I just did what the instructions from Eve said to do. Reduce the SOC to about 20%. Then clamp the cells together using no force but just be firm and allow no movement. Now charge them up and they will provide their own clamping pressure.
Straight from the seller. I believe this document is in the archives.
Do you really think Chinese supplier will create a defective product and expect you to purchase from them again? No benefit in producing inferior product with internet reviews and demonstrated quality being constantly reviewed. We all know not to buy Littokala now, right? Even someone buying from liito will not do it twice. The only way to get repeat buyers and new buyers is to produce a solid product. If you have an inferior product, you will only sell to bargain-hunting nubes.
Again that's not from a manufacturer, and suggests that fibra-taping the pack together is an adequate way to apply compression to the cells....
This makes sense, and the other consideration is that we're only getting scraps left over from industry-- the real customer base is automotive and industrial OEMs that purchase huge quantities of the cells and have large engineering and R and D departments that are no doubt testing these cells independently. If chinese manufacturers were deliberately including some type of planned obsolescense or faulty product, presumably they would quickly find themselves out of business. It would be a no-win scenario for the battery maker.
As far as I can recall that document was supplied to Amy Wan by another forum member as a favor to her. It's a basic guide and compression is tricky unless using springs. It's good to keep in mind too much compression is worse than no compression.
That may be true of some Chinese companies. But I am quite certain battery manufacturers like EVE, CATL, Lishen and the other big ones including Samsung and LG stick by whatever they document in their spec sheets. There have been people post on this forum who have good functioning cells after 10 plus years in service.
As far as I can recall that document was supplied to Amy Wan by another forum member as a favor to her. It's a basic guide and compression is tricky unless using springs. It's good to keep in mind too much compression is worse than no compression.
EVE has made recommendations for compression and there is an abundant of information on this forum regarding that. I don't know of any other manufacturer that has made compression recommendations with regards to aluminum cased cells.
I came to many of the same conclusions as you with regard to the strength of the corners but ended up at a different solution.
An interesting interpretation. I wonder what would cause a 300kgf load (and subsequent motion) on a cell under test in a laboratory environment?
I would see that coming from the normal expansion of the cell as it nears full charge. The specs say that they should increase in thickness by about .5mm.
Mine are in a spring compression fixture and that's about the amount of expansion I see. Actually slightly less, but in that ballpark.
Yes, they can increase by 0.5mm (0.4mm for my 230 Ah cells), but that is specified under 300+/-20 kgf. If you don't constrain the side walls, you aren't providing that force. Holding by only the corners is not meeting the specification.
If you are holding the cells in place with springs, then they will move outward due to swelling. If you are using a typical flat buss bar, that movement will create a tention force between each coupled pair of terminals and they are the weakest link. That does not sound too healthy to me.
I agree for the most part. Many of the "spring" Afficianatos actually calculate the spring force to match or exceed cell expansion criteria to reduce that risk.
It doesn't really matter what "spring force" it is rated for because that would be in units of kg/mm which will always by design, allow for movement. That is what springs do. That movement will create tension in the buss bar which will then stress the terminals. I cannot see that as a good thing.
I know there was a photo posted somewhere of the hydraulic fixture they use for testing. It does apply the same force no matter the SOC. and this came from another source.
