Compress or not, flexible busbar or not

[Cheap 4-life]

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

View attachment 111212View attachment 111213

It appears that your cells have spacers to keep them separated so that any expansion would not put pressure on the terminals or loosen your nuts. so your cells are not compressed to each other enough for the swelling to matter. That’s kinda what Offgridgarage is doing but he has no compression. Just mats between the cells.

Seems you are using hard spacers in the corners where the cell doesn’t swell. Compress at these spacers and use soft mats in the middle between the cells. This would stop movement at the busbars when the cells swell. What did you use in the space between the cells.
But are these cells actually compressed in your configuration? Doesn’t seem so with the large gap between each cell.
Edit: the insulators between the cells are also hard so there is compression throughout the entire side of the cell.

 

[brb58]

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.

I wouldn't be doing multiple wires if I didn't have to. I actually do on the ends. Even with my 8MM posts, there really isn't much room left.

I made sure to order my cells with 8mm posts.

 

[Cheap 4-life]

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.

Looks good.
How are you achieving that amount of compression and keeping it constant? I’ve read to much compression is actually worse than no compression. Having the balance wires rings on some nuts and not on others is making the connections from cell to cell different causing different resistance and different cell voltage readings with more one wire ring on some nuts, I guess that’s why I see a lot of the solid busbars tapped (you can’t with braided flexible) so the cells nuts can all be torqued the same without having wire rings on them, so every cell is supplying the same amount of power with same resistance and same bms voltage reading for each cell.. not trying to pick apart your setup, just trying to decide out loud what’s best for me

 

[brb58]

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.

what you using for insulators between the cells?

 

[brb58]

It appears that your cells have spacers to keep them separated so that any expansion would not put pressure on the terminals or loosen your nuts. so technically your cells are not compressed to each other enough for the swelling to matter. That’s kinda what Offgridgarage is doing but he has no compression. Just mats between the cells.

That might be the winner.. using hard spacers in the corners where the cell doesn’t swell. Compress at these spacers and use mats between the cells. This would stop movement at the busbars when the cells swell

My spacers are 3D printed. Probably don't compress very much.

 

[Cheap 4-life]

My spacers are 3D printed. Probably don't compress very much.

Is there any spacers/insulators between your cells other than the blue 3d printed spacers that go across the top and bottom?

 

[brb58]

Is there any spacers/insulators between your cells other than the blue 3d printed spacers that go across the top and bottom?

Yes...they are black in color. Hard to see.

 

[Cheap 4-life]

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.

In response to #1; there is advantages known like reduced swelling in high amp demand situations. Disadvantage is loosening busbars/nuts/screws have been noticed when using solid busbars due to swelling/expansion contraction that is uncontrollable which is why welding the busbars to the cells is preferred and often done when compression is used.
#2 yes the manufacturers recommend it but I’d assume that recommendation really only matters for high amperage draw situations when there’s severe swelling possible. It’s been logically proven by Will and Offgridgarage that compression doesn’t matter for cycle life for solar storage.
#3 yes proper compression won’t hurt the cells at all if using flexible busbars are used. With compression and solid busbars the nuts/screws can constantly loosen and need retighten due to uncontrollable expansion and contraction. I’m not make that up. Several users have reported this.he flexible busbars you are using add a lot more resistance to the battery bank. How many amps are they rated for? Also then the bms balance wires would have to be attached to the cell terminals because you can’t tap those type of flexible busbars for the balance wires

 

[rhino]

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.

Not sure you are referring to these laminated busbars but these are extremely flexible: https://www.aliexpress.com/item/3256803043965156.html

 

[Cheap 4-life]

Yes...they are black in color. Hard to see.

View attachment 111221

Are those black spacers hard plastic?

 

[brb58]

Are those black spacers hard plastic?

yes

3d printed PLA with 20% infill so very firm.

 

[Cheap 4-life]

Not sure you are referring to these laminated busbars but these are extremely flexible: https://www.aliexpress.com/item/3256803043965156.html

They dont look very flexible. Looks like just a bend in a solid busbar. So they are flexible? Ok that’s another option. Thanks for confirming that.

 

[Cheap 4-life]

yes

3d printed PLA with 20% infill so very firm.

So then your busbars/nuts would loosen (if it is possible) with your compression and no space between the 3d printed parts. How long has this setup been supplying power to loads? How many amps has been going into/out of them?

 

[cinergi]

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.

Those flexible busbars are empirically infinitely better than my solid busbars in my build. I used to have problems with varying cell resistance requiring loosening and re-tightening my solid busbars (some of which became nearly impossible to remove due to expansion). Ever since installing those flexible ones, I've had zero problems. Details are in the latest posts of my build thread (in my sig).

The ones that @rhino mentioned above are the ones I'm using. Quite flexible.

 

[Cheap 4-life]

Those flexible busbars are empirically infinitely better than my solid busbars in my build. I used to have problems with varying cell resistance requiring loosening and re-tightening my solid busbars (some of which became nearly impossible to remove due to expansion). Ever since installing those flexible ones, I've had zero problems. Details are in the latest posts of my build thread (in my sig).

We’re your cells compressed?

 

[cinergi]

We’re your cells compressed?

They're in a spring-based compression setup.

 

[Cheap 4-life]

They're in a spring-based compression setup.

Reading thru your build now. You still using chargery bms?

 

[cinergi]

Reading thru your build now. You still using chargery bms?

No, I dropped Chargery due to so many problems. I'm using Orion now. Happy to answer off-topic questions in that thread.

 

[Nobodybusiness]

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.

All I can tell you is mine are setup like Andy’s and I have never had one swell yet. Some are 18 months old. YMMV..

 

[Skypower]

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

Worried about cable stiffness? Think diagonally. The the short red ones are 2/0. You don’t want them straight, but with a bow. When you crimp the second lug on put the bow into cable to lock in the shape and make it more flexible in that range. Remember to keep the lugs rotated on the same plane, they won’t twist easily after crimping. You want to use fine strand cable like Windy Nation welding cable or the most flexible but more expensive Ancore brand cable. I’ve found found that Ancore or Selterm are the best lugs for the job and crimp down the tight with my dies( nice crisp hex corners). Just before crimping I do a very light polish on the inside of the lug to remove oxides of the tin surface or copper. Use 320 or finer Emory on a wood dowel, steel wool or Scotch bright. The idea is just to knock down only the high spots, remove oxides but not scratch it or remove the thin tin plate. A #2 is plenty for most needs but nothing beats the low resistance of a solid, tin plated copper buss bar(supplied).