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

Last spring I rewired most of my Transit-based camper and fitted a Victron Orion-Tr Smart 12/12-30A DC-DC charger to properly charge my 200Ah lithium from the alternator. Brilliant bit of kit, no complaints. But I kept the old 40A split-charge relay in the circuit as well because I wasn't sure I trusted the Orion on its own at the time. Classic belt-and-braces thinking.

Now I'm second-guessing myself. As far as I can tell the relay is basically redundant — the Orion already handles the isolation and charge management on its own. If anything I'm worried the relay occasionally cuts in and dumps unregulated current straight at the lithium before the Orion can react, though honestly I'm not 100% sure that's how it works in practice. My BMS hasn't complained yet but it's niggling at me.

Has anyone actually run a similar setup and worked out what's really happening? Worth pulling the relay out entirely and simplifying things, or is there a sensible reason to keep it? The van's a 2019 Transit so it has a smart alternator, which is exactly why I went DC-DC in the first place.

MeadowHermit | Posts: 847

@Rodney47 Short answer - ditch the relay. The Orion-Tr is doing all the heavy lifting, and the split-charge relay alongside it is essentially redundant now you've got lithium. The relay was fine for AGM days when you just wanted bulk voltage dumped across the battery, but lithium genuinely needs that controlled charge profile the Orion provides.

Leaving both connected can actually cause headaches - the relay may try to equalise your starter and leisure batteries directly, which is exactly what you don't want with lithium. The Orion isolates them properly and protects your alternator from the lithium's hungry initial draw.

Keep your relay if you want a backup path for emergencies, but I'd wire it so it can't operate simultaneously with the Orion. Otherwise honestly just remove it and simplify your setup - fewer components to fault-find later.

FET_Queen | Posts: 312

@Rodney47 Ran the exact same combo in my van conversion for about six months before I pulled the relay out. The issue I kept hitting was the relay occasionally back-feeding during engine-off periods — nothing catastrophic, but my Victron BMV-712 was showing unexplained small draws.

Once I removed it, monitoring got cleaner and I could actually trust my state-of-charge readings.

Worth double-checking your Orion-Tr has engine detection configured properly through VictronConnect though — either via the VE.Smart network or the remote L-line from ignition. If that's not set up correctly you'll get the Orion trying to charge from a stalled alternator, which is a separate headache entirely.

The relay was a sensible belt-and-braces approach in the lead-acid days, but with lithium it's genuinely redundant alongside a DC-DC charger.

SolarJason | Posts: 1,204

Worth understanding why the relay feels redundant before pulling it. The Orion-Tr isn't just a charger — it's actively protecting your starter battery by monitoring voltage thresholds before it even begins pulling current. A split-charge relay is comparatively blind to that.

Had a similar setup on my LiFePO4 bank (Fogstar Drift 200Ah) and the relay would occasionally try dragging current through at weird moments — engine just cranking, alternator not properly settled. The Orion-Tr handles that elegantly with its input threshold settings.

Only scenario I'd consider keeping both is if you're running something like a basic flooded lead-acid leisure battery alongside the lithium, where the relay handles a completely separate circuit. But on a single lithium bank? The relay is just introducing potential conflict rather than adding any genuine redundancy.

@Rodney47 what's your starter battery situation — standard lead-acid up front?

ForestDaz | Posts: 2,156

@Rodney47 The relay's about as useful as a chocolate fireguard now — your Orion-Tr already handles voltage sensing, charge profiling, and won't murder your alternator on a cold start like a dumb relay cheerfully will. Only caveat: if your relay is wired into something else (habitation fusing, 12v feed for accessories, etc.) don't yank it without actually tracing the circuit first, because I once spent four hours in the dark outside my static caravan wondering why nothing worked before realising I'd removed something load-bearing. Check what it's actually doing before the screwdriver comes out — basic stuff, but apparently not obvious stuff.

SuffolkSolar | Posts: 847

@Rodney47 Pulled mine out after about a year running both in my Hymer. The Orion-Tr handles everything the relay was doing, just properly.

One thing nobody's mentioned — if you've got a smart alternator (variable voltage, common on newer Transits), the relay can actually cause grief by confusing the BMS with weird voltage spikes. The DC-DC isolates all that.

Only reason I'd keep a relay is if you needed a massive dump charge bypassing the Orion's 30A limit, but honestly for 200Ah lithium you don't want that anyway.

Pull it. Tidy the wiring up and enjoy the extra space in the cab.

LauraCole | Posts: 412

@Rodney47 One thing worth considering before you yank it out — does your Transit have any other 12V consumers that you want powered directly from the starter battery regardless of the Orion's state? I kept my relay purely because I wanted my water pump and a USB socket accessible even when the DC-DC charger wasn't running. Nothing to do with charging the leisure battery at all.

Also worth double-checking whether your relay is doing any accidental load-sharing in the background. I had mine quietly pulling current from my lithium back into the starter circuit before I noticed. Isolated it sharpish after that! The Orion handles the actual charging side perfectly, as @SuffolkSolar says, but just map out your full circuit before deciding. Sometimes the relay earns its keep for reasons unrelated to charging.