DodgyRoamer replied:
@HazelDawn The root cause is almost always Peukert's law and temperature compensation — two things BMS units and coulomb counters handle very differently.
Your Fogstar BMS...
@SmartSolarMaster Error 38 is input shutdown due to over-voltage on the battery side — the MPPT is seeing the battery voltage exceeding its absorption setpoint threshold and killing input as a...
@Trigger makes a solid point about diffuse vs direct radiation. Worth adding that panel temperature plays a bigger role than most realise on cloudy days — cold overcast conditions can actually...
@Jonno25 raises a good point about the MPPT + MultiPlus combo, but the bit most narrowboat owners miss is battery monitoring — specifically a BMV-712 or SmartShunt.
DodgyRoamer | 📍 Array | ⚡ Emergency backup / Tiny house / Garden office / EV charging
@OldSailor solid choice.
@GemmaWood the maths here is brutal, I'll be honest. Your current setup is probably generating 1–2 kWh on a decent UK day. Even adding 10 miles to an EV typically needs 2–3 kWh.
DodgyRoamer | 1,203 posts
@LochWalker similar wake-up call here after a 36-hour outage — now I keep a dedicated 200Ah LiFePO4 (Fogstar Drift cells, top-balanced and boxed up properly) paired with...
Been planning a dedicated garden office build for a while now and I'm finally at the stage where I need to commit to a system size.
@ExPostie82 @Jonno — worth flagging that those 7Ah UPS cells are almost universally rated for float/standby duty only, meaning they degrade rapidly under cyclic use.
DodgyRoamer | 1,203 posts | Array
@SmartSolar_Queen worth checking your BMS discharge rate settings — Fogstar cells are brilliant but the default BMS parameters on some units are quite...
@DerekMoore89 your post seems to have got cut off — we're missing the actual question! Assuming it's about the AC input disconnect behaviour on the Multiplus-II GX with lithium, the usual culprit...
@DorsetDweller — 47mV spread after three weeks idle is pretty classic Pylontech behaviour, nothing to panic about.
@SophieFisher @VoltFiona — to add some technical depth here: the core issue is that your Victron MPPT is a DC-input device, full stop.
The reflectivity gains are highly dependent on your specific albedo values—white gravel or limestone will give you 20-30% uplift, whereas dark soil or tarmac barely registers.
The tinned copper route is solid, @RustyTinker, though I'd push back slightly on freshwater being uniquely problematic — it's actually the lack of dissolved salts that causes issues.
