Multi Rs Solar 48/6000 /100 max charging voltage

Been mulling this one over for my shepherd's hut build and thought it worth raising here.

Running a 48V Victron system, and I've been looking closely at what headroom the Multi RS Solar 48/6000/100 actually gives you on the charging side. The manual quotes a 62V maximum charging voltage, which works neatly for a standard 16S LiFePO4 arrangement — but what happens when you push beyond that?

Someone in another discussion mentioned they'd bumped their bank up to 17S, which puts the per-cell charge voltage at around 3.65V — and suddenly you're nudging right up against or potentially beyond that 62V ceiling depending on how you've set things up.

For my cabin setup I'm sticking with a Fogstar 48V server rack battery, so this isn't directly my problem right now. But I've got mates running DIY cell packs who are always fiddling with their configurations, and I can see this being a real gotcha.

My questions for the community:

• Has anyone here actually run a 17S bank with this inverter-charger, and how did you manage the voltage ceiling?
• Did you derate your per-cell max to stay within the 62V limit, or did you find another workaround?
• Is there any risk of nuisance shutdowns if you're sailing close to that limit on absorption?

Feels like one of those things where the maths looks fine on paper but real-world charging curves can throw a spanner in the works. Particularly interested in anyone who's done this off-grid rather than in a domestic grid-tied setup — the use case is quite different.

@SteveBurns99 this is something I've been puzzling over too, actually. On my narrowboat I'm running a similar 48V setup and the absorption/float ceiling on the Multi RS has caught me out a few times when dialling in the battery profile.

Quick question for you — are you planning to use Victron's own lithium batteries or third-party cells? The reason I ask is that the max charge voltage behaviour seems to differ quite a bit depending on whether DVCC is controlling things or whether the Multi RS is running standalone.

Also wondering whether the 100A DC input limit becomes the real bottleneck before you even hit the voltage ceiling? That's what I found on mine with a larger solar array — the current constraint bit first.

What battery chemistry are you going with for the shepherd's hut? Fogstar or similar?

Good point being raised here. The Multi RS Solar's maximum charge voltage tops out at 58.4V for 48V systems, which matters enormously when you're selecting your battery chemistry.

For a shepherd's hut build specifically, if you're running 16-cell LiFePO4 (which most of us are — Fogstar Drift packs are popular for this), your absorption voltage sits around 57.6V, leaving you roughly 0.8V of headroom before hitting the inverter-charger's ceiling. That's workable but tighter than I'd like.

Where it gets interesting is configuring this via VictronConnect rather than assuming defaults are sensible — they often aren't for non-standard battery configurations. Check your BMS communication settings too; if you're using CAN-bus to a compatible BMS, the battery will assert its own charge voltage ceiling, which can override your manual settings entirely.

@SteveBurns99 what BMS are you planning to pair with this?

@BordersExplorer that 58.4V ceiling is worth keeping in mind if you're planning to push absorption on a LiFePO4 pack — most 16S configs sit comfortably under it but worth double-checking your BMS cutoff has a sensible gap above your charge voltage setting.

For my garden office build I've got a Fogstar Drift 48V and the Multi RS handles it no problem, but I did spend a fair bit of time in VictronConnect making sure the charge profile wasn't nudging too close to the BMS high-voltage disconnect.

@SteveBurns99 for a shepherd's hut you're probably not running massive loads so the 6000VA headroom is plenty — just nail the charge voltage config before you commission it properly.

@MidlandsSolar makes a fair point. Worth adding — if you're using Fogstar or similar cells and building your own pack, double-check your BMS cutoff sits comfortably below that 58.4V ceiling rather than relying on the Multi RS to play nice with your BMS as a last resort. That's not what it's there for.

On my static van setup I deliberately set absorption a good 0.5V below the inverter's hard limit. Belt and braces. Had a mate who didn't bother and ended up in a "why is my BMS constantly tripping" conversation that lasted three weekends.

Also worth noting — the 100A charge current on this unit can fill a decent pack surprisingly fast, so don't just focus on voltage ceiling, factor in your pack's max charge rate too.