Chargers talk OCPP to your CPMS — that stays. ConnectMQ carries everything around it: grid meter, battery and PV data for load management, live connector and session status for operator dashboards and driver apps, and events between your own backend services.
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PUBLISH charging/austin-04/grid-meter/power
{"ts":"2026-10-22T18:05:00Z","import_kw":342.8,"limit_kw":400,"pv_kw":12.4,"battery_kw":-60.0,"sessions":9}QoS 1 · TLS 8883 · PUBACK
OCPP connects each charger to the CPMS, but a charging site depends on more: the grid connection meter, on-site batteries and PV, the building load and the apps that need live availability. Integrating each of these point-to-point with the CPMS — and fanning charger status out to apps, maps and support tools — becomes the bottleneck as the network grows.
A site controller or gateway publishes grid import, battery state of charge, PV output and transformer temperature to the site’s topics, read over Modbus or the device’s own API.
Your CPMS keeps managing chargers over OCPP and publishes connector status, session start and stop and meter values to MQTT for every other consumer.
Your load-management service subscribes to site and charger data and calculates the power available per charger; the CPMS applies it to the chargers as OCPP charging profiles.
Driver apps and operator dashboards subscribe over secure WebSocket to retained connector status, and threshold rules alert operations when a site nears its grid limit.
Retained status per connector means an app or map shows live availability the moment it connects, then every change.
The CPMS publishes an event once; apps, billing, support and analytics each subscribe instead of all calling the CPMS API.
Per-topic ACLs keep site controllers, fleet or roaming partners and internal services to the topics they are allowed to see.
Meter data flows as it is measured, and limit commands to site controllers use QoS 1 on their own topics.
charging/austin-04/grid-meter/power
charging/austin-04/battery/state (retained)
charging/austin-04/cp-07/connector-1/status (retained)
charging/austin-04/limits/setNo. OCPP remains the protocol between chargers and the charging station management system. MQTT complements it by moving site energy data, charger status and session events between your CPMS, load-management service, apps and dashboards. ConnectMQ does not speak OCPP to chargers itself.
Measure the grid connection and other site loads, publish those readings over MQTT, and let a load-management service calculate the power available per charger. The CPMS then sets the limits through OCPP smart charging profiles. MQTT keeps the loop from measurement to decision fast and decoupled.
Yes. Publish connector status as retained messages per charger; the app subscribes over secure WebSocket, gets the current status instantly and then every change. Read-only ACLs make sure apps cannot publish anything.
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