Anyone else running a split-charge relay alongside a DC-DC charger? Wondering if it's worth keeping both

Last summer I rewired the leisure setup in my Transit-based van and fitted a Victron Orion-Tr Smart 12/12-30 DC-DC charger to handle charging from the alternator properly. Before that I had a basic 20A split-charge relay which I just left in place rather than pull the whole loom apart. So currently I've got both running in parallel, which I know sounds a bit daft.

The DC-DC does its job brilliantly — the 200Ah lithium bank sits happy and the Victron handles the absorption and float stages properly so I'm not hammering the alternator. But I've noticed the old relay occasionally kicks in as well when voltage gets above a certain point, essentially bypassing the Orion's charge profile. I'm not 100% sure if that's actually causing any harm or just adding a few extra amps inefficiently.

Has anyone run a similar hybrid setup, even temporarily? I'm trying to decide whether it's worth properly removing the relay or just leaving well alone. The relay's wired into a 30A blade fuse block near the engine bay and honestly the thought of pulling it all out on a cold Sunday morning isn't exactly appealing.

@CoveChris I ran exactly this combination on my narrowboat before simplifying things. The split-charge relay becomes largely redundant once you've got a proper DC-DC charger in place — the Orion-Tr is doing the intelligent work anyway, protecting your starter battery and managing charge profiles correctly.

The only reason I'd keep the relay is as a dead-simple backup if the Orion ever packs in, but realistically it adds complexity and potential fault points.

One thing worth checking — if your relay is wired to close at a set voltage, it could theoretically fight the Orion under certain conditions. Might not be an issue in practice but worth understanding your exact wiring before leaving both active simultaneously.

Personally I'd pull the relay out, keep the wiring diagram, and free up the space.

@CoveChris Worth keeping the relay in one specific scenario: if your Orion-Tr Smart ever develops a fault, you lose all alternator charging. A relay wired in parallel as a backup—even a simple VSR—gives you a fallback. That said, I've got my Orion configured with the remote on/off tied to ignition, and I've removed the relay entirely on my Sprinter build.

One thing nobody mentions: the relay can actually interfere with the Orion's voltage sensing if wired incorrectly, causing erratic charge behaviour. If you're keeping both, ensure the relay's downstream output feeds a completely separate load bus, not the same positive bar the Orion's output connects to.

For most setups the relay is genuinely redundant—the Orion handles the load management far more intelligently than a VSR ever could. Simplifying is almost always the right call.

@Taffy29 raises a good point about redundancy, which is actually what concerns me most with my own setup. I'm primarily using mine for emergency backup rather than full-time van living, so reliability when it matters is everything.

Quick question for the thread — if you do keep the relay as a backup, does it need to be wired so it can be switched in manually? Or do most people leave it permanently connected in parallel with the DC-DC charger and just accept the slightly messy charging behaviour?

I've been looking at fitting a Victron Orion-Tr Smart myself but I'm wary of removing my existing split-charge relay entirely before I fully understand the implications. Is there a clean way to wire both so the relay only cuts in if the DC-DC charger fails, perhaps using a simple isolator switch somewhere in the circuit?

@CoveChris I'd lean towards removing it personally. The Orion-Tr Smart is doing the heavy lifting properly with its DC-DC conversion, and having the split-charge relay sitting there dormant is just another potential failure point and a source of confusion if someone else ever works on the van. That said, if the relay is already wired neatly and not causing any issues, there's no urgent reason to rip it out either. One thing worth checking — make sure the relay isn't somehow creating a parallel charging path that could interfere with the Orion-Tr's operation, particularly if it's voltage-sensing rather than ignition-switched. @Taffy29's redundancy point is fair but honestly how often does that scenario actually materialise in practice? I'd rather trust the Victron and simplify the system.

@CoveChris I'd lean towards removing it personally. The Orion-Tr Smart is doing a proper multi-stage charge rather than just slamming bulk voltage through whenever the engine runs — the relay can't compete with that. One thing worth considering though: with the relay gone, make absolutely sure your cable sizing and fusing to the Orion is properly rated. Some people remove the relay but leave undersized wiring from the previous install in place, which creates its own headaches. Also, if you've got the Orion set up via Bluetooth, have you experimented with the input voltage lockout settings? Getting those dialled in correctly means it won't pull from your starter battery when the engine's just ticking over in traffic, which is where a lot of folk find the DC-DC approach genuinely earns its keep over a basic relay.

@CoveChris had almost this exact dilemma when I was sorting the electrics on my narrowboat a few years back. Kept the split-charge relay in parallel "just in case" for about six months, then realised it was actually causing confusion — the relay would occasionally crack open a connection before the Orion had finished its absorption cycle, which wasn't ideal.

Pulled the relay out completely, never looked back.

One thing worth considering though: if your Orion ever develops a fault mid-journey, you've got nothing getting charge into that leisure bank whatsoever. On the boat that was a real concern. Might be worth keeping the relay wired in but with a manual override switch rather than automatic — gives you a proper backup without the two systems fighting each other day-to-day.

@CoveChris one thing worth considering before you rip the split charge out - it can act as a useful backup if the Orion ever develops a fault or needs a firmware update mid-trip. I've left mine in place on my Sprinter but wired it so it only cuts in manually via a switch rather than automatically. Gives me peace of mind on longer tours without the two systems fighting each other or the relay undoing the Orion's proper charge profile. Belt and braces approach I suppose, but out in the middle of nowhere you'll thank yourself for the redundancy.

@KeithWard77 makes a fair point about backup but honestly in my static caravan setup I went through something similar — kept two overlapping systems "just in case" and it just created confusion about what was doing what. Ended up chasing a weird voltage issue for weeks before I realised the old relay was occasionally kicking in and interfering with the Orion's charge profile.

If you're running Victron kit with proper BMS comms, let it do its job cleanly. Document where everything is, stick a spare relay in your locker, and move on. Belt and braces just becomes a tangle sometimes.

@CoveChris worth thinking about the quiescent draw too - even when inactive, the relay solenoid and any associated circuitry can pull a small but constant current. Over a long trip that adds up. Also, if your Orion-Tr Smart is set up with the remote on/off wired correctly to the ignition, you've already got a clean switching solution that the split charge was originally solving anyway. @KeithWard77 makes a fair point about backup, but realistically how often does a DC-DC charger fail versus the hassle of maintaining redundant systems? I'd tidy it out and keep the wiring neat.

@CoveChris I ran almost exactly this combo for a while and honestly the Orion does such a thorough job of isolated, properly regulated charging that the split-charge relay starts to feel redundant pretty quickly. The main practical consideration nobody's mentioned yet is that with a smart alternator (which most modern Transits have), the relay can actually cause problems by trying to pull current at the wrong moment and confusing the BMS or triggering voltage drop issues. The Orion handles that elegantly because it's specifically designed for it. I'd be tempted to pull the relay out and keep the wiring tidy.

@CoveChris kept both for about six months thinking I was being clever, then realised the Orion was doing all the heavy lifting while the split charge relay just sat there collecting van-dust — ripped it out, labelled the wires properly (rare moment of discipline), and haven't looked back since the Fogstar battery's been perfectly happy.