The "Invisible Lifesaver" of EV Chargers: Relay Adhesion Detection, the Last Line of Defense for Electrical Safety

In the daily operation of AC charging piles, relay adhesion detection acts as an "invisible judge" safeguarding user safety. As the core mechanism controlling the on/off state of the main circuit, relays are constantly exposed to high-current impacts and are highly prone to contact welding—commonly known as "relay adhesion"—caused by arc erosion. Once adhesion occurs, the risk of a live gun cable persists even after the charger sends a stop command, exposing users to 220V/380V electric shock hazards when unplugging the connector.

To prevent such incidents, compliant AC charging piles must strictly implement two detection logics: pre-charge static detection samples the voltage at the gun end when the relay is disconnected, allowing startup only after confirming no residual mains power; post-charge dynamic detection verifies both voltage and current after the stop command is issued, double-checking that the circuit is fully cut off. These two detection methods are not only the last line of defense against live gun cables, but also mandatory market access requirements under national standards including GB/T 18487.1.

It is worth noting that some manufacturers cut costs by replacing hardware detection with software logic, overlooking the fact that relay feedback contacts can fail as well. A robust relay adhesion detection system can also enable safety early warning by monitoring contact voltage drop and temperature rise, locking the equipment at the early stage of faults. This extends device lifespan while avoiding the trust crisis brought by accidents.