Bolted Busbar battery pack for 18650

sj1021

1 µW
Joined
Sep 2, 2019
Messages
3
Hello everyone,
I am a part of an FSAE team and we're currently making our own 18650 battery pack which is divided into 5 modules that are connected in series. Each module having 22p6s cells. It is a 100V, 7.1KWh pack with average current draw of 250A and peak currents of 500A. Since the current draw is high, looking up the ampacity charts we'll require the busbar of the individual modules to be atleast 1.4mm thick made of copper. Due to this we cannot spot weld them using the locally available sunkko spot welders. Soldering is not allowed. So that leaves us to use clamped busbars on to the cells at both ends. I have a few questions regarding the same. I have attached my designs below
OnIWJ4a.jpg

d3HLqU1.jpg

Through the empty holes bolts will pass that'll be used to clamp the busbars against the cell. The bolts will be insulated from the busbar using the FR4 sheet which will be machined in that manner.
hXAtPbQ.jpg

1) Is there any data regarding damage caused to cells due to compression caused by clamping busbars.
2) How can I minimize contact resistance? I plan on using a 0.1mm copper sheet(used as gaskets) and then bolting on the thick copper busbar on to it which will result in better contact. Any concerns regarding this?
3)Any other better method or any suggestions?
 
Grantmac said:
Before going to extensive solutions look at how people use a sandwich of copper under nickel to spot weld.
I did look into them, but the max thickness that they could achieve was by spot welding 0.2mm copper to 0.2mm nickel.
 
If you use nickel sheet, the sheet only needs to carry the current of 2 cells, whatever that works out to, except at the ends where you need a very heavy copper bus. The cells can't handle huge currents individually.

Here is a 12p pack I built. On the ends, I used 8ga copper soldered to the nickel before welding. This has worked well so far.



There have been all kinds of compression pack builds but I personally wouldn't trust them long term. You need very high contact pressures to prevent oxidation at the junction. Thermal expansion and vibration will tend to loosen the contacts over time unless there is a very good spring element.
 
I have very little knowledge about building packs.
I have a question, if you need a 1.4mm copper bus bar, can you spot weld 2- 0.7mm bus bars together? basically 2ply
would it not just be a matter of calculating how many spot welds needed to carry 500 amps?
 
Back
Top