When a driver plugs in, a short conversation happens before any energy flows. The car tells the charger it is connected, the charger tells the car how much current it may draw, and both keep checking that everything is safe. The rules for this conversation, and for the different ways of charging, come mainly from the international standard IEC 61851.
This guide explains the four charging modes, the control pilot signal behind Mode 3 and Mode 4, and how these low-level states appear in your charging management system through OCPP.
- Mode 1 and Mode 2 use ordinary or industrial sockets; Mode 2 adds a protection box in the cable.
- Mode 3 is dedicated AC charging equipment, the standard for wallboxes and public AC chargers.
- Mode 4 is DC charging with the converter in the charging station.
- The control pilot signals connection state (A–F) and maximum current (PWM duty cycle); OCPP statuses build on these states.
The four charging modes
| Mode | Supply | Protection and communication | Typical use |
|---|---|---|---|
| Mode 1 | Household or industrial socket, AC | No communication; relies on the installation's protection | Light vehicles; restricted or not allowed for cars in many countries |
| Mode 2 | Household or industrial socket, AC | In-cable control and protection device (IC-CPD) with control pilot | Portable "granny" chargers, occasional use |
| Mode 3 | Dedicated AC charging equipment | Control pilot and proximity detection in the station | Wallboxes, public AC chargers |
| Mode 4 | DC from an off-board charger | Pilot plus digital communication (e.g. ISO 15118, DIN 70121, CHAdeMO, GB/T) | DC fast chargers |
Mode 1
The car connects directly to a normal socket without any communication. Because there is no control or extra protection, many countries restrict or prohibit Mode 1 for electric cars. It is mostly relevant for e-bikes and very light vehicles.
Mode 2
A portable cable with a control box (IC-CPD) connects the car to a household or industrial socket. The box provides residual current protection and a control pilot signal. Mode 2 is convenient as a backup, but sustained high currents on household sockets can overheat wiring, so it is not a replacement for a dedicated installation.
Mode 3
The charging equipment is permanently installed, with protection and pilot control built into the station. This is what most people mean by an AC charger or wallbox, and it is the mode used by public AC charging points with Type 2 sockets in Europe. See our guide to connector types.
Mode 4
The AC-to-DC conversion happens inside the charging station, which supplies DC directly to the battery. Because the charger must follow the battery's needs precisely, Mode 4 uses digital communication on top of the pilot circuit.
The control pilot: how car and charger talk
In Mode 2, 3 and 4 a dedicated control pilot (CP) wire carries a simple but clever signal. The charger applies a voltage; the car changes it by switching resistors. The resulting voltage level tells both sides the current state.
| State | Pilot voltage (approx.) | Meaning |
|---|---|---|
| A | +12 V | No vehicle connected |
| B | +9 V | Vehicle connected, not ready to charge |
| C | +6 V | Vehicle connected and charging |
| D | +3 V | Charging with ventilation required (rare today) |
| E | 0 V | Error, e.g. short circuit or no power |
| F | −12 V | Charger not available or fault |
PWM: telling the car how much current it may draw
Once a vehicle is connected, the charger switches the pilot to a 1 kHz square wave. The duty cycle, the share of time the signal is high, tells the car the maximum current. In the common range, the current in amperes is roughly the duty cycle in percent multiplied by 0.6. A 50% duty cycle, for example, means about 30 A. A duty cycle of 5% has a special meaning: it tells the car to use digital communication, which is how high-level protocols such as ISO 15118 are started.
This is also how smart charging reaches the car on AC. When your management system sends a lower power limit to a charger through OCPP, the charger lowers the PWM duty cycle and the car reduces its charging current. Our guide to smart charging and load management explains the back-office side.
The proximity pilot
A second signal, the proximity pilot (PP), confirms that a plug is inserted and, on Type 2 cables, indicates the cable's current rating through a resistor in the plug. The charger never offers more current than the cable can carry. A damaged or wrong cable resistor is a common cause of "plugged in but not charging" problems.
From pilot states to OCPP statuses
Your charging management system does not see pilot voltages directly, but the charger translates them into OCPP connector statuses:
| Pilot situation | Typical OCPP 1.6 status |
|---|---|
| State A, no car | Available |
| State B, car connected, waiting for authorisation or not ready | Preparing, or SuspendedEV during a session |
| State C, charging | Charging |
| Charger limits current to zero | SuspendedEVSE |
| State E or F, fault | Faulted, with an error code |
Understanding this mapping helps when troubleshooting. A connector stuck in Preparing often means the car is in state B and waiting for authorisation, or that the pilot is not reaching state C. Our article on StatusNotification and connector statuses goes into detail.
Frequently asked questions
Which charging mode do public AC chargers use?
Mode 3. The charging station contains the protection and pilot control, and the car connects through a Type 2 socket or tethered cable in Europe.
Is Mode 2 charging safe?
Mode 2 includes protection in the cable box and is safe for occasional use on a suitable socket. For daily charging, a dedicated Mode 3 installation is recommended.
What does a 5% duty cycle mean?
It signals that digital communication is required, for example ISO 15118, rather than the simple PWM current signal.
Why does my charger show Preparing but not start?
Common reasons are missing authorisation, the car not requesting energy (staying in state B) or a cable problem detected through the proximity pilot.
See every connector's live status and fault codes from any OCPP charger in one dashboard. Explore Üreticy OCPP software or contact us.