Step-by-step: Setting up Victron SmartSolar MPPT

Been wondering the same thing myself, @MuddySkipper. I've got a narrowboat setup and the cable run from my roof panels to the charge controller in the cabin is about 8 metres — nightmare routing it without creating voltage drop issues.

What gauge cable are you using? I went with 6mm² initially and kicked myself when the MPPT started throttling output on high-load days. Switched to 10mm² and made a proper difference. The Victron calculator on their website is worth a look — it factors in cable length and current.

Also worth considering conduit if you're running through living spaces. Keeps things tidy and protects the insulation from wear, especially on a narrowboat where everything gets damp vibration.

Are you planning to run negative and positive separately or bundled? I've seen folk debate this endlessly but most seem to keep them together with ferrite clamps to reduce interference with other systems.

What's your panel array looking like in terms of voltage? That affects your cable requirements as well.

Right, cable routing is where the fun really starts, isn't it? I've learned this the hard way in my van conversion — watched a mate run his cables along the outside and spend half the summer replacing sun-damaged insulation.

The trick I've sussed is keeping runs as short as physically possible and tucking them where they won't get roasted. Roof to charge controller

Cable routing can be a right pain, but it's worth getting sorted properly. I've got mine running through conduit down the side of my cabin — keeps it protected from UV and any sharp edges that'll shred the insulation over time.

The key bit nobody mentions: keep your solar cables as far as possible from your battery cables. Even though they're low voltage, having them bundled together creates noise that the MPPT can pick up, especially on longer runs. I learned that one the hard way — my charge controller was throttling back randomly until I separated them by about 30cm.

Also, use proper MC4 connectors if you haven't already. The cheaper alternatives oxidise something fierce in damp conditions, and you'll be chasing phantom voltage drops for months. Victron's own connectors are pricey but they just work.

One more thing @VanLee — if you're running a long roof-to-controller distance, consider going up a cable gauge. The voltage drop over distance matters more than people think, especially with a 150/35. Reckon you'd save more in lost generation than the extra quid spent on thicker cable.

Cable gauge is absolutely critical — I made the mistake of undersizing mine initially and saw voltage drop of nearly 2V across a 6m run. Recalculated properly using the Victron sizing tool and bumped to 10mm² (4mm² was nowhere near adequate). The MPPT's performance depends entirely on clean voltage at its input terminals.

Done this dance with my narrowboat setup — what folks miss is the sheer importance of DC cable resistance over distance. I went from 10mm² to 16mm² between panels and controller, dropped my losses from 0.8V to 0.2V. @Nessa's spot on about undersizing. The voltage hit compounds everything downstream.

@BoxerCamper spot on about distance — I've seen folks run 10m of undersized cable and wonder why their panels are sulking. Equally daft is mounting the controller next to the engine bay on a van, then acting shocked when it throttles itself in summer. Victron's got decent thermal management but it's not magic. Keep it somewhere sensible and

Exactly — and it's worse when you've got panels metres away from the controller. I calculated mine at 4m² cross-section for a 15m run. The voltage loss calculator on the Victron site is brilliant for working backwards from your acceptable drop. Saved me a fortune in wasted panel output versus chasing a slightly cheaper cable spec.