Cell-Lock: The modular battery assembly system

During the course of some real-world testing (riding my bike around town), I ran into a fairly serious flaw with the current version of Cell Lock. I’ve been using a 36v 5Ah (10s2p) setup, connected to my motor controller through a Daly BMS as pictured below.  Most of the time this works great, delivering 20-30A peak at full load when I’m going uphill, and keeping the cell voltages from dropping too low. 

The problem with the current design only shows up when the ground gets bumpy: Currently, Cell-lock consists of two end caps attached to each individual battery. These end caps are joined to each other with locking connectors, and then secured to aluminum standoffs. For the cells in the middle of the battery, this is completely fine: each symmetrical pair of standoffs keeps the cap in line with the axis of the cell, and ensures the copper plate in the cap has good contact with the cell. This doesn’t work nearly as well for the cells on the edges of the battery: because the standoffs can only be attached on one side, the cap ends up at a slight angle to the battery. This doesn’t cause a problem during the initial assembly, but all it takes is a good jolt to briefly disconnect a cell. This in turn makes the BMS very unhappy, and it promptly cuts all power to the motor, often right at the steepest part of the hill. 

The solution:

I’m getting rid of the standoffs entirely. This will hopefully have the benefit of fixing the contact issue, and as a bonus, help to simplify battery assembly. The downside is that the caps now need to be significantly taller to snap together without any extra components. I’ve printed a few concept designs out, and they seem much better at withstanding external vibration, however I’m waiting on some new copper tabs to come in to fully rebuild the battery. I’ll upload the new design when I’m satisfied that it works better than what I’ve got now. Sorry Vittorio, the thermal testing will have to wait a bit!