Anyone running lithium on a narrowboat without blowing up their alternator?

Fitted a 200Ah Fogstar Drift LiFePO4 on the cabin boat last spring and the alternator's been throwing a wobbly ever since — apparently lithium's near-zero internal resistance just hammers the thing when it's bulk charging.

Running a Victron Orion-Tr Smart DC-DC charger as a proper alternator isolator now, but wondering if that's the right call or if I'm just adding complexity. Boat's also got a 200W Renogy panel on the roof doing most of the heavy lifting when we're moored up.

Has anyone fitted a dedicated alternator protection setup on a narrowboat, or just throttled the charge current down on the BMS? My old AGM never gave me this grief — lithium's brilliant until it isn't.

Gibbo39 | Posts: 847

@AlanJones63 Classic problem mate. The fix that sorted mine was fitting a Wakespeed WS500 regulator — it's specifically designed to handle lithium's charge characteristics and protects the alternator from exactly that scenario. Expensive mind, around £400, but cheaper than a new alternator every season.

Also worth looking at whether your alternator is properly rated for continuous duty — most automotive-spec ones fitted to boats aren't, they're designed for short bursts of charging. A Mastervolt or Balmar unit with external regulation handles sustained lithium charging much better.

Some folk also wire in a simple DC-DC charger (Sterling or Victron B2B) between alternator and lithium bank — isolates the two completely and lets each work at its own pace. Bit less efficient but very tidy solution if you don't want to touch the alternator setup.

LochStu | Posts: 1,203

@AlanJones63 Worth looking at a DC-DC charger (B2B) as an alternative approach — something like a Victron Orion-Tr Smart. It sits between your alternator and the lithium bank, essentially presenting the alternator with a sensible load rather than letting the lithium demand everything at once. Bit less elegant than a smart regulator perhaps, but dead simple to install and your existing alternator doesn't need touching.

Also worth checking whether your alternator has an internal or external regulator before spending anything — some older Bosch units on canal boats run surprisingly hot regardless of battery chemistry. Might be worth a temp sticker on the casing just to see what you're actually dealing with before throwing money at regulators. What engine have you got?

CamperAndrea | Posts: 412

@AlanJones63 Both suggestions above are solid, but worth mentioning a third angle — have you considered adding a sacrificial load on the alternator output? Some narrowboaters fit a resistive dump load (a decent sized resistor bank or even a small water heater element) that kicks in when the lithium approaches full charge. It stops the alternator suddenly losing its load and overspeeding. Not as elegant as a Wakespeed or a B2B but it's cheaper and surprisingly reliable on older boats with simple electrics. I ran something similar on mine for a season before upgrading properly. Also worth checking your alternator's actual rated output — marine alternators on canal engines are sometimes undersized to begin with, so a 200Ah lithium is asking a lot of something that was only ever meant to top up a leisure battery gently.

DODQueen | Posts: 2,156

Running a Fogstar Drift myself (on a static cabin setup, not a boat, but same chemistry applies). One thing nobody's mentioned yet — check your alternator's duty cycle and whether it has any thermal protection built in. Older marine alternators weren't designed for sustained 100% output, which is exactly what a hungry lithium bank demands.

A proper alternator-mounted temp sensor feeding into whatever regulator you go with (@Gibbo39's Wakespeed suggestion is solid) can save you from a meltdown even before you sort the underlying charging strategy.

Also worth knowing — some BMS units have a dedicated alternator protection mode that deliberately introduces a small absorption delay. Fogstar's own BMS docs mention this. Might be worth checking if yours supports it before spending on additional hardware.

Trevor1986 | Posts: 847

@AlanJones63 One thing nobody's mentioned yet — check whether your alternator has an internal regulator that's being fooled by the lithium's flat charge curve. The alternator sees what looks like a permanently discharged battery and just keeps pushing hard indefinitely, which is where the heat damage comes from.

If you go the B2B route as @LochStu suggests, make sure you're sizing it properly for your engine run times. A lot of narrowboaters underestimate how long they need to be cruising to get a meaningful charge into a 200Ah bank through a B2B.

Also worth having a word with Fogstar directly — their tech support is genuinely helpful and they know the Drift well. They might have specific recommendations for marine alternator setups that aren't obvious from the documentation.

ExPostie | Posts: 634

Not a boat setup here — shepherd's hut with a Victron system — but the alternator hammering issue is well documented and it's not unique to Fogstar. Any lithium will do it.

The fix that actually works long-term is a DC-DC charger (B2B) between the alternator and the lithium bank. Victron Orion-Tr Smart is the go-to, Sterling do a decent one too. It basically isolates the alternator from seeing that hungry lithium load directly.

@Trevor1986 makes a fair point about internal regulators but honestly most marine alternators aren't built with lithium in mind regardless of what the spec sheet implies.

Worth knowing — some narrowboat owners are voiding their engine warranty fitting lithium without proper isolation. Worth a check before you go further down this rabbit hole.

WonkyRigger | Posts: 312

Running a similar setup in my motorhome — Fogstar Drift 100Ah and had the same alternator drama before I fitted a Victron Orion-Tr Smart DC-DC charger between the alternator and the lithium bank. It isolates the battery from seeing that massive initial charge demand directly. Transformed the whole thing overnight.

Worth asking — is your alternator externally regulated or internally? @Trevor1986 seems to be heading that direction but an Orion is arguably the simpler fix regardless of alternator type. Would a narrowboat's engine bay even have room for one? Curious what engine you're running.