solar to an existing victron battery?

Done exactly this on my Transit build last spring — had a 200Ah Fogstar Drift lithium already wired up to a Victron SmartShunt and wanted to bolt on solar without replacing the whole setup.

The key thing I found is that Victron kit plays incredibly nicely with itself. I ran a 100W Renogy panel into a Victron SmartSolar MPPT 75/15, and because the MPPT talks directly to the SmartShunt over Bluetooth via the VE.Smart networking feature, it actually knows the real state of charge rather than guessing. Made a massive difference to how intelligently it charged — no overcharging, no faff.

A few things worth checking before you connect anything:

• BMS charge limits — make sure your solar controller's absorption/float voltages match what your battery's BMS expects. Lithium and AGM are very different here.
• Fusing — add an appropriate fuse close to the battery on the solar feed. Obvious, but easy to skip.
• Charge controller sizing — calculate your panel's max current and leave yourself headroom.

The VictronConnect app is genuinely brilliant for monitoring all of this once it's running. You can see exactly what the panel is pushing in versus what the loads are pulling out, all from your phone.

What battery have you got, and is it lithium or AGM? That'll change the advice quite a bit. Also — are you planning to add more panels later? Worth oversizing the MPPT now rather than swapping it out in six months.

@CoastalCamper did something very similar on my static caravan setup, though rather than a Transit I had the joy of routing cables under skirting boards and through increasingly creative holes in chipboard flooring.

What I'll add — because nobody mentioned it yet — is to make sure your MPPT charge controller is set to lithium profile before it ever sees the battery. I made the rookie mistake of connecting my Victron SmartSolar 100/30 on the default AGM settings and it spent a happy afternoon trying to bulk charge my cells somewhere it really shouldn't have been.

The SmartShunt will still read everything correctly regardless, it's purely the MPPT profile that matters. Five minutes in the VictronConnect app before you commission it properly saves a rather anxious afternoon checking cell voltages one by one.

My Fogstar's been happily slurping solar for two years now — turns out lithium doesn't care where the electrons come from, just that they keep coming.

Same setup in my garden office — Fogstar Drift into a Victron SmartShunt, then bolted on a couple of Renogy panels later with an MPPT controller. Took maybe an afternoon.

One thing worth checking: make sure your MPPT is configured for lithium charge profile rather than the default AGM settings. Caught me out initially — the SmartShunt was reading odd SOC figures until I sorted the absorption/float voltages properly.

@WayneKnight is right that lithium doesn't care about the source, but it absolutely cares about the charge parameters. Get those wrong and your BMS will start disconnecting under load, which is annoying to diagnose.

Great thread — I did exactly this on my narrowboat last autumn. One thing worth flagging that nobody's mentioned yet: if you're adding an MPPT controller into an existing Victron setup, it's absolutely worth getting a Victron SmartSolar rather than a third-party unit. The VE.Direct connection means it'll talk directly to your SmartShunt and give you proper combined data in the Victron app — you can see solar input alongside consumption in one place rather than guessing. @WattHamish the Renogy route works fine electrically, but you'll be flying blind on the monitoring side compared to native Victron kit. The SmartSolar 100/20 is genuinely reasonable money these days and the integration is seamless. Made a real difference to how I manage the boat's power over winter.