Anyone else had their JK BMS trip out randomly at low SOC — or is it just my setup?

Been scratching my head over this one for a few weeks now. I've got a 280Ah LiFePO4 bank (four Eve cells in series) with a JK BMS — the 200A active balancer version — and it keeps disconnecting the load when the pack drops to somewhere around 20-25% SOC. No obvious over-current, no temperature alarm, nothing obvious in the logs. Just cuts out, then reconnects fine about 30 seconds later.

I'm running it in my van with a Renogy 40A DC-DC charger on the alternator side and a Victron SmartShunt keeping an eye on things. The SmartShunt reckons I'm only pulling around 60-70A when it trips, so I'm well under the BMS rated limit. I did wonder if it's a cell voltage sag issue — maybe one cell is drooping below the under-voltage threshold momentarily under load — but when I check the BMS app afterwards the individual cell voltages all look fairly balanced, within about 15mV of each other.

Has anyone seen this with JK units specifically? I've had a poke around the protection settings in the app and I'm wondering if my cell under-voltage protection value is set a touch too high — I've got it at 2.90V at the moment. Could that be enough to cause a momentary trip if there's any voltage sag under load, even if the resting voltage looks fine afterwards?

Hey @StuThompson, classic one this! Worth checking your cell voltage differentials when you're approaching that low SOC — the JK can be quite aggressive if one cell is sagging ahead of the others and triggers the undervoltage protection before the others catch up.

What have you got your cell UVP set to? I had mine at 2.8V initially and kept getting nuisance trips under load. Dropped it to 2.75V with a 500ms delay and it sorted it right out. Also worth checking your protection release voltage is set sensibly above the trigger point, otherwise it can chatter on and off repeatedly.

The active balancer won't really help you much at low SOC either — it needs a decent voltage spread to kick in properly, so that's unlikely to be masking a problem there.

What firmware version are you running on the BMS?

@StuThompson had almost identical behaviour with my garden office setup last winter. Turned out my cell internal resistance had drifted unevenly across the four cells — the JK was seeing one cell dive faster than the others and triggering the undervoltage protection before the overall pack voltage looked concerning.

Worth pulling the BMS data logs if you haven't already — the JK app shows per-cell resistance readings. If one cell is noticeably higher than the rest, that's your culprit.

Also double-check your undervoltage cutoff threshold in the JK settings. Mine was factory-set quite aggressively at 2.8V per cell; bumping it slightly to 2.9V with a wider release voltage gave much more stable behaviour without meaningfully affecting usable capacity.

Eve cells from reputable suppliers like Fogstar tend to be well-matched, but they do drift over time.

@StuThompson mine did exactly this and I nearly blamed the BMS for a solid month before realising one of my Eve cells had gone slightly rogue — check if the voltage sag on that weakest cell is triggering the undervoltage protection before the pack reads low, because at high discharge rates (I was pulling hard for EV charging) a dodgy cell nosedives way faster than the others and the JK just nopes out entirely. Drop your protection voltage threshold by about 50mV as a temporary test and see if the trips stop — if they do, you've found your culprit cell, not a BMS fault.

@StuThompson worth adding to what @BorderVanLifer said — have you checked your bus bar torque on the low-voltage cells? I had almost the exact same random disconnects on my garden office setup last winter, and it turned out to be a slightly loose connection on one cell causing a voltage spike under load that the JK was interpreting as a genuine undervoltage event.

Also look at your protection delay settings in the JK app. Mine was set to trip after just 200ms, which was way too sensitive for any decent load surge. Bumping it to 500ms stopped the nuisance trips immediately.

The active balancer version can also be a bit aggressive near the bottom — worth checking your balance start voltage isn't kicking in and dragging a weaker cell down further at low SOC.

@StuThompson one thing nobody's mentioned yet — check your cell undervoltage recovery threshold in the JK app. If your trigger and recovery values are set too close together (say, 2.80V trip and 2.85V recovery), the BMS can get into a rapid disconnect/reconnect loop under load at low SOC, which looks like random tripping but is actually the protection cycling. I'd suggest a wider hysteresis gap — something like 2.80V trigger with 3.00V recovery gives it proper breathing room. Also worth logging your cell voltages during a discharge to see if one cell is consistently leading the drop. The JK app has built-in data logging which makes that fairly painless.