WebSocket

Chargers connect to Capacitor via WebSocket using the OCPP 1.6J protocol. The connection is established automatically when the charger is configured with the correct URL.

Connection endpoint

WebSocket URL

text

wss://capacitor.live/ocpp/:chargeBoxId

Example: wss://capacitor.live/ocpp/CHARGER-001

Connection requirements

Charger must be registered via the REST API first
WebSocket path must include the registered chargeBoxId
Protocol: ocpp1.6 (subprotocol negotiation)
Connection is validated before the WebSocket upgrade

Unregistered chargers will be rejected at the WebSocket handshake. Register the charger via POST /api/v1/chargers first.

Charger → Capacitor

OCPP messages sent by the charger to the backend:

Message	Description
`BootNotification`	Charger announces itself on first connection
`Heartbeat`	Periodic keep-alive (default every 300s)
`StatusNotification`	Connector status change
`Authorize`	Validate an idTag before starting
`StartTransaction`	Charging session has started
`StopTransaction`	Charging session has ended
`MeterValues`	Energy meter readings during session
`FirmwareStatusNotification`	Firmware update progress
`DiagnosticsStatusNotification`	Diagnostics upload progress

Capacitor → Charger

Commands sent from the backend to the charger (triggered via REST API):

Command	API Endpoint
`RemoteStartTransaction`	`POST /chargers/:id/remote-start`
`RemoteStopTransaction`	`POST /transactions/:id/stop`
`Reset`	`POST /chargers/:id/reset`
`UnlockConnector`	`POST /chargers/:id/unlock`
`ClearCache`	`POST /chargers/:id/cache/clear`
`TriggerMessage`	`POST /chargers/:id/trigger`
`ChangeAvailability`	`POST /chargers/:id/availability`
`GetConfiguration`	`POST /chargers/:id/configuration/get`
`ChangeConfiguration`	`POST /chargers/:id/configuration/change`
`UpdateFirmware`	`POST /chargers/:id/firmware/update`
`GetDiagnostics`	`POST /chargers/:id/diagnostics`

OCPP message format

OCPP 1.6J uses JSON-RPC over WebSocket. Messages have three types:

Call (request)

json

[2, "unique-id-123", "RemoteStartTransaction", {
  "connectorId": 1,
  "idTag": "USER001"
}]

CallResult (response)

json

[3, "unique-id-123", {
  "status": "Accepted"
}]

CallError (error)

json

[4, "unique-id-123", "InternalError", "Something went wrong", {}]