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

I've been having a frustrating few weeks with my 280Ah LiFePO4 pack (four EVE cells in series) and the JK BMS-24S15P. We've had some proper cold nights here in Yorkshire — down to about -4°C in the van — and the BMS keeps tripping the low-temperature protection and cutting off the load entirely. Fair enough that it's protecting the cells, but it's happening even when I'm just running a small 12V compressor fridge and a couple of USB chargers, so the draw isn't enormous.

I've had a look through the settings in the JK app and the low-temp protection is currently set to cut out at 5°C with a recovery at 10°C. I'm wondering if that's a bit conservative for LiFePO4 chemistry, which I thought could handle discharge down to around -10°C or so without serious damage — obviously not charging below 0°C, I know that much. Has anyone adjusted these thresholds, and if so what are you running yours at?

Also wondering whether fitting a small self-regulating heat mat under the cells (I've seen the Chinese ones on AliExpress for about £15) would actually keep them warm enough overnight, or if that's just wishful thinking in a poorly insulated van floor. The cells are currently sitting in a wooden box with a bit of Celotex either side but nothing underneath.

SamWhite | 847 posts

@HeatherOllie Aye, classic cold weather behaviour this. LiFePO4 cells genuinely don't like being charged below 0°C — you risk lithium plating which permanently damages capacity. The JK BMS has a low temperature charge cutoff setting, and if yours is set around 0–5°C it'll trip exactly as you're describing.

Check your BMS app under "Protection Parameters" — look for the charge low temperature protection value. Mine's set to 5°C cutoff with a 10°C recovery threshold, which means it won't allow charging again until the cells warm up a bit.

The real fix though is cell insulation in the van. A decent wrap of closed-cell foam makes a massive difference overnight. What temperatures are your cells actually reading when it trips? That'll confirm whether it's the BMS protecting correctly or something else going on.

NorfolkSolar | 1,243 posts

@HeatherOllie Worth checking your Low Temperature Protection setting in the JK app — mine was left at the factory default of 0°C which caused exactly this. I bumped the recovery threshold up to 5°C and dropped the protection trigger to -10°C, which stopped the nuisance trips while still protecting the cells from actual charging damage.

Also, are you seeing this during charging or discharge? If it's cutting out under load rather than during charge cycles, that points more toward a cell voltage sag issue amplified by the cold rather than the temperature protection itself triggering. Cold cells have noticeably higher internal resistance, so voltage can momentarily dip below your Low Voltage Protection threshold even when the cells aren't genuinely depleted.

What have you got your LVP set to currently?

BordersExplorer | 2,156 posts

@HeatherOllie One thing neither @SamWhite nor @NorfolkSolar has mentioned — check whether your Low Temperature Charge Protection and Low Temperature Discharge Protection are set to different thresholds. They should be. I run mine at 5°C charge cutoff but allow discharge down to -10°C, because discharging cold cells is far less damaging than charging them.

Also worth verifying: is the BMS temperature sensor actually mounted on the cells rather than floating loose? Mine was reading ambient air temperature in the motorhome habitation space — a good 8°C warmer than the actual cells — which meant it was tripping later than it should have been.

The JK app can be counterintuitive with which protection is actually triggering. Enable the alarm log if you haven't already; it'll tell you precisely which threshold fired.

WFS_Camper | 412 posts

@HeatherOllie Something worth adding to what @BordersExplorer is getting at — have you got any heating on the cells themselves? A self-heating LiFePO4 setup is the proper long-term solution for Yorkshire winters rather than just tweaking BMS thresholds. Some people wrap cells in a bit of closed-cell foam insulation and add a small silicone heat mat on a thermostat, triggered around 5°C. Keeps the cells above the danger zone overnight without drawing much from the pack.

Also, what's your resting voltage looking like when the trips occur? If cells are sitting low and cold, that's a double whammy — the BMS sees high internal resistance and panics. Keeping the pack at a reasonable state of charge through winter helps considerably.

StormyDrifter | 847 posts

Had this exact drama on the boat last February — turns out my Low Temp Charge Protection was set to 5°C but the release temperature was also 5°C, so it was tripping and immediately resetting in a loop like some kind of confused Victron firmware update. Set the release a couple degrees above the trigger (so 5°C trip, 8°C release) and she's been solid since. The JK app labels it as "Low Temp Charge Release" and it's easy to miss because it's right below the main setting. @HeatherOllie Yorkshire in January is basically the same as being moored in the North Sea, so your cells will thank you for a bit of hysteresis in those values. 🥶