Update as of 10/23/23 - Greenway reached out to me and informed me that there is a newer version of the app that will actually display the cell-group voltages. Thank you Greenway!
I had the idea of trying to see if I could read all of the cell group voltages with the bluetooth app, rather than going group by group with the DVM, recording the voltages and then doing some spreadsheet math to get the actual values. The app is OK, but doesn't give individual group voltages, at least it doesn't display these voltages in the app (come on Greenway). So, are the voltages there but just not displayed? I had to find out.
So, I got out the Saleae logic analyzer, which is one of my favorite debugging tools, soldered a couple of wires onto the tx/rx pins between the BTLE module and the BMS, and started the data capture. Looks like asynchronous serial and while I was able to capture values, I had no idea what I was looking at. Thanks to HexEd.it - Browser-based Online and Offline Hex Editing and the SCADACORE online hex converter Online Hex Converter - Bytes, Ints, Floats, Significance, Endians - SCADACore, I was able to make some sense of the data.
It turns out that the devices talk to each other with 13 frames of data as shown below.
After some work with the hex converter, I was able to read the battery serial number in frame 11 and also what I think are the cell group voltages in frame 12.
Battery Serial Number
Battery Cell Group Voltages
The next steps are to work toward a debugging tool that I can plug into the BMS and use that to quickly determine which cell groups are low and also be able to extract any other useful debug information from the BMS. It looks like the BMS also stores an error record of sorts as well as the number of charging cycles on the pack in its eeprom, but I have yet to decode those frames yet. More to come!
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