Replacing bad cell #65

The ECE Lotus has 4 battery packs with in total 100 cells. Based on the fiber optical cable which runs from the VMS thru all 4 packs I guessed that cell #65 would be in pack #3. Pack #1 has 24 cells and is behind the driver seat. Pack #2 is above the gearbox and Pack #3 is next to it, both have 24 cells. Pack #4 is behind the passengers seat an has 28 cells

Lifting battery pack #3

Lifting battery pack #3

Pack #3 removed

Pack #3 removed, Pack #2 above the gearbox and Pack#4 slightly vissible

After Pack #3 was removed it was placed up-side down and opened up.

Battery pack (Up side down) showing wires to LOM modules

Battery pack (Up side down) showing wires to LOM modules

The top cell of the lower 8 cells was defect.

Disassemble battery pack

Removing the bad cell from the pack

The replacements cell was at it’s nominal voltage of 3.7V it need precharging to match the other cells at 4.10V. The picture shows two cells in serie.


Precharging the replacement cel

After charging the pack was assembled and bench tested. Each set of two cells is monitored by LOMs (Lithium Optical Monitoring system by AC Propulsion). Each LOM is connected to the next cell with a fiber cable.

Bench test of new assembled pack of 8 cells.

Bench test of new assembled pack of 8 cells.

Lom module

LOM module

LOM module

LOM Utility test software screendump.

New cel 65 in pack

New cel 65 in pack

After some testing the 8 cells where placed back in Pack #3 and the car was put together. I’m getting better at it 🙂

The VMS showing nice voltage levels (first line). The second line shows the temp of the cells. Pack #3 is a few degrees warmer since 8 of the cells where in doors for a day or two.

VMS display after replacement of defect cell #65

Defect cell in battery pack

One of the 100 cells, cell #65 is dying. This is noticeable under hard acceleration and the top speed has dropped to 141 Km/h.

VMS display defect cell

VMS display showing cell #65 dropping in voltage

It will be quite an operation to get to the defect cell. First te body needs to be removed and than I need to open the black box.

battery pack, rear clam removed

Battery pack, rear clam removed.