after 80%? (Taper / gradual reduction)

Especially in DC fast charging, you will notice that after the battery reaches a certain state of charge, often around 80%, the charging speed drops significantly. This is called 'taper', that is a gradual slowdown, and it is not a fault but a deliberate protective behaviour.

When batteries are full they cannot safely accept high current; to prevent overheating and the shortening of cell life, the vehicle requests progressively less current from the station. The station complies with this demand and lowers its output. That is why in fast charging the most efficient range is generally the portion from a low state of charge up to 80%; the final 20% can take disproportionately longer. In AC charging, because the power levels are already lower, this slowdown is often less noticeable.

Summary: what does a charging station actually do?

An EV charging station is a controlled device that communicates with the vehicle, directs energy safely, and, where needed, authorises and can be managed remotely. In AC models the vehicle handles the conversion, in DC models the station does; but in every case safety (residual current protection, earthing, socket lock) and correct communication (the pilot signal) are the heart of the operating principle.

Bemis E-V Charge is a Bursa-based domestic brand that manufactures every link of this operating principle, with AC Wallbox units, portable chargers, Type 2 cables, V2L/C2L adapters and CCS2 DC fast-charging units. With its CE and IP65-IP66 compliant, OCPP-compatible models, it offers products for both individual and corporate use.