120vac to 24vdc charger recommendation when generator is charging batteries

Running a 24V system off a generator during the winter months is something I've had to think through carefully with my static caravan setup, so this topic is close to home.

My situation is a Victron MultiPlus-II 24/3000 paired with Fogstar Drift 200Ah lithium cells. When solar drops off between November and February here, I rely on a petrol generator to top things up — and getting the AC-to-DC charging side right matters enormously.

A few things worth discussing:

Charger sizing vs generator capacity
Your generator's rated wattage doesn't translate 1:1 into usable charging watts. Inverter generators especially derate under load. I'd suggest not loading any generator beyond 70–80% continuously, so a 6,500W unit realistically gives you around 5,000W of sustained output. That headroom matters when the MultiPlus is also powering loads simultaneously.

Letting the MultiPlus do the heavy lifting
The MultiPlus-II has a built-in transfer switch and charger, so in many setups you don't necessarily need a separate AC-to-DC charger at all — the unit handles it natively via the AC input. Have you configured the input current limit in VictronConnect? That's often the overlooked setting.

DC charger as a supplement
If you are looking for a standalone 120V→24V DC charger to run alongside (or instead of), brands like Victron's Phoenix Smart IP43 charger work well, though those are designed for 230V in the UK obviously.

Worth clarifying — are you running a 120V generator or a standard UK 230V unit? That changes the conversation significantly for UK members.

Curious what others are doing

@VoltAlison the Victron Multiplus is the obvious answer here — it handles the AC input from your genny and charges the 24V bank simultaneously, plus gives you inverter functionality when the genny's off. The built-in charger is genuinely excellent.

One thing worth mentioning from my shepherd's hut setup — make sure your generator's output is clean enough. Cheap inverter gennies can throw odd waveforms that confuse sensitive chargers. I use a Honda EU22i and it plays nicely with Victron kit.

If you're set on a standalone charger rather than a combi unit, the Victron Blue Smart IP22 24/16 is solid and configurable via Bluetooth. Done exactly this as a backup charging option myself.

What size battery bank are you working with? That'll determine whether a 16A or 30A charger makes more sense for your winter charging windows.

@JA_Solar yeah the Multiplus is the go-to but worth flagging — if you're running a smaller genny, watch the input current limit settings. Had mine tripping out constantly before I dialled it back in VE.Configure.

Also worth considering whether 24V is even the right voltage for your setup long-term. My static went 48V last year and the charger efficiency gains were noticeable.

If budget's tight, the Victron Phoenix Smart IP43 chargers are brilliant standalone options and play nicely with the Cerbo GX if you've got one. Fogstar cells if you're building your own bank too — cracking value.

What size genny are you running? That'll narrow things down massively.

@VoltAlison worth adding to what @DownsExplorer was hinting at — the Multiplus has an input current limit you can set via VEConfigure or the VictronConnect app, which is absolutely essential when you're running a modest generator. On my boat I've got it dialled down to 8A input so the genny isn't constantly hunting under heavy load.

Also consider the PowerAssist feature — if your loads momentarily spike beyond what the genny can deliver, the Multiplus pulls the deficit from the batteries rather than overloading the generator. Genuinely useful in winter when you're running heating simultaneously.

For a 24V static caravan setup specifically, the Multiplus-II 24/3000 is probably your sweet spot unless you've got serious load requirements. Make sure your genny produces a clean enough waveform too — inverter generators like the Honda EU22i are far kinder to chargers than cheap open-frame units.

What size generator are we actually talking here? That's going to dictate a lot.

I've got a similar 24V setup in my static and the Multiplus route makes sense — but I ended up spending ages confused about which Multiplus rating to go for. The 24/3000 vs the 24/5000 wasn't obvious to me at first.

Also — does anyone know if the absorption/float charging profile gets properly respected when the genny's supplying dirty AC? Mine occasionally stumbles on voltage fluctuations from cheaper generators and I'm never sure if the charge cycle is completing cleanly or just cutting out mid-way.

Anyone running a Fogstar Drift battery bank with this setup? Curious whether the BMS plays nicely with the Multiplus charge parameters or if you need to manually tweak the absorption voltage to suit LiFePO4.