24v to 12v DC step down converter questions

Running a 24v system on the boat and looking to add a few 12v appliances without rewiring the whole thing.

Got a Victron Orion-Tr 24/12-20 sitting in my basket but not pulled the trigger yet. Few questions before I do:

1. Load capacity — I've got a 12v diesel heater (Webasto clone, draws about 10a peak on startup) plus a couple of USB hubs and a 12v compressor fridge. Will 20a be enough headroom or should I be looking at the 30a version?

2. Isolated vs non-isolated — the Victron comes in both flavours. My 24v bank is Fogstar Drift 200ah lithium. Does the isolated matter if everything shares the same chassis ground on a narrowboat? I've read conflicting stuff on this.

3. Efficiency losses — roughly how much am I losing pushing power through a step-down? Worth factoring into my solar calculations or is it negligible?

Also considering just running two separate banks (24v and 12v) but that feels like more hassle than it's worth for a handful of 12v devices.

Anyone running a similar setup on a boat? Curious whether the Victron is overkill and something like a Renogy DC-DC would do the same job for less.

LiamWalker | Member

@BenJohnson95 Good choice on the Orion-Tr, it's a solid bit of kit. Few things worth considering before you buy:

The 20A model gives you 240W of 12v power, so just add up your 12v loads to make sure that covers you. If you're running anything substantial like a fridge, you might find yourself pushing close to the limit.

Also worth noting - are your 12v appliances running simultaneously or just occasionally? If it's the latter, you might get away with the 18A (non-isolated) version which is a bit cheaper, though the isolated model is generally recommended for marine installs due to earthing considerations on boats.

What 12v appliances are you actually planning to run? That'll help narrow down whether the 20A is sufficient or if you'd be better sizing up.

DownsCruiser | Member

Had the Orion-Tr 24/12-20 in my motorhome for two years, no issues. One thing worth knowing — the 20A is continuous rating, so 240W max on the 12v side. Add up your appliance loads before you buy. Easy mistake to underspec it and then wonder why it's running hot.

Also check whether you need the isolated or non-isolated version. Boats especially — if your 24v and 12v negatives aren't already tied together you'll want isolated. Got caught out with that once, not fun diagnosing the resulting weirdness.

Victron's app integration is a bonus if you're already on a GX device.

MickWebb82 | Member

Got an Orion-Tr in my static van setup (12v system but same principle). One thing I'd add — double-check whether you want the isolated or non-isolated version. Boat installs often benefit from isolated due to earthing/bonding considerations, can save headaches with galvanic corrosion issues on marinised setups.

The 20a version gives you 240w continuous which sounds plenty but add up your 12v loads carefully — people always underestimate. If you're anywhere near the limit, jump to the 30a version now rather than retrofitting later.

Also worth grabbing the Victron Connect dongle if you don't already have one — being able to monitor output on your phone is genuinely useful.

DucatoSolar | Member

One thing nobody's mentioned yet — pay attention to the input voltage range under load. On a 24v LiFePO4 system, resting voltage can sit around 27-28v fully charged, and if you've got regenerative loads or a shore power charger pushing higher, the Orion-Tr's upper input limit (35v on that model) is worth verifying against your actual system peaks.

Also worth considering: the 20A output gives you 240W continuous. Map out your 12v appliances and their combined draw simultaneously, not just individually. People often underestimate this and find themselves thermally throttling the unit in a confined locker with poor airflow.

Mount it somewhere with decent ventilation — mine in the Ducato runs noticeably warm under sustained load. Victron's own guidance recommends derating in elevated ambient temperatures, which on a boat in summer is very much a real consideration.

Squib82 | Member

Worth flagging on the boat specifically — the isolated variant of the Orion-Tr is almost certainly what you want. Non-isolated units share a common ground between input and output, which becomes problematic on a vessel where you're dealing with bonding, NMEA networks, and the potential for corrosion-inducing ground loops. Learned that the hard way on my own narrowboat before I knew better.

The 20A unit gives you 240W continuous — map out your actual 12V loads before assuming that's sufficient. Chartplotters, VHF, nav lights, and a compressor fridge can eat through that budget surprisingly quickly.

@DucatoSolar makes a valid point about input voltage under load — doubly relevant if you're running a lithium bank that sits high most of the time but dips under heavy draw.