EV Charging Ports

by with Comments Off on EV Charging Ports
December 14, 2012

Those unfamiliar with the design or use of EVs may be interested to discover there is a heated debate going on about EV charging. As everyone is probably well aware, EVs’ Achilles heel is their range, which is a direct function of their battery capacity and thus their ability to charge quickly.

There are two basic schemes available today for charging EVs today. The most popular one (based on vehicles sold) is the SAE J1772 standard “charging station” that operates off of single-phase AC household current. The charging station manages the link from household

EV Charging Ports 1

Figure 1: J1772 Charge Plug and Port

power to the vehicle much like an automated disconnect or GFCI does. The vehicle then has an intelligent, on-board AC/DC converter that rectifies the provided household current and steps up (or down) the AC voltage to a voltage that allows for charging the on-board DC battery pack. The original standard was written to provide for 80-A charging at 240V, although most implementations are 30A or less. “Level 1” indicates 120VAC charging (usually less than 16A), “Level 2” indicates 240VAC charging (less than 32A). Actual current usage is defined by the AC/DC in the vehicle. Most EVs and plug-in hybrid sold today are provided with some form of portable J1772 (Level 1) charging station that the operator can plug into the wall. Open-source DIY kits have even sprung up for these chargers due to their popularity and simplicity (essentially a contactor w/processor to communicate with the vehicle to negotiate the connection).

The second (and much less popular) scheme is DC fast charging. In this case the charging station not only provides a connection to the vehicle but also rectifies and steps up the AC to DC and provides a DC source that can be directly connected to the vehicle.

EV Charging Ports 2

Figure 2: J1772 “Combo” Connector (both Level 2 AC and DC Fast Charging)

Direct DC charging has one primary advantage: the speed of charging. Every EV is designed to charge at slightly different rates, but when you consider the battery pack size (16kWh for the Volt, 24kWh for the LEAF, 85kWh for the upgraded Tesla Model S), it becomes readily apparent that with a maximum of 200A, 220V service at home, it takes a while to charge. If you need a charge in a hurry (especially crucial when on the road), high current and voltage is needed.

EV Charging Ports 3

Figure 3: Nissan LEAF J1772 Level 2 and CHAdeMO DC Fast Charge Ports

The primary detractor for DC fast charging is the requirement for a large and expensive power supply to provide the AC/DC conversion. This is not a DIY home project! Voltages greater than 400V and currents greater than 100A may be supplied to fast charge the vehicle (a depleted 24kWh LEAF battery can be recharged from nearly dead back to full in less than 30 minutes). These are not small systems and require a hefty electrical service from the local utility company to operate.

There is also a raging debate over the specification and connectors for DC fast charging, which has not been standardized yet. As of today, the two competing styles are the CHAdeMO and SAE J1772 “Combo.” CHAdeMO is a consortium of Japanese automakers that have specified a DC fast charge scheme and connector which has already been deployed on multiple vehicles (Nissan LEAF, Mitsubishi iMiEV, and others). The odd name is an abbreviation of “CHArge de MOve”, equivalent to “charge for moving,” also a pun for O cha demo ikaga desuka in Japanese, translating to “How about some tea?”.  This connector has the advantage of being the first put into production, as well as the flexibility of being deployed in conjunction with, or instead of, a Level 1 or 2 J1772 charge port.

The SAE J1772 “Combo” is, as the name implies, an extension of the original J1772 specification that combines DC fast charge contacts with the Level 1/Level 2 contacts in one connector and port. This simplifies the design, but the design is already at a disadvantage being second to show up to the party.

For certain this debate will rage on for at least a short while. Only time will tell which standard emerges as dominant.

Comments are closed.