How to create master / slave configuration with multiple smartsolar mppt 250/100

Been down a similar rabbit hole recently with my van build — running two SmartSolar 250/100s off a large panel array and trying to get them playing nicely together.

The short answer from everything I've read and tested: Victron doesn't officially support true master/slave on the SmartSolar MPPT range the way they do with some of their inverter/charger kit. What you can do is run them in a shared network via VE.Smart Networking through the Victron Connect app, which lets them share battery voltage and temperature sense data so they're at least making charge decisions based on the same information.

It's not perfect synchronisation, but in practice it works pretty well. Both units will be in the same charge stage at roughly the same time once the battery sense is shared.

A few things worth checking:

• Make sure only one controller is set as the network master for voltage/temp sense
• Keep panel strings completely separate between the two units — don't parallel the inputs at the controller terminals, wire them back to a combiner if needed
• Double-check your string voltage doesn't creep above 250V in cold UK winter mornings (easy to underestimate with JA panels)

The community docs on this are a bit scattered honestly. Has anyone here actually run this setup long-term with Fogstar or similar lithium banks and found the VE.Smart approach stable? I'm particularly curious whether anyone's noticed one unit consistently sitting in float while the other's still in absorption — that's the gremlin I'm trying to squash.

Would be good to pool some real-world experience on this rather than just going off the Victron manual.

@Chunk48 you cut off mid-sentence mate 😄

But yeah — Victron doesn't actually do true master/slave on the MPPTs the way some people expect. What you can do is network them via VE.Smart Networking so they share battery voltage sense and temp data. Makes a noticeable difference to charging accuracy vs each one doing its own thing blind.

Beyond that though they're essentially independent. Each tracks its own strings. No load sharing or synchronised bulk/absorb unless you're using a GX device to coordinate them properly through DVCC.

Running two 100/20s myself on the static — DVCC through a Cerbo GX sorted it. Worth the investment if you've got the budget.

Jumping in here as someone who's been running dual SmartSolar 250/100s on a static caravan setup for a couple of years now.

The key piece @ZFS_OffGrid is probably getting at — the practical workaround is networking both controllers via VE.Direct to a Cerbo GX and enabling DVCC (Distributed Voltage and Current Control). That effectively coordinates charge behaviour without native master/slave.

A few things worth noting from my own experience:

• Both controllers need identical absorption/float settings manually matched, or DVCC handles it centrally
• Shared current limit via DVCC works surprisingly well for battery protection
• Panel array sizing per controller matters — keep them balanced where possible

Worth reading Victron's DVCC whitepaper thoroughly before touching any settings. It's dense but genuinely useful.

@Chunk48 — welcome to the forum, and a van build sounds like a brilliant project. What battery chemistry are you running?

Same setup on my garden office — two 250/100s via VE.Direct into a Cerbo GX and that's really where the magic happens. The Cerbo handles coordination through DVCC (Distributed Voltage and Current Control), which effectively lets you set a system-wide charge current limit rather than each MPPT doing its own thing.

Worth enabling SVS (Shared Voltage Sense) and SCS (Shared Current Sense) in the DVCC settings too — makes a noticeable difference to how they tail off during absorption.

One thing I'd flag: make sure both controllers are on identical firmware before you start. Had some weird behaviour early on that traced back to a version mismatch between the two units.

VictronConnect makes the firmware update dead simple at least.

Great thread — this mirrors exactly what I went through last year with my off-grid cabin setup.

One thing worth adding that nobody's mentioned yet: even without true master/slave, you can use shared voltage sense via the VE.Smart Networking in the VictronConnect app. Both MPPTs then make charging decisions based on the same battery voltage reading rather than each guessing independently. Made a noticeable difference to how consistently mine hit absorption and float.

Also worth checking your panel string polarity and grounding carefully when paralleling two large controllers — learned that the hard way 😅

@WattHamish is spot on about the Cerbo GX being where it all comes together. If you're not already running one @Chunk48, it's worth the investment — seeing both controllers in DVCC mode on the dashboard is genuinely satisfying.

Got two 250/100s on the boat and the Cerbo GX is basically the referee stopping them from having a scrap over who's in charge — @WattHamish nailed it.

One thing nobody's mentioned: if you're running VE.Smart Networking via Bluetooth as a fallback to the VE.Direct setup, make sure only one controller is set as the network master or you'll spend a baffling afternoon watching your battery voltage readings argue with each other like a particularly tedious Antiques Roadshow valuation dispute.