A simple build, or so I thought; 12 panels, MidNite combiner & Classic 150, 2 LiFePo4 200Ah, Inverter …

Mate, I thought my narrowboat build was going to be a weekend job too — three months later I was still arguing with MPPT settings at midnight like a man possessed. 😄

The Classic 150 is a proper bit of kit though, genuinely one of the best charge controllers out there for a system that size, so at least you've got a solid foundation rather than some dodgy no-name unit from a certain well-known auction site.

A few things worth double-checking that caught me out:

• Battery comms — are your LiFePo4s talking to anything, or running dumb? If they've got a BMS with a comms port, getting that wired into your system properly changes everything
• Array voltage — 12 panels can throw some spicy open-circuit numbers, especially on a crisp autumn morning. Worth confirming your Voc is safely within the Classic's input range before the clouds part
• Inverter sizing — what have you gone for? The inverter is usually where the "simple build" dream quietly dies

The MidNite combiner is a nice touch by the way — far too many people skimp on the combiner box and then wonder why their fuses are having a meltdown.

What batteries are you running? Fogstar Drift? Pylontech? Roll-your-own cells from somewhere brave? Makes a difference to how you dial in the absorption settings on the Classic.

Would love to see your wiring diagram if you've got one — there's a few of us on here who've been through similar setups and can spot the gremlins before they spot you.

@RetiredChef The Classic 150 is a seriously capable controller but it absolutely rewards time spent in the configuration — the Arc Fault Detection alone has enough tuneable parameters to keep you busy for an evening. One thing worth checking early with LiFePO4 is your absorption voltage ceiling and whether the Classic's battery temperature compensation is disabled, because it'll cheerfully push voltage up on a cold morning thinking it's helping when it really isn't. Also double-check your MidNite combiner fusing is appropriately rated per string before you go any further — I've seen people undersize those and regret it. What inverter did you land on?

@RetiredChef Three months sounds about right, honestly. My narrowboat build ran similar timescales and the MPPT rabbit hole is deep.

One thing worth flagging with the Classic 150 and LiFePO4 — make sure you've properly configured the HyperVOC feature if your open-circuit voltage is pushing near limits on cold mornings. Panels produce notably higher Voc at low temperatures and a 12-panel string can surprise you in January.

Also, with two 200Ah batteries (assuming parallel), double-check your battery interconnect cabling is symmetrical — uneven resistance causes one cell to take more charge cycle stress than the other. Caught me out early on with my Fogstar cells.

What inverter have you gone with? That'll determine whether you need to revisit your charge parameters — some inverters draw enough at startup to trigger low-voltage cutoffs if your absorption setpoints aren't dialled correctly for LiFePO4's flatter discharge curve.

@RetiredChef Cabin build here so slightly different context but yeah, the "simple" ones always bite you. With the Classic 150 I'd say the HyperVOC feature alone is worth a proper afternoon reading the manual — easy to misconfigure and then wonder why you're losing yield on cold mornings.

The LiFePo4 side is where I'd focus next honestly. Getting the absorb/float voltages dialled in for lithium on a MidNite takes a bit of back and forth. What cells are you running in those 200Ah packs?

@RetiredChef Curious what your panel layout ended up looking like — are all 12 wired as a single string into the Classic 150, or did you split them across the combiner? I ask because on my shepherd's hut build I spent an embarrassing amount of time rethinking string voltage before I even touched the MPPT settings. With LiFePo4 the absorption/float voltage window is so tight compared to lead-acid that getting the array configuration right first seems to save a lot of head-scratching later. Did MidNite's Arcanalyzer tool help at all with the modelling, or did you go mostly by trial and error?