Anyone else had issues with JK BMS dropping Bluetooth mid-charge on a 280Ah LiFePO4 build?

Been pulling my hair out with this one. I've got a 4S 280Ah LiFePO4 pack (EVE cells) paired with a JK BMS-8S20P, wired up in my converted Sprinter alongside a Victron MPPT 100/30 and a B2B charger from the alternator. Everything works a treat electrically — balancing looks spot on, cells sitting nicely between 3.2 and 3.45V — but the Bluetooth on the JK keeps dropping out after about 20-30 minutes of active charging. Have to kill and reopen the app every single time to reconnect.

I'm running the JK BMS app on Android 13 (Samsung A52), and I've tried turning off battery optimisation for the app, keeping the screen on, the lot. Makes no difference. Seems to happen most consistently when the MPPT is pushing anywhere above 15A into the pack. Not sure if it's interference, a heat thing, or just a firmware gremlin. The BMS itself is mounted on the side of the battery box, maybe 30cm from the MPPT controller.

Has anyone else seen this? I've seen a few mentions of it on some Facebook groups but nothing conclusive. Wondering whether a firmware update might sort it — I'm currently on v11.25 — or whether moving the BMS further from the MPPT could make a difference. Would love to know if there's a fix before I start pulling things apart again.

MPPT_Fan | 847 posts

@Ollie1991 Classic JK Bluetooth gremlins! Had exactly this on my build. Worth checking whether it's dropping during bulk charge specifically — the BMS can get quite warm when the B2B and MPPT are hitting it simultaneously, and the Bluetooth module seems sensitive to that.

Try logging into the JK app and bumping the "Bluetooth disconnect time" setting if yours has it — some firmware versions have it buried in the advanced settings.

Also, are you on the latest firmware? JK pushed an update a while back that improved Bluetooth stability noticeably. The flashing process is a bit fiddly but worth doing.

If you're just monitoring rather than actively configuring, Victron's VRM alongside a Cerbo might honestly save you the headache long-term. What firmware version are you currently running?

Worth adding something that took me ages to figure out with my shepherd's hut build — the JK BMS has a known conflict where high charge current combined with the Bluetooth stack causes the processor to prioritise protection logic over comms. Essentially the radio gets starved.

What sorted it for me was dropping the balance start voltage slightly in the JK app — counterintuitively, when active balancing kicks in hard during bulk charge it seems to push the CPU load over a threshold. Set mine to 3.45V rather than the default and the dropouts almost entirely stopped.

Also worth checking your cable routing — I had my BMS data cable running parallel to the main positive for about 300mm and the interference was horrific. Separated them and shielded with some split loom and things improved dramatically even before the software tweak.