Some car owners perceive the charging station to be slow. According to common knowledge, a 7 kW charging station should ideally charge at a rate of 7 kWh per hour.
For instance, the power capacity of the battery in the Deep Blue S7 520Pro version is 66.8 kWh. In theory, it should take less than 10 hours to fully charge. However, in practice, the battery is typically not completely depleted before charging, resulting in shorter charging times. Despite this, the actual time required to fully charge is often higher than the calculated value.
Why is this the case?
Additionally, some attentive car owners pay attention to the charging power during charging sessions. They may notice that the actual charging power of a 7 kW charging station does not reach 7 kW, leading to concerns about potential malfunctions. As shown in the figure below, the vehicle’s display indicates a charging power of only 5.4 kW. Why does this discrepancy occur?
Today, let’s delve into the factors influencing the actual charging power when charging an electric vehicle with an AC charging station, as well as the underlying working principles. If you lack patience or interest in the technical details, feel free to skip ahead to the final solutions.
Several factors affect the actual charging power when an electric vehicle is charged using an AC charging station, as outlined in the diagram below:
Firstly, the power source from the grid determines the maximum charging power that can be utilized.
When applying for an electric meter from grid companies like the State Grid or Southern Power Grid, it’s advisable to request a larger capacity. For instance, if only a 3.5 kW capacity is requested, even with a 7 kW charging station installed, the maximum achievable effect will be limited to 3.5 kW, failing to fully exploit the charging station’s capability. Therefore, if intending to install a 7 kW charging station, a minimum of a 7 kW electric meter capacity should be applied for, or even larger.
Apart from power, the voltage stability of the grid also significantly affects the actual charging power. In some regions where voltage fluctuations are substantial, the nominal 220V voltage may drop to less than 180V. This voltage fluctuation, as shown in Figure 2—where the voltage is only 178.8V, is a primary reason for the power being only 5.4 kW. Additionally, excessively low or high voltage can trigger the under-voltage or over-voltage protection function of AC charging stations, leading to errors and halting charging. The next time a charging interruption occurs due to these reasons, drivers should not blame the vehicle or charging station. This issue lies with the grid.
Secondly, the vehicle side serves as the brain directing the entire charging system’s operation, and the actual charging power will not exceed the power demand specified by the vehicle.
So, what determines the power demand of the vehicle?
1. Vehicle settings: On the vehicle’s system, owners can adjust the charging current size, typically available options include 8A, 10A, 16A, and 32A.
2. Vehicle’s own status:
This includes factors such as the current battery level, temperature, etc. The vehicle dynamically adjusts its charging demand based on its own status to achieve a balance between safety and efficiency.
3. The onboard charger (OBC) inside the vehicle converts the AC input from the charging station into DC power before charging the battery. The rated power of the OBC is usually 6.6 kW or 3.3 kW, and even lower, such as 2 kW. For example, if the OBC’s power is only 3.3 kW, then even when using a 7 kW charging station, the maximum achievable charging power will be limited to 3.3 kW.
Finally, as the bridge between charging vehicles and the grid, AC charging stations determine the maximum power allowed to flow from the grid side to the vehicle side while ensuring safe operation.
The rated power of the charging station typically determines the maximum allowable power to enter the vehicle.Portable EV Charger
Currently, the most common rated power for charging stations is 7 kW. Additionally, there are 3.5 kW charging stations, which are often used for small electric cars or hybrid electric vehicles. Charging stations with 11 kW and 21 kW ratings are more commonly found in models with battery capacities exceeding 80 kWh. (Currently, the maximum battery capacity is around 100 kWh. With a 7 kW charging station, it can be fully charged overnight, or even if it’s not fully charged, it can continue charging the next day. Of course, 11 kW and 21 kW will be faster, but the charging station itself and installation costs will be higher. Additionally, some regions may not approve applications for charging stations exceeding 7 kW.)
The rated power of the charging station is indicated on its nameplate, typically located on the right side of the body.EV Charging Parts
To summarize:
1. Under normal circumstances, the actual charging power is the minimum of the power allowed by the grid, the rated power of the AC charging station, and the power demand of the vehicle, denoted as P. Additionally, factors from other aspects may also lead to a decrease in the power demand of the vehicle, resulting in actual charging power being less than P.
2. Under abnormal circumstances, such as issues with the grid (e.g., voltage fluctuations), charging station (the station itself and installation), or vehicle, any one of these factors may lead to actual charging power being less than P.
