The North American Charging Standard (NACS) is a charging standard for electric vehicles launched by Tesla Inc. in November 2022. The NACS was initially called the Tesla Charging Connector, a unique charging interface for Tesla vehicles. This new charging standard addresses ac and dc charging on a single platform. The NACS standard is now publicly available for other manufacturers’ technical specifications.
SAE International said in June 2023 that it would standardize the NACS standard. This would help ensure that everyone in the business uses the same one. Several EV manufacturers have also shown interest in integrating the NACS standards into their upcoming vehicles.
When comparing NACS and CCS, the charge interface size is the main difference, as shown in Figure 1. The NACS interface is much smaller because it charges with ac and dc power using the same pins. Even though the NACS and CCS are physically different in size, it’s important to note that NACS and CCS use the same protocol (CCS) to talk between the EV and the charge station. This lets the charging station and car agree on the charging parameters and ensure the charge is safe.
Figure 1. A physical comparison of the NACS (black) and CCS (white) chargers. (Image: Tesla)
When a single-phase system is available, the NACS can deliver up to 48 A of current at 240 V. It translates closely into 11.5 kW of charging power. However, with three-phase power supply availability, the current delivery boosts to 80 A at 277 V, a significant increase in power delivery. The NACS can deliver up to 250 kW of power with version 3 of the Tesla Supercharger.
Figure 2. Simplified charging system of NACS. (Image: Tesla)
The NACS charging system
The entire NACS can be divided into three phases, as shown in Figure 2. The first phase is the charging station, the second is the vehicle connector, and the last is the vehicle itself.
The first phase, the charging station, is an assembly of different components, including controllers, that will charge the EV battery. The main components include the power source, isolation monitor, chargepost controller, and contactors.
The role of the isolation monitor is to measure the isolation between the earth and the vehicle chassis. The isolation monitoring is applicable when dc charging is carried out. The chargepost controller interacts with the vehicle controller to regulate the charging process.
The second phase is the vehicle connector, which consists of five pins for different purposes. Two pins are power terminals to deliver ac or dc power to the battery. The control pilot (CP) pin is a digital communication link between the vehicle and the charging station. The different charging states of the EV battery are communicated with the help of pulse width modulation.
The proximity pilot (PP) pin determines the status of the vehicle connector with the help of low-voltage signals. The ground pin, just like in any electrical connection, provides the ground path between the vehicle chassis and the earth.
The last phase, the vehicle, consists of the EV battery, onboard charger, vehicle controller, and necessary contactors. The purpose of the onboard charger is to convert ac power to dc power when an ac charging system is used.
It is worth mentioning that the contactors K3 and K4 are open during ac charging and closed during dc charging. It also implies that the onboard charger is inactive during dc charging. The vehicle controller works closely with the chargepost controller for critical safety through the CP and PP.
The NACS is compatible with vehicle-to-X power transfer, which means it’s compatible with vehicle-to-load, vehicle-to-grid, and vehicle-to-home. However, there’s still a requirement for technical specifications for vehicle-to-X power transfer to occur.
Summary
Tesla has the largest electric vehicle charging network in the world. Therefore, it seems logical for them to open their charging protocol to the public, now known as NACS. Such a move enables a win-win situation for their business and the EV users, including the government and private bodies. The EV manufacturers have welcomed this move and have shown interest in incorporating NACS into their EVs.
Additionally, the NACS charger is significantly smaller in size and compact in structure compared to CCS while still using the CCS protocol.
References
- North American Charging Standard, Tesla
- Opening the North American Charging Standard, Tesla
- SAE International Announces Standard for NACS Connector, Charging PKI and Infrastructure Reliability, SAE
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