Anyone else finding their JK BMS cutting out in cold weather? Temps, settings, wording...

Been having a frustrating few weeks with my 280Ah LiFePO4 bank (4 x 70Ah EVE cells in series) and the JK BMS I picked up last spring. The BMS keeps tripping the low-temperature cutoff even when I don't think it should be — we had a run of nights down to around 4°C here in mid-Wales and it was shutting down charging at what felt like a fairly conservative threshold.

I've got the low-temp charge protection set to 5°C in the JK app, which I thought was sensible, but I'm now wondering if the NTC sensor placement is the issue rather than the setting itself. Mine is just loosely sitting between two cells with a bit of kapton tape, and I suspect it's reading ambient air temp in the battery box rather than actual cell surface temp. Anyone moved theirs to a specific spot and seen a difference?

Also slightly confused by the app wording — there's "Cell Low Temp Protection" and separately "Charge Low Temp Protection" and I'm not 100% sure which one is actually doing the cutting out. The JK documentation is pretty thin on explaining the difference between the two. Would really appreciate if anyone who knows the JK internals well could shed some light on that distinction.

@WendyLewis this is a known quirk with the JK units — the default low-temp cutoff is often set aggressively at around 5°C, which is perfectly reasonable for charging protection but unnecessarily conservative for discharge.

In the JK app, navigate to Protection Parameters → Low Temperature Protection. You'll want to distinguish between:

• Charge low-temp cutoff — keep this at 5°C or even raise to 8°C to protect the cells during charging
• Discharge low-temp cutoff — EVE cells will discharge fine down to around -20°C, so you can legitimately drop this to 0°C or even -5°C

The other gotcha is the recovery temperature threshold — if it's set too close to the cutoff, you get rapid cycling on/off as temps hover around that boundary. Set the recovery at least 3-4°C above the cutoff value.

What firmware version are you running? Older JK firmware had a bug where these values weren't saving correctly.

@WendyLewis I had exactly this with my setup last winter. Worth checking whether your temperature sensor is actually making good contact with the cells — mine had worked slightly loose and was reading a couple of degrees colder than the actual cell surface, which was enough to trigger the cutoff unnecessarily.

Also, if you're charging from solar, consider setting the low-temp charge cutoff separately from the discharge cutoff. LiFePO4 really doesn't want to be charged below 0°C, so that protection is legitimate, but you can often be a bit more relaxed on the discharge side. The JK app lets you set these independently which is handy.

Wrapping the battery bank in some basic insulation (even old camping mat material) made a noticeable difference for me once the nights started dropping.

@WendyLewis mine did the same in my static van last January — turned out the sensor was reading the air around the BMS rather than the cells themselves, so it was cutting out at 3°C while the cells were sat comfy at 9°C. Taped the sensor directly onto a cell with some self-amalgamating tape and sorted it overnight. Worth checking your cell temp vs BMS-reported temp gap before fiddling with thresholds — JK's app shows both if you dig into the real-time data screen.

@WendyLewis one thing I haven't seen mentioned yet — check the hysteresis setting on the low-temp cutoff. On my JK the cutoff was triggering at 5°C but wouldn't recover until the temperature climbed back above 10°C, which in a cold shed meant it was staying tripped for hours even after things warmed up a bit. In the JK app it's sometimes labelled something like "Low Temp Charge Recovery" — worth bumping that down closer to the cutoff value itself, maybe 1-2°C difference rather than the default gap. Also, are you on the latest firmware? There was a version a while back that had some odd temperature threshold behaviour that got patched. What does the app actually show as the cell temperature when it trips?

@Steve1978 raises a valid point about hysteresis, though I'd add a small but important distinction: there are actually two separate temperature parameters to check — the cell low-temperature charge protection and the cell low-temperature discharge protection. They're configured independently in the JK app, and people often only adjust one.

On my narrowboat last February, I found the charge cutoff was the culprit — cells were perfectly happy to discharge at 4°C, but the BMS was correctly refusing to accept charge current at that temperature. LiFePO4 genuinely shouldn't be charged below roughly 5°C without risking lithium plating, so before simply raising the threshold, it's worth establishing which protection is triggering and whether the underlying temperature reading is actually accurate.

Fogstar will confirm the same — it's in their documentation for their EVE-based builds.