Anyone else had issues with JK BMS cutting out under load on LiFePO4 builds?

Fitted a JK BMS (the 200A active balancer version) to my 280Ah LiFePO4 battery bank last month — four 3.2V cells in series, wired up in my campervan alongside a Victron SmartSolar 100/30. Everything looked great on paper and the app is genuinely nice to use, but I keep getting random cut-outs when I pull more than about 80A. Inverter trips, everything goes dark, then it resets itself after 30 seconds or so.

Checked the settings and the over-current protection is set to 150A with a 300ms delay, so it shouldn't be triggering at 80A. Cell voltages look balanced (within 10mV under normal load), temperature sensors are reading sensibly — around 18°C in the van — and all my connections are torqued down properly with the right cable sizes. I'm genuinely stumped.

I've seen a few people mention firmware being a bit dodgy on some of the JK units that came out late last year. Mine's on v11.25 and I haven't updated it yet, partly because I'm wary of bricking it. Has anyone updated firmware on one of these and found it helped with nuisance tripping? Or is there something obvious I'm missing in the protection settings?

RussMitchell75 | Posts: 847 | Location: Derbyshire

@Declan1985 Had exactly this with my 150A JK last summer. Worth checking your BMS connection cables first — the JK is surprisingly sensitive to voltage drop across undersized cable runs to the sense wires. Also double-check your overcurrent protection settings in the JK app; the default values are often quite conservative and don't account for brief inrush spikes.

One thing that caught me out: the "cell overdischarge recovery" threshold was set too high from factory, so the BMS was tripping before cells actually needed protecting.

What inverter or loads are you running when it cuts? If it's something with a compressor or motor, you might need to adjust the short-circuit delay timing slightly. Post your BMS parameter screenshot if you can — someone here will spot it quickly enough. 👍

CotswoldCamper | Posts: 312 | Location: Gloucestershire

@Declan1985 Worth checking your cell-level voltage readings in the JK app during the cutout — mine was doing something similar and it turned out one cell was sagging badly under load, triggering the undervoltage protection even though resting voltage looked fine. The BMS was doing exactly what it should, annoyingly!

Also double-check your protection settings. The factory defaults on some JK firmware versions are quite aggressive — I had my discharge undervoltage threshold set too high out of the box. Dropping it slightly (carefully, mind you) sorted it for me.

One more thing — are your cell interconnects properly torqued? Loose busbars create resistance that shows up as voltage drop under load and confuses the BMS. Grabbed a cheap torque wrench off Amazon and it was genuinely transformative. 😄