Anyone else had grief with JK BMS dropping Bluetooth mid-charge?

Been running a 280Ah LiFePO4 bank (4 x EVE 280K cells) in my shed setup for about eight months now, paired with a JK BMS (the 200A active balancer version). Generally really happy with it — balancing is spot on and it's handled everything I've thrown at it. But I've started noticing that the Bluetooth connection drops out almost every time the bank hits around 95% SOC during a decent charge from my Victron MPPT.

I'm pulling roughly 40–50A from a 600W array on a good day, so it's not like it's being hammered. The JK app just goes grey and won't reconnect until the charge tapers right off or I power-cycle the BMS. It does come back, and I haven't seen any protection events in the logs, so it doesn't seem to be a safety trip. Just really annoying when you're trying to keep an eye on cell voltages during a full absorption cycle.

Has anyone else seen this on the JK units specifically? I've seen a few mentions on the Facebook groups of interference from the balancer kicking in at high SOC, but nothing concrete. I'm on firmware 11.25 — wondering if it's worth trying to update, or whether there's a known fix floating around. Any thoughts appreciated.

@Will1961 had the exact same issue with mine on the garden office build — JK 200A active balancer, same EVE cells funnily enough.

Turned out to be a power supply problem to the BMS communication board rather than a Bluetooth fault as such. When the bank gets near top of charge and the balancer kicks in hard, there's enough noise on the supply rail to reset the BT module.

A few things that helped me:

• Updating firmware via the USB cable rather than OTA sorted it temporarily
• Adding a small ferrite bead on the communication wires made a noticeable difference
• Keeping phone within 2 metres during charge — the signal seems weaker than advertised

Still drops occasionally at around 95-98% SoC which I suspect is just a quirk of this BMS generation. Curious whether yours drops at a consistent SoC point or randomly?

@Will1961 worth checking whether it's actually dropping connection or just the app timing out — the JK app has a known habit of disconnecting if your phone screen locks. Try keeping the screen active while monitoring and see if it's more stable.

Also had this on my setup when I first commissioned it. Turned out the BMS was throttling Bluetooth during heavy balancing activity — presumably a firmware prioritisation thing. Updated to the latest firmware via the PC tool (not the app) and it largely sorted it.

One other thing — physical distance and interference matters more than you'd expect with these. My Victron kit nearby was causing occasional dropouts until I repositioned the BMS slightly.

What firmware version are you running? Worth checking before assuming it's a hardware fault.

Been running the same JK 200A unit here for about a year and found the Bluetooth dropout was actually heat-related in my case — the BMS is tucked in a fairly confined battery box and once ambient temps crept up during charging the connection became really flaky. Added a small 12v fan on a thermostat and it improved dramatically.

Also worth checking your phone's battery optimisation settings @Will1961 — Android in particular will aggressively kill background Bluetooth connections. Whitelisting the JK app made a noticeable difference for me before I sorted the thermal issue.

@NQ_Sparks makes a fair point about the app timeout too — I've seen folk confuse the two. Try the Xiaoxiang alternative app as a secondary test, behaves a bit differently with connection handling.

@Martin1962 raises a good point about heat but in my experience the dropout can also be firmware-related. I had the same grief with my garden office build — JK 200A on a 280Ah EVE bank — and updating to the latest firmware sorted it almost completely. Worth grabbing the JK BMS app from their official site rather than whatever version you might have downloaded months ago, as they've pushed a few updates that specifically address BLE stability.

One other thing to check: phone proximity matters more than it should. The JK's Bluetooth range is pretty mediocre through any kind of enclosure. I mounted mine in a vented IP65 box and had to be practically leaning on the cabinet to get a reliable connection until the firmware fix.

@Martin1962 and @BrianKnight both raise valid points, but worth being pedantic here — there are three distinct failure modes people lump together as "Bluetooth dropout":

1. App timeout (software)
2. Heat-induced BMS reset
3. Firmware bug causing BLE stack crash

They present identically to the user but have completely different fixes. Before chasing your tail, grab a USB-to-UART cable and log what the BMS is actually doing when it drops. If it's restarting, you'll see it in the data.

On my narrowboat setup I had this exact grief last winter. Turned out to be none of the above — dodgy micro-USB power feed to the BMS causing brownouts during high charge current. Embarrassingly simple fix.

Don't assume it's Bluetooth at all until you've ruled out the basics.

@ShedGenius fair point on the three failure modes but would love to know what the third one is — genuinely curious.

Had this exact issue on my narrowboat setup last summer. Turned out to be the USB-to-Bluetooth adaptor on the BMS itself working loose from vibration. Worth checking the physical connection before diving into firmware or heat fixes. Boats move around obviously but even in a static shed, a loose fit from factory isn't unheard of.

Fixed mine with a tiny bit of electrical tape to hold it snug and haven't had a dropout in months. Dead simple if that's your culprit.

Worth ruling out before flashing new firmware anyway — less risk of bricking anything.