Compress or not, flexible busbar or not

[Cheap 4-life]

I have a couple hundred pounds of 280ah CATL cells on the way.. I’ve read a lot on here about this.. Seen Wills videos and his sideways cell configuration with solid busbars. Seen Offgridgarages videos and his are not sideways but he leaves space between each cell for expansion and uses solid busbars.. both options seem like good ideas.. Also realize that a lot of premade batteries have the busbars welded to the cells and just straps around the cells with spacers.. Wills way imo isn’t clean looking due to the cells not being put together wide side to wide side so I would prefer Offgridgarages method but is the amount of space between his cells enough for expansion to not cause the busbar nuts to loosen over time? I am getting CATL cells (all that’s available atm) and from what I have read they are more prone to expansion than EVE cells so that makes me wonder if compression is more important than it is with EVEs.. Will the CATLs need more room to expand than what Offgridgarage has between his EVE cells.. If the CATL cells do expand more then should I want to stop that expansion, should I worry about that expansion more than if I was getting EVE cells and therefore compress the CATLs. And since they might expand more, instead use flexible busbars of some sort due to the extra expansion.. wish there was a definitive list some where that tells us exactly what to do with each type of cell for solar storage.. I understand compression isn’t needed due to the whole calendar life will come before any kind of degradation to worry about due to cycles. But does that theory change due to damage to the cells from expansion and more so with CATLs that could expand more so than EVEs due to CATLs thinner wall construction.. Open to any advice, opinions or thoughts..

 

[chrisski]

.. I understand compression isn’t needed due to the whole calendar life will come before any kind of degradation to worry about due to cycles.

I wonder how many people feel this way after finding their cells bloated from a slight overcharge. I compress my cells with plywood and quarter inch threaded rod barely more than hand tightened with the cells fully charged with locktite on the nuts, spaced by flexible cutting board, for a RV build.

Open to any advice, opinions or thoughts..

Honestly the safest way is the one that makes you most comfortable based off what you've seen based off what you and seen. Which Youtuber you have the most confidence in. You're right, there is no definitive guide put out by a manufacturer.

 

[Cheap 4-life]

I wonder how many people feel this way after finding their cells bloated from a slight overcharge.

Shouldn’t the bms prevent overcharge? I suppose bloating is different than swelling. Swelling would (i guess) go way? Or does swelling not go away once it occurs? Bloating is permanent damage to the cell due to overcharging? Would compressing prevent the bloating that occurs from overcharging and instead cause the pressure to come out the vent valve?

 

[Wet1]

EVE seems to recommend compression for max longevity, does CATL also? I ask because I've never really looked at their spec sheets or documentation.

 

[Cheap 4-life]

Yes I assume compression is recommended for all of these LIFEPO4 cells (unless cylindrical). But as Offgridgarage and Will explain in their videos and as I said above, calendar aging will be a problem well before degradation due to cycle life.. my main concern is if I don’t compress, will my cells possible become damaged due to not having compression. And have more so of a chance of cell damage due to CATLs being more prone to swelling.

 

[Wet1]

My take on the compression issue is, EVE recommends it and it's cheap and easy to do with a couple of scrap pieces of wood, four valve springs/pieces of threaded rod. So why not do it if the mfg recommends it for longevity? Given the investment, it seems like cheap insurance.

With that said, I know little about CATL batteries. I would see what they recommend. Either way, bloated cells would bother me. I see no point in charging above 3.5V/cell, so limiting voltage to that or less would help minimize the risk, but I'd still strongly consider some spring-loaded compression...

 

[Cheap 4-life]

Compression can (from what I’ve read) cause problems. Like loosening of the busbars nuts do to swelling that is uncontrollable. Possibly part of the reasons a lot of premade batteries have welded busbars, which makes the terminals safely absorb the small amount of movement from swelling. and possibly part of the reason why Will and Offgridgarage do not compress.. both of those YouTubers do different methods to make swelling not affect the busbars at all. Will puts the busbars/cells sideways so the busbars go across the narrow side of the cell that doesn’t swell so there’s no pressure on the terminal/busbars/nuts. Offgridgarage leaves space between his cells in the hops that any expansion will not push on the other cell..

 

[Wet1]

If that's your only concern, use wire or braided.

 

[Cheap 4-life]

Well no that’s not my only concern as I explained other concerns in the original post. Thanks to Rays youtube channel I know that If using wire then I would need 1/0 to have close to the same resistance as a tin plated copper busbar that comes with these cells. With 1/0 it is no longer flexible..The braided from what I am reading/seeing on YouTube) do not flex barely at all in the direction they need to flex and have a much greater resistance than the copper busbars..
Multiple 10 gauge wires crimped into lugs seem like the best flexible busbar option to actually be flexible but idk, just seems wrong using 4+ 10 gauge wires crimped into into lugs

 

[BradCagle]

Yes it's a good idea to compress them (not with much force) , they will swell overtime under normal usage.

 

[Skypower]

EVE seems to recommend compression for max longevity, does CATL also? I ask because I've never really looked at their spec sheets or documentation.

Mail from Eel battery 10/31/21;

thanks Karl
we really appreciate your support，
we have consulted CATL because of the slight bulging problem. Their answer is that the battery needs to be clamped at 300KG, so the life cycle will be better, which can reach more than 4000 times.
if you have any questions，please let us know.
we hope to do business with you again
Best Regards
Howard

 

[Wet1]

Well no that’s not my only concern as I explained other concerns in the original post. Thanks to Rays youtube channel I know that If using wire then I would need 1/0 to have close to the same resistance as a tin plated copper busbar that comes with these cells. With 1/0 it is no longer flexible..The braided from what I am reading/seeing on YouTube) do not flex barely at all in the direction they need to flex and have a much greater resistance than the copper busbars..
Multiple 10 gauge wires crimped into lugs seem like the best flexible busbar option to actually be flexible but idk, just seems wrong using 4+ 10 gauge wires crimped into into lugs

These wires are pretty flexible. They will do custom for you as well.

