35cm × 35cm, 350 Kilowatts: The Satellite Terminal at the Heart of Fleet Charging

When a fleet depot commits to electrification at scale, the question of where the charging equipment goes becomes as important as how much power it delivers. A 50-bay bus garage cannot accommodate 50 large power cabinets. The physics of power distribution demands hardware at bay level; the economics and operational constraints of a working depot demand that it takes as little space as possible.

The Neutron DC Satellite Terminal is the hardware that resolves this tension. It stands approximately 1.5 metres tall, occupies just 35cm × 35cm of floor space, and serves as the power distribution node for a cluster of charging bays. Each connector port can deliver up to 600kW with the liquid-cooled cable upgrade. The same terminal supports any combination of Neutron's three connector types: side-mount, drop-down (NSNF0014DDC), and in-ground (NSNF0015GRC).

What the Satellite Terminal Actually Does

The Satellite Terminal is not a charger in the conventional sense. It contains no AC-to-DC conversion. It does not connect to the mains supply. Instead, it receives high-voltage DC from the Master Unit via a single DC bus cable and distributes that power to the connector ports it serves, under instruction from the Master Unit's power management system.

At each charging event, the vehicle requests a charge. The Satellite Terminal reports the request to the Master Unit, which allocates power from its total available capacity based on current demand across all terminals and all bays. If five bays are active simultaneously and two more vehicles connect, the Master Unit re-optimises the allocation in real time. No power is wasted on idle bays. No vehicle waits longer than the system's overall capacity requires.

The terminal also handles metering, communications (CAN bus and Ethernet), and the display interface that drivers and ground crew interact with. In the event of a fault at the terminal or connector level, isolation is at terminal level only: the rest of the system continues operating unaffected.

A Neutron Satellite Terminal in service at a London bus depot. The compact white column serves multiple bays; the Neutron Master Unit is visible further back in the depot.

Three Connector Types, One Terminal

One of the less obvious advantages of the Satellite Terminal architecture is connector flexibility. A single terminal can simultaneously serve bays fitted with different connector types, because the terminal is the hub from which any of the three Neutron connector types hang:

• Side-mount connectors: wall or post-mounted, the most common arrangement for new-build depots with clear wall runs.
• Drop-Down connectors (NSNF0014DDC): overhead gantry-mounted for covered depots where floor space is the constraint.
• In-Ground connectors (NSNF0015GRC): flush-mounted in the tarmac for zero above-ground footprint in open yards.

This means a single Satellite Terminal serving a mixed bay layout, part covered, part open yard, can simultaneously support an overhead connector on one bay and an in-ground connector on an adjacent bay. Operators are not locked into a single installation strategy at the point of deployment: the terminal hardware remains the same regardless of the connector type at the vehicle end.

Safety by Architecture

Conventional DC chargers present live high-voltage connections at vehicle level: the charger cabinet carries the full DC bus, and the cable between cabinet and vehicle inlet operates at 400-1000V DC depending on platform. This requires permanent safety exclusion zones around each cabinet and means that maintenance at bay level always involves isolation procedures.

In the Satellite Terminal architecture, there is no high-voltage equipment at bay level. The terminal's connector ports present less than 36V DC on their external surfaces until a handshake with a connected vehicle has been verified and the power path opened at the Master Unit. A technician can work at the terminal or disconnect a cable at bay level without isolating the system or the Master Unit. Only the specific connector path is de-energised, and only for the duration of that intervention.

The Full System: Master, Satellite, and Connectors

A typical 50-bay bus depot might deploy two 480kW Master Units (960kW total conversion capacity), eight to ten Satellite Terminals distributed across the yard, and a mix of connector types matched to the specific characteristics of each bay cluster. The total cabling between components is dramatically less than an equivalent installation of 50 individual DC chargers, because the high-current DC bus from the Master runs to each Satellite Terminal via a single cable route, not 50 separate conduit runs from the grid connection point.

