Hello,
I am attempting to repair the high voltage battery in a 2012 Tesla Model S.
The battery pack consists of 16 modules.
Each module consists of 6 sections called bricks.
Each brick consists of qty 72 lithium batteries of the 18650 type.
All 72 batteries are housed in between 2 plates that act as bus bars.
Each individual battery cell has a short piece of aluminum wire connecting the anode to one bus plate and the cathode to another bus plate. This wire is ultrasonically welded.
One of the battery cells is going resistive and draining the other 71.
Since they are all connected in parallel, they all have the same voltage reading.
Cutting the wire would allow me to test each cell individually, but then I would need to replace 72 wires. I don’t have this wire or the ultrasonic welder.
I’ve attempted to charge the battery and look for a heat difference between the batteries with a FLIR one camera. No difference.
The cells currently are at around 3.6965 vdc and drop about 10-20mV per day.
The other bricks in the pack do not change voltage, so they are fine.
The goal is to locate the bad cell and isolate it by cutting the fuses on each end. The brick will have a slight less capability but only like 1.5%.
I am looking to design something that can do the following:
Detect DC current flowing into or out of a cell through this fuse wire.
The wire is short and close to the cell. I can clip onto it or press next to it, but there is not enough space to use a current clamp like on a CT or other toroidal current meter around it.
The only device I’ve found that can read current as a probe is the iprober 520, but it’s $800 new.
I was wondering if a circuit could be designed using a Hall effect sensor that could detect the current if the face of the IC Chip was pressed against the wire.
I’m not looking for a reading or accuracy. I’m looking for comparing against the other cells current.
I think this cell would be taking in current and the others are giving it. So the current direction would be different.
Let me know what you think.
A photo of the cells and the fusible links is attached. For those not familiar with the 18650 battery just think of it like an AA battery cell.