How to start troubleshooting JBD BMS


10 µW
Sep 27, 2022
Hi all,
I built a 20S battery and tried to connect it to my Jiabaida sp20s031 LiIon BMS + Bluetooth and am trying to troubleshoot it.

In brief - all I've gotten the device to do so far is beep and make/break the connection from C- to B-. The "instructions" I've found to date are, shall we say, somewhat lacking in detail and language skills.

I understand that the device expects the B- to be connected first. I'm not sure beyond that - I connected the B0-B15 balancing wires and the device starts beeping. I then connected B16-B20 and the beeping stops - at which point C- to B- goes from open to closed - so far so good. Nothing else is notable.

I tried plugging in the bluetooth but the XiaoXiang software never sees the device in order to connect. I tried with location enabled. I also don't see the module in my normal Android bluetooth connection list (or in Windows 10).

My main question is - are there any additional "clues" for troubleshooting? Should I expect any LEDs to turn on anywhere? I haven't noticed any puffs of smoke, arcs, odd-smells so that's promising. On the other hand - I measured the pins on the bluetooth connector and was very surprised to find 75V on it - perhaps that's why the blue-tooth module has heat-shrink? Not sure if there's any risk hot-plugging the module, but I don't see any obvious damage to it either - so perhaps it's designed to operate at battery voltage. The data pins on the connector are at 3V so that seems reasonable - I'll next try with a scope on it and also connecting a power supply and seeing what flows - I'm hoping to get the bluetooth working and the device configured before proceeding - failing that may try to wire it to a USB serial port.

Thanks for any tips.
Made a first attempt at debugging. Can confirm occasional bursts of a UART-looking signal at 3V, ~9600baud on the data line to the BT-module. Also found another reference to that the BT module describing its 3.3V voltage regulator - pulling up that datasheet indicates a maximum voltage of 30V IIRC - well below the 75V on offer. It also has what looks like a 100Ohm resistor in series to the regulator input (marked 101) - but my ohmmeter puts it at ~25kOhm - so that's disappointing. I'll try to lower that resistance and slowly bring up the voltage via my benchtop to see if the regulator is blown - if so, try to bypass the regulator and feed the module w/ 3.3V and see what happens. Not sure if something is blown on the main board that caused it to connect the positive line to the maximum battery voltage (when I only connect through cell 15 it is ~52V). Not inspiring a lot of confidence in me at the moment...
Just a note on this - I finally got it working by bypassing the regulator between the board and the BT module - wiring the 3.3V from the main JBD module directly to the BT-module. Once the module had 3.3V it came up correctly and worked and the whole BMS was accessible and appears to be normal. Not sure what the design intention was - although I assume there is a defect with my module. There is a lower voltage feed on the board (either 12V or 15V, I forget) that is energized once the batteries are in the correct state (during connection, the module beeps until all batteries are in place) - would expect that should be the feed to the BT module instead of the full battery voltage. Perhaps this might help someone in a similar situation.