Batterie moteur plomb, batteryprotect, orion et batterie de bord LFP

Been thinking about this a lot lately with my shepherd's hut setup, so figured it was worth raising here.

I've got a Victron Orion-Tr Smart 12/12-30 pulling from a vehicle lead-acid starter battery to top up my Fogstar 200Ah LFP leisure battery. Works a treat generally, but I've been mulling over whether it makes sense to drop a Victron BatteryProtect between the lead-acid and the Orion input.

The logic being: if the engine battery drops too low whilst the Orion is doing its thing — say you've left something on, or it's a cold morning and the battery's already stressed — you don't want the DC-DC hammering it further and leaving yourself stranded.

The counter-argument I keep coming back to is that the Orion Smart already has a configurable input voltage threshold. You can set it to cut off below, say, 11.5V or 12.0V. So is a BatteryProtect on the input side actually redundant in that case, or does it add a meaningful layer of protection the Orion alone doesn't cover?

I suppose the BatteryProtect reacts faster and is a dedicated low-voltage disconnect, whereas the Orion's threshold is more of a soft setting that could theoretically drift or be misconfigured.

Anyone running this combination? Particularly interested if you've got a larger Orion (the 30A version seems popular but I know some are running the 18A for lighter loads).

Also — does the BatteryProtect placement matter here? Input side of the Orion only, or would you bother on the LFP side too given the BMS should handle that anyway?

Curious what others have landed on

@NeilBurns91 worth flagging — the Orion-Tr Smart has a specific "engine detection" threshold you'll want to configure carefully when the source is lead-acid. Default setting assumes alternator voltage, but a resting LA battery sitting at 12.7V can occasionally fool it into thinking the engine's running.

On the BatteryProtect side, make sure you're not routing any charge current through it — it's load disconnect only, common mistake. Seen people damage them doing exactly that.

My own narrowboat setup runs a similar topology; Orion feeding Fogstar Drift LFP house bank, with the BatteryProtect handling DC loads independently. Key thing is configuring the Orion's absorption/float voltages to suit LFP properly — 14.2V absorption, no float essentially.

What's your LFP bank capacity and BMS spec? That'll affect whether the 30A Orion is adequate for your use case.

Good shout @NeilBurns91 — one thing worth adding: pair a Victron BatteryProtect on the lead-acid side before the Orion input. Protects your starter battery from getting dragged too low if the Orion's engine detection ever misbehaves or you're running off hook-up with the engine off.

Done exactly this in my shepherd's hut rig — BP set to disconnect around 12.2V, LFP house bank (Fogstar Drift 100Ah) on the output side. Works a treat.

Also worth knowing: the Orion-Tr Smart in standalone mode vs engine detection mode behaves quite differently. Check which you've actually got active in VictronConnect — easy to miss.

Good points from @PanelEwan and @BirchLover already, but one thing worth considering that nobody's touched on yet — the Orion-Tr Smart's output profile when charging LFP.

The default absorption/float curve is designed around lead-acid assumptions. You'll want to configure it in DC-DC charger mode via the VictronConnect app and set a proper LFP charge profile (typically 14.2V absorption, no float or a very low one ~13.5V). Otherwise you risk either undercharging or keeping the LFP at elevated voltage longer than necessary.

Also worth noting: the 30A output sustained in a confined shepherd's hut setup will generate meaningful heat on the Orion unit itself — mine runs noticeably warm. Mount it somewhere with decent airflow, ideally metal contact for passive heatsinking.

@Squib82 raises something important there. One thing I'd add from my own experience running a similar Orion-Tr Smart setup — check your alternator type before assuming the 30A output is safe long-term. Many modern vehicles have smart alternators (variable voltage regulators) that don't play nicely with LFP loads; the Orion handles this better than a direct connection would, but if you're seeing the alternator hunting or the Orion repeatedly dropping out, you may need to dial the charge current back to 20A or even 15A to keep things stable.

Also worth noting: the Orion-Tr Smart's Bluetooth configuration via the VictronConnect app lets you set absorption voltage and tail current precisely for LFP — don't leave it on the default lead-acid profile or you'll either undercharge or stress the cells depending on firmware version.