MPPT 100/30 mit zwei Batterien nutzen

Been thinking about this setup lately and wondered if anyone's tackled something similar.

Running a Victron MPPT 100/30 with a 200Ah LiFePO4 (Fogstar Drift) as my main house bank, fed by two 175W panels. Works a treat for the leisure side of things, but I've been scratching my head about whether I can also keep my starter battery topped up from the same controller.

The way I understand it, the 100/30 only has one battery output, so you can't simply wire two separate banks directly to it without some kind of intermediary. A few options I've been mulling over:

• DC-DC charger (like a Victron Orion-Tr Smart) between the house bank and the starter battery — probably the cleanest solution but adds cost
• A battery-to-battery charger triggered by the MPPT output
• Some kind of VSR/relay, though I've read these can be problematic with LiFePO4 chemistry

The concern with the relay approach is that LiFePO4 holds voltage so flat for most of its cycle that the VSR might never actually trigger properly — has anyone found a reliable threshold setting that works?

Main priority is keeping the starter battery healthy so the van doesn't leave me stranded, but I don't want to overcomplicate the wiring either.

What are others doing in a similar dual-battery setup? Is the Orion really the go-to solution here, or is there something simpler I'm missing?

@George1972 welcome to the forum — great first post and a solid bit of kit to be working with!

One thing worth flagging: the MPPT 100/30 only has a single battery output, so you can't connect two separate banks directly and expect independent charge profiles. What you can do is:

• Connect both batteries in parallel (assuming same chemistry and ideally same age/capacity)
• Use a Victron BatteryProtect or a DC-DC charger (like the Orion-Tr Smart) to feed a secondary battery from the main bank

If your second battery is a different chemistry — say, an AGM starter battery — the Orion-Tr Smart isolated version is really the proper solution there.

What's the second battery intended for? That'll determine the best approach.

@George1972 the 100/30 only has one battery output so you can't run two banks independently from it — not without external switching anyway.

What some people do is run a Victron BatteryProtect or a simple relay/VSR between the main bank and a secondary, so the second battery only charges once the primary is topped up. Works reasonably well in a motorhome context.

Alternatively if the second battery is just for a specific load (engine start, etc.) a Victron Orion DC-DC isolates it properly and charges it correctly without the banks fighting each other.

What's the second battery actually for? That changes the answer quite a bit.

@OffGridMax is right — one output, full stop, but if you're dead set on keeping the starter battery topped up, a DC-DC charger (Victron Orion-Tr Smart isolated) off the house bank is the proper way to do it, not some bodged parallel connection that'll have your LiFePO4 trying to resurrect a knackered lead-acid at 3am.

Been running exactly this in my static — Fogstar Drift house bank, Orion-Tr keeping the van starter battery happy, MPPT does its one job without getting confused about chemistry differences.

Worth noting: the 100/30 will get stroppy if you mismatch charge profiles between a LiFePO4 and a lead-acid on the same output — one of them's getting the wrong voltage, and it won't be the one you wanted to sacrifice.

@Rob1963 nailed it — DC-DC charger is the move, and before anyone asks: yes, a Victron Orion-Tr Smart is worth every penny even when it makes your wallet cry.

@EssexNomad and @Rob1963 have covered the DC-DC route well. One thing worth adding for @George1972 — make sure you get the isolated version of the Orion-Tr Smart rather than the non-isolated one. With a LiFePO4 house bank and a lead-acid starter battery, isolation prevents any ground loop issues that can cause headaches down the line.

Also worth checking your Fogstar Drift's charge profile is properly configured on the MPPT — Victron's default lithium preset is a reasonable starting point but Fogstar publish their own recommended settings. Little things like that make a real difference to battery longevity.

What's your van/boat setup like? Knowing whether the alternator is also in the mix would help give more complete advice.