GenSet charger blocked by Victron charger

Had a similar head-scratcher on the boat last winter when I was trying to top up my LiFePO4s with the genny during a run of grey days.

The Victron Multiplus was essentially sitting in the circuit doing nothing useful (no solar, flat batteries) but it was still "present" on the DC bus and blocking the generator's charger from registering properly. Took me ages to work out what was happening.

From what I understand, it comes down to priority and detection logic — the Victron kit is so dominant on the system that other chargers can struggle to assert themselves. Some folks on here have mentioned it's worse when you've got a MPPT controller also wired in, as there are multiple devices all trying to "own" the charge state.

A few things that helped me sort it:

• Checked the charger enable input on the Multiplus — worth looking at whether it's inadvertently suppressing external charge sources
• Used VictronConnect / VEConfigure to look at the assistant settings, as some assistants can override external charging behaviour
• Made sure the battery monitor (I'm using a SmartShunt) was seeing the genny input properly

Not 100% sure I've cracked the root cause fully if I'm honest — it's been fine since but I'm not certain what actually fixed it.

Anyone else running a mixed Victron + generator setup had this? Particularly curious whether it behaves differently on 24v vs 48v systems, as mine's 24v. Would also be interested if anyone's used a Fogstar or other managed LiFePO4 pack — wondering if the BMS comms add another layer of complication here.

@BoatMel I'm having a similar puzzle with my garden office setup — did you manage to figure out what was actually causing the block?

I've got a Victron Multiplus 12/3000 and I'm wondering whether it's the PowerAssist function interfering, or whether it's something to do with the AC input current limit being set too low and the Multiplus just deciding to take over rather than pass through cleanly.

Was your genny a "pure" sine wave output? I've read that some cheaper generators confuse the Multiplus's input sensing. Did you end up adjusting anything in VEConfigure, or was it more of a wiring/isolation issue?

Really keen to understand this before winter hits and I'm relying on the genny as backup for the office.

@BoatMel yeah this got me proper confused on the motorhome last year 😤

The Multiplus has PowerControl which throttles incoming current — if it's misconfigured it basically swallows your genny's output before the charger even sees it properly.

Check your AC input current limit in VictronConnect — mine was set stupidly low, like 6A, so the Multi was hogging it all for loads and leaving nowt for actual charging.

Also worth checking if your genny's output is clean enough — cheap gensets produce rubbish sine waves and the Victron gets sniffy about it. Had to fiddle with the weak AC input setting to sort mine.

@Liz1979 garden office is probably same issue tbh, doesn't matter what the source is

Hey @BoatMel, classic one this! What you're likely seeing is the Multiplus in passthrough mode essentially acting as a bottleneck between your genny and the batteries. The inverter/charger wants to be in control of what goes to the bank, so it'll limit or even block the genset's own charging current if it thinks it knows better.

Worth checking your AC input current limit setting in VEConfigure — if it's set too low, the Multiplus will throttle incoming current from the genny accordingly. Also double-check your charge current settings aren't conflicting.

@Liz1979 for a garden office you'll want to look at whether your system is set up for ESS or standalone — makes a difference to how it handles external AC sources.

What firmware version are you running on the Multiplus? That can matter quite a bit with LiFePO4 setups.

@BoatMel worth checking your shore power / genny input current limit setting in VE.Config — if it's set too low, the Multiplus will actually consume most of the available input current itself before the external charger gets a look in.

Also, are you running ESS or just straight inverter/charger mode? In ESS particularly, the Multiplus can aggressively claim the AC input for its own charging algorithm and effectively starve anything else on that leg.

On my narrowboat I had a Victron IP22 and a Multiplus on the same genny circuit — absolute nightmare until I set the input current limit correctly and let the Multiplus manage everything rather than fighting with a second charger. Honestly easier to just let the Multiplus do all the heavy lifting from the genny and ditch the separate charger entirely.