The charging handshake is the sequence of checks and communications between the EV, the charging station (EVSE), and, sometimes, the CPMS/back-end that confirms it is safe and authorized to start charging. It covers electrical safety signaling, connector locking, authentication, and (for DC) detailed power negotiation controlled by the vehicle’s Battery Management System (BMS).
What Is a Charging Handshake?
A successful handshake ensures four things before energy flows:
– The vehicle is properly connected
– The system confirms grounding/earthing and basic electrical safety conditions
– The user/vehicle is authorized to charge (where required)
– The charger and vehicle agree on charging parameters (especially for DC)
Handshakes occur at the start of every session and are a common root cause of start failures.
Why Charging Handshake Matters in EV Charging
Handshake reliability directly drives session success rate and customer satisfaction. It matters because it:
– Prevents unsafe energization of the connector or cable
– Ensures the charger only delivers power when the EV is ready
– Enables billing integrity by tying authorization to a specific session
– Reduces failed starts and support calls
– Supports advanced features like Plug & Charge and managed charging
– Helps troubleshoot issues where chargers appear “online” but cannot start sessions
For public charging, handshake failures are one of the most visible user pain points.
How the Charging Handshake Works
Handshake steps vary by AC vs DC charging:
AC Charging Handshake
AC charging uses control signaling between EV and EVSE (often via the control pilot):
– Plug-in detection and proximity signal indicates connector is inserted
– Control pilot communicates available current limits from the EVSE
– Vehicle validates supply, grounding, and internal readiness
– Connector locking engages (depending on vehicle/connector design)
– If authorization is required, the charger checks the RFID/app/token with CPMS
– Charging begins when the vehicle closes internal relays and draws current within allowed limits
In AC, the vehicle controls charging through its onboard charger, while the EVSE mainly provides a safe supply and current limits.
DC Charging Handshake
DC fast charging includes deeper digital communication and negotiation:
– Physical connection and locking
– Safety checks and insulation monitoring readiness (system-dependent)
– Authentication and authorization (RFID/app/terminal/Plug & Charge)
– Vehicle and charger exchange parameters: voltage, current limits, target SoC
– The BMS requests power, and the charger ramps output accordingly
– Continuous monitoring adjusts limits based on temperature, SoC, and faults
DC handshakes are more complex and therefore more prone to interoperability edge cases.
Common Causes of Handshake Failures
Typical failure points include:
– Poor connector insertion or worn pins/contacts
– Cable or connector locking mechanism faults
– Grounding or protection device trips (RCD/RCMU behavior)
– Communication issues (pilot signal issues, PLC communication issues for ISO 15118)
– Authentication failures (RFID token not recognized, backend timeout)
– Firmware compatibility and protocol mismatches in multi-vendor environments
– Certificate management issues (expired certificates for secure connections)
– Vehicle-side BMS restrictions or safety checks failing
These failures can appear as “charger not working,” even when the charger hardware is healthy.
How Handshake Issues Are Diagnosed
Operators typically diagnose handshake issues using:
– CPMS event logs (authorization results, stop reasons, error codes)
– Charger diagnostics logs and fault codes
– Session traces showing when the process failed (pre-authorize vs power ramp)
– Comparing multiple vehicles on the same charger to isolate vehicle vs charger issues
– Inspecting connectors/cables for wear, contamination, or damage
– Checking network connectivity and certificate status
Clear logging and consistent error mapping are critical to reduce time-to-repair.
Typical Use Cases
– Public charging networks are reducing failed start rates
– Fleet depots optimizing reliability and readiness
– Installer commissioning and acceptance testing for new sites
– Troubleshooting roaming sessions where authentication is complex
– Deploying ISO 15118 Plug & Charge with certificate-based trust
Key Benefits of a Robust Charging Handshake
– Higher session success rate and better user experience
– Safer operation through proper validation before energization
– Better billing integrity and fewer disputes
– Improved interoperability across different EV models and charger vendors
– Faster troubleshooting through clear diagnostic events and logs
Limitations to Consider
– Handshake complexity increases with DC charging, roaming, and Plug & Charge
– Vehicle firmware differences can cause inconsistent behavior across models
– Poor site connectivity can turn authorization into a failure point
– Without good logging, handshake failures are hard to diagnose remotely
– Physical wear on cables/connectors remains a common real-world cause
Related Glossary Terms
BMS Handshake
OCPP
ISO 15118
Plug & Charge
Certificate Management
Session Success Rate
Charger Diagnostics
Cable Locking Mechanism
EMC Compliance
Charging Curve