Can the Victron SmartSolar MPPT RS 450/100 support a -48V DC battery bank (positive ground)

Been scratching my head over this one for my shepherd's hut build and wondering if anyone here has actually tried it.

I'm looking at the Victron SmartSolar MPPT RS 450/100 as the centrepiece of my system, but I've got a fairly unusual battery arrangement — essentially a negative ground configuration isn't something I need, but I am curious about the positive ground / -48V scenario because I've seen it crop up in discussions around certain legacy setups and specialist telecoms-derived battery banks that occasionally appear secondhand in the UK market.

The Victron manual is thorough in most respects but I couldn't find a definitive statement on whether the RS 450/100 supports a positive ground (i.e., -48V nominal) bank. The wiring diagrams all seem to assume conventional negative ground as standard.

A few specific questions:

• Has anyone actually wired a positive ground 48V bank to one of these controllers in the UK?
• Would doing so void the warranty or potentially damage the unit?
• Is there a Victron technical bulletin that addresses this I might have missed?

I realise this is a fairly niche scenario — most of us running Fogstar or similar lithium packs wouldn't encounter it — but it feels like the kind of thing that could matter if you're repurposing older equipment.

Keen to hear from anyone who's dug into the RS series specifically rather than the older SmartSolar range, as the RS has a quite different internal architecture from what I understand.

RelayLife | Posts: 847

@AlanWard Short answer: no, the RS 450/100 won't support a negative ground / positive ground configuration. Victron are pretty explicit that the MPPT RS series requires a negative ground system — the internal architecture assumes that, and attempting to run it inverted risks damaging the unit and likely voids your warranty immediately.

For a shepherd's hut I'd genuinely question whether -48V positive ground is even necessary for your use case? What's driving that requirement? If it's telecoms or legacy equipment, there may be easier workarounds on the load side rather than building your whole solar system around it.

Worth posting in the Victron Community forum too — their engineers do respond there occasionally. But I wouldn't expect good news on this one.

@RelayLife is right, and worth understanding why rather than just hitting a wall.

The RS 450/100 uses a common negative topology internally — the PV array negative, battery negative, and load negative are all tied together on the same copper plane. Flip that to positive-ground and you're essentially asking the MOSFET driver circuitry to reference itself against earth in a way Victron never designed for. Magic smoke territory.

If you genuinely need positive-ground for some legacy reason (old comms equipment? telephone systems?), your options get painful quickly. Isolated DC-DC converters, separate inverter arrangements... nothing elegant.

For a shepherd's hut though @AlanWard — what's actually driving the -48V requirement? Most modern builds I've seen get away perfectly well with standard 48V negative-ground, and the RS 450/100 is otherwise an absolute beast of a controller for high-voltage panel strings. Worth questioning the constraint before redesigning around it.

Really useful thread — I had almost the exact same question when planning the electrical setup on my narrowboat where positive-ground configurations sometimes come up in older DC systems.

@TracyAllen would you say this limitation is specific to the RS series, or does it apply across Victron's MPPT range generally? I'm wondering whether a standard SmartSolar 100/50 (which I've actually got running as emergency backup on the boat) has the same constraint, or whether the architecture is fundamentally different between the two product lines.

Also curious whether @AlanWard has considered just redesigning around a conventional negative-ground 48V bank from the outset — sometimes fighting the controller to match a legacy polarity convention costs more time and money than it saves.

@AlanWard worth double-checking Victron's own docs rather than just taking forum word for it — but yeah, everything I've seen confirms the RS series assumes negative ground throughout. No isolation between PV and battery sides on that unit.

For a shepherd's hut you're unlikely to need positive ground anyway unless you're inheriting some legacy setup. What's driving the +48V requirement? If it's just a quirky battery bank config, might be easier to just rewire it conventional negative ground and save yourself the headache.

I run a standard negative ground setup in my van with a Victron SmartSolar 100/50 and it's completely uneventful — exactly what you want off-grid tbh.

@AlanWard short answer: no, and attempting it will likely destroy the unit faster than you can say "warranty void."

The RS 450/100's internal topology references battery negative to chassis ground — flip that polarity and you're not just fighting convention, you're sending current through paths that were never designed to carry it.

If positive-ground is genuinely non-negotiable for your shepherd's hut (legacy 48V telecom batteries sometimes ship this way), you'd need an isolated DC-DC converter between the MPPT output and the bank — messy, lossy, and frankly more expensive than just rewiring the bank to conventional negative-ground.

Fogstar and Pylontech LiFePO4 units all ship negative-ground as standard; far easier to build your system around that from the start than retrofit isolation gear later.