Slow Charging

Slow charging (AC charging) refers to replenishing an electric vehicle's (EV) high-voltage battery using lower-power alternating current (AC). Compared to high-output DC fast charging, AC charging operates at lower current and voltage levels, resulting in longer charging times that typically take several hours or even overnight to reach a full charge. It serves as an essential pillar of the EV charging ecosystem, primarily utilised for overnight home charging, workplace charging, or extended parking durations.

Working Principle and Equipment Types

An EV battery pack stores electrical energy as direct current (DC), whereas the electrical grid supplies alternating current (AC). During AC charging, AC power from the grid is routed via the charger to the vehicle, where the built-in On-Board Charger (OBC) converts it into DC power before the Battery Management System (BMS) directs it into the battery pack.

In terms of equipment format, AC slow charging is generally divided into two main categories: 

Portable 3-pin EV charger: Plugs into standard domestic power sockets (such as a 230V household outlet), typically delivering between 1.5 kW and 3.3 kW, primarily intended for emergency top-ups.

Dedicated AC Wallbox: Wall-mounted or pedestal-mounted at parking bays, commonly delivering between 7 kW and 22 kW. These units primarily handle safety monitoring and power delivery, while the AC-to-DC conversion is handled entirely by the vehicle's OBC.

Technical Characteristics and Battery Preservation

Compared to high-power DC fast charging, AC slow charging offers notable benefits for battery longevity. With lower current and steady power delivery, minimal heat is generated during charging and electrochemical stress remains low. This significantly mitigates battery degradation and extends the overall operational lifespan of the traction battery.

Furthermore, installing AC chargers incurs substantially lower capital expenditure and places minimal strain on the electrical grid compared to high-output DC fast charging hubs. Given their compact footprint and simpler hardware, AC chargers are ideally suited for widespread deployment in residential carparks, condominiums, commercial office developments, and long-stay parking facilities.

Modern Applications and Charging Strategies

In day-to-day EV ownership, AC slow charging remains the primary charging method. While DC fast charging provides essential quick top-ups during long-distance driving, frequent DC fast charging can accelerate battery degradation. As such, most carmakers advise owners to rely primarily on AC charging for regular commuting, taking advantage of lower off-peak electricity tariffs overnight.

With advancements in Vehicle-to-Grid (V2G) and smart grid integration, modern AC chargers are increasingly equipped with bidirectional power transfer and scheduled smart charging capabilities. This enables an EV to not only charge safely but also discharge power back to the home or grid during peak demand periods, enhancing the overall efficiency and resilience of the energy ecosystem.