Anyone else had their JK BMS trip out mid-charge on a warm day? Trying to nail down the cause

I've been running a 280Ah LiFePO4 pack (four EVE cells in a 4S configuration) in my campervan for about eight months now, managed by a JK BMS — the 200A active balancer version. Generally it's been rock solid, but last weekend parked up in a sunny spot in the Brecon Beacons, ambient temps probably nudging 28°C inside the van, and the BMS tripped out twice during the bulk charge phase. Both times the solar was pushing around 45A through a Victron MPPT 100/50.

When I pulled the JK app logs afterwards, the over-temperature protection had triggered at 45°C on cell sensor 2. I've got the OTP threshold set at 45°C which I know is fairly tight — I left it at default when I set it up. I'm thinking either I bump the threshold up to 50°C, or I look at improving airflow around the pack because right now it's just sitting in a plywood box under the bed with no ventilation gaps worth mentioning.

Has anyone dealt with this on warm days, particularly with higher charge currents? I'm a bit wary of just raising the threshold without understanding whether 45°C is actually a safe ceiling for EVE 280Ah cells or if there's genuine headroom above that. Also wondering whether one cell running warmer than the others points to a balance issue or just its position in the pack.

@Tel1997 had almost exactly this with my shepherd's hut setup last July — scorching week, south-facing roof, and my JK kept cutting out around 2pm each day like clockwork.

Turned out the BMS itself was getting too warm sitting in an enclosed compartment. The protection tripped on MOS temperature rather than cell temperature. Easy to miss because most people assume it's the cells misbehaving.

Two things that sorted it for me:

• Moved the BMS somewhere with actual airflow
• Dropped my absorption voltage slightly in the Victron MPPT settings during summer months

Worth pulling the JK app log and checking which protection actually triggered — it records the fault reason, which is genuinely useful. Mine showed MOS_TEMP_PROTECTION clear as day once I looked properly.

Also worth checking your cell-level temps if you have the NTC probes fitted. Warm EVE cells charge fine but they do have tighter tolerances than people realise.

@Tel1997 worth checking your cell temp sensor is actually making proper contact with the cell surface — mine was barely touching and giving readings 4-5°C lower than reality. BMS thought it was fine, cells were actually cooked. Ended up with a false sense of security for weeks before it finally tripped.

Also double-check what your high temp cutoff is set to in the JK app. Default from factory can be surprisingly low — think mine was 45°C which is easy to hit inside a van in summer even without direct sun on the battery.

What's your ventilation like around the pack? My EVE cells in the van needed a small 12v fan pulling air through once ambient crept above 25°C. Game changer.

@Tel1997 I've chased this exact gremlin on both my shepherd's hut pack and my narrowboat. One thing nobody's mentioned yet — check whether your over-temperature protection and your charge over-temperature protection are set to the same value in the JK app. They default differently, and if your charge OTP is set lower than your general OTP, you'll get seemingly random cut-offs on warm afternoons when the cells are barely warm to the touch.

Mine was tripping at 38°C charge OTP whilst the general protection sat at 45°C. Bumped the charge OTP to 42°C (still well within EVE's spec) and the phantom trips vanished entirely.

Worth cross-referencing your cell temps against the EVE 280Ah datasheet — they're remarkably tolerant, and the JK's factory defaults are arguably overcautious for the UK climate anyway.