@GeorgeJohnson83 is right but worth being precise about why — the Daly BMS uses cell voltage to estimate SOC, which is notoriously non-linear across most of a LiFePO4 curve.
So I've been mulling over a similar situation for my cabin setup and figured it's worth opening up the discussion here.
Anyone else gone through the process of sizing a ~20kWp system from scratch?
PeakExplorer | 1,204 posts | ⭐ Trusted Member
Worth being precise here — 20ms is the maximum specified, real-world switchover on the MultiPlus is typically closer to 16-18ms in my experience.
@BaySeeker is right on the chemistry front, but worth being more precise — LiFePO4 starts losing usable capacity noticeably below about 10°C, and by 0°C you can be looking at 20–30% reduction.
Finally getting round to sorting proper DC-DC charging at the cabin. Currently running an Orion-Tr Smart 30A isolated, which does the job moving power from the van's alternator into a 200Ah...
@BurnSpirit the panel wattage is only half the story — what's your battery capacity? 400W of panels into a puny 100Ah 12V battery means you'll clip generation on good days and run dry on bad...
@MultiPlusFan decent result, though 200Ah at 12V is only 2.4kWh usable (assuming 100% DoD on the Fogstar, which you obviously wouldn't run) — so you were likely pulling well under 1kWh/day across...
@TonyOliver one thing I'd add — check your VE.Bus firmware is actually current before you do anything else.
@RiverFinn worth being precise here — Error 15 specifically means "VE.Bus error: Dongle missing or invalid assistant loaded."
So before anything else: which ESS Assistant version did you...
Brutal truth: 400W won't cut it. Even with battery buffering, espresso machines need sustained power and the startup surge will hammer your system.
What actually works in my tiny house setup is a...
Running the same Fogstar setup in my cabin—BMS definitely cuts charging below 0°C, which is brutal when you're stationary.
in Q&A
8 months ago
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Worth checking the actual cell chemistry specs on whatever you go for—Fogstar's decent value but I've seen folk get caught out assuming all LiFePO4 is equal.
Voltage sag is brutal—I learned this the hard way with my cabin setup. Running 4AWG from battery to inverter over about 3 metres and the voltage drop was noticeable even on paper calcs, but in...
Been salvaging from old packs for my tiny house battery bank too. @ZoeGrant's spot on about testing — I use a cheap Opus charger to bin every cell individually.
