Looking for a 3-port bi-directional DC-DC converter

Been wrestling with something similar on the boat for the last few months, so this feels timely.

My situation: I've got a 48V lithium bank (Fogstar Drift cells, lovely bits of kit), a 12V starter battery, and I want to intelligently route power from shore hookup and the solar array depending on state of charge across both banks. Basically a three-way conversation between sources and loads.

The Victron SmartShunt plus a couple of Orion-Tr Smart DC-DC converters can bodge this together, but it's not truly bidirectional — you're essentially managing two separate one-way streets and hoping your automation logic glues it together. Works, but feels like using a fork to eat soup.

What I actually want is a single unit that:

• Sees all three ports simultaneously
• Makes priority decisions autonomously (or via a simple config)
• Handles regenerative scenarios — e.g. if the 12V side is being charged by the alternator while cruising, that energy should spill upward to the 48V bank

Victron's ecosystem is brilliant but I haven't found anything that genuinely does this natively without a Cerbo GX plus custom Node-RED flows acting as the brain.

Has anyone actually deployed a true 3-port bidirectional converter in a narrowboat or marine context? I've seen some industrial units from Chinese manufacturers on AliExpress but the lack of documentation makes me nervous for a live-aboard setup.

Curious whether this is a gap in the market or whether I'm just not looking in the right places.

@TorDweller not going to lie, I went down this exact rabbit hole for my static van last winter and nearly lost my mind 😅

The Victron Orion-Tr Smart series is your friend here, but you're basically daisy-chaining two of them rather than getting a true 3-port unit in one box. Bit inelegant but it works.

Proper 3-port bidirectional DC-DC converters do exist but they're mostly industrial/EV stuff with price tags to match. Nothing really aimed at our market yet.

Might be worth posting over on the Victron Community forum too — their engineers actually reply sometimes, which is either brilliant or terrifying depending on what you've bodged.

What's your target transfer wattage between the banks? That'll narrow it down sharpish.

@DustyCaptain nearly lost your mind is an understatement — I spent three weeks convinced I'd cracked it, built a beautiful wiring diagram, then realised I'd essentially reinvented a product that already exists and costs £40 😂

@TorDweller the magic phrase you want is **"multi-port bidirectional DC-DC converter

@TorDweller the narrowboat setup you're describing took me a good while to untangle on my own cabin build. What I eventually landed on wasn't a true three-port bidirectional unit — they're genuinely rare at sensible prices — but rather a Victron Orion-Tr Smart handling the 48V→12V side, with a separate DC-DC charger running the other direction when shore power topped the 48V bank up. Two units rather than one elegant box, yes, but the Victron ecosystem means they actually talk to each other via VE.Smart networking, so priority logic is manageable.

Not the tidy single-converter solution you're after, I know. But sometimes the mythical perfect component just doesn't exist at our budget level, and two well-chosen pieces of kit that communicate properly beat one mysterious unit that doesn't.

What voltage tolerance does your starter battery actually need to stay happy?

@TorDweller the 3-port bidirectional topology you're after is genuinely niche kit — most manufacturers split this into two separate converters and call it a day.

Worth looking at the Victron Orion-Tr Smart family, but you'd need two units orchestrated via VE.Direct or a Cerbo GX to manage priority logic between your 48V bank and 12V starter bat. Not elegant, but it works reliably.

The cleaner solution I've actually implemented on my cabin EV charging setup is using a BMS with a dedicated aux output to handle the 12V side independently, letting the main DC-DC handle your primary conversion path. Keeps the power flows from fighting each other.

@MoorLee's "beautiful build that didn't work" is basically a rite of passage here — the issue is usually shoot-through current when two sources compete for the middle rail simultaneously. What's your peak current requirement? That narrows things down considerably.

@TorDweller been running a similar lash-up on the narrowboat for two seasons now and honestly the "three separate converters" approach @DailySolar alludes to nearly broke me before I admitted defeat and just did it properly.

What actually solved it was a Victron Orion-Tr Smart handling the 48→12V side, paired with a properly configured MPPT that treats the 48V bank as master. Not sexy, not a single magic box, but it's reliable — and on a narrowboat that matters more than elegance when you're moored somewhere with no mobile signal and something goes wrong at midnight.

The genuine 3-port bidirectional units do exist but they're industrial kit priced accordingly. Unless your budget's flexible, I'd stop hunting that particular unicorn and just embrace the multi-device solution. Painful to accept, but there it is.