Balancing batteries is an important part of maintaining pack health. Especially with a battery pack that doesn’t have an active cell-level BMS monitoring every cell.
TWIKE 560 currently has three 100-cell stacks which all would need an own balancing connection – a BMS would be adding weight, considerable amounts of cabling and complexity to the setup. Furthermore, one of the really neat features of Dreifels‘ DFC 3.0 controller, being able to completely and physically disconnect the battery from the vehicle when not in use and effectively go to zero amps would be rendered useless as the BMS controller is connected to the battery all the time.
As I’m planning on going on another major ~3500km European TWIKE adventure in just over a week and I’ve been on one earlier this year, I need to ensure that the full cycles I’m planning on making during the trip don’t harm my pack.
What I don’t really have too much of is time. However, with 42 balancing ports and at least 20 minutes per port, I’m going to be stuck with balancing for at least a weekend!
This is why I decided to reach out to the community and borrow some battery workstations and daisy-chain them together to deliver three times the throughput.
Before I start – it is very important to make sure all chargers are at the same firmware level.
V3.33 has some very useful features around fuel-level calculation and recovery charging. Luckily updating is just a button press in FMA’s interface.
With this done – time to get the tool necessary to access the battery bay:
By opening the battery bay cover of a TWIKE you are exposing yourself to the risk of death by electrocution! Do NOT go ahead without knowing what you’re doing. DC voltages of 400V+ are not trivial and can kill very efficiently.
With 3 battery workstations, there are a few more cables coming into the TWIKE than usual. 🙂
And off we go! The first cycle is easy and balancing is done within a few minutes of each other, giving me enough time to plug the charger in the next port and start the next balancing cycle. After a certain amount of ports, I’m just sitting in the TWIKE waiting for the next port to finish. It’s much faster but much more intensive, as I can’t really leave the TWIKE to do something else.
The speed with which I’m balancing the pack is staggering – 24 cells per cycle – I’ll be done in half a day and this motivates me to balance my pack even more often.
One very interesting part of balancing is checking on cells that showed some kind of anomaly during the last charge. This is only possible if you log the balancing charge every time and take the time to single out the ones you want to check back on next time.
As TW560’s last battery pack was decaying after 8 year because of cell wear and age, checking cell degradation was something I did religiously.
If necessary, I took single cells and re-balanced them where necessary. This ensured that I had maximum cell capacity with minimal cell failure until the very end.
I’m happy to report that the pack is in top health, voltage differences across all 300 cell ports are minimal and within thousandths of a volt and only one cell is showing slight signs of weakness. After just a little more than 4 hours TW560’s pack is ready for TDE2019! #gogogo!