BMS Testing
12 December
Time flies when you're having fun! Sadly little of the available time was spend on the z3. I did manage to find some time to finish the crimps on the rear BMS wire harness. Also I wrapped each group of wires in high strength and high temperature rated tape. To add a 2nd layer of defense I put the wires into a split corrugated tube. This should prevent the harness from externally induced damage .
Also I tested the harness with the BMS module to see if it worked. A little moment of joy seeing all battery voltages being reported with no abnormalities.
All good:
Charger
2 December
For charging I have been struggling trying to make the decision on what to buy or build. At this moment there are no chargers available which can charge my battery pack (131 cells in series) other than the Brusa NLG5xx chargers. A moment of hope after finding the Sinexcel charger (19" quick charger of 12kw upto 700V) was lost again after hearing no response what so ever from my inquiries.
The only other option at this time is to build my own charger, but that may take a while also it would require a fair bit of testing and tweaking and perhaps a hardware revision to make it work as desired & compliant with european electronic emissions.
I don't want a project within a project. Since I only have two hands and one brain and limited time that I want to devote to the project.
Choosing a ready made charger makes sense. So it became the Brusa NLG513 with the air-cooled option.
BMS
2 December
Initial plan was to go without a BMS. But after some tests with the pack installed I noticed quite some divergence in capacity or self-discharge rate. This causes some cells to hit low earlier and when charging reach the high voltage cut off point much later. I want something to be able to find the weak-cells and filter them out. A BMS may be off help here. I chose for a decentralized BMS which allows split pack (front & back of the vehicle) configuration. Fast sample rate, high resolution, vast range of CAN bus customizations are possible. Also SOC Health can be calculated.
There's a downside to decentralized BMS'es compared to distributed, the wires! There are lots of them. Luckily its all rather simple and straight forward. I took my time to make the harnesses. Each crimp is made with care to ensure a high quality connection.
Here's the almost finished harness for the (104 series) cells in the back of the vehicle:
The front harness will be much less of a impressive set as those will be only for 27 series connections.