For a detailed explanation of the Master-Terminal architecture and how it reduces civil works costs by up to 30%, see our article on scaling fleet depot charging to 4MW. For a full overview of how this architecture applies to van and HGV logistics depots, see our Fleet Depot Charging solutions page.

How Does the Satellite Terminal Architecture Work?

Understanding the satellite terminal's role requires understanding the full power delivery chain. Power conversion from AC mains to DC charging current happens once, in the Master Unit, which is housed in a plant room or weatherproof external cabinet away from the vehicle bays. From the Master Unit, a single high-voltage DC busbar cable runs to each Satellite Terminal. This DC bus operates at the system voltage — typically 500–1000V DC depending on the vehicle platform being served — and carries the full cluster capacity on a single cable pair.

At the Satellite Terminal, the DC bus is distributed internally to each connector port. There are no further power conversion stages: the terminal is a managed DC distribution point, not a converter. When a vehicle connects to a port, the terminal reports the charge request to the Master Unit, which opens the relevant power path and begins allocating current from the bus. The allocation is dynamic: if six bays are drawing simultaneously and a seventh vehicle connects, the Master Unit re-optimises the current distribution across all active ports in real time, without any intervention from the operator.

Power Sharing: How the Bus Manages Competing Demands

The DC bus from the Master Unit is a shared resource. Its total capacity is the rated output of the Master Unit — 240kW or 480kW per unit. The Satellite Terminals connected to that bus collectively cannot draw more than the Master Unit's rated output at any instant. The Master Unit's power management algorithm ensures this constraint is enforced while also prioritising vehicles based on configurable rules.

In practice, most fleet depots do not experience simultaneous maximum-demand charging across all bays. Buses arrive at staggered times; some are fully charged before others connect; battery management systems on the vehicles themselves reduce demand as state of charge rises. The Master Unit's real-time allocation makes effective use of this natural diversity, ensuring the available bus capacity is distributed to where it is needed most. The Electron CMS provides operators with historical demand data and peak demand profiles, which inform decisions about whether to add a second Master Unit as the fleet grows.

Cabling Reduction: The Economics of One Bus vs. Many Runs

A 20-bay installation of individual standalone DC chargers requires 20 separate high-current cable runs from the grid connection point to each bay. In a UK bus depot, each of those runs is typically 50mm² to 95mm² armoured cable, buried in conduit at a minimum 600mm depth. The material cost alone for 20 runs at an average 30-metre length is substantial; the groundwork cost — breaking, trenching, reinstating — multiplies it several times over.

The Satellite Terminal architecture replaces those 20 runs with one: the incoming AC supply to the Master Unit, and the DC bus from the Master Unit to the first Satellite Terminal. From there, short inter-terminal DC links connect each subsequent Satellite Terminal in the cluster. The total cable installed is a fraction of the standalone equivalent, and the groundwork reduces to a single conduit route rather than a grid of trench lines crossing the entire yard.

DNO Application: One Connection, Not Twenty

Each standalone DC charger rated above 75kW requires its own connection agreement with the Distribution Network Operator (DNO). For a 20-bay installation of 150kW standalone chargers, the operator would typically need a single high-power connection agreement covering the full site demand, but the technical complexity of specifying and agreeing that connection is front-loaded by the DNO's engineering review. What the Master-Satellite architecture simplifies is the on-site LV/HV infrastructure: there is one metering point, one incoming supply termination, and one main switch. The DNO review is straightforward because the load profile is simple.

By contrast, a retrofit of 20 individual chargers to an existing depot would often require 20 separate metered connections if each charger was a separate asset under a CPO or landlord billing arrangement. The Master-Satellite model keeps the metering point at the Master Unit, with sub-metering at Satellite Terminal level for per-bay billing granularity where required.

