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

Been having a frustrating few weeks with my 280Ah LiFePO4 build in the van. Running a JK BMS (the 200A 4S one) and it's been tripping out overnight when temperatures drop below about 4°C. Wakes me up with no 12v at all — fridge off, lights dead, the lot. Reset the BMS and everything comes back fine, so it's definitely the BMS shutting things down rather than a wiring fault.

I've had a look through the settings in the JK app and I've got the low temperature protection set to 0°C with a 5°C recovery. Wondering if the sensor placement is causing issues — mine is tucked between two of the 280Ah EVE cells in the middle of the pack. I've read some people mount it on the outside of the cell casing and get wildly different readings depending on ambient vs cell temp.

Has anyone dialled in their low-temp settings specifically for a van environment in the UK? I don't charge below 0°C obviously, but I'd like to be able to discharge when it's cold — the cells should handle discharge down to around -20°C according to the spec sheet. Feels like the BMS is being overly cautious or the sensor is reading colder than the actual cell temperature.

@Wardy26 This is almost certainly your low temperature charge protection kicking in — JK defaults are often set too conservatively from the factory.

In the JK app, look for:

• Cell Low Temperature Protection — typically defaults around 5°C
• Cell Low Temperature Protection Release — the hysteresis point before it reconnects

LiFePO4 genuinely shouldn't be charged below 0°C, but 4°C is cutting it unnecessarily tight for a van environment. I run mine at 2°C protection / 5°C release which gives more headroom without risking the cells.

Worth clarifying though — is it cutting the charge FET only, or full disconnect? If full disconnect, check your discharge low temperature settings too, which shouldn't really be triggering above freezing.

My emergency backup setup taught me to always export and save your BMS settings before changing anything — easy to lose track of what you've altered.

@Wardy26 Had almost identical issues last winter in the motorhome — waking up to a dead 12V system is grim isn't it.

One thing worth checking beyond the charge protection @Keith1977 mentioned: are you also looking at the discharge low temp cutoff? On my JK it was set to 0°C but the release temperature was only 2°C above that, meaning it kept cycling on and off repeatedly rather than staying connected once temps crept back up.

Bumping the recovery/release differential to around 5°C sorted it for me. You set it in the JK app under the protection parameters — easy to miss because it's a separate value from the cutoff itself.

Also worth checking what your actual cell temperature sensor reads vs ambient — mine reads noticeably colder than the van interior.

@Wardy26 mine did exactly this in the van last January — turns out the temperature sensor placement matters as much as the settings, because if it's reading the ambient air rather than the actual cell surface you'll get premature cutoffs even when the cells themselves are still perfectly happy.

Great thread, this catches a lot of people out. Worth checking your low temp discharge protection as well as charge — @Keith1977 is right about the charge side, but JK also has separate discharge cutoff thresholds that can trip if the BMS body itself gets cold, not just the cells. The sensor reads ambient near the BMS rather than cell core temp sometimes, so it can be overly cautious.

One thing nobody's mentioned yet — have a look at your recovery hysteresis setting. Some JK firmware versions need the temperature to climb several degrees above the cutoff before they'll reconnect, meaning even a mild morning can leave you waiting ages for the system to come back online. Bumping that hysteresis value down (carefully!) made a big difference on my setup. What firmware version are you running?

@Wardy26 Worth checking your cell wire connections at the BMS itself — I had a similar issue and found that cold temperatures were causing just enough resistance at a slightly loose connector to push the BMS into protection mode, even though it was fine in warmer conditions. Tightened everything up with proper crimps and it sorted it.

Also, if you're using the NTC temperature sensor that ships with the JK, make sure it's actually making good contact with the cells rather than just floating loose in the battery box. Mine was barely touching and giving wildly inaccurate readings. A bit of thermal paste and some kapton tape to hold it against the cell made a noticeable difference to the accuracy of the readings in the JK app.

@Wardy26 one thing nobody's mentioned yet — the JK BMS has separate low temperature cutoff thresholds for charge and discharge, and they're both enabled by default at relatively conservative values. In the PC software (connect via Bluetooth or USB), navigate to Protection Parameters and check your Cell Low Temperature Protection values. Factory default is often around 5°C for charge protection, which explains exactly your 4°C symptom.

For LiFePO4, discharge down to around -10°C is generally acceptable, so you can safely drop that threshold. Charge protection I'd leave conservative — charging below 0°C genuinely damages lithium cells.

My cabin setup with a 200Ah Fogstar Drift pack had identical behaviour last winter. Adjusted the discharge cutoff to -5°C and the false trips stopped entirely. Just make sure your temperature sensor is actually touching the cells rather than floating loose inside the case.

@Wardy26 mine did exactly this last January parked up in a Lidl car park at 2am — turned out my cell temperature sensor had worked itself loose from the cell surface, so the BMS was reading ambient air temp instead of actual cell temp and panicking accordingly. Worth pressing those little sensors firmly back down with some kapton tape before diving into the settings rabbit hole. Fogstar cells run warm enough under load that a loose sensor can cause all sorts of ghost readings in the cold.