LF628 batteries just arrived, compress or nah?

[jedics]

I was just going to wire them up with a space between each to allow for expansion and not stress the terminals and call it a day but then I got on the internet.

Does the expansion and contraction of charge/discharge delaminate the layers and reduce cycle life or are the alloy boxes they are made with enough?

searched here for battery compression and found nothing surprisingly!

[Dacian Todea (electrodacus)]

Yes the expansion and contraction will significantly reduce the cycle life thus the need for compression to improve cycle life.

Check the spec of your cells and they will provide you with a range of compression force for optimal cycle life.

The cells will still expand and contract even with compression but much less and thus the significant cycle life difference.

Here is the spec for your particular cells https://paircycle-batteriespeicher.de/wp-content/uploads/EVE_MB56_628Ah_Datasheet.pdf

So they recommend a 2mm EVA foam between cells or silicone foam those will act like a spring.

Then while cells are relatively discharged 15 to 40% SOC you apply 3kN to 7kN of compression force.  This force will of course increase while cell is fully charged 100% SOC

With age this force will increase and mention 45kN at 70% SOH so by the end of life.

Max pressure on poles (Table 11) is 0.5kN (500N) so you need to use flexible bus bars else cells will be damaged.

[Dan Karau]

There is no need to over think this, I used ready rod with nylock bolts and 3/4" plywood and just ensured that everything was tight but nothing crazy.   Pack has been in use (fulltime RVing) for 4 years now and still balance to within 6-7mv.  Also need to consider that this pack has driven 1000s of miles across Canada/US in that time.  If you watch any of Andy's videos as he puts together his packs you will see just how little pressure is needed (0.5kN) is across all your bolts not for each bolt!   https://www.youtube.com/@OffGridGarageAustralia

There is no better resource than Andy when it comes to these batteries.

[jedics]

Thanks for simplifying the process, seems straight forward enough now. I will probably put it all together with the 2mm foam separators and hand tighten the nuts, then use a spanner until the foam begins to slightly deform to get about the right compression?

[jedics]

But he is the main person I found who says you dont need to compress the cell at all.

[jedics]

I have these already, anyone see a problem with me just curving the fine stranded wires like the connector at the back of this photo to become the "play" to take up the expansion?

[Dacian Todea (electrodacus)]

There is no problem to bend those as the one in the back.

[jedics]

thanks, your a credit to your species answering all our questions so quickly after 7 years :)

[jedics]

I will probably use 6mm aluminium plate to compress, I feel