TECHNOLOGY BASICS: What are EVSEs?
Electric Vehicle Supply Equipment (EVSE) refers to devices that manage the transfer of electrical energy between the power grid and electric vehicles (EVs). Commonly referred to as EV chargers, these systems function as interfaces that regulate power flow—either from the grid to the vehicle for charging or, in some configurations, from the vehicle back to the grid or other electrical loads.
EVSE products are commonly advertised and categorized by their “levels” defined in the SAE J1772 standard. These levels are distinguished by nominal voltage and maximum current, with higher levels indicating higher energy throughput. AC and DC levels are defined in the tables below.
| Charge Method | Nominal Supply Voltage (V) | Max Current (Amp-continuous) |
|---|---|---|
| AC Level 1 | 120 VAC, 1-phase | 50 A |
| AC Level 2 | 208 – 240 VAC, 1-phase | 80 A |
| Charge Method | EVSE DC Output Voltage (VDC) | Max Current (Amp-continuous) |
|---|---|---|
| DC Level 1 | 50 – 1000 V | 80 A |
| DC Level 2 | 50 – 1000 V | 500 A |
AC Charging
AC charging delivers alternating current to the vehicle, where the onboard charger converts it to DC to charge the battery.
AC Level 1 typically operates at 120 V, single-phase, up to 50 A, providing a theoretical maximum throughput of 6 kW (120 V x 50 A). In practice, Level 1 charging is used primarily in residential contexts due to slower charge rates.
AC Level 2 operates at 208–240 V, single-phase, up to 80 A, with a maximum power delivery of approximately 19.2 kW (240 V x 80 A). This configuration is the most common for commercial, fleet, equipped residential, and workplace charging.
The actual charge rate achievable through a given charger may additionally be limited by vehicle-side constraints, including the onboard charger’s power conversion capacity and efficiency, state of charge, and thermal management systems. For example, a vehicle equipped with a 7.2 kW onboard charger will not benefit from connecting to a 19.2 kW AC Level 2 system, as charging current will be limited internally.
DC Charging
DC charging systems convert alternating current from the grid into direct current within the EVSE itself, bypassing the vehicle’s onboard charger. This enables higher power delivery directly to the battery.
DC Level 1, as defined in SAE J1772, operates from 50 to 1000 VDC and supports up to 80 A, providing a maximum theoretical throughput of 80 kW (1000 V x 80 A).
DC Level 2 extends the current capability to 500 A, allowing up to 500 kW (1000V x 500 A) in optimal conditions.
In practice, DC Level 1 chargers typically operate in the 20 kW to 80 kW range, depending on equipment design and available site power. This power level makes them well-suited for locations requiring faster charge rates than AC systems can provide, but without the extensive electrical infrastructure upgrades associated with higher-power DC Level 2 installations. Typical applications include fleet depots, workplace environments, and public charging sites.
DC Level 1 systems can also be considered for high-capacity residential or light-commercial installations, particularly where sufficient electrical service and appropriate utility coordination are available. In these cases, they offer substantial reductions in charging duration compared to AC charging while maintaining relatively compact equipment form factors and manageable installation complexity.
As with AC systems, DC charging has some limitations, typically on the vehicle end. Maximum charge throughput, determined by system’s wiring and terminals thresholds, and allowable thermal conditions, may constrain the realized power throughput to the equipment’s rated capacity.
Additional Considerations
Power delivery and installation methods can vary between chargers. Residential AC chargers are typically plug-connected for flexibility, while hardwired installations are preferred for higher-power or commercial systems to ensure consistent performance, safety, and load management.
Modern EVSE designs increasingly support bidirectional operation, enabling energy discharge from the vehicle battery back to a building, home, or the electric grid. These capabilities, often termed Vehicle-to-Grid (V2G) and Vehicle-to-Home (V2H), expand the role of EVSE beyond charging, allowing them to participate in energy storage, grid support, and resilience functions.