OCPP Communication: The Master as the OCPP Endpoint

The Satellite Terminal communicates with the Master Unit over a local CAN bus and Ethernet connection — an internal, high-speed industrial protocol optimised for real-time power management commands. OCPP does not run from the cloud to each individual satellite: the Master Unit is the single OCPP Charging Station entity that communicates with the Electron CMS or any third-party charge management platform.

OCPP 2.0.1 introduced a hierarchical EVSE model that maps precisely to the Neutron architecture. Under OCPP 2.0.1, a Charging Station contains one or more EVSEs, and each EVSE contains one or more Connectors. In the Neutron system, the Master Unit is the Charging Station. Each bay group served by a Satellite Terminal maps to one or more EVSEs within that Charging Station. Each physical connector port maps to a Connector object within its EVSE. This means the cloud platform — whether Electron CMS or a third-party CSMS — receives a single OCPP connection from the Master Unit, through which it can address, monitor, and control every individual connector across the full installation.

OCPP 2.0.1 also introduces Smart Charging profiles, which allows the CSMS to send composite charging schedules to the Master Unit specifying the maximum power available to each EVSE at each time interval. Electron CMS uses this capability to implement overnight load-shift schedules: the operator configures a grid demand cap for peak hours, and the Electron platform pushes the corresponding OCPP Smart Charging profiles to the Master Unit automatically. The Master Unit enforces the schedule locally, meaning charging continues to operate correctly even if the upstream network connection drops temporarily.

Cable Management and Footprint: Satellite vs. Standalone

The footprint comparison between the Satellite Terminal architecture and an equivalent installation of standalone chargers is stark, but the cable management story matters as much as the hardware size. A standalone 150kW DC charger has a floor footprint of roughly 0.5m × 0.6m for the cabinet itself, plus a 1.5m exclusion zone on each side, plus protective bollards. The total consumed bay width is typically 0.5–1.0m narrower than a standard bus bay, meaning adjacent bays are constrained during charging activity.

The Satellite Terminal's 35cm × 35cm floor footprint — smaller than a sheet of A3 paper — allows it to be positioned at the edge of a bay without encroaching on the parking envelope. In a 3.5m-wide bus bay, the terminal sits against the structural column or kerb line and leaves the full lane width clear. No exclusion zone is required because, as described above, there is no high-voltage equipment at the terminal: surface voltage is below 36V DC until a verified vehicle handshake opens the power path.

Cable management between the Master Unit and the Satellite Terminals is either overhead — running along structural steelwork or cable trays — or in a single buried conduit. In either case, there is one cable route to plan and install, not a separate route per bay. In covered depots, the overhead route is often the simplest: the DC bus cable is clipped to existing structural members and requires no groundwork at all beyond the incoming supply trench to the Master Unit cabinet.

Liquid Cooling and High-Power Delivery

Standard Satellite Terminal connectors operate at up to 250kW per port on air-cooled cables. The liquid-cooled upgrade increases this to 600kW per connector by circulating coolant through the cable core, removing the heat generated at full rated current and allowing a physically lighter and more flexible cable to carry the higher amperage.

The cooling circuit is managed entirely by the Satellite Terminal. There is no separate cooling infrastructure required at the connector end. For depots deploying high-capacity buses with 400kWh batteries or larger, the liquid-cooled option significantly reduces overnight charging dwell time per vehicle.

HV Direct and the MCS Upgrade Path

The Satellite Terminal is designed with the next vehicle generation in mind. As 800V battery platforms enter the UK bus and coach market, and as MCS (Megawatt Charging System) becomes the standard for high-capacity charging events, the terminal architecture supports the transition without requiring replacement of the bay-level infrastructure.

Neutron's HV Direct capability extends the Master Unit's output voltage range to support 800V operation. The Satellite Terminal passes this higher voltage to the connector, where an updated connector head (CCS2 to MCS) is the only hardware change at bay level. The terminal column, its mounting, the DC bus cable from the Master Unit, and the civil infrastructure all remain in place.