Short answer: Heavy-duty electrical switches inside the charger and car that connect and disconnect the high-voltage DC power circuit during charging.
Explanation
Contactors are high-voltage switches that physically close or open the electrical circuit between the charger and your car's battery. When you plug in and authenticate, the charger and car communicate to verify everything is safe. Only then do the contactors close, allowing high-voltage DC power to flow. When you stop the session, the contactors open to safely disconnect.
You might hear a distinctive click or thunk from the charger or your car when contactors engage or disengage. This is normal. The click at the start means the power circuit is connecting. The click at the end means it is safely disconnecting. If the contactors detect a fault (ground fault, overcurrent, communication loss), they open immediately to protect both the car and the charger.
Contactor failures are one reason a charger might show an error or fail to start a session. If the charger cannot close its contactors safely, it will not deliver power. This is a safety feature, not a bug. The charger is refusing to connect rather than risking an unsafe connection.
Where you'll see this
- On the charger screen
Common confusion
The clicking sound at the start and end of a DC fast charging session is the contactors, not something breaking. It is a normal and expected part of the charging process.
Example
When you hear a loud click from the charger 2-3 seconds after plugging in, that is the high-voltage contactors closing. If you hear rapid clicking without charging starting, it may indicate a contactor fault.
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