Anyone else had their JK BMS trip out randomly on a warm day — 16S 280Ah LiFePO4 build

I've been scratching my head with this one for a couple of weeks now. Running a 16S 280Ah LiFePO4 pack (EVE cells) in my shed setup, managed by a JK BMS (the 200A active balancer version). Everything was rock solid through winter, but now we're getting the odd warm day the BMS keeps tripping off — no obvious error on the app, just cuts out and comes back after a few minutes.

Temps in the shed are getting up to maybe 28–32°C on a sunny afternoon. I've got the over-temperature protection set to 45°C on the BMS, and the cell temps I can see on the app are nowhere near that — hovering around 30–33°C max. The cut-outs seem to happen mid-afternoon when the solar harvest is peaking, so I'm wondering whether it's a high charge current issue rather than temperature. I'm pushing roughly 80–90A in from a pair of Victron SmartSolar 100/50s.

Has anyone seen the JK do something odd around the MOSFET temperature threshold specifically? I've read it has a separate internal thermal limit that isn't always obvious in the app. Also open to the idea it's a dodgy cell group causing a voltage spike that I'm missing — cell 14 has been drifting slightly high during bulk charge for a while now.

@MuddyRigger had almost identical grief with my shepherd's hut build last summer. Turned out my JK was triggering on cell overvoltage during high charge current on warm days — cells hitting 3.65V briefly before the balancer could react.

Few things worth checking:

• What's your charge voltage set to? I dropped mine to 3.55V per cell (56.8V total) and the random trips stopped almost immediately
• Check your OVP and OVPR settings — the gap between them matters
• Warm weather = cells charge faster, so the BMS sees spikes it wouldn't in winter

Also worth pulling the JK app logs — it records the trip reason which saves a lot of guesswork. Mine was showing OVP every time, took me ages to actually look at the logs properly.

@MuddyRigger mine did exactly this in the garden office last July — blamed the Victron, blamed the cells, blamed my life choices, turned out the JK's temperature sensor had shifted off the cell surface and was reading ambient air instead, so it thought everything was fine right up until it wasn't 🌡️

Check your sensor is actually making proper contact with the cell body — a bit of kapton tape to hold it flush works wonders and costs approximately nothing.

@MuddyRigger worth pulling the BMS log data via the JK app and filtering by timestamp against the warmest part of the day. I had this exact mystery on my narrowboat build — turned out one cell group was sitting slightly high after a partial charge cycle, and on warm afternoons the internal resistance dropped enough that a load spike pushed it fractionally over the OVP threshold. The BMS wasn't wrong to trip; the threshold just needed nudging up by about 20mV.

Also check your cable terminations on the sense wires. Loose connection on a hot day (expansion and all that) can feed the BMS a phantom voltage reading. Sorted mine with fresh ferrules and a proper torque check — ran clean ever since.

Really useful thread this — I had a similar head-scratcher last spring with a 16S build in my garage. One thing nobody's mentioned yet: check your cell temperature sensor placement. If the sensor is sitting between cells that are getting direct sunlight through a window or near a heat source, it can read artificially high and trigger the over-temperature protection even when the bulk of the pack is fine.

Also worth checking the OTP (Over Temperature Protection) threshold in your JK app — mine had shipped with it set to 45°C which is quite conservative for a warm shed environment. You can nudge it up slightly, though obviously don't go daft with it.

@SolarJo's point about the BMS log is spot on — cross-referencing timestamps with ambient temp genuinely saved me hours of guesswork.

@MuddyRigger one thing worth checking that hasn't been mentioned yet — the JK's temperature sensor placement. If it's sitting too close to the cells rather than measuring ambient, on a warm day the BMS might be reading a few degrees higher than reality and nudging against its OTP (over-temperature protection) threshold. Default on a lot of JK firmwares is set quite conservatively around 45°C.

Pop into the JK app and check your temperature protection settings under the protection parameters — you might find it's tripping on temp rather than voltage. Also worth checking if the BMS itself is getting direct sunlight or radiant heat from nearby equipment; they don't love that either.

What's your OTP threshold currently set to, and are you seeing any temperature fault flags in the log alongside the trip events?

@MuddyRigger one thing worth checking that hasn't been mentioned — are your cell interconnect busbars torqued properly? Thermal expansion on a warm day can actually expose a slightly loose connection that's borderline at cooler temps. Resistance creeps up, one cell starts lagging during charge, BMS sees a voltage delta it doesn't like and pulls the plug.

Had almost identical grief with my tiny house build before I went back over every terminal with a torque wrench. Found two that had backed off slightly. Night and day difference afterwards.

Also double-check your BMS isn't mounted directly against anything that's absorbing heat — mine was touching a metal bracket and the BMS itself was overtemping before the cells were anywhere near their limits.

@MuddyRigger worth looking at your OVP (overvoltage protection) threshold settings in the JK app. On warm days, cells charge slightly more efficiently and can hit the protection threshold faster than expected — especially if one cell is running a touch high before balancing kicks in. I'd check whether any single cell is briefly spiking past your OVP limit right at the top of charge. Try logging via the JK app during a full charge cycle on a warm afternoon and watch individual cell voltages carefully. Sometimes dropping the OVP trigger by just 10-20mV sorts it completely.