Anyone else had their JK BMS trip out in cold weather — or is it just me?

So I've been pulling my hair out this past week. I've got a 280Ah LiFePO4 bank (four EVE 280K cells in a 12V configuration) managed by a JK BMS — the 2A active balancer version, 100A model. It's sitting in my shed which, as you can imagine, has been absolutely freezing lately. Temps were dropping to around 2–3°C overnight and the BMS kept cutting out, which then knocked off my inverter and killed the heating. Not ideal.

I'm pretty sure it's the low-temperature charge protection kicking in, which I know is there to protect the cells — fair enough. But what I'm not clear on is whether I should be adjusting the cutoff threshold or whether the better fix is to insulate the battery box properly and maybe add a small heat mat. I don't really want to be disabling safety features if I can help it.

Has anyone dealt with this on a JK specifically? I'd be interested to know what temperature thresholds people are actually running, and whether the UART app gives you enough control to fine-tune it without bricking anything. I've only had the BMS about three months so still finding my feet with it.

DalesSolar | Posts: 847 | Location: North Yorkshire

@JaneGrant Yes, absolutely seen this — it's a known quirk with JK units in cold conditions. Worth checking your low temperature cutoff settings in the JK app; they sometimes ship with surprisingly conservative presets (I've seen them set to 5°C from the factory).

Also worth mentioning — LiFePO4 cells genuinely shouldn't be charged below 0°C anyway, so the BMS is arguably doing its job correctly there. The issue is usually distinguishing between a legitimate protection trip and a dodgy temperature sensor reading.

Try checking the NTC sensor is actually making solid contact with the cell surface. If it's lifted even slightly it'll read ambient air temp rather than the cell itself, which in an uninsulated installation will trigger false cutoffs.

What temperatures are you actually seeing up in your location?

ThistleWalker | Posts: 312 | Location: Cumbria

@JaneGrant Chiming in here as someone who's dealt with this exact thing last winter. Worth checking your low temperature cutoff threshold in the JK app — mine had shipped with it set at 5°C which sounds reasonable until you realise the BMS sensor is reading cell temperature, not ambient. On a cold morning my cells were sitting at 3°C before I'd run anything, so it was tripping before I'd even put a kettle on.

I nudged mine down to 0°C and added a small self-regulating heat mat under the battery box on a simple thermostat. Sorted it completely. As @DalesSolar says it's a known thing, but the JK app does at least give you proper control over those parameters unlike some cheaper units. Just don't go too low on that cutoff threshold — charging below 0°C will damage LiFePO4 cells.

NorfolkDweller | Posts: 1,204 | Location: Norfolk

My JK pulled the same stunt last February — turned out my cells were sitting directly on a concrete floor like absolute idiots (the cells, not me... debatable), and even Norfolk "cold" was enough to tank the internal resistance readings and spook the BMS into protection mode. Slapped some 20mm foam insulation underneath the EVE cells and haven't had a single nuisance trip since. Worth checking your low-temp cutoff settings in the JK app too — mine had shipped with the charge cutoff set to 5°C, which is basically always in an uninsulated British shed between October and March.

WattHelen | Posts: 1,203 | Location: Array

Adding a layer nobody's mentioned yet — the cell internal resistance spikes in the cold, which the JK reads as a fault condition even when the cells themselves are perfectly healthy. Mine did exactly this in my garden office setup last January, scared me half to death at 0630 on a Monday morning.

What fixed it for me: I wrapped the battery box in 25mm Kingspan and chucked a small Reptile/terrarium mat heater underneath — runs off a tiny Victron SmartSolar trickle — keeping the bank above 5°C overnight. JK hasn't tripped since.

@DalesSolar makes a fair point about the BMS settings, but if you're in an uninsulated enclosure, you're fighting a losing battle tweaking parameters alone. Sort the thermal environment first, then fine-tune.

MoreTeaVicar60 | Posts: 847 | Location: Shropshire

@JaneGrant One thing worth checking that I haven't seen mentioned — have a look at your JK's low temperature charge protection settings in the app. Mine shipped with the cutoff set at 5°C, which sounds reasonable until you realise the temperature sensor is tucked inside the case rather than actually touching a cell. My cells were genuinely sitting at 2°C whilst the BMS was reading 6°C and scratching its head wondering why charging kept tripping.

I ended up repositioning the sensor with some thermal paste directly onto the middle cells and suddenly everything made much more sense. Worth five minutes of investigation before you go down any rabbit holes. The JK app makes adjusting those thresholds straightforward enough once you've spotted the issue.