Swapped out the old Victron MPPT on the narrowboat – few questions about the new settings

Right, so I finally ripped out the old 75/15 and slapped in a 100/30 on the boat last weekend. Difference is already noticeable — panels are actually doing something useful before 10am now instead of sitting there looking decorative.

Few things I'm wrestling with though:

Absorption voltage — I've got a 200Ah lithium bank (Fogstar Drift cells, not the cheap stuff). Currently set at 14.2V. Some folks say go lower, others say higher. What are you lot running?

Float — dropped mine to 13.5V. Seems sane but the BMS is doing odd things occasionally. Might be unrelated.

Tail current — this is where I get confused with lithium. The MPPT wants a percentage of the panel capacity to trigger the switch from absorption to float. I've got 400W of panels feeding into it. Does the 2% default even make sense here or am I just inviting grief?

Also worth noting — narrowboat life means I'm on shore power at marinas occasionally, so the Victron's not always the only thing topping the bank up. That complicates things a bit when trying to dial in proper settings.

Anyone else running lithium on a boat with a setup like this? I've seen loads of threads about static installs but marine stuff has its own quirks — humidity, vibration, the constant paranoia that something's going to arc and set the whole bloody thing on fire.

Would genuinely appreciate input from people who've actually done this rather than the usual copy-paste from the Victron manual. I can read, thanks.

Nice one @SOC_Nerd, the 100/30 is a proper upgrade especially if you've got any expansion plans for the panel array down the line.

One thing worth double-checking on the narrowboat specifically — make sure your absorption voltage is set correctly for your battery chemistry and that you've accounted for the cable runs. Boats often have longer DC runs than folk realise, and voltage drop can skew what the controller thinks it's seeing at the battery end. If you haven't already, remote battery sensing via the VE.Direct cable or a separate sense wire is well worth doing.

What batteries are you running? Flooded, AGM, or lithium? Makes a difference to where you want your float and absorption figures sitting. Also worth enabling the streetlight or load output settings if you're running any 12V cabin lighting directly from the controller.

Not a boat person myself — I've got a Victron 100/30 on my shepherd's hut and the thing practically earns its keep before I've finished my morning brew. 🌄

Got the same unit on my static — not a narrowboat obviously, but damp enough inside to feel like one most days.

One thing nobody's mentioned: double-check your absorption voltage is set correctly for your battery chemistry, the defaults out of the box aren't always where you want them. Wasted two weeks wondering why my Fogstar lithiums weren't hitting full charge before I realised Victron had shipped it set for AGM.

Also worth enabling the streetlight function as a load disconnect if you're leaving the boat unattended — learned that the hard way when I came back to a very flat bank after a fortnight away.

@SOC_Nerd what batteries are you running? Makes a difference to which settings actually matter.

Really interested to hear how you've got on with this @SOC_Nerd — I've been debating the same swap on my van build and wondering whether the 100/30 handles the damp marine environment any differently in terms of settings vs a land-based install.

Couple of questions if you don't mind:

• Did you need to adjust your absorption/float voltages specifically for the boat, or just run the standard Victron presets?
• Are you running AGM or lithium on the narrowboat? I've heard the charge profiles can behave slightly differently in consistently humid conditions

Also curious whether you're using the VictronConnect app to monitor remotely — seems like it'd be dead handy when you're not aboard. Does the Bluetooth reach well enough through the hull?

Hoping this thread gets some good input from the narrowboat regulars here! 🚢

Got a 100/30 on my static caravan and honestly the absorption voltage setting is the one that'll catch you out — lithiums and lead-acid want completely different numbers and the Victron app will happily let you fry either if you don't double-check your battery spec sheet first 🔥

Also worth enabling the "tail current" cutoff if you're on lithium (Fogstar Drift cells especially seem to appreciate it) — stops it sitting in absorption forever like a confused golden retriever.

@BorderCamper the van swap is worth it, the 75/15 always felt like trying to fill a bath with a watering can.