Extreme Battery Cable - Dual Insulated for Extra Protection

www.batterycablesusa.com

 

[Cheap 4-life]

Mail from Eel battery 10/31/22;

thanks Karl
we really appreciate your support，
we have consulted CATL because of the slight bulging problem. Their answer is that the battery needs to be clamped at 300KG, so the life cycle will be better, which can reach more than 4000 times.
if you have any questions，please let us know.
we hope to do business with you again
Best Regards
Howard

This video explains why the cycle gains from compressing don’t matter. My thinking is that if compression is done then it should be done to prevent damage to the cells from swelling, because calendar aging will destroy the cell before cycle life.. that’s if the cells swell enough to actually be damaged when not compressed. I’m not saying swelling damage from overcharging because I have a bms. I’m saying swelling damage due to normal swelling and that CATL cells possibly swelling more than EVEs.

 

[Cheap 4-life]

These wires are pretty flexible. They will do custom for you as well.

https://www.batterycablesusa.com/extreme-battery-cable[/URL

1/0AWG is simply not flexible. Any smaller gauge wire is adding resistance to the system. Also 1/0awg is very hard to bend to go from cell to cell and causes stress/pushing on the cells terminals. Those laminated busbars that are supposed to be flexible (with the bend in the middle) imo are not flexible enough to make a difference.

 

[brb58]

I clamped my cells so they won't expand. In my opinion, there is no downside to clamping and only upside so why not do it.

 

[Cheap 4-life]

I clamped my cells so they won't expand. In my opinion, there is no downside to clamping and only upside so why not do it.

My understanding is that there's expanding and contracting that is uncontrollable therefor causing constant loosening of the busbar nuts and stress on the terminals. However the more i think about it, it’s starting to make sense to compress them. A lot of premade packs come with welded busbars so the terminal stress shouldn’t matter, but there’s still the loosening of the busbars that are instead attached with nuts (not welded) from the uncontrollable swelling and contracting. If I could weld the busbars on then yeah no brainer, compress the cells because then the busbar nuts can’t loosen because the busbars are welded. But I can’t weld on the busbars and kinda wouldn’t want to weld the busbars to the cells so I could replace a cell if I had to..So then I’m back to flexible busbars but none of them are good enough. The flexible kind that come close to matching the resistance of the tin plated copper solid busbars are no longer flexible due to the thickness required. The laminated busbars with bend in the middle don’t seem flexible enough. The braided busbars are not flexible in the right direction..
I’d like to here from users tha5 have compressed their cells for years and have used the solid busbars.. and if there nuts needed constant tightening or not, if they loosened from uncontrollable expansion/swelling and contraction

 

[Wet1]

1/0AWG is simply not flexible. Any smaller gauge wire is adding resistance to the system. Also 1/0awg is very hard to bend to go from cell to cell and causes stress/pushing on the cells terminals.

Hence my comment that they will make custom for you. 1/0 is not very flexible, but 3 6ga. are.

 

[brb58]

My understanding is that there's expanding and contracting that is uncontrollable therefor causing constant loosening of the busbar nuts and stress on the terminals. However the more i think about it, it’s starting to make sense to compress them. A lot of premade packs come with welded busbars so the terminal stress shouldn’t matter, but there’s still the loosening of the busbars that are instead attached with nuts (not welded) from the uncontrollable swelling and contracting. If I could weld the busbars on then yeah no brainer, compress the cells because then the busbar nuts can’t loosen because the busbars are welded. But I can’t weld on the busbars and kinda wouldn’t want to weld the busbars to the cells so I could replace a cell if I had to..So then I’m back to flexible busbars but none of them are good enough. The flexible kind that come close to matching the resistance of the tin plated copper solid busbars are no longer flexible due to the thickness required. The laminated busbars with bend in the middle don’t seem flexible enough. The braided busbars are not flexible in the right direction..
I’d like to here from users tha5 have compressed their cells for years and have used the solid busbars.. and if there nuts needed constant tightening or not, if they loosened from uncontrollable expansion/swelling and contraction

I will likely be checking the nuts. I used lock nuts.

 

[Cheap 4-life]

Hence my comment that they will make custom for you. 1/0 is not very flexible, but 3 6ga. are.

Yeah I here ya,,..it’s an option, just not a fan of multiple wires in one lug.. would make DIY them myself if that’s what I was going to do.. I’d just really like to here from users that have had their cells compressed for years and if they have noticed their busbars/nuts/screws loosening.

 

[Skypower]

Yup, I’ve seen Andy’s video as well and I understand his thinking. But there’s other considerations. #1 time. Yes there’s calendar aging, but advantage/disadvantages of physical restraint/compression won’t be known for years yet. #2 if the manufacturers are recommending it and have data supporting it’s use, I’m not going pretend to know better. #3 from what I’ve seen so far, the 32 (302ah) compressed cells look fine and have excellent capacity.

I’m not running at 300kg (660lbs/12psi) but 550lbs/10psi). The cells are are close, no gaps between them and no appreciable bulge across the top. My cells had a 1/16” bulge and went away before reaching full force. I’m betting that most cells 280 and less will be flatter than the larger ones.