GX displaying charge current from Inverter

Been scratching my head over something similar with my own setup and wondered if anyone else has run into this.

Running a Cerbo GX with a Victron Phoenix 500VA (VE.Direct connected) in my tiny house build, purely for emergency backup rather than continuous use. The Cerbo insists on displaying it as "Inverter/Charger" even though the Phoenix is inverter-only — minor annoyance, but not the issue.

The real oddity: when the inverter kicks in, my DC loads reading on the Cerbo jumps up noticeably — figures that don't match what's actually being drawn by my 12V circuits. Took me a while to realise the GX seems to be calculating a phantom charge current from the inverter side and lumping it in with genuine DC consumption.

My suspicion is it's a measurement/calculation quirk — the Cerbo works out DC loads as a derived figure (battery current minus inverter AC output minus solar input), and if the Phoenix efficiency losses aren't being accounted for properly, that gap shows up as phantom DC load.

Has anyone:

• Seen this with a Phoenix specifically, or other inverter-only units misidentified as inverter/chargers?
• Found a way to correct the device type in VictronConnect or via the GX settings?
• Confirmed whether this is just cosmetic or whether it's actually skewing SOC calculations?

Worth noting I've got Fogstar lithium cells with a separate BMS, no Victron battery, so the Cerbo is relying on a BMV-712 for battery data — not sure if that changes the maths at all.

Curious what others are seeing.

Has anyone checked whether the Phoenix is actually in inverter mode or if it's somehow seeing a back-feed and misreporting? On my narrowboat I had a weird one where the Cerbo was showing charge current from the Phoenix because there was a slight voltage differential causing confusion on the VE.Direct bus.

Worth checking in VRM > Advanced > Raw Graphs — is the current genuinely bidirectional or just displaying oddly?

Also, what firmware is the Cerbo on? There was a known quirk in some earlier versions where the Phoenix 500VA specifically would occasionally report its output current on the wrong register. Victron community forum has a thread on it if you search "Phoenix 500 charge current VE.Direct".

What does the device list in the GX menu show for the Phoenix — is it listed as inverter or charger?

@AGM_Pro raises a fair point about back-feed, but I'd look at this slightly differently.

On my shepherd's hut build I had the Cerbo reporting spurious charge current figures from a Phoenix 375VA — turned out the VE.Direct cable had a marginal connection on the Phoenix end. The GX was interpolating garbage data and presenting it as charge current rather than throwing a comms error.

Worth checking:

• Reseat the VE.Direct connector both ends
• Check firmware — Phoenix units on older firmware can misreport operating mode to the GX
• In VictronConnect, look at the raw device state; if it's showing "inverting" but the Cerbo disagrees, that's your smoking gun

Also worth confirming there's no BMS or MPPT on the same VE.Direct network feeding conflicting current data that the Cerbo is attributing to the wrong device.

Bit of a tangent from what @AGM_Pro and @Bomber78 are discussing, but has anyone ruled out the VE.Direct cable itself as the culprit? I had something similar on my narrowboat where the Cerbo was showing odd readings from a connected device — turned out to be a dodgy VE.Direct connection causing garbled data.

Worth trying:

• Swap the VE.Direct cable if you have a spare
• Check the device list in VRM to see what the Phoenix is actually reporting its mode as
• Is the 500VA the only load path, or could something else be back-feeding through that circuit?

Also curious — what firmware is the Cerbo on? I've read that some older builds had quirks with how Phoenix units reported current direction. Could be worth forcing an update before chasing a hardware fault.

@ExJoiner's VE.Direct angle is worth pursuing, but before swapping cables — check the VE.Direct RX/TX pins aren't corroded; tin-can humidity is brutal on those tiny connectors.

More likely culprit though: the Phoenix 500VA has a Power Assist quirk where it can briefly report negative DC current during AC waveform transitions, which the Cerbo GX logs as "charge current" — it's a firmware interpretation issue, not actual back-feed.

Pull the VRM portal data and check if the phantom current spikes correlate with load changes on the AC output side. If they do, that's your answer right there.

Updating the Cerbo GX to the latest Venus OS (currently v3.x branch) tightened up precisely this kind of misreporting — I saw identical behaviour on my own setup before the update sorted it.

Good shout from @OldSailor on the pin check — burnt that particular finger myself on the Wayfarer when I had a dodgy VE.Direct connection sending phantom readings to the Cerbo.

One thing nobody's mentioned yet: check whether AC loads are connected to the inverter output while you're also feeding in from shore power or solar via a charger. I had the Cerbo briefly showing charge current from my Phoenix 375VA because of exactly that — the device was essentially seeing circulating current during a brief overlap condition.

Quick test: disconnect everything from the AC output side and observe whether the reading normalises. Took me an embarrassingly long Sunday afternoon to figure that one out, involving three cups of tea and one muttered apology to my boat.

Might be completely unrelated to your tin but worth five minutes before diving deeper.