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

Just finished wiring up my 4x280Ah Eve cells in a 12V setup with a JK BMS (the 200A one, JK-B2A24S15P I think). Everything seemed spot on during initial balancing — all cells sitting between 3.27 and 3.29V, which I was pretty chuffed with for budget cells from Alibaba.

Problem is, the Bluetooth on the JK keeps dropping out when the Victron MPPT kicks in properly. I'm running a 100/50 SmartSolar and once it hits the bulk phase and starts pushing decent current (anywhere above 30A or so), the app just loses connection. Reconnects fine when charge current drops, or if I kill the solar input entirely. Bit odd.

I've tried moving my phone closer, ruled out interference from the inverter (a Victron Multiplus-II 3000, which is a fair distance away in the van). The BMS is mounted on the side of the battery box with a decent bit of airflow. Firmware is up to date as far as I can tell — v11.25 I believe.

Has anyone seen this before? Wondering if it's a power supply issue within the BMS itself, or just a known quirk with these units. I'd rather not have to run a separate RS485 adaptor and laptop every time I want to check on things during a proper charge cycle.

Chris1984 | 847 posts | ⚡ Solar Addict

@Jake1977 Had exactly this on my 16S build last spring. Worth checking a couple of things — first, make sure the JK app is updated, the older versions had a known reconnection bug. Second, and this caught me out for ages, the Bluetooth module on these JK units can be quite sensitive to interference from the BMS's own balancing activity. Try disabling active balancing temporarily and see if the drops stop.

Also check your phone's battery optimisation settings — Android in particular will aggressively kill the Bluetooth connection in the background. Whitelisting the JK app sorted it for me about 80% of the time.

If none of that helps, the small Bluetooth dongle on the board itself can work loose during transport. Give it a gentle reseat.

What firmware version are you running?

Midge66 | 234 posts | 🔋 Off-Grid Enthusiast

@Jake1977 One thing I'd add that hasn't been mentioned — check your phone's Bluetooth settings aren't automatically dropping the connection due to battery optimisation. Android is notorious for killing background Bluetooth connections, especially during longer charge cycles. Go into your app settings and disable battery optimisation for the JK BMS app specifically.

Also worth trying the desktop tool via USB if you've got a Windows machine handy — far more stable for monitoring during a full charge cycle and you can tweak the Bluetooth transmission interval in the BMS settings, which sometimes helps with dropouts.

What firmware version are you running? Some earlier versions had known connectivity issues that were patched in later releases.

LutonLife | 412 posts | ☀️ Solar Tinkerer

@Jake1977 Something worth checking that I haven't seen mentioned yet — the JK app has a "Bluetooth disconnect protection" setting buried in the device settings menu. It's off by default on some firmware versions and can cause the BMS to drop the connection when it detects high current draw, seemingly as a protective measure. Updating to the latest firmware (I'm on 11.25 on my similar build) sorted it for me completely. Also make sure your phone isn't aggressively killing background apps — Android in particular can be brutal for this. Xiaomi phones are notorious for it. Give the JK app battery optimisation exemption in your phone settings and see if that helps before you start pulling the BMS apart. 👍