The world is entering a period of rapid buildout of EV charging infrastructure. Average total cost of EV ownership is falling below that of comparable internal combustion vehicles while EV adoption rates continue to trend upwards. Expect to see more and more electric vehicle chargers in parking lots and gas stations.
Porticos has broad experience in the engineering design of electric vehicle chargers. In this series of posts we’ll explore the intricacies of electric vehicle chargers from the perspective of new product development.
“It would be reasonable to suppose that an EVSE must be a much simpler device than a gas pump. The truth of the matter is that they are rather complex, with a unique set of engineering challenges.”
What is an EV Charger?
In simplest terms, an EVSE provides electrical power to EVs in order to charge their onboard batteries.
At low charging rates, EV Chargers act as a switch that allows 120, 208, or 240V AC power available in a home or commercial site to pass to the EV. Since batteries must be charged with DC, the EV then performs AC to DC power conversion with its on-board charger (OBC). In this situation, the main function of an EVSE is to safely manage when power is available to the EV, ensuring the connector is not energized when it is being handled by a user or when electrical faults occur.
At higher charging rates, EVSEs negotiate charging rates and perform the AC to DC power conversion in addition to the safety functions stated above. Along with these core functionalities, EV chargers commonly have energy meters, indicators or displays to inform the user of the state of the device, as well as wireless communications to relay performance data and facilitate billing.
Terminology
Before too many details are discussed, it would be wise to establish common terminology for some pieces of charging hardware. Luckily, the European Automobile Manufacturers Association has standardized on the following terms:
Charging Standards
There are two major standards for charging EVs with cables. SAE J1772 governs North America, and IEC 61851-1 governs the EU, with most of the rest of the world employing a mixture of the two. The exceptions are China and Japan who have developed their own standards.
These standards control the physical layout of the connector and vehicle inlet, the electrical safety strategy, the communications protocol between the EV and EVSE, and the overall performance of the system. Of great interest to the consumer is the last piece, as this defines the charging speed of each standard.
For SAE J1772, AC Level 1 represents charging by plugging a portable EVSE into a standard North American electrical outlet. AC Level 2 represents charging through a 240V outlet, commonly seen as oven, dryer, or water heater connections, using a portable or permanent charger. These connections, while convenient, are rather slow, requiring several hours to add appreciable range to an EV. Coupled with their low cost, AC Level 1 and 2 charging is ideal for residential locations where charging can occur overnight. DC chargers require more power than typical residential service can provide, and are also cost-prohibitive.
The table below details the various types of charging defined by the SAE and IEC standards, as well as how they translate into real-world charging rates for two modern EVs.
| Standard: | SAE Level, or IEC Mode: | Current (A) | Voltage (V) | Power (kW) | Charge Rate, mi/h, 2022 Ford Mustang Mach E, Base | Charge Rate, mi/h, 2022 Nissan Leaf Plus |
| SAE J1772 | AC Level 1 | 12 | 120 | 1.44 | 4.9 | 5.8 |
| 16 | 120 | 1.92 | 6.5 | 7.7 | ||
| AC Level 2 | 80 | 208-240 | 19.2 | 36* | 27* | |
| DC Level 1 | 80 | 50-1000 | 80 | 270 | 323 | |
| DC Level 2 | 400 | 50-1000 | 400 | 389** | 404** | |
| IEC 61851-1 | Mode 1: AC Single Phase | 16 | 250 | 4 | 14 | 16 |
| Mode 1: AC Three Phase | 16 | 480 | 11 | 37 | 27* | |
| Mode 2 AC Single Phase | 32 | 250 | 7.4 | 25 | 27* | |
| Mode 2: AC Three Phase | 32 | 480 | 22 | 36* | 27* | |
| Mode 3: AC Single Phase | 63 | 250 | 14.5 | 36* | 27* | |
| Mode 3: AC Three Phase | 63 | 480 | 43.5 | 36* | 27* | |
| Mode 4: DC | 200 | 400 | 80 | 270 | 323 | |
| Megawatt Charging System (MCS) *** | TBD | 3000 | 1250 | 3,750 | n/a | n/a |
* While many AC charging standards are capable of delivering more power, the Mustang Mach E onboard charger is capable of charging its battery at a maximum of 11kW. The Nissan Leaf onboard charger can charge at 6.6kW.
** The maximum charging rate is 115kW for the Mustang Mach E and 100kW for the Nissan Leaf Plus. Their batteries cannot handle this rate for long, however. Average charging rates are around 200mi/h over a one-hour span for both vehicles.
*** MCS is an emerging standard being developed by the CharIN electric mobility non-profit primarily for charging heavy-duty vehicles such as semi-trailer trucks, busses, and municipal waste trucks.
The above standards dictate the use of the following connectors:
Mliu92, CC BY-SA 4.0, via Wikimedia Commons
Mliu92, CC BY-SA 4.0, via Wikimedia Commons
Both connectors feature upper zones with pins responsible for communications and AC charging, and optional lower zones dedicated to DC charging. When the DC pins are included, these connectors are commonly referred to as Combo 1 and Combo 2 connectors.
As mentioned above, electrical safety, power electronics, user-centered design, and wireless communications are just a few of the many topics we will cover in detail in future posts. Be on the lookout for these to appear in the coming months, and please reach out to Porticos for answers to all of your EV Charger development questions!
