Anyone else had their JK BMS trip out in cold weather? Trying to figure out if it's a settings issue

I've been running a 280Ah LiFePO4 pack in my van since last spring and it's been brilliant — but we've had a couple of proper cold nights recently (down to about 3°C inside the van) and the JK BMS has tripped the charge protection twice now. Both times it was when the B2B charger kicked in first thing in the morning off the alternator.

From what I can gather, LiFePO4 really doesn't like being charged below 5°C, so the BMS is probably doing exactly what it's supposed to. My cells were sitting at around 4°C according to the BMS app when it happened. The JK has a low-temp charge cutoff setting and mine is currently set to 5°C — so it's right on the edge and presumably tripping as the threshold. I'm wondering whether I should bump that up to 8°C to give it a bit more headroom, or whether that just means it'll trip more often on cool mornings.

Has anyone dialled in their low-temp settings for UK autumn/winter use? I'm also curious whether fitting a self-heating element to the cells is worth the faff, or if just raising the cutoff and waiting for the van to warm up naturally is good enough for most people. I don't do extreme cold camping, mostly just chilly autumn layby overnighters.

MuddyGrafter | Posts: 847 | Location: Brecon Beacons

@Frank1999 Classic cold weather behaviour with JK units — worth checking your Cell Low Temperature Protection setting in the app. Mine was factory-set to 5°C which tripped it constantly last winter in my shepherd's hut setup.

The critical distinction is whether it's cutting off charging or discharging — LiFePO4 genuinely shouldn't be charged below 0°C (damages the cells), so if it's blocking charging at 3°C that's arguably doing its job correctly.

If it's cutting discharge too, that's probably just an overly cautious threshold you can adjust downward, maybe to -10°C for discharge only.

Also worth checking whether your temperature sensor is actually touching a cell rather than floating loose — mine was giving phantom low readings for exactly this reason.

What does the app show as the actual cell temp when it trips?

FogstarFan | Posts: 412 | Location: Array

@Frank1999 Check your low temperature charge cutoff setting in the JK app — mine was factory-set to 5°C which meant it was cutting charging at exactly the temps you're describing; bumped it down to 0°C for the van (lithium can discharge fine at low temps, just hates being charged) and the drama stopped immediately.

Tom1979 | Posts: 203 | Location: Array

Mine did the same last January — turns out my cell undervoltage recovery threshold was set so close to the cutoff that 3°C was enough to make the internal resistance spike and trigger a false alarm; nudge that gap wider and it'll stop being so dramatic about a bit of frost. 🥶

HUO_Boats | Posts: 1,204 | Location: Norfolk Broads

@Frank1999 Worth checking your low temperature charge protection threshold — JK units default to around 5°C on some firmware versions, which would explain exactly what you're seeing at 3°C inside. Bear in mind ambient air temp around the cells themselves could be a degree or two lower than your general van temp too, especially if the pack is near an exterior wall or floor.

Also, is it cutting out completely or just blocking charge whilst still allowing discharge? That distinction tells you a lot. If it's discharge cutting out as well, you might be looking at a cell voltage imbalance that cold temps are exaggerating — cold knocks capacity and makes weak cells look worse than they are.

What firmware version are you running? Some earlier JK versions had slightly aggressive defaults that are worth updating.

SprinterProject | Posts: 847 | Location: Array

Something nobody's mentioned yet — check your cell temperature sensor placement. On my JK I found the sensor was sitting against the busbars rather than flush against a cell body, so it was reading 2-3°C higher than actual cell temperature. BMS thought cells were warmer than they were and the protection was triggering inconsistently.

Also worth noting: 3°C ambient can mean cells sitting at 1°C or below if they've been sitting overnight with no load. LiFePO4 genuinely shouldn't be charged below 0°C — the BMS tripping is arguably doing its job correctly.

If you want to charge in cold conditions properly, a small self-regulating heat pad (I use a 20W one from Amazon, thermostat-controlled) under the battery resolves it entirely. Running mine through a Victron relay triggered off the BMS temperature output.