Typically, charging stations with power ratings below 22 kW are categorized as AC slow chargers. Among these, 7 kW AC chargers are the most common and are well-suited for both residential and commercial use due to their practicality and cost-effectiveness. However, you might wonder: why do 7 kW DC chargers also exist in the market?
7 kW DC charging stations are relatively rare but can exist for specific use cases and market conditions. Here's why such stations might be deployed:
Vehicle Compatibility: Some smaller electric vehicles, e-bikes, or low-speed EVs have limited charging capabilities and are designed to work with lower power DC chargers.
Consistent Power Delivery: Unlike 7 kW AC chargers, which depend on the vehicle's onboard converter, 7 kW DC chargers deliver a consistent 7 kW directly to the battery, bypassing any limitations of the onboard charger.
The key difference between a 7 kW AC charger and a 7 kW DC charger lies in where the power conversion occurs and their specific applications. Here's a detailed breakdown:
| Comparison Items | AC 7kW Charger | DC 7kW Charger |
|---|---|---|
| Charging Speed | Slower. It needs to convert AC to DC via the on-board charger of the vehicle. | Faster. Directly supplies DC power to the vehicle battery. |
| Output Voltage | Commonly 220V (single-phase) or 380V (three-phase), e.g., around 220V±10% for household ones. | Varies according to the vehicle battery, usually in the range of 200 - 750V. |
| Output Current | For 220V, 7kW charger, about 32A (I = P/U = 7000W/220V≈32A), adjustable within a safe range. | Varies with different voltages. For example, when the output voltage is 350V, it is about 20A (7000W/350V = 20A). |
| Charging Efficiency | About 85% - 95% due to the conversion loss in the vehicle. | Around 90% - 98% as it directly outputs DC. |
| Equipment Structure | Relatively simple, mainly including control and protection circuits for AC input. | More complex, with rectifiers and other components to convert AC to DC. |
| Charging Interface | Different from DC, following specific AC charging interface standards. | Different from AC, with its own DC charging interface standard. |
| Price | Generally lower. | Higher due to more complex technology. |
| Application Scenarios | Suitable for places where vehicles park for a long time, such as shopping mall parking lots and residential areas. | Preferred in locations requiring rapid charging, like highway service areas and large charging stations. |
While 7kW DC chargers are not standard on most modern EVs, they play a special role in meeting specific needs, including cost, grid limitations, vehicle compatibility, or usage scenarios. Their deployment is often driven more by strategic considerations than by a preference for lower charging speeds. If you want to install a charger at home and your car supports an AC charging port, 7kW AC charger is a better choice.
