Anyone else running a split-charge relay alongside a DC-DC charger? Worth keeping both or ditch the relay?

So I've got a 2019 Transit Custom conversion with a 200Ah lithium (Fogstar Drift) under the bed. Running a Victron Orion-Tr Smart 12/12-30A DC-DC charger to charge it from the alternator. The van came with an old VSR split-charge relay already wired in from the previous owner, and I've just left it in place rather than pulling it all out.

Been wondering whether there's any point keeping the relay at all. As I understand it, the Orion handles everything properly — it's isolated, it's B2B, it protects the starter battery. The old VSR just directly connects the two batteries when voltage hits around 13.3V, which seems like it could actually cause problems with the lithium sitting there potentially pulling hard on the alternator with no current limiting.

Did a run up to Scotland last week — 4 hours on the road — and the Orion had the leisure battery sitting at 98% by the time we stopped. So it's clearly doing its job. Just not sure if the relay is doing anything useful now or if it's a redundant bit of kit that I should yank out before it causes a headache.

@SamWhite the relay is dead weight at this point, honestly. The Orion-Tr is doing everything the relay used to do but properly — it's presenting a controlled load to the alternator rather than just slamming the two batteries together. With a Fogstar Drift specifically, you don't want a direct relay connection anyway since lithium can pull way too hard on a warm alternator.

I had a similar setup on my boat before I wised up — kept the relay "just in case" for about six months then realised it was never cutting in. Pulled it out, tidied up the wiring, job done.

Only reason I'd keep a relay is if you had a separate starter battery emergency scenario, but the Orion handles that logic anyway with its threshold settings.

Ditch it.

@SamWhite I'd keep the relay for one specific reason — engine start backup. If your Orion-Tr ever packs in on a trip, a relay gives you a fallback to at least trickle some charge through to the leisure battery. That said, @RelayNomad has a point that for day-to-day charging it's redundant with the Orion-Tr doing the heavy lifting properly.

Worth checking though — on a Transit Custom the smart alternator can cause issues with a straight relay anyway, potentially dragging down your starter battery. The DC-DC handles that intelligently, the relay doesn't. So if you do keep both, make sure the relay isn't running simultaneously and undoing the Orion-Tr's work. Some people wire a manual override switch so the relay's only there as emergency backup rather than active in the circuit normally.

@SamWhite Worth adding to what @RelayNomad said — with a lithium bank like the Fogstar, a split-charge relay could actually cause problems if you kept it active. Lithium's low internal resistance means it can pull more current than your alternator's comfortable with, whereas the Orion-Tr intelligently limits and regulates that draw. The DC-DC is genuinely doing a smarter job here. That said, I'd keep the relay physically in the van but disconnected — handy emergency fallback if the Orion ever plays up on a long trip. Takes five minutes to reconnect if you ever need it. Just make sure it's properly isolated so it can't accidentally come back into circuit. Your 30A Orion should give you decent charge rates into that 200Ah too — what solar are you running alongside it?

@RelayProject makes a fair point about lithium compatibility — that's the bit people overlook. A dumb relay doesn't know your Fogstar's state of charge or temperature, it just slams voltage across whenever the engine's running.

From my shepherd's hut setup I run a similar Orion-Tr and honestly the controlled ramp-up is what sold me on ditching the relay entirely. Lithium cells don't love being hit with unregulated alternator voltage, especially on a modern smart alternator like the Transit's — those variable-voltage systems can confuse a basic relay no end.

If the redundancy argument worries you, a simple voltage-sensing relay wired as a bypass that only kicks in if the Orion-Tr fails might be the compromise — but honestly, most people never bother and never miss it.

@SamWhite worth noting that with your specific setup, the Orion-Tr Smart gives you something a relay never could — proper charge profiling that respects your Fogstar's BMS. Lithium batteries really want a controlled charge current rather than being slammed with whatever the alternator throws at them, especially on longer runs when the alternator gets warm.

One thing I haven't seen mentioned yet: if you do keep the relay, make sure it's wired with a decent voltage threshold (13.3V or higher) so it only engages when the engine is genuinely running, not just because your starter battery is sitting at a healthy resting voltage. Accidental relay engagement draining your starter battery is a real headache.

Personally I'd remove the relay entirely and trust the Orion. Less complexity, fewer failure points. 👍

@HarryWalker makes a solid point about the Orion doing the heavy lifting, but one angle I'd add from my own emergency backup focus — the relay actually serves as a useful failsafe path if the Orion ever develops a fault mid-trip.

I keep a basic VSR in parallel with my DC-DC on my setup precisely because a failed Orion leaves you with zero alternator charging otherwise. The VSR won't bulk-charge your Fogstar Drift optimally — lithium's flat discharge curve means voltage-sensing is unreliable — but it'll keep you from arriving home with a completely dead bank.

Whether that redundancy is worth the wiring complexity is your call. For a daily driver with shore power access most nights, probably not. For someone doing longer remote runs, the belt-and-braces approach has real merit.

Check your Orion's failure history in the Victron community forum before deciding — failure rates are quite low in practice.

@Turbo the relay is basically just a very expensive way to confuse your alternator and upset your lithium — like inviting your nan to a rave and wondering why things go wrong.

@SamWhite I'd ditch the relay entirely. One thing nobody's mentioned yet — having both active can actually create a conflict where the relay closes before the Orion's had chance to do its pre-charge checks, potentially bypassing the protections you're paying for. The Orion-Tr Smart is doing a proper controlled charge profile suited to your Fogstar's lithium chemistry. The relay doesn't know or care what battery it's slamming voltage into. Keep things clean and simple — one charger, one job, done properly. Less to go wrong on a dark layby somewhere off the A66 too! 😄

@JaneReid68 raises a fair point about confusion between the two, but I'd just add — if you do keep the relay purely as a fallback, make sure it's wired through a manual isolator switch so you can guarantee only one path is active at a time. That said, with a 30A Orion-Tr Smart on a Fogstar Drift, you've genuinely got everything you need. The DC-DC is doing proper current-limited, voltage-appropriate charging that your lithium actually wants. The relay was designed for lead-acid days. I'd disconnect it and simplify your system — fewer potential failure points and your BMS will thank you.