The grid connection is the limit.
Not the charge points.
How Stackbox built a site controller that distributes the available grid capacity right at the location: containerised services on an industrial PC in the switch cabinet, wired to the electrical components over Modbus and to the back end over OCPP. Site intelligence that keeps working when the link upstream drops.
01 · Challenge
More charge points than the connection carries.
At a fast charging location, space is rarely the problem. The limit is the grid connection – and it cannot be moved at short notice. Anyone who still wants to expand has to distribute the available power more intelligently instead of waiting for more of it.
The connection is the hard limit
How many charge points fit a location is decided by the connected load, not by the parking bays. Reinforcing the grid takes time and is outside the operator's control – the build-out waits in the meantime.
Controlling from a distance is too slow
If load distribution is computed in the back end, it depends on the link to the site. Every delay and every dropout hits a decision that has to be made within seconds – and the installation still has to keep running safely.
Every component speaks its own protocol
Meters, contactors and the transformer sit on Modbus, the charge points on the OCPP back end, the distribution system operator behind its own gateway. Without a translating layer on site, any control logic stays piecemeal.
Otherwise you test on the construction site
Without simulation, load management can only be verified once connection, switchgear and charge points are physically in place. Every change turns into a site visit – and every mistake shows up in live operation.
Load distribution is a control task at the installation, not a back-end feature. It needs readings by the second, direct access to the switching devices, and a decision that is still made when the link upstream is gone. That layer is exactly what is missing between charge point and grid connection.
02 · Solution
A computer in the switch cabinet that runs the site itself.
For a major player in the e-mobility sector, Stackbox built a site controller: modular, containerised services on an industrial PC right at the location. It measures, decides and switches on site – and reports to the back end instead of waiting for its instructions.
Industrial PC chosen for site conditions
Environmental conditions, connectivity and required performance determine which hardware is even an option inside the switch cabinet. The choice fell on an industrial PC that serves as one common platform at every location.
Software in containers, not as a monolith
A purpose-built device-container component deploys the services onto the device in containerised form and runs them there. Each building block can be updated or replaced on its own, without touching the rest of the site.
Load distribution over Modbus, in real time
A dedicated load-management service talks to the on-site electrical components over Modbus and distributes the available power between charge points and grid connection – within limits configured per location.
Back-end integration over OCPP
The device-management module maintains a persistent WebSocket connection to the CSMS. The controller appears there as a regular device and can be controlled and monitored remotely with the familiar OCPP means.
Grid-side functions included
Reactive power compensation for power quality, remote configuration of the circuit breakers for maintenance and load distribution, plus integration with the distribution system operator's gateway wherever that communication is foreseen.
A virtual site for testing
A Modbus simulator acting as a slave, a station simulator extended to speak Modbus, and a cloud-hosted virtual site controller replicate a complete location. Integration and regression tests run on that, before any hardware is on site.
System architecture
Industrial PC in the switch cabinet · containerised services
Protocols & components
03 · Impact
What the location can do afterwards.
The site controller turns the grid connection into a managed resource: available power is distributed on site, the installation stays capable of acting without a link, and things are verified before anyone drives out.
Load distribution happens at the location – not at the end of a mobile connection
The site keeps controlling itself even when the link to the back end drops
The controller is remotely operated and monitored through the existing back end like any device in the network
Direct access to meters, contactors and circuit breakers in the switchgear
Containerised services can be updated individually, without touching the site
pieces of on-site hardware needed to run integration and regression tests
Stackbox · Site Controller
Is your location hitting the connection limit?
We look at topology, meters and charge points and tell you how much charging power is possible without reinforcing the grid – and what a site controller has to do to get there.
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