Anyone else had grief with JK BMS cutting out under load on a 24V LiFePO4 build?

Been pulling my hair out this past week with my 280Ah LiFePO4 bank (8 x Eve 280Ah cells in 8S configuration) and a JK BMS — the 200A active balancer version. Everything looks fine at rest, cells balanced to within a few millivolts, but the moment I kick on the inverter (a Victron Multiplus 24/3000) and pull anything over about 1,800W, the BMS trips out. No obvious over-current alarm, just shuts down and comes back after 10–15 seconds.

I've checked all the busbar connections and they seem solid, torqued to spec. The BMS is set to 150A continuous with a 200A short-circuit threshold. At 1,800W on a 24V system that's only about 75A, so it really shouldn't be anywhere near the limit. I did notice one cell (cell 3) occasionally dips a bit lower than the others under heavy load — maybe 50–60mV below the rest — but I wouldn't have thought that alone would cause a shutdown.

Has anyone seen this kind of behaviour before? I'm wondering if it's a dodgy cell causing a low-voltage cutoff rather than an over-current trip, or whether there's a known firmware quirk with the JK units. I'm running firmware V11.25. Also curious whether the cable between the BMS and the negative busbar could be an issue — I used 70mm² but it's about 600mm long.

JimWilliams71 | 847 posts | ⚡ Solar Addict

@GillGibson had almost identical grief last spring. Worth checking your cell internal resistance readings in the JK app — even brand new Eve cells can have one slightly higher resistance outlier that causes voltage sag on that cell alone under heavy load, triggering the low voltage protection before the others even notice.

Also, what have you set your cell undervoltage cutoff at? Factory default on the JK is often 2.8V which can be a bit twitchy. I nudged mine to 2.75V with a 200ms delay and it sorted a lot of nuisance trips.

One more thing — make sure your cell interconnect busbars are properly torqued. Loose connections cause resistance spikes that show up as voltage anomalies under load specifically, not at rest. Easy to overlook.

CraftyRanger | 312 posts | 🔧 Tinkerer

@GillGibson one thing worth checking that nobody's mentioned yet — have a look at your cell voltage differential under load rather than at rest. JK BMS units are notorious for triggering overcurrent protection when one or two cells sag faster than the others, even if your overall pack voltage looks reasonable. The BMS sees that differential and panics.

Also double-check your protection settings in the JK app — specifically the "Cell Voltage Difference Protection" value. Factory defaults can be surprisingly aggressive. I'd also verify your busbars and cell terminal connections are properly torqued; a dodgy connection creates resistance that amplifies exactly this kind of problem under heavy draw. What inverter are you running, and what sort of load triggers the cutout?

JennyPalmer | 203 posts | 🔌 Off-Grid Enthusiast

@GillGibson I had something very similar with my 24V JK build last year. Worth looking at your cell interconnect busbars — even tiny resistance differences across connections can cause one cell to sag under load, which the BMS reads as an undervoltage trip even when the overall pack looks healthy. I used a proper torque wrench on mine (4 Nm for M6 bolts on Eve cells IIRC) and that sorted a persistent cutout issue I'd been chasing for weeks.

Also double-check your BMS protection settings in the app — the default undervoltage trip point can be quite aggressive. I nudged mine down slightly and it made a real difference without compromising cell safety.

What inverter are you running? Surge loads can catch the JK out if the settings aren't dialled in properly.

JohnBaker | 1,247 posts | 🚤 Narrowboat/Van Obsessive

@GillGibson worth looking closely at your OCP (overcurrent protection) trip threshold in the JK app — the 200A active balancer unit ships with surprisingly conservative defaults. On my narrowboat 24V build I found mine was set to 150A with a 200ms delay, which sounds plenty until you've got an inverter plus a 1200W induction hob starting simultaneously.

Also check your busbars and cell interconnects under load. Eve 280Ah cells with slightly undertorqued terminals can show near-zero resistance at rest but drop enough voltage dynamically to fool the BMS into thinking a cell is out of spec. Torque to the manufacturer spec (typically 4Nm) and recheck.

The JK app's real-time waveform logging is genuinely useful here — trigger a load event and watch which cell diverges first. That'll tell you whether it's a protection setting issue or a genuine weak cell.

Moorey79 | 847 posts | ☀️ Solar Obsessive

@GillGibson had almost identical grief last summer with my 8S Eve build. One thing nobody's touched on yet — check your cell internal resistance readings in the JK app. If one cell is showing noticeably higher IR than the others, it'll sag harder under load and can trick the BMS into thinking there's an undervoltage event even when your overall pack voltage looks healthy.

Also worth double-checking your bus bar torque. I'd convinced myself mine were tight but when I went back with a torque wrench properly, two were definitely under-spec. Loose connections create resistance which shows up exactly as you're describing — fine at rest, falls over under load.

What firmware version are you running on the JK? Some earlier versions had dodgy OCP behaviour that got sorted in later releases.