Charging a Lead acid battery from An Orion xs supplied by a smart solar

Been mulling over a similar topology for my tiny house emergency backup setup and thought it worth raising here.

My primary bank is a 200Ah Fogstar Drift LiFePO4, charged via a Victron SmartSolar MPPT 100/30. What I'm exploring is whether I can hang a pair of legacy lead-acid batteries off the back of that system using an Orion-Tr Smart (or the newer Orion XS) as a DC-DC charger — essentially treating the lithium bank as the "source" and the lead-acid banks as secondary loads that also happen to need proper charge profiling.

The Orion XS is engine-start-detection capable, but in a static off-grid context that feature is irrelevant — you'd just configure it for continuous mode. The more pressing question is whether the SmartSolar's absorption/float cycling on the lithium side will cause the Orion XS to behave oddly, given the lithium voltage curve is quite flat compared to what the Orion expects from a "source" battery.

In theory the Orion XS doesn't care what the source is, it just regulates output to whatever profile you've set for the lead-acid destination bank. So a lithium source sitting at 13.4V float should drive a perfectly respectable AGM charge cycle on the output side.

Has anyone actually run this configuration long-term? Specifically curious whether the SmartSolar's bulk-to-float transition causes the Orion XS to cut in and out repeatedly, or whether it just tracks smoothly. VictronConnect logging would presumably show this, but real-world experience would be more useful than my bench testing.

@SaltyRanger the Orion XS is a solid choice as a DC-DC charger between banks, but watch your absorption/float profiles carefully when using it to charge lead acid downstream of a LiFePO4 source.

The SmartSolar will be optimised for lithium, so the Orion XS needs to be set independently for your lead acid chemistry — sealed, AGM, gel, whatever you're running. Don't assume the upstream profile carries through correctly.

Also worth enabling the Orion's engine detection or remote on/off if you're triggering it conditionally, otherwise it'll just run continuously draining your primary Fogstar bank.

VE.Smart networking between the SmartSolar and Orion XS helps enormously here — temperature and voltage compensation shared across devices makes the whole thing considerably more reliable as a backup topology.

@SaltyRanger one thing worth flagging that often gets overlooked in this topology — your SmartSolar will see the Orion XS as essentially a resistive load during bulk, which is fine, but if your LiFePO4 BMS trips under any condition (cell imbalance, low temp cutoff, whatever), the Orion XS loses its input mid-cycle. Depending on your lead acid state at that point you could end up with a partially charged LA bank that then self-discharges into a disconnected circuit.

I ran a similar setup at my cabin for about eight months — Victron SmartSolar 100/30 into a 100Ah Fogstar, then an Orion TR Smart (older unit, not XS) feeding a flooded LA buffer. Added a simple voltage-triggered relay on the LiFePO4 output side so the Orion only enabled above 13.2V. Crude but effective.

What's your intended discharge path from the LA bank specifically?

Ran almost exactly this topology on my narrowboat for two seasons — LiFePO4 bow bank feeding an Orion XS into a wet lead-acid starter battery amidships.

The bit that caught me out wasn't the charging profiles @RetiredPlumber mentions, or what @WezWhite72 is alluding to — it was temperature. Lead-acid wants a proper temp-compensated charge, especially in an uninsulated stern locker through a British winter. Without a Victron Smart Battery Sense on the lead-acid side, you're essentially charging blind.

Worth fitting one. They're not expensive and they talk to the Orion XS via VE.Smart networking. Made a noticeable difference to my battery longevity.

Also — size your Orion XS conservatively relative to the LiFePO4 bank. You don't want the DC-DC pulling hard enough to drag your SmartSolar into a compensation loop it wasn't designed for.

@OldSailor86 that narrowboat experience is reassuring actually. I ran something loosely similar in my static caravan — Victron SmartSolar into a Fogstar LiFePO4, then a smaller Orion (not the XS, older model) feeding a knackered AGM for my 12v lighting circuit.

The bit that caught me out was the Orion not knowing the AGM was full. It just kept pushing. Ended up gassing the battery something rotten before I realised what was happening.

Worth double-checking your Orion XS output profile is actually set correctly for lead acid chemistry in the VictronConnect app — it doesn't always default sensibly. Took me an embarrassingly long time to find that setting buried in the adaptive charging options.