Anyone else had issues with the JK BMS dropping Bluetooth randomly on a 24V LiFePO4 setup?

Picked up a JK BMS (the 2A active balancer version, 200A continuous) a few weeks back to pair with my 8x 280Ah EVE cells. Got everything wired up, cells top-balanced to within about 5mV of each other, and the thing works brilliantly overall — balancing is dead quiet and the cell voltages are looking lovely across the pack.

The problem is the Bluetooth drops out constantly. Doesn't matter if I'm standing right next to the unit with my phone, it'll just vanish from the app mid-session. Sometimes it reconnects after 30 seconds, sometimes I have to fully restart the app, and occasionally I've had to power-cycle the BMS entirely to get it back. Running the JK BMS app on Android 13, tried two different phones. Firmware on the BMS is showing V11.25.

Wondering if it's a known firmware issue, a dodgy antenna on my particular unit, or whether I'm just missing something obvious in the settings. Has anyone managed to sort this, or found a third-party app like Xiaoxiang or something similar that handles the connection more reliably? Would love to get this logging consistently before I close up the battery box.

NigeScott98 | Posts: 847

@HarryJackson Yeah, had exactly this with my JK on a similar EVE setup. Turned out to be a power supply issue to the BMS communication board rather than a Bluetooth fault as such. Worth checking your balance lead connections are properly torqued down — a slightly loose one was causing voltage fluctuations that seemed to confuse the unit and drop the BT connection.

Also, are you using the JK app on Android or iOS? Android works considerably better in my experience. iOS drops connection far more frequently regardless of the hardware.

One other thing — keep your phone within about 5 metres initially to rule out simple signal range issues. The Bluetooth on these units isn't particularly strong compared to something like a Victron setup.

What firmware version is showing on yours?

WD40Wizard78 | Posts: 1,203

Worth checking the BMS firmware version first — JK pushed out some dodgy builds mid-2023 that had known Bluetooth stack issues. The JKBMS app will show your firmware on the device info screen.

Also, on my 24V EVE build in the shepherd's hut, I found the Bluetooth dropout was temperature-related rather than a software fault. Once ambient dropped below about 8°C, the BT module would lose its mind. Wrapping the BMS in some light insulation sorted it entirely.

One other thing @HarryJackson — are you running the BMS near a Victron MPPT or inverter? I had significant RF interference from my SmartSolar 100/30 causing intermittent dropouts until I repositioned the BMS away from it and ran a short RS485 cable instead for monitoring. Physical separation made a noticeable difference.

FL_Solar | Posts: 1,243

@HarryJackson Worth checking whether it's specifically dropping when there's a heavy load event or during balancing activity — I found on mine the Bluetooth would cut out momentarily whenever the active balancer kicked in hard.

The fix that worked for me was updating the firmware through the JK app whilst connected via USB rather than relying on OTA. There were a couple of firmware versions that had known BT stability issues, and the latest release sorted it completely.

Also double-check your BMS supply voltage isn't dipping — if your cell interconnects have any resistance the BMS sense voltage can wobble about and cause all sorts of odd behaviour including comms dropouts.

What firmware version are you currently running? Should show in the app if you can keep it connected long enough! 😄

NorfolkVanLifer | Posts: 312

Mine did the same in the garden office — swapped to wired monitoring via the RS485 port and now the Bluetooth can ghost whenever it likes, couldn't care less 🤷

Tommo10 | Posts: 847

Had the exact same headache with mine, @HarryJackson. Turned out the Bluetooth antenna on the JK board sits really close to the balancer circuitry, and when the active balancer kicks in hard (especially if cells are more than ~20mV apart), it generates enough interference to drop the BT connection. Try setting your balance start voltage a bit higher in the app so it's only balancing at the top of charge rather than constantly. Also worth checking your phone's Bluetooth isn't set to power-save mode — Android in particular will kill the connection after a few minutes of inactivity. The JK app has a "keep connection alive" tick box buried in settings that helped mine no end. What firmware version are you running? As @WD40Wizard78 says, some builds were definitely flaky.

KeithYoung | Posts: 634

Worth mentioning something nobody's touched on yet — the JK app itself can be part of the problem. Older versions had a known issue where the connection would silently time out after a few minutes of inactivity, making it look like the BMS was dropping Bluetooth when it was actually the app losing its keep-alive. Make sure you're on the latest version from the JK website directly rather than whatever's cached on the Play Store, as the Play Store version often lags behind by a revision or two.

Also @HarryJackson, are you running this in a fairly confined space? I found interference from an inverter nearby was enough to cause intermittent drops on mine. Moving the phone to within about a metre for initial diagnostics helped me rule that out fairly quickly.