High Voltage battery MPPT

Been running a 24V Victron SmartSolar MPPT on the boat for a couple of years now, but I've recently been looking seriously at moving to a 48V lithium setup — primarily Fogstar Drift cells wired in series — and the whole MPPT compatibility question has become rather important to me.

The key thing I've been trying to work out is whether my existing MPPT can handle the higher battery voltage, or whether I'm looking at a full controller swap. Most Victron units are rated across multiple battery voltages and auto-detect, but there's a hard ceiling depending on the specific model. Worth checking the datasheet carefully rather than assuming.

What's more interesting to me technically is the charge algorithm side. A higher nominal battery voltage means the MPPT is operating across a narrower duty cycle at any given panel input voltage, which should improve efficiency — but only if your array voltage is sized sensibly above the battery voltage with enough headroom. On a narrowboat roof you're already constrained on panel count, so this balance matters quite a lot.

A few things I'm genuinely uncertain about:

• Does anyone have real-world data on MPPT efficiency gains moving from 24V to 48V battery systems with the same panels?
• Are there gotchas with Fogstar Drift packs and communication protocols with Victron BMSs that affect charge profiling?
• Has anyone used Renogy's higher-voltage MPPTs as a cheaper alternative in a 48V setup?

Interested to hear from anyone who's made this jump, particularly on boats where weight, space, and cable runs all interact in awkward ways.

@AshChild interesting timing — I'm in almost exactly the same position on my boat. Been eyeing up a move to 48V with Fogstar Drift cells too.

One thing I'd want to confirm before committing: does your existing SmartSolar actually support 48V battery charging? Some of the older Victron MPPT units top out at 36V nominal. Worth double-checking the exact model number against Victron's compatibility list.

Also — what's your current solar array voltage? If you're planning to keep the same panels, reconfiguring them for a higher voltage input to suit a 48V MPPT might affect how many strings you can practically run on a boat with limited roof space.

Has anyone here done this specific swap with Fogstar cells? Curious whether the BMS comms play nicely with Victron's VE.Smart networking.

Hey @AshChild and @Taffy — worth knowing that Victron's SmartSolar range goes up to 150V or 250V input depending on the model, so your existing MPPT might already handle the higher panel voltage that often comes with a 48V system redesign. The key thing to check is your actual panel VOC in cold conditions — that's where it spikes highest and can catch people out.

That said, if your current unit is a lower-spec 75V input model, you'd likely need an upgrade regardless. The 100/50 or 150/70 are popular choices for 48V lithium on boats. Also make sure whatever you go with supports lithium charge profiles properly — the Fogstar Drift cells are brilliant but they want a fairly precise absorption voltage. 😊

@AshChild one thing to watch — with 48V system your array voltage headroom changes. The MPPT needs Voc (cold morning peak) to stay below the controller's rated input, but also needs to be meaningfully above 48V to actually charge.

Worth running your string calcs through Victron's MPPT calculator before committing. I made the mistake of under-stringing when I bumped my garden office setup to 48V and lost loads of low-light performance.

Also check your existing SmartSolar model number — some 24V-era units are not field-upgradeable to 48V operation even if the voltage spec looks fine on paper. Might need a new unit regardless.

Fogstar Drift cells are solid btw, running them myself. Just make sure your BMS comms play nice with whichever Victron unit you land on — VE.Can or VE.Direct depending on model.

@AshChild another thing worth flagging — if you're going Fogstar Drift cells, double-check your BMS communication options early on. Some folk wire everything up beautifully then realise their MPPT and BMS aren't talking to each other properly, meaning the battery's charge parameters aren't actually being respected. Victron's ecosystem is quite good here if you use a Cerbo GX as a hub — it'll pull data from a compatible BMS via CAN bus or VE.Direct and let the MPPT respond accordingly. On a boat especially, that kind of integration gives you proper protection if something goes sideways. @QuietTrekker's point about Voc headroom is spot on too — worth modelling your worst-case cold morning voltage before committing to a controller.

Good shout from @ShaunHamilton on the BMS comms side — that caught me out when I upgraded my motorhome setup to 48V last spring.

One thing nobody's mentioned yet: reconfigure your charge profile from scratch when you switch. Don't just scale up your old 24V settings. Lithium absorption windows are tighter at 48V and it's easy to accidentally push cells harder than they'd like if you're copying old habits.

I spent a weekend with a multimeter and the Victron Connect app going through absorption voltage, float, and tail current settings methodically. The Victron docs for lithium profiles are actually quite solid — worth reading end to end rather than just tweaking defaults.

The SmartSolar handled the transition well for me. Just give it the right parameters and it'll reward you.