What I learned integrating 30+ EV chargers into a live OCPP network

The assumption you start with: OCPP is an open standard. Therefore, integrating a new charger should be a matter of following the spec.

The reality: every manufacturer treats the standard differently. Some treat it as a strict contract. Others use it as a rough suggestion.

What diverges

Here's what you actually encounter in the field:

Custom status codes. OCPP defines a fixed set of status values: Available, Preparing, Charging, SuspendedEVSE, SuspendedEV, Finishing, Reserved, Unavailable, Faulted. Manufacturers add their own. Some chargers send Occupied — a status that isn't in the spec at all.

Non-standard field values. The Reason field in StopTransaction has a defined enum. Chargers send free-text strings. Your parser breaks.

Timing edge cases. The spec defines heartbeat intervals. Some chargers don't send heartbeats at the negotiated interval. Others send them multiple times per second. Your connection manager needs to handle both.

Silent reconnections. A charger that drops the WebSocket and silently reconnects mid-session creates a ghost session in your system. Your state machine needs to detect stale sessions and clean them up.

What good integration tooling looks like

Each manufacturer needs a thin adapter layer — a normaliser that maps their specific behaviour onto your internal state model. The OCPP message comes in raw; your adapter canonicalises it before anything downstream sees it.

For testing: you can't rely on a real charger being available. You need a simulator that can replay the specific message sequences each manufacturer produces, including the edge cases. That's what lets you catch the status-code divergence before it hits production.

What this taught me about standards

A standard defines a contract between implementations. But contracts only work when both parties have interpreted the clauses the same way. In practice, OCPP leaves enough ambiguity — and enough optional fields — that every manufacturer's implementation reflects their own engineering culture.

The standard is the start of the conversation, not the end of it. The integration work is figuring out what each charger actually does.