Configuring a three-phase Victron charger array

This is a procedural guide for actually setting up a three-phase Victron charger array — three identical MultiPlus-II or Quattro units on a 48 V LiFePO₄ marine bus. If you're still picking between a single, parallel, and three-phase topology, start with the Victron three-phase inverter/charger selection guide first — this article assumes you've already decided three-phase is the right choice.

The configuration you'll end up with answers seven separate questions:

1. Which physical unit is L1, which is L2, which is L3?
2. What's the charge profile (bulk / absorption / float / tail) for the lithium pack?
3. How does each unit talk to the BMS?
4. How do the three units coordinate so the BMS's charge-current limit is respected?
5. What is the shore-power input current limit, per phase?
6. What happens when shore is undersized (PowerAssist)?
7. How do you test that all of the above is correct before pulling away from the dock?

Get those right and the array runs reliably for the life of the boat. Skip any one and you'll see intermittent contactor disconnects, unbalanced phase currents, or charging that fights the BMS.

→ The configurator outputs your continuous AC load and battery DC charge limits — both required inputs to this setup →

Prerequisites — what you need on the bench before you start

Before powering up, verify all three units are on the same firmware version. Mismatched firmware is the most common cause of "VE.Bus error 17" on first commissioning. If they're not aligned, update them individually (one at a time, AC off, DC on, MK3-USB connected) before proceeding.

Step 1 — Physical wiring of the VE.Bus

The VE.Bus is what makes three independent inverter/chargers behave as one. It carries phase, sync, command, and telemetry — at RS-485 levels with a CAN-style framing layer on top. Get the topology right or the bus will be intermittent.

                Cerbo GX
                  │
                  │ VE.Bus
                  ▼
[Term]──Unit L1──cable──Unit L2──cable──Unit L3──[Term]
         │               │               │
         └─ AC out: phase L1 (+N + PE)
                         └─ AC out: phase L2 (+N + PE)
                                         └─ AC out: phase L3 (+N + PE)

Rules:

• One terminator at each end of the daisy chain. Skipping either causes random "VE.Bus error 11" (sync loss).
• Cerbo GX hangs off any free RJ45 socket on any unit — it's not on the end of the chain. It's a listener.
• Cable length total ≤ 100 m. On a sailboat, you'll never approach this.
• Star topology is not allowed. Pure daisy chain only.

Common wiring mistake: branching the Cerbo GX off a Y-splitter in the middle. Don't. The Cerbo's VE.Bus port is just another bus drop — pick any RJ45 socket on a unit that isn't already a chain endpoint.

Step 2 — VE.Bus System Configurator: assigning phase roles

This is the one-time tool that tells the array which unit is L1, which is L2, which is L3. Once written, the assignment is stored in non-volatile memory on each unit.

1. Plug the MK3-USB into a free VE.Bus RJ45 (any unit, any port) and the laptop's USB.
2. DC on, AC off. All three units should be powered from the battery but not energized from shore.
3. Run VE.Bus System Configurator (not VEConfigure3 — different tool). It scans the bus and lists the three units by serial number.
4. Click "Set up a new system". Choose Three-phase.
5. Drag-assign roles:
   • One unit → L1, master
   • Second unit → L2, slave
   • Third unit → L3, slave
6. Set AC output voltage (230 V for European installs) and frequency (50 Hz EU, 60 Hz US/Caribbean).
7. Click Send settings. The tool reboots all three units — about 30 seconds. After reboot the array is logically a three-phase device.

You only do this once. Subsequent per-unit configuration changes happen in VEConfigure3 on the master, which propagates to the slaves.

If you ever need to convert the array back to parallel single-phase or to single units, you must factory reset all three first — the System Configurator refuses to change topology in place.

Step 3 — VEConfigure3: charge profile and lithium settings

VEConfigure3 is the per-unit configuration tool. With the array three-phased, configuring the master propagates most settings to the slaves. A few (DC charge current; PowerControl current limit) are per-unit and must be set on each.

Open VEConfigure3 with the MK3-USB connected, point it at the master unit (it's labelled L1 in the device list), and configure these tabs:

Tab: General

Tab: Inverter

Tab: Charger

This is the most important tab. All three units must have the same charge voltages — the master propagates these to the slaves, but verify after the upload.

The DC charge current is per-unit. A 3 × MultiPlus-II 48/5000 array can push 3 × 70 A = 210 A combined — but if your BMS limits charging to 100 A, you must either:

• Set per-unit charge current to 35 A (3 × 35 A = 105 A, slight overshoot rounded by DVCC), or
• Leave per-unit charge current at the unit's maximum (70 A) and let DVCC throttle in real time. This is the recommended approach — DVCC adapts as cell temperature and SoC change, where a static cap doesn't.

If you go with DVCC throttling, leave each unit's DC charge current at its rated maximum (70 A on a 48/5000) and configure the cap in Cerbo GX (Step 6).

Tab: Virtual switch

For a marine install, leave Virtual Switch disabled. It's used to drive an external relay based on conditions (e.g. start a generator at 40% SoC) — the Cerbo GX does the same job more reliably via a generic "relay" function.

Tab: Assistants

This is where BMS-Assistant lives — covered in Step 4.

After configuring the master in VEConfigure3, click Send settings. The tool propagates charge profile and inverter settings to L2 and L3 automatically. Verify by reading L2 and L3 individually after — particularly the absorption and float voltages.

Step 4 — BMS-Assistant: how the chargers talk to the BMS

Three connection methods, in order of preference:

Method A — CAN-bus BMS (Lynx Smart, REC, Batrium, etc.)

The BMS publishes pack voltage, current, SoC, CCL, and DCL on the VE.Can / BMS-Can port of the Cerbo GX. The Cerbo arbitrates DVCC and tells the inverter array what to do. The chargers themselves don't need a BMS-Assistant configured — the Cerbo handles it.

Configuration on Cerbo GX:

• Settings → Services → VE.Can port → CAN-bus BMS (500 kbit/s)
• Settings → DVCC → Enabled
• Settings → DVCC → Controlling BMS → select your BMS by name
• Settings → DVCC → Limit charge current → Enabled

This is the cleanest, most robust setup. Use it if your BMS supports it.

Method B — VE.Bus BMS (Victron's pre-CAN-era BMS)

The VE.Bus BMS plugs into the same VE.Bus daisy chain. It uses a "Two-Signal BMS Support" Assistant on each MultiPlus-II to drive the charger and load disconnect lines.

Configuration in VEConfigure3:

1. Tab: Assistants → Add assistant → Two-signal BMS support.
2. Map AUX1 input to "BMS charge disconnect signal".
3. Map AUX2 input to "BMS load disconnect signal".
4. Configure all three units identically.

When the BMS detects over-voltage, it pulls the charge-disconnect signal — all three chargers stop charging instantly, regardless of what the master is commanding. Symmetric behaviour for over-discharge on the load side.

Method C — Voltage-only (no BMS comms)

Don't. On a marine LiFePO₄ install you should have a BMS that can talk to the charger. A voltage-only setup means the BMS's contactor is the only protection — and that means every cell-level fault becomes a hard disconnect, which is hard on the contactor and on you (sudden loss of AC).

If you absolutely must run voltage-only (e.g. a packaged drop-in pack with internal BMS that doesn't expose comms), set absorption voltage 0.2 V below the BMS's cell-over-volt threshold and accept that you'll see occasional contactor trips on hot days.

Step 5 — Cerbo GX: DVCC and the master orchestration

DVCC (Distributed Voltage and Current Control) is a Cerbo GX setting that coordinates all charge sources — the three inverter/chargers, MPPTs, DC-DC chargers — to respect the BMS's CCL. Without DVCC, each device sees only pack voltage and acts independently. With three chargers and several MPPTs, this is how packs end up over-charged.

On the Cerbo GX touchscreen (or web interface):

1. Settings → DVCC → DVCC: Enabled
2. Settings → DVCC → Limit charge current: Enabled
   • Set to the BMS's CCL minus 10% safety margin (e.g. 90 A if BMS publishes 100 A). If your BMS publishes CCL on CAN, this field is greyed out — Cerbo reads CCL directly.
3. Settings → DVCC → SVS (Shared Voltage Sense): Enabled
   • Lets the chargers use the BMS's pack voltage reading rather than their own — more accurate at high current.
4. Settings → DVCC → STS (Shared Temperature Sense): Enabled
   • Pack temperature comes from the BMS, not the inverter's internal sensor.
5. Settings → DVCC → Controlling BMS: select your BMS
6. Settings → System setup → Battery monitor: select the BMS
   • Not the MultiPlus-II's internal monitor.

Verify on the Cerbo's "Charge sources" view that all three MultiPlus-IIs appear with their per-phase charge current, and that the total respects the BMS's CCL.

Step 6 — PowerControl and PowerAssist: shore-input limits

Each MultiPlus-II has a configurable input current limit per phase. Set this to match the shore-power supply.

The PowerControl setting (in VEConfigure3 → General → Shore current) caps how much current the unit draws from shore at any moment. If shore is undersized, the unit reduces charging first, then load passthrough.

PowerAssist is the boost-from-battery feature: when AC load exceeds shore's available current, the inverter discharges the battery onto the AC bus to fill the gap. Configure:

• VEConfigure3 → General → PowerAssist: Enabled
• VEConfigure3 → General → PowerAssist boost factor: 2.0 (max 2× shore current as battery-sourced boost)

PowerAssist is the feature that lets a 16 A three-phase pedestal supply a 30 kW peak load — the missing 14 kW comes from the battery for the duration of the transient. On a sailboat with an electric induction range, this is what stops the marina pedestal breaker from tripping every time the cook flips on a burner.

The shore-current limit can also be set live on the Cerbo GX (Settings → System setup → Shore current limit). Useful for marina-by-marina adjustment without booting up a laptop.

Step 7 — Verification: the dockside test plan

Before you trust the array, run this sequence:

If any test fails, fix before sailing. The most common failure on first run is the BMS disconnect not propagating to all three units — almost always caused by missing the BMS-Assistant on one of the slaves (Step 4, Method B) or the Cerbo's DVCC controlling-BMS not being selected (Step 5).

Common error codes and what they mean

The Cerbo GX surfaces these on the front panel and remotely via VRM. Subscribe an email/SMS alert in VRM Portal so you see error 11 from the boatyard, not from the marina.

Firmware updates: do all three at once

A three-phase array running mismatched firmware will sometimes work and sometimes throw error 3 / 25 randomly. The supported procedure is to update all three units in a single session:

1. Disconnect AC (so the array isn't actively running).
2. Plug MK3-USB into unit 1.
3. Open VictronConnect or VEConfigure3 → Update firmware.
4. Apply the latest firmware. Wait ~3 minutes per unit for write + verify.
5. Move MK3-USB to unit 2. Repeat.
6. Move MK3-USB to unit 3. Repeat.
7. Power-cycle the DC bus. All three boot together.

The Cerbo GX firmware is updated separately and from any Cerbo GX firmware version you can talk to a MultiPlus-II from any 2024+ firmware — no need to upgrade Cerbo first.

After update, run the verification test plan (Step 7) again. Firmware updates occasionally reset PowerControl / PowerAssist values to defaults — check, don't assume.

A complete worked example: 3 × MultiPlus-II 48/5000 on a 50 ft motoryacht

System: 48 V / 60 kWh LiFePO₄, Lynx Smart BMS over CAN. Loads: induction range 7 kW, two AC units 4 kW total, watermaker 2 kW. Shore: 32 A three-phase CEE at home marina.

Total commissioning time, with all hardware on the bench and firmware pre-aligned: about 90 minutes. About a third of that is the laptop talking to the array — VE.Bus is not fast.

Putting it together

The order of operations matters — skip a step and the next one will silently misconfigure. Concretely:

1. Wire VE.Bus daisy chain with terminators at both ends.
2. VE.Bus System Configurator: assign L1/L2/L3 roles. (Done once, propagates to firmware.)
3. VEConfigure3 on the master: set inverter, charger, and lithium charge profile values. (Propagates to slaves.)
4. BMS comms: CAN-bus on Cerbo (preferred) or VE.Bus BMS-Assistant per unit.
5. Cerbo GX: enable DVCC, select controlling BMS, enable shared voltage and temperature sense.
6. PowerControl: shore-current limit per unit, PowerAssist enabled.
7. Verification test plan — eight tests, all must pass before first cruise.

Get those seven right and the array is set-and-forget for the life of the boat. The reason Victron documentation reads as long as it does is that any one of those steps left half-done shows up as intermittent disconnects three weeks later, not on the bench.

For the topology decision (single vs parallel vs three-phase) see the Victron three-phase inverter/charger selection guide. For the broader BMS context that DVCC depends on, see the electric boat BMS guide. For sizing the chargers in the first place, see the charger and inverter selection guide.