Differing bus bars

[alexcl]

I have a weird space to install my battery in (around the wheel well of a van). I am upgrading from off-the-shelf batteries to 280aH DIY LiFePO4 eve cells in a 3p8s setup. Because the space I'm putting them in is not a rectangular prism I was thinking I would use welding cable to connect terminals in the irregular parts to the terminals in the main parts. Below is a (very crude) top down 2D layout of the layout. A few questions:



1. Is there a problem mixing fixed busbars with the welding cable for connecting terminals?
2. Is there a problem using different lengths of cable to connect terminals? I'm assuming resistance is pretty negligible using 4/0 cable over very short distances.
3. Does having a BMS with active cell balancing negate any problems from the above 2?

Thanks!

 

[Lt.Dan]

Take a look at this video, it might answer your questions.

 

[RCinFLA]

BMS sense wires are shared between two adjacent cells so you have to match the interconnect bus bar or cable extension resistance as close as possible.

Cell containing the bus bar or cable extension in series with its two measure sense wires will have added voltage drop in the BMS cell voltage measurement, with current, from interconnect resistance.

 

[rhino]

BMS sense wires are shared between two adjacent cells so you have to match the interconnect bus bar or cable extension resistance as close as possible.

I am wondering if you have to do that with a BMS that allows you to manually adjust the resistance of the sense wires via the BMS app?

 

[RCinFLA]

I am wondering if you have to do that with a BMS that allows you to manually adjust the resistance of the sense wires via the BMS app?

Nothing to do with sense wire resistance.

All BMS's momentarily shut down balancing current when making cell voltage measurements to avoid sense wire voltage drop due to balancing current.

It is the voltage drop across the bus bar connections between cells due to high current flowing through battery array.

Each cell having its own two BMS sense wire pairs directly on each cell terminals would avoid this but that doubles the number of sense wires and makes BMS mux'g of cell sensing more complicated.

 

[alexcl]

BMS sense wires are shared between two adjacent cells so you have to match the interconnect bus bar or cable extension resistance as close as possible.

Cell containing the bus bar or cable extension in series with its two measure sense wires will have added voltage drop in the BMS cell voltage measurement, with current, from interconnect resistance.

I'm not understanding something.

As far as I understand, in my case I would have one sense wire per group of 3 cells (each group in parallel). Are you saying they are shared between the positive terminal of the first group and negative terminal of the second? And that connecting these groups with different methods results in incorrect voltage readings per group? Not sure why that would be the case.