Multiplus 48/6500 ac load showing low value

Noticed something similar with my setup recently — running a Multiplus-II 48/5000 for the garden office and the AC load reading on VRM has started doing odd things.

Normally sitting around 150W during the day (couple of monitors, a small heater on low, misc stuff). But over the last week it's been flickering between 0W, 20W, and then jumping back to the correct-ish value within the same minute. Nothing's actually changed in the loads themselves — kettle still pulls its 2kW when I use it, so the inverter's clearly working fine.

Got a Cerbo GX here with a Carlo Gavazzi meter on the grid side. Few things I've been poking at:

• Meter comms — wondering if it's a flaky RS485 connection causing dropouts in the readings rather than actual load changes
• VRM polling intervals — could just be a display/logging artefact rather than real fluctuation?
• Firmware — updated the Cerbo a few weeks back, which is roughly when this started 🤔

Anyone else seen this after a Cerbo firmware update? I'm hesitant to roll back but it's bugging me that the data looks unreliable. Makes it hard to track actual consumption patterns.

Also curious whether this is purely a display issue or if it could affect the ESS calculations in any meaningful way — don't want it chasing phantom loads overnight when the batteries need looking after.

What are others seeing? Worth raising a support ticket or is this a known quirk?

@DownsWanderer welcome to the forum — great to have you here, and don't worry, these head-scratching VRM moments are pretty much a rite of passage!

I had something oddly similar when I first commissioned my van build with a Multiplus-II. Turned out my AC load readings were doing strange things because of a firmware mismatch between the Multiplus and the Cerbo GX I was using to report everything.

Worth checking:

• Are your VE.Bus firmware versions all consistent?
• Is VRM pulling data through a Cerbo or Venus device, or direct?
• Any non-linear loads on that circuit (certain LED drivers can confuse the measurement)

The garden office context is interesting — any chance you've got something cycling on and off in the background? A fridge compressor or similar can make the reported average look misleadingly low if the polling catches it mid-cycle.

What does the live readout in VictronConnect show versus VRM?

@DownsWanderer — great first post, jumping straight in with a proper technical question rather than just "hi I'm new" 😄

Had something similar on my boat setup a while back. Turned out the AC load reading was going haywire because of a dodgy CT clamp connection on the Multiplus. Worth checking those are seated properly.

Also — is your VRM firmware up to date? There was a patch a few months back that sorted some dodgy AC load reporting on the Multiplus-II specifically. Check your Remote Console → Device List → Firmware and see if anything's pending.

What's your grid/generator input situation? Sometimes when the inverter's switching between modes the readings can drop temporarily and look wrong in VRM's graphs.

@DownsWanderer the AC load figure in VRM is calculated, not directly measured — it's essentially grid input + inverter output - known loads. If your CT clamp is slightly misaligned or there's a loose connection on the AC input wiring, the maths goes wonky and you get weird readings.

Few things to check:

• CT clamp orientation (arrow pointing correct direction)
• AC input voltage sensing — sometimes a dodgy neutral connection causes this
• Check if it correlates with grid fluctuations using the VRM advanced graphs

Also worth looking at whether it's consistently low or just spikes down momentarily. Consistent offset usually means a wiring/sensing issue. Intermittent drops can be firmware-related — Victron pushed a few Multiplus-II updates lately that touched power measurement.

What firmware version are you on?

@MarineGaz that's a useful clarification on how the figure's calculated — so if either the grid input reading or the inverter output reading drifts slightly, the derived AC load value goes wonky as a result?

Wondering whether a firmware update could shift calibration on one of those inputs without touching the other, which would explain why @DownsWanderer's readings changed suddenly rather than gradually.

Have you checked whether the Multiplus itself agrees with VRM? The local CCGX or Cerbo display should show the same figures — if they match, the calculation is consistent at least. If they differ, there's something odd in the data pipeline to VRM.

Also worth checking: are there any AC loads connected to the AC2-out circuit rather than AC1-out? Those can sometimes be accounted for differently depending on firmware version.