Anyone else had their JK BMS cut out randomly on a 24V lifepo4 build?

Been scratching my head over this one for a few days now. Running a 280Ah 24V LiFePO4 pack (8 cells in series, EVE cells) with a JK BMS — the 200A active balancer version. System feeds a Victron Multiplus 2000 and charges via a 400W solar array through an MPPT 100/30. Everything looks solid on paper but I'm getting random disconnects, sometimes mid-afternoon when the sun's cracking and loads are light. No obvious overtemp, no overcurrent that I can see.

When I plug into the JK app after one of these events the protection log just says "other fault" which is spectacularly unhelpful. Cell voltages look balanced beforehand — all sitting between 3.31 and 3.33V — so it doesn't seem to be a cell-level issue. I've checked the sense wire connections on the BMS and they all seem snug, but I haven't torqued them with anything precise yet.

Has anyone seen this kind of intermittent fault on a JK unit? I'm wondering whether it's a loose sense wire causing a momentary voltage spike reading, or possibly a setting in the BMS that's too aggressive — my OVPR is set at 3.65V and OVP at 3.60V which seemed reasonable. Any pointers would be well appreciated.

@RussMartin had almost identical grief on my boat last winter with a JK on a 24V EVE pack.

Worth checking your cell voltage differential under load. The JK's overvoltage protection can trip seemingly randomly if one cell is running slightly high — it'll spike past the protection threshold during absorption even though pack voltage looks fine on the Victron side.

Specifically:

• Connect to the JK app via Bluetooth while charging and watch individual cell voltages in real-time
• Check your balance start voltage — I had mine set too low which caused the balancer to thrash during bulk
• Also verify your wire gauge on the BMS sense leads — a dodgy crimp on mine caused phantom cell voltage readings

What firmware version are you running? The older JK firmware had some known instability with active balancing triggering protective disconnects under certain charge profiles.

@RussMartin my JK on the shepherd's hut did the exact same thing until I realised the temperature sensor wasn't making proper contact with the cells — BMS thought it was charging in a Siberian winter and threw a tantrum.

@RussMartin had this exact headache with my emergency backup setup. Check your BMS communication cable — the ribbon connector on the JK units can work loose and trigger phantom protection trips. Reseated mine and the random cutouts stopped immediately.

Also worth pulling up the BMS app and checking your over-voltage protection threshold — sometimes they ship with it set quite tight (3.65V per cell), and if your Victron absorption voltage isn't spot on it'll clip the top and the BMS panics.

What's your Victron charge profile set to?

@RussMartin one thing nobody's mentioned yet — check your cell capacity settings in the JK app. If the capacity figure is set too low, the BMS can calculate a false state of charge and trigger protection cutoffs that aren't actually warranted. I had mine set to the default 100Ah on a 280Ah pack (forgot to update it during commissioning, embarrassingly) and it was cutting out under heavy load thinking it was deeper into discharge than it actually was.

Also worth double-checking your overcurrent protection threshold in the app — the 200A model sometimes ships with quite conservative defaults that don't suit a Victron Multi's surge draw on startup. Bumping mine up slightly sorted random cutouts under inverter load immediately.

@RussMartin worth checking the overvoltage protection threshold in the JK app. If your Victron absorption voltage is set even slightly above what the BMS will tolerate, the BMS trips out as a protection event — looks random but it's actually triggered right at end of charge.

On my 24V EVE build I had the Victron pushing 29.2V and the JK was set to 3.65V per cell (29.2V total) with basically zero hysteresis. Tightened the Victron absorption down to 28.8V and the cutouts stopped immediately.

Also double-check the "Cell OVP Recovery" value in the app — if that's set too close to the trigger threshold the BMS can oscillate in and out of protection rapidly, which can look like a communication fault rather than an OVP event.

@RussMartin one thing I'd add — check your balance start voltage setting in the JK app. If it's set too close to your absorption voltage, the balancer kicks in hard right as cells are nearly full, and the resulting current draw can momentarily spike a cell voltage reading above your OVP threshold, triggering a cutout.

On my shepherd's hut build (EVE 280Ah, same 8S arrangement) I had similar phantom trips until I nudged the balance start voltage down to around 3.40V per cell rather than the 3.45V default.

Also worth confirming your cell voltage differential in the logs — JK app keeps history. If one cell is consistently leading the pack by even 20–30mV, that's your culprit and the balancer alone won't fix a weak cell.

@RussMartin something nobody's pinned down yet — have you checked your wire gauge on the BMS communication/sense leads? I had a similar phantom cutout on my boat build (24V EVE pack, different BMS but same principle) and it turned out to be a loose sense wire causing the BMS to read a false cell voltage spike, triggering OVP.

Also — are your cell busbars torqued properly? EVE cells specifically have a recommended torque spec (around 4Nm if memory serves, though double-check that). Loose connections create resistance, resistance creates voltage differential, BMS panics.

What firmware version are you running on the JK?