Anyone else running lithium on a narrowboat with a traditional alternator setup?

Just converted my motorhome to a 200Ah Fogstar Drift LiFePO4 and now I'm helping a mate sort his narrowboat. He's got a 65ft cruiser stern with the original 70A alternator still charging a mix of old lead acid and a new lithium leisure bank — absolute mess.

Main concern is the alternator overheating. From what I've read, lithium just hoovers up whatever the alternator can throw at it until something gives. He's looking at either a Victron Orion-Tr Smart DC-DC or maybe a Sterling B2B, but not sure which way to go on a boat versus a van setup.

Any narrowboaters here actually running this combo day-to-day? Curious what isolator or charger you've settled on and whether the engine hours vs charge time works out on a liveaboard.

RachelCooper | 847 posts

@StormyViking great timing on this thread! One thing that catches people out on narrowboats specifically is that the engine often runs for relatively short periods compared to a motorhome, so alternator protection becomes even more critical.

Your mate absolutely needs a DC-DC charger (B2B) between the alternator and the lithium bank - something like a Victron Orion-Tr Smart. Without it, the lithium will just hammer that 70A alternator continuously since lithium accepts charge so aggressively at lower states of charge. On a narrowboat engine that alternator could overheat within the hour.

Also worth mentioning the mixed bank situation - keeping old lead-acid as a starter battery and running a separate lithium leisure bank is usually the sensible approach rather than trying to replace everything at once.

What inverter setup is he running? That changes the conversation quite a bit.

WattGemma | 312 posts

@StormyViking the big danger with a standard alternator into LiFePO4 is that lithium accepts charge so readily at the start that it can pull the alternator into thermal overrun - especially an older 70A unit that's probably already working hard. Worth fitting a decent DC-DC charger (B2B) between the alternator and the lithium bank rather than connecting direct. Victron Orion-Tr Smart is popular for narrowboats and protects the alternator beautifully. Also worth checking whether your mate's BMS has a low-temperature cutoff - narrowboat bilges can get properly cold over winter and you don't want charging cutting out mid-cruise on the Llangollen!

Chris1984 | 1,203 posts

@StormyViking done almost exactly this on my own narrowboat last year, so happy to share what worked. The key thing I'd add beyond what @WattGemma is getting at - you really want a decent DC-DC charger (B2B) between the alternator and the lithium bank rather than charging direct. I use a Victron Orion 30A and it's been brilliant. Keeps the alternator loaded sensibly and gives the lithium a proper charge profile.

Also worth checking the alternator's temperature rating - older narrowboat engines often have the alternator tucked away with poor airflow, and lithium's willingness to gulp current can cook them quickly. A temp sensor on the alternator casing is cheap insurance.

What engine has your mate got? Beta or Isuzu based? Makes a difference to what B2B size makes sense.

OldSailor79 | 634 posts

@StormyViking worth flagging that on narrowboats specifically, the alternator runtime is often quite short — lock-to-lock or quick engine runs to top up. That actually makes the "alternator cooking itself" problem worse, because lithium will demand full current right up to near-full charge with no gradual taper like lead-acid gives you.

I'd strongly recommend a Victron Cyrix-Li-Charge or similar battery-to-battery charger (B2B) between the alternator and the lithium bank. Renogy do a decent budget option if cost is tight. Separates the alternator from the lithium BMS completely — much safer.

My static caravan setup runs something similar for emergency backup and it's transformed reliability. On a narrowboat where you can't exactly pull over to a garage, peace of mind matters more than saving a few quid upfront.