I arranged a visit the bike and determine the fault.After much thought trying to figure out how to remove the covers and expose the battery pack, we finally opened the enclosure with 102 cells arrange in two blocks. The rear block is 9 cells long, 2 wide and 3 cells deep. The front block is 8 long, 2 wide and 3 cells deep. Each set of 8 / 9 is bound by a steel compression band to prevent the cells from expanding when heated during charging and discharging. Each layer comprises of two rows of 8 / 9 in a plastic frame. Each of the 3 layers is held together by long threaded rods extending between the rows and also by duct tape around the outside of the plastic frames.
The top of the rear block was removed and some evidence of heating and corrosion was visible on one of the cells.
Leaky cell and voltage - temperature sensors
The cell had overheated, the plastic frame the cell sits in was melted, and the pressure relief valve on the top of the cell had released causing some corrosion and crystallisation of electrolyte around the top of the cell. We verified the cell had failed electrically also. It measured only 32mV.
The temperature and voltage sense boards were also disconnected at the connectors at the front and rear of the bike.
There are temperature and voltage sensing elements screwed to some of the battery terminals. These were numbered with a marker on each sense board and also on the cells they were removed from to ensure they were replaced in the correct locations. Each sense board was wrapped in insulation tape to prevent them accidently touching the battery terminals once removed.All the other cells were of the correct voltage (~1.3V) and had no physical signs of failure. Disassembling the blocks was fiddley. The cells are assembled in plastic frames that are then joined with steel compression bands to prevent cell swelling.
I have made a jig for compressing the packs in order to remove and replace the steel bands more easily. To make things more tricky, the brittle locating tabs
I proceed to replace the 3 cells in a string of 9. Each ½ layer of cells is bound in steel a binding strap to prevent the cells swelling during charging and discharging. I have made a jig for compressing the packs in order to remove and replace the steel bands more easily.
An interesting point is that each cell is electrically insulated from the next by plastic spacers.
Reassembling the pack consisted of reversing the disassembly process. Extra care was taken to double check visually and with a volt meter that each 9 / 8 cell bank was reassembled correctly and the temperature and battery voltage monitoring sensors were installed in the correct locations.
All interconnects and battery terminals that had been removed were tightened to a specified to torque of 10Nm.
After reassembly the owner took the bike for a ride and came back with a memorable grin. The bike performed better than it had for a long time.
The final task for the owner is to deep discharge the pack 5 times to condition the batteries and ensure longevity of the new batteries. This procedure is recommended by Vectrix to remove any ‘memory’ effect in the batteries in order that they can provide the maximum usable capacity.