Automatic generator start-up with Victron and Cerbo GX: complete configuration

In off-grid installations, the generator provides backup power on days when there is no sunshine. The Cerbo GX (or any GX model) can to start and stop it by itself depending on the battery status or power consumption, and the MultiPlus/Quattro uses it to charge and power loads whilst it is running. This is the full configuration and the errors that cause “the generator not to engage”.

Requirements

• Generator with automatic start (dry contact input or 12 V signal) or with an ATS/AMF module.
• GX device (Cerbo GX, Ekrano GX) connected to the MultiPlus/Quattro.
• GX relay (Cerbo relay 1 or 2) wired to the generator’s start input. If the generator requires 12 V, use an auxiliary relay.
• Generator connected to AC-in 2 on Quattro (AC-in 1 for mains) or to AC-in on MultiPlus.

Step 1: Configure the inverter for generator operation

In VEConfigure (or VictronConnect on the MultiPlus-II with recent firmware):

• Network tab: active “Weak AC input” (low AC input) and deactivates the “UPS function”. This increases the inverter’s tolerance to unstable voltage and frequency from the generators.
• Accepted frequency range: 45–65 Hz. Voltage: 180–270 V.
• AC input current limit: Set it to the generator’s actual power output minus 20 % (a 5 kVA unit at 230 V → approx. 16–17 A). If you leave it set too high, the inverter will overload the unit and it will shut down.
• Active PowerAssist: when the loads exceed the input limit, the inverter draws power from the battery rather than shutting down the generator.
• In Quattro: assign the generator input to AC-in 2 and the mains supply (if present) to AC-in 1.

Step 2: Enable automatic start-up on the GX

Settings → Starting and stopping the generator:

1. 1. Relay function: Generator start/stop (relay 1).
2. 2. Enable “Automatic start”.
3. 3. Configure the terms and conditions. Several conditions can be combined; the generator starts when any one of them is met and stops when none of them are met:

Condition	Example values (48 V lithium)	Comment
State of charge (SOC)	Start at 30 %, stop at 85 %	The most reliable status when the battery is connected
Battery voltage	Starts at 47.5 V, stops at 53 V	For banks without a reliable SOC; adds a delay of 30–60 seconds
Battery current	Starts at -80 A for 60 seconds	Heavy downpours
AC load on the inverter	Starts at 4,000 W for 30 seconds, then runs at 1,500 W	Avoid overloading the inverter
Inverter temperature	Starts at 60 °C	Summer support
Regular exercise	Every 7 days, 20 mins	Keep the engine running

4. Minimum operating time: 30–60 mins. Avoid short starts, as these can damage the engine. 5. Warm-up and cool-down time: 30–60 s. The GX waits before connecting loads and disconnects them before stopping. 6. Quiet hours: for example, 23:00 to 07:00, with stricter conditions (starts only when SOC reaches 15 %).

Step 3: Boot detection

Enable “Detect generator on AC-in”: the GX checks that voltage is actually reaching the inverter following the start command. If it is not, it triggers the “Generator not running” alarm, which you can receive on the VRM.

Step 4: Test

In the same menu, select “Manual Start”: the generator should start, the inverter should engage (the ‘Mains On’ LED should remain lit) and the battery should begin charging. Once the operating time has elapsed, it stops.

Why won’t the generator engage?

• Frequency out of range: Petrol-fuelled carburettor units produce 51–53 Hz at idle. Set the engine governor to 50 Hz or use an inverter unit.
• Unstable voltage: The inverter rejects the input and the Mains LED flashes. Weak AC is activated.
• Neutral not earthed: Many generators have a floating neutral. The inverter detects “neutral-to-earth voltage” and fails to engage. Please refer to the generator set and inverter manuals for information on the earth relay.
• Input limit too high: The group falls when the loads are connected, and the inverter disconnects it.
• Loads with a hard start (pumps): use PowerAssist and a conservative input limit.
• Incorrect AC input in Quattro.

Charging the battery using the generator

With DVCC and lithium batteries, the BMS limits the charging current (see DVCC). If the generator is small, also limit the charging current in VEConfigure to leave some headroom for the household loads: the generator’s power is split between charging and supplying the household.

For information on the reference connection of an off-grid system with a generator, see the Victron MultiPlus diagram.

We are authorised Victron Energy installers and provide free technical support for equipment purchased from FV Componentes. If the problem persists, please open a ticket at Technical support including the model, serial number and the link to your VRM installation. You can find diagrams and parameters on our Victron Resource Centre.