Anyone else running Victron MPPT alongside a split-charge relay — worth ditching the relay entirely?

Currently got a 175W Renogy panel feeding a Victron SmartSolar 100/20 into a 100Ah Fogstar lithium in my mate's Transit camper we're refitting. Works brilliantly on its own, but he also wants the alternator to top things up on longer drives.

Most people seem to bolt on a split-charge relay as an afterthought, but I keep reading that a proper DC-DC charger (like the Victron Orion-Tr Smart 12/12-18) is far kinder to lithium — the relay just dumps unregulated alternator voltage straight in. On my shepherd's hut build I never had to think about this, shore power only, so this is new territory for me.

The Orion-Tr is around £130–£160 depending where you catch it, which isn't nothing. But if a basic relay risks the BMS cutting out mid-drive and potentially confusing the alternator, that feels like a false economy. Has anyone actually run both a SmartSolar MPPT and an Orion-Tr on the same lithium bank — any issues with them fighting each other for charge priority, or does the Victron ecosystem handle that cleanly via VE.Direct/Bluetooth?

Not exactly a camper setup but ran a split-charge relay alongside Victron MPPT in my tiny house backup system for a while — honestly the relay felt like a bodge once the Victron was doing its job properly.

Worth looking at the Victron Cyrix-Li-CT instead. Plays nicely with lithium BMS signals and the SmartSolar can talk to it directly if you're using the VE.Smart network. Relay just doesn't know what the battery's actually doing — Cyrix does.

@BoatSteve only caveat — make sure your alternator can handle sustained lithium charging loads. Fogstar cells will hammer it if SOC is low. Might want a DC-DC charger (Victron Orion-Tr Smart is the obvious choice) rather than a direct relay connection full stop.

EmmaButler | 📍 Yorkshire | ⚡ 312 posts

We ditched the relay in our Sprinter build last year and went with a Victron Orion-TR Smart DC-DC charger instead — genuinely night and day difference. The relay was causing all sorts of grief with the lithium's BMS not playing nicely; voltage drop across the relay meant the alternator wasn't properly charging anyway.

The Orion isolates the starter battery properly, charges the leisure battery with an actual charge profile suited to lithium, and you can monitor everything through VictronConnect alongside your MPPT. It's all talking the same language essentially.

Only caveat — @BoatSteve worth checking your mate's alternator isn't too small. The Orion pulls a decent sustained current and older Transits with weedy alternators can run warm. Size the Orion accordingly rather than just grabbing the biggest one.

Cost is higher than a relay but the reliability is absolutely worth it.