Best way to charge an EV from solar + battery bank without killing the batteries?

Looking at adding EV charging to my existing setup — currently running a 48V system with 15kWh of Fogstar Drift LiFePO4 and about 4kW of panels through a Victron MultiPlus-II. Works brilliantly for the house loads but I want to occasionally top up my Nissan Leaf (24kWh battery) without absolutely hammering the bank.

The maths are obviously brutal — even getting 20 miles of range back means pulling maybe 6-7kWh, which is nearly half my usable capacity in one go. I've been experimenting with scheduling the Zappi charger to only run when SOC is above 80% and solar is genuinely covering most of the draw, but it feels like I'm just guessing at the settings rather than doing it properly.

Has anyone set up proper automation for this — maybe through Node-RED or the Victron Venus OS — so the charger throttles back or stops entirely based on battery SOC and real-time solar yield? Interested in whether the Zappi's eco modes actually talk nicely to a Victron system or if I need something like a current transformer arrangement to make it behave. Would love to hear from anyone who's cracked this rather than just winging it like me.

@PanelJulie the key thing most people miss here is minimum SOC before EV charging kicks in. I run a similar setup for my garden office plus occasional van charging, and I've got the MultiPlus-II configured via Node-RED to only allow EV draw once the battery hits 80% SOC, cutting off entirely below 60%.

With 15kWh of Fogstar you've got decent capacity, but an EV will absolutely hammer it if you're not careful — especially on overcast days when your 4kW array is delivering maybe 800W net.

Look into scheduled charging tied to your Cerbo GX if you have one — charge overnight on cheap Octopus Agile rates and let solar top up during the day. Your batteries will thank you long-term by avoiding those deep partial cycles.

@Finn1991 makes a solid point on SOC thresholds. I'd add — watch your charge rate vs panel input ratio carefully. If your EV is pulling 7kW but panels are only generating 3kW, the deficit comes straight off the battery bank faster than most people expect.

On my boat setup I use Node-RED with Victron MQTT to dynamically throttle the EVSE based on actual solar yield. Keeps the bank above 80% most days.

Practically speaking:

• Set EVSE to 6A minimum (Type 2) so you can actually dial it low enough
• Use a smart EVSE like Hypervolt or Zappi — Zappi's eco mode plays nicely with excess solar logic
• Don't rely on Victron's built-in ESS alone for this; it's not granular enough

15kWh is decent headroom but it'll disappear quickly if you're not watching the draw rate.

Zappi + Node-RED automation watching your Victron MQTT feeds is the combo that'll stop you accidentally hoovering your Fogstar empty at 2am because you forgot the kettle was on 🔌

@BenJackson the Zappi + Node-RED combo is great until you've spent three evenings debugging a MQTT topic typo while your van sits uncharged on the drive like a very expensive ornament.

For what it's worth, the Victron DVCC settings doing the heavy lifting here is underrated — pair that with the MultiPlus-II's grid setpoint and you can throttle EV charging dynamically without needing to become a home automation wizard first. Simpler starting point before you go full Node-RED rabbit hole.

@PanelJulie 15kWh of Fogstar is a lovely bank but I'd still set a hard floor of around 40% SOC before any EV draw kicks in — ask me how I learnt that lesson on a cloudy October weekend in a marina car park.

@SussexBoater honestly felt that in my soul 😅

Worth flagging a simpler middle ground — Victron's ESS assistant with a minimum SOC floor set in VRM. No MQTT faff, just tell the MultiPlus-II "don't go below 40%" and let the Zappi read the output meter. Crude but bulletproof.

On the actual battery side — 15kWh Fogstar Drift is decent capacity but EV charging will cycle it hard. Even a 7kW home charger will drain that in ~2hrs. I'd keep max discharge rate under 0.5C if you're doing this regularly, otherwise you're burning cycle life faster than you'd expect.

Slow overnight solar top-up into the car is actually the most battery-friendly approach if you've got the time.