Swapping out a 75 15 smart solar controller for a 100 30 smart solar controller

Been thinking about doing something similar with my shepherd's hut setup, so this feels timely.

I'm currently running a Victron SmartSolar 75/15 with a single 200W panel into a 12V system — originally paired with a lead acid leisure battery but I've since swapped to a Fogstar 100Ah lithium. Works fine for my current setup, but I'm seriously considering adding a second panel (another 200W) and upgrading to the 100/30 to give myself proper headroom.

A few things I'd flag for anyone considering this swap:

• The 75/15 maxes out at 15A, so with two 200W panels you're potentially pushing it depending on your voltage configuration. Parallel wiring on 12V especially — worth doing the maths before you fry anything.
• Swapping to lithium means you absolutely need to update your charge profile. The SmartSolar makes this dead easy via the Victron Connect app, but don't assume it carries over automatically if you're replacing the unit entirely.
• The 100/30 is a meaningful upgrade — same SmartSolar ecosystem, Bluetooth built in, and future-proofs you if you add more panels later.

The physical swap itself is pretty straightforward if you're keeping the same wiring gauge, though obviously double-check your cable ratings handle the higher potential current.

Anyone on here actually done this specific upgrade on a hut or cabin install? Curious whether the 100/30 made a noticeable difference to charge times in practice, particularly through our famously grim British winters where every amp counts.

@SophieHobbs74 the 75/15 is basically the "learner plates" of the Victron world 😄 nothing wrong with it but yeah, you'll outgrow it faster than you think.

Upgraded mine on the garden office last spring — went straight to the 100/30 and immediately added another panel because suddenly I *

@SophieHobbs74 oh this is exactly what I did with my shepherd's hut last spring — started with a 75/15 and two 200W panels and kept hitting the input voltage ceiling on bright mornings. Swapped to the 100/30 and suddenly the system actually breathed properly.

Worth noting: when you swap controllers in the VictronConnect app, your battery history resets but your charge profile settings don't transfer automatically — learned that the hard way when my lithium bank got a nasty absorption charge it didn't need. Double-check everything before you reconnect the battery.

The 100/30 also opens the door to adding a third panel later without touching the wiring — which, knowing shepherd's hut people (myself very much included), will happen eventually.

@SophieHobbs74 worth checking your panel's Voc before anything else — the 75/15 limits you to 75V open circuit, which is fine for a single 200W panel but becomes relevant if you're thinking about adding more later. The 100/30 opens up more options on the input side as well as giving you the extra current capacity.

Done this swap myself on the static caravan — took about 20 minutes, existing wiring was fine. The SmartSolar app carries settings across reasonably painlessly if you're already using VictronConnect.

One thing people miss: the 100/30 will actually find more power from your existing panel in cold weather because of how Voc rises in low temps. Not dramatic, but it's there.

@BigAl makes a good point on Voc — worth adding that on a cold winter morning those voltages can spike higher than the panel spec suggests, so leave yourself headroom.

On the 100/30 specifically: the jump from 15A to 30A charge current is where you'll really feel the difference if you're adding panels. I run one in my garden office and it handles a 600W array comfortably on a 12V bank.

One thing nobody's mentioned — make sure your cable runs and fusing are rated for 30A if they weren't before. A lot of people swap the controller and forget the wiring hasn't changed. The VictronConnect app will migrate your battery settings across automatically once you pair the new unit, which is handy.