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Powering Up

Let’s Discover AC Level 1 and Level 2 Chargers

Let’s dig into charging your EV. Alternating Current (AC) charging is the most available as this is the type of current that the world’s power grid uses. This technical article will focus on Level 1 and 2 AC charging. DC fast-charging is a subject large enough to need its own article, which will be released in a future issue of EV Builder’s Guide, so stay tuned! 

…charging speeds might be limited by power availability from the grid or, in some instances, battery health and status as reported by the battery management system.

Level 1 Versus Level 2 Charging

Level 1 Charging

This is AC charging based on a 120V circuit. While this charging type is slow, it uses a standard residential electrical socket, meaning it is available virtually anywhere.

Level 2 Charging

This is AC charging on a 220V circuit. This standard charging connection is available at most public and private charging stations. A charging power of 6.6 kW is standard in most residential installations, however, charging capacity of up to 19 kW can be found in commercial installations.

Standard Charging System Components

Most modern battery charging systems have five separate components to ensure safe and efficient charging of the battery banks. These include:

  • On Board Charger (OBC)
  • EV Charge Controller (EVCC) (Sometimes a function of a VCU or a MCU)
  • 1772 Port
  • EV Service Equipment (EVSE)
  • DC/DC Converter

OBC

The onboard charger is responsible for converting AC current from the electrical grid into DC current that can be used to charge the batteries. The EVCC or VCU controls the rate at which it charges. The OBC typically has three input wires from the J1772 plug (L1, L2/N, PE) and two HVDC output wires connected to the battery bank. The onboard battery charger will also likely include a CANbus connection with two wires (CAN-low and CAN-high), used to communicate with other components in the charging system.

EVCC

The Electrical Vehicle Charging Controller (in some cases built into the function of a VCU), communicates with the BMS system, the OBC, and the EVSE to control safe and efficient charging according to vehicle battery and power grid status.

J1772 Port

J1772 is the standard connection protocol for most EVs and charging systems using Level 2 charging in North America. The port features three connections for power transfer and two connections (often referred to as Proximity Pilot and Control Pilot) for communication between the vehicle and charging station/EVSE.

EVSE

The EV Service Equipment (EVSE) is also known as a charging station. These are found installed in parking lots or inside people’s homes. They feature a J1772 plug on one side of the cable that connects the vehicle to grid power.

DC/DC Converter

The DC/DC converter takes the high-voltage DC power in the battery pack down to 12 volts, thus charging the 12-volt battery in the car. Its role is to replace the alternator in ICE vehicles. In some cases, the DC/DC converter is a function built into the onboard charger.

Calculating Charging Speed

Calculating the estimated charging speed is done using the following formula:

Battery Capacity to be Charged (kWh) / Charging Power (kW) = Charging Time (hours) 

So, if we have a 50 kWh battery pack that we need to charge to from 0% to 100% state of charge, and we are using a 6.6 kW OBC on a residential circuit, we would use the formula as shown below:

50 kWh / 6.6 kW = 7.57 hours 

This formula is helpful, but only as an estimate, as charging speeds often slow down as a battery approaches 100% state of charge to protect the battery from overcharging. Furthermore, charging speeds might be limited by power availability from the grid or, in some instances, battery health and status as reported by the battery management system.