Recently I’ve noticed that the battery is getting out of balance, with a voltage difference as big as 0.3V, and the BMS does not seem to be able to balance it automatically. I do not have a home charging facility, instead I mainly use public charger with an adapter. I know that’s not the best way to charge a Roadster and I did try to find always-on chargers for a few times to hope the car can balance the cells but it didn’t seem to work, maybe I should’ve have let it charge for longer. However, instead of doing that, I decided to pull the BMB boards and balance it myself, which turned out to be a stupid decision…
So I inhibited the APS, and the first problem happens when I pulled the service plug, the handle of the plug broke… Since I’ve already pulled it out I decided to continue any way… I then pulled two BMB boards out and find the one with minimum voltage (3.68V), and put the other one back in. The other bricks are about 3.99V. I then inserted a “trickle charging” BMB board (thanks Nick for designing those boards) to the slot that has the lowest voltage brick, and connected to a power supply that can do constant voltage and constant current charging. I originally set the charging current at 0.1 A for a few hours and realised it is gonna take forever to charge it from 3.68V to 3.99V. So I increased the current to 0.4A, let it charge for about 2 days and only got to 3.72V. I lost my patience and also worried that other cells may also go out-of-balance so I stopped it and put the BMB board back in.
Since the service plug handle is broke I then glued a customised handle and plugged back in. After about 30 seconds, the VDS screen turned on with a “VMS-VDS communication fault, ID: 1900” message, and everything seemed reset, time is out of sync. The VDS also asking for a new Pin for the vehicle but after entering the Pin there’s no response. It couldn’t go to diagnostic mode either. Everything else e.g. doors, keys, hazard lights does not work either. Car couldn’t start. I then realised that OVMS was left plugged in during this time and that might have drained the 12 V battery. So I measured the voltage across the 12V battery, it was 13.2V. However when I disconnect the cable that connected to the 12V battery, the voltage of the battery was only 8.3V. So it seems that the battery is dead, but the main ESS is able to provide 13V to supply the vehicle… I got confused, the problem seems like the VMS is not started or faulty but the VDS is on and working. I thought maybe the BMB boards or the ESS disconnect plug were not inserted properly but how could the ESS still supply 13V if that is the case? I did try pull out and put back in the ESS disconnect a few times but is the same problem. I also tried to supply the 12V a power supply and noticed a 50W power draw and slowly settled to 37W, the two amber lights in the front of the car turned on and I guess that's drawing the power. Even with the 12V power supply the VDS screen does not turn on, it only turns on when the ESS disconnect is plugged in, and VDS stills shows the same VMS-VDS fault message. I also tried to flap the charging port door many times and that did not help.
I then thought could it be a fuse blown due to the high current surge to charge the low-voltage 12V battery when I put the ESS disconnect back in? If that’s the case where should I check and replace the fuse?
Any other ideas about what is going on?
Thanks for your time!