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SAE J2847/5: Communication Standards for Plug-in Vehicle AC V2L and V2V Charging
🛠️ Note: this article focuses on engineering interpretation, not clause-by-clause translation.
The SAE J2847/5 standard, published in October 2023, defines the communication requirements for plug-in electric vehicles (PEVs) to interact with customers for alternating current (AC) vehicle-to-load (V2L) and vehicle-to-vehicle (V2V) applications. This recommended practice extends the existing SAE J1772 interface to enable bidirectional charging and clear identification of operating modes.
Understanding SAE J2847/5: Scope and Purpose
SAE J2847/5 is part of the SAE J2847 series that provides functional messaging requirements for various PEV functions. Specifically, this section addresses customer-to-PEV communication for reverse power flow use cases identified in SAE J2836/3. The document establishes signaling and architecture requirements, leveraging the SAE J1772 proximity circuit to distinguish between conventional charging, V2L, and V2V modes. It also covers system variations—software-initiated and hardware-initiated controls—and includes safety requirements for the bidirectional onboard charger (OBC). Appendices provide guidance for Type 2 and GB&T connector recommendations.
Standard interactions with related SAE documents (J2836, J2847/1, J2931, J2953, J3072) ensure a comprehensive framework for vehicle-to-everything (V2X) communications.
Prox Resistor Signaling for Mode Identification
A critical design element is the use of the SAE J1772 proximity (prox) resistor circuit to signal the PEV’s onboard charger which operating mode is requested. By modulating the resistance value and thus the voltage on the proximity pin, the system can indicate whether the connection is for normal charging, V2L (single or dual outlets), or V2V power transfer. This approach maintains backward compatibility while enabling advanced functionality.
The table below summarizes the key prox resistor values and corresponding voltage thresholds defined in J2847/5 for a 120 V system at 12 A nominal (refer to the standard for full details and tolerances).
| Mode | Prox Resistor Value (Ω) | Approximate Voltage (V) |
|---|---|---|
| Normal Charging | 3300 | ~4.5 |
| V2L – Single Outlet | 1000 | ~2.9 |
| V2L – Dual Outlet | 330 | ~1.8 |
| V2V | 150 | ~1.2 |
Engineers must adhere to the tolerance requirements specified in the standard (e.g., ±1% or ±5% depending on the operating region) to ensure robust detection across temperature and manufacturing variances.
🛠 Design Insight: By reusing the SAE J1772 prox circuit, J2847/5 enables mode detection without additional pins or complex protocols. Combined with both software-initiated (digital handshakes) and hardware-initiated (dedicated switch sensing) control mechanisms, systems can be engineered for flexibility and failsafe operation. Always validate voltage level compliance under worst-case load conditions.
Engineering Design Insights and Safety Considerations
Implementing J2847/5 compliant systems requires careful attention to several design and safety aspects:
- Prox Resistor Accuracy: Using the incorrect resistor value or overlooking tolerance can misidentify the operating mode, leading to unsafe energy transfer.
- Voltage Tolerance Compliance: The detection thresholds must account for cable voltage drops, connector aging, and temperature effects.
- Bidirectional OBC Safety: The OBC must handle reverse power flow safely, including ground fault detection, overcurrent protection, and proper isolation.
- Software-Hardware Coordination: The handshake between vehicle control modules and the OBC must securely manage transitions between operating modes.
- Backward Compatibility: Systems must gracefully fall back to standard J1772 operation when connected to conventional EVSE that does not support V2L/V2V.
⚠ Common Pitfall: A frequent mistake in early implementations is failing to properly coordinate software-initiated and hardware-initiated controls. In all cases, the hardware layer must provide a failsafe that overrides software in the event of a communication failure. Always reference the full J2847/5 for detailed state diagrams and timeout requirements.
Frequently Asked Questions
- What is the primary purpose of SAE J2847/5?
- It defines the communication signals and architecture for plug-in vehicles to interact with customers for AC V2L and V2V bidirectional charging, using SAE J1772 as the base connector standard.
- How does the proximity resistor distinguish between different modes?
- The prox resistor value is set by the connected cable or device, causing a specific voltage on the proximity detection pin. The vehicle monitors this voltage level to determine whether to operate in normal charge, V2L, or V2V mode.
- What safety requirements are placed on the onboard charger (OBC)?
- J2847/5 requires the OBC to support bidirectional power flow with mandatory safety protections, including ground fault interruption, overcurrent limiting, and isolation monitoring, aligned with UL and ISO standards.
- Can J2847/5 work with international plug types?
- Yes, Appendix A of the standard provides recommendations for Type 2 (IEC 62196) and GB&T connectors to enable global applicability of AC V2L and V2V functions.
For engineers developing V2L or V2V products, close study of the latest SAE J2847/5 document is essential to avoid common integration pitfalls and to meet industry interoperability expectations.
