Fast Charging and Slow Charging Interfaces for Electric Vehicles

For new energy vehicles powered by batteries, charging is an essential part. Even if there may be battery replacement services similar to refueling in the future, it is conservatively estimated that within 10 years, various fast and slow charges will have to be relied upon to replenish power batteries. This time I will briefly introduce to you the charging system of new energy vehicles.
The charging system can be divided into two methods: regular charging and fast charging. Judging from the appearance and size, the difference between the charging ports is actually very simple. The fast charging port is large and has 9 holes, and the slow charging port is small and has 7 holes. In this way, even novice users will not make mistakes. Generally, two charging ports will be designed at the front and rear of the car. Some models will also design two charging ports together, such as the front or rear of the car. Car owners can choose the charging method according to their charging time needs.

Car fast charging interface

Quick charging interface (fast charging)
Fast charging is a DC charging method. The charging current needs to be larger, which requires the construction of fast charging stations. It does not require the power battery to be fully charged, but only meets the needs of continued driving. In this charging mode, only 50% to 80% of the power battery can be charged in 20 to 30 minutes. The ground charging pile (equipment) directly outputs DC power to charge the vehicle power battery. The electric vehicle only needs to provide charging and related communication interfaces.

Car fast charging interface schematic diagram

The advantages of fast charging: short charging time, fast flow of charging vehicles, and saving parking area at the charging station.

Disadvantages of fast charging: lower charging efficiency, higher charger manufacturing, installation and working costs. The charging current is large and requires high charging technology and methods, which has a negative impact on the life of the power battery. It is easy to cause abnormalities in the power battery and pose safety risks. Moreover, high-current charging will have an impact on the public power grid and affect the power supply quality and safety of the power grid.

CC1 charging pile connection detection schematic diagram

Regular charging (slow charging)
This charging mode is AC charging. The external power grid provides 220V civilian single-phase AC power to the electric vehicle on-board charger, and the on-board charger charges the power battery. It usually takes 5 to 8 hours to fully charge.
The advantages of ordinary charging: the charging pile (charging box) is low in cost and easy to install. The power grid’s low valley power at night can be used for charging to reduce charging costs. During the charging period, the charging current is small and the voltage is relatively stable, which can ensure the safety of the power battery pack and extend the service life of the power battery.
Disadvantages of ordinary charging: The charging time is too long and it is difficult to meet the needs of emergency operation of the vehicle.

Fast charging interface
DC+: DC power positive
DC -: DC power supply negative
PE: Ground (ground)
S+: Communication CAN-H
S-: Communication CAN-L
CC1: Charging connection confirmation
CC2: Charging connection confirmation
A+: 12V+
A-: 12V-

Car fast charging interface wiring diagram

How do you confirm whether CC1 and CC2 are connected properly?
The following is the CC1 charging pile connection detection schematic diagram.
As you can see from the chart below, to determine whether the connection is normal, you can confirm it by the voltage at the detection point. Different voltages are obtained by dividing voltage by different resistors.

Then there is the CC2 vehicle control device connection confirmation schematic diagram.
After it is turned on, the two resistors divide the voltage to obtain a voltage of 6V, otherwise a voltage of 12V is obtained.

Taking the BYD e6 as an example, the vehicle body connection device is used to conduct and input external electrical energy to the power battery when the vehicle is charging. The charging port cover has damping characteristics, that is, check whether the resistance between “CC1” and “PE” on the charging port is 1KΩ; at the same time, you need to check whether the connection between the charging port and the power manager is normal.

Slow charging interface
CC: Vehicle control device connection confirmation
CP: Charging pile connection confirmation
PE: Ground (ground)
L: Three-phase alternating current “U”
N: Three-phase AC “neutral”
NC1: Three-phase alternating current “V”
NC2: Three-phase alternating current “W”
Normally NC1 and NC2 are empty.
L and N are the two wires connected to our household 220V.

How do CC and CP confirm whether the connection is normal?
The “cable control box” and the “vehicle control device” mutually confirm whether the connection is correct.

First, the “cable control box” will pass CP detection point 1 and detection point 4 to detect whether the voltage is 12V. If it is not connected properly, there will be no ground at detection point 4, and the voltage will not be detected. If the connection is good, detection point 4 is connected to the vehicle ground through PE, and the voltage is 12V at this time. After there is 12V power, the “cable control box” will connect S1 to PWM, otherwise S1 will be connected to +12.

Car slow charging interface

Then, the vehicle control device will detect the R3 resistance through CC to confirm whether the charging gun is connected to the vehicle socket. If not, the resistance will be infinite, otherwise there will be a corresponding resistance value.

Here, the vehicle control device will set the power of the on-board charger (usually set by the manufacturer by default):

The on-board charging device determines the maximum charging current of the control box on the cable through the duty cycle signal of CP. The general setting ratio is as follows:

At the same time, the on-board charging device will also determine the rated capacity of the cable through the RC on the CC.

Finally, after calculating the rated capacity of the charging cable and the current of the control box on the cable, the vehicle control device sets the maximum power of the on-board charger to their minimum value.

Having said so much, some people must ask: “Why are there two charging interfaces? Isn’t it good to unify them into one?” This is mainly determined by fast charging.

Car slow charging interface schematic diagram

You must know that the charging process of a vehicle is not just from the power grid to the battery, but also requires passing through charging piles, charging cables, charging plugs, and vehicle socket interfaces before entering the vehicle. From the previous principles, we also know that for AC charging, after entering the vehicle, it does not go directly to the battery, but also passes through the two levels of on-board charger and BMS.

For fast charging, compared with AC charging, the charging power is not limited to the specific charging voltage and current, ranging from 20kW, 40kW, 60kW to 200kW, 250kW, and 350kW. As long as the input (grid) and output (vehicle) support it, it can be done very well.

The power from the grid first enters the charging pile and then reaches the vehicle through the charging cable. Most charging cables are fixed on the charging pile, and the other end is a gun-shaped plug connected to the vehicle (this connection method is called connection method C in the standard).

There are also a small number of charging piles that are isolated and require an independent cable, with both ends connected to the charging pile and the vehicle (connection method B). As for the way the charging cable is fixed on the vehicle (connection method A), it has almost no application. AC charging can use connection mode B and connection mode C. For AC charging current greater than 32A and DC charging, only connection method C can be used.

Since the vehicle’s power system is a DC system, when charging with AC, AC power cannot directly charge the battery. It needs to go through a component called an on-board charger (OBC, On-board Charger) to convert AC to DC and transform the voltage according to the command of BMS before supplying it to the battery.

In this car charger composition diagram, there are two core components-ACDC rectifier and DCDC transformer (power unit in the picture). The former is used to convert alternating current into direct current that is acceptable to the vehicle battery, and the latter is used to adjust the voltage of the direct current.

According to the BMS command, the charging current and voltage are dynamically adjusted to adapt to the charging needs of the battery at different stages. For example, during constant current charging, as the battery power increases, the charging voltage also needs to increase. It is also responsible for converting low voltage and charging the 12V small battery.

During DC charging, the DC pile itself is an ACDC rectifier plus a DCDC transformer, which directly converts AC power outside the vehicle according to the needs of the BMS, replacing the role of the on-board charger. Therefore, DC charging piles are also called off-board chargers.