Has anyone actually managed to run a 1200W inverter purely off a 200Ah lithium bank without a split charge relay?

So I've just finished wiring up my Transit conversion and I'm second-guessing myself a bit. I've got a 200Ah LiFePO4 (Fogstar Drift) connected to two 175W solar panels via a Victron SmartSolar 100/30 MPPT. The inverter is a Giandel 1200W pure sine — nothing fancy, but it's done the job in testing.

My concern is that I deliberately skipped a split charge relay or DC-DC charger from the van's alternator, thinking the solar would cover everything. But now that we're heading into autumn and I'm planning longer trips up into Dartmoor, I'm starting to wonder if 350W of panels is going to be enough on cloudy days. Yesterday I only pulled about 40Ah back in over a full overcast day, which felt pretty grim.

Has anyone else relied solely on solar through the winter months in the UK, particularly in the South West? Tempted to add a Victron Orion-Tr Smart 12/12-30 as a backup, but I don't want to spend £120 if it's genuinely unnecessary. What's your actual real-world experience been?

Hey @DevonCruiser, short answer is yes, absolutely doable. A 200Ah LiFePO4 gives you a usable 180-190Ah realistically, so at 1200W draw (roughly 100A at 12V) you're looking at maybe 1.5-2 hours continuous before you're digging into reserve territory. That's usually fine for most van use cases unless you're running something hefty constantly.

Your Fogstar Drift has decent discharge rates so no issues there technically. The bigger question is what you're actually running through that inverter - a 1200W kettle for 3 minutes is very different to a 600W device running for hours.

Without a split charge relay you're entirely dependent on your solar for replenishment, so two panels on cloudy Devon days might leave you chasing your tail. Have you considered a DC-DC charger from the alternator as backup? Makes a big difference in winter.

Ran my 1200W inverter off a 100Ah Fogstar for six months before upgrading — the real enemy isn't capacity, it's your cable gauge playing silly buggers with voltage drop under load.

Hey @DevonCruiser, good setup you've got there! One thing worth mentioning that nobody's touched on yet — keep an eye on your battery's BMS discharge rating. The Fogstar Drift 200Ah is rated for 100A continuous discharge, which at 12V gives you roughly 1200W before inverter inefficiency eats into it. So at full load you're basically sitting right at the limit. In practice your 1200W inverter will rarely hit peak draw unless you're running something like a kettle, so you'll likely be fine day-to-day. Just avoid stacking multiple high-draw appliances simultaneously. Your solar setup should keep things nicely topped up during decent weather too. 👍

Great setup @DevonCruiser! One thing I'd add that hasn't been covered — make sure your inverter's low voltage cutoff is properly configured for LiFePO4. A lot of inverters come set up assuming lead-acid, so the cutoff might kick in too early (or worse, too late and stress your cells). On a Fogstar Drift you ideally want to be cutting off around 20% SOC, roughly 51.2V on a 12V bank, so somewhere between 12.8-13V depending on your load. Also worth double-checking your cable sizing between the battery and inverter — at 1200W you're pulling 100A and undersized cable will cause voltage drop that triggers nuisance shutoffs before you've actually run the battery down. 16mm² minimum, ideally 25mm² for that sort of run. What length cable are you working with between the two?