Anyone else had their JK BMS trip out in cold weather? Trying to figure out if it's the low temp cutoff setting

I've been pulling my hair out this past week. We've had a few nights down to around -3°C here in the Scottish Borders and my 280Ah LiFePO4 bank (four 3.2V EVE cells in series) has been shutting down overnight. The JK BMS (the 200A active balancer version) is cutting out and I'm getting a low temperature protection fault in the app. I've got the low temp cutoff set to 0°C at the moment, which I thought was sensible, but I'm wondering if the sensor placement is the issue — mine's just cable-tied to the side of one cell with a bit of foam over it.

From what I've read, LiFePO4 discharge down to around -20°C is actually fine, it's charging below 0°C that causes the dendrite damage. So I'm thinking about dropping the discharge low temp cutoff to maybe -10°C but leaving the charge cutoff at 5°C. Does that sound reasonable to people, or am I missing something? I don't want to knacker the cells but I also can't have the van going dead on a cold night.

Has anyone else played around with these settings on the JK app? I'm also curious whether better insulating the battery box would just solve this without touching the BMS config — the box is currently just bare plywood with no insulation at all.

@LisaKelly mine did exactly the same on the narrowboat last February — turns out the JK low temp cutoff was set to 5°C from the factory, so it's not even that cold before it throws a strop.

Hey @LisaKelly, classic cold weather issue this! On the JK BMS, go into the app and check your Low Temperature Protection setting - it's often set to 0°C from factory which would definitely cause dropouts at -3°C. You'll want to lower the trigger threshold but honestly the bigger concern is whether your cells are actually being charged when they're that cold. LiFePO4 really shouldn't be charged below 0°C as it causes lithium plating which permanently damages the cells.

If it's just discharge cutoff tripping, that's less critical to override. But if your charger is trying to push amps into frozen cells, the BMS is arguably doing you a favour!

Worth checking whether it's cutting out on charge or discharge first - the JK app will show you the fault log. What's your setup for heating the battery bank? 🙂

Even my cabin setup in the van — yes, I run both, don't ask — trips the JK below 0°C and the cell temp sensor placement is half the problem; if it's cable-tied to the outside of the cell casing rather than wedged between cells, you're reading ambient air temp and it'll cut off way before the actual cell chemistry cares.

Good shout from @Scouse12 and @MultiPlusNerd on the sensor placement — that's caught a few people out. One thing worth adding: even once you've sorted the settings, do be careful about charging those EVE cells if they're genuinely cold. LiFePO4 really doesn't like being charged below 0°C, it can cause lithium plating which permanently damages capacity. If your charger source allows it, set a low-temp charge cutoff rather than disabling cold protection entirely. Some folks fit a small self-regulating heat mat under the battery bank with a thermostat, which solves the problem properly rather than just masking it. Given you're in the Scottish Borders, probably worth the investment before next winter hits properly. What's your current charging setup — solar, mains, both?

Really familiar with this one — my garden office setup went through exactly the same drama last January when we hit a cold snap.

What sorted it for me was wrapping the battery bank in closed-cell foam insulation (the stuff from Screwfix, nothing fancy). The cells themselves retain heat from normal discharge cycling, so once you slow that heat loss the BMS stops seeing those scary sub-zero readings at night.

Also worth checking — are you actually charging when it trips, or just discharging? LiFePO4 will happily discharge at -3°C but charging below 0°C genuinely damages the cells, so if the JK is tripping on a charge cycle it might actually be doing you a favour rather than misbehaving. Two very different problems with similar symptoms.

What's your charging source — solar, mains, or both?

Really useful thread this. One thing I'd add that hasn't been mentioned yet — have you checked what your JK's low temp cutoff is actually set to? The default from the factory on a lot of units is 0°C, but the hysteresis (recovery temp) is sometimes set to 5°C above that, meaning it won't reconnect until the cells warm back up to 5°C. So you can end up in a frustrating loop where it keeps dropping out through the night even after brief recovery periods.

Worth connecting via the JK app and screenshotting your current protection parameters before changing anything. If your cells genuinely are sitting at -3°C, that's a separate concern — LiFePO4 really shouldn't be charged below 0°C anyway, so the BMS is arguably doing its job. @LisaKelly have you got any heating in that battery enclosure?