High level of enthusiasm in electric vehicles from the automakers and the governments of the world and increased awareness of consumers on the impact of automobiles on environment have created an opportunity for EV/PHEVs to be adopted as major mode transportation by common man. The biggest hurdle in bringing the EVs to the mainstream is the lack of readily available refueling infrastructure which can eliminate charge anxiety of EV/PHEV owner. The gasoline vehicle owner can drive around without being concerned about running out of options if he is out of fuel. Though the cost of refueling electric vehicles is significantly lower, the market needs to close the gap of lack of refueling infrastructure for it to compete with gasoline vehicles.
Based on the specification of the manufacturer, the Energy Storage Unit (ESU) or a battery pack can be charged at certain power supply (source) voltage and charging profile which is generally managed by a management system. Theoretically, charging at higher voltage would move the current faster and that would recharge the ESU faster; but there are several safety constraints when using high voltages and significant reduction in the life of the battery pack. The charging management system which is generally a part of the ESU needs to ensure the safety for the rated high voltages.

The following are the 3 levels of charging and their definition specified by the National Electrical Code (NEC, 1999). This standard has been widely accepted by the automakers across the world. The outlet standardization is now been done and published by society of automotive industries (SAE, 2009) and has been accepted by most automakers.

  Voltage Current Power Frequency Phase Outlet Standard
Level I 120 12 1.44 60 single NEMA 5-15 R
Level II 208/240 32 6.7/7.7 60 single SAE 1772/3
Level III 480 400 192 60 three NA

The total charging time of the ESU is dependent on its capacity and the charging voltage. In a household facility, the time needed to charge the ESU at those voltages could be as high as 8-10 hours. Some ESUs as discussed above allow being charged at higher voltages for a faster recharge.

The Charge Replenishment Unit (CRU) would service all electric vehicles with Li-ion batteries with the specific voltage rating. The rating of the CRU installed would depend on the demand (driven by EV/PHEV models) at the location. Market research shows that most the EV/PHEVs would be allowed to be charged at either Level I or Level II and Level III would be favored by more niche markets with large battery units. The CRU system with the plug-point spread around could be accessed by as many 6 vehicles at the same time depending on the design and layout.

The CRU system is basically an automated station with user interface which distributes and manages the power supply to the plug points distributed at the parking spots based on the consumer requirements, battery state and the overall load on the CRU. Each CRU is designed specifically to the standard rating as needed. The main components of the CRU remain unchanged but will need different rating depending on the specifications. CRUs are equipped with hardware for wireless network communication and secure transaction/customer authentication.

Further, CRUs can be designed with retractable cable / plug, which is accessible to the customer after authentication.


  • Operation Voltages: 110V (Level I) / 220V (Level II) / 480 (Level III)
  • Operation Temp Range: 20° F – 245° F
  • Charging Unit Type: Conductive charging using SAE standard Electrical Output / Cable (JL 1772/3)

The CRU is connected to a high voltage power source from the utility provider based on the specific requirement of the installation. If a high voltage source is used, then a step-down voltage reducer might be necessary.

The following are the key components of a CRU:

  • Housing
  • Automation Software / Hardware
    • Battery State of Charge Monitoring System
    • Security and safety control features
    • Reporting and printing
    • Other operational software
  • Power Transfer and metering
    • Power distribution Unit (Intelligent Power)
    • Metering and security system
  • Communication (Secure Transaction and data transfer)
    • User Interface (Software and Hardware)
    • Wireless secured database connectivity (GPRS/CDMA)
    • Secure Transaction (Point of Sale)
    • Status/State Communication
    • Plug-in points
    • Secured Coupling – power point connection

During the operation in a CRU, current is transferred at high voltages. The CRU design ensures complete safety using automated locks and protective features necessary to handle the electrical danger. During the charging of the EV, power transfer is not initiated until the cable is secured. The CRUs are kept under periodical maintenance schedule to ensure the unit and its safety systems are not physically damaged due to inclement weather or user handling. Further, the system status is updated automatically to monitor the CRUs from an offsite station.

Charge Replenishment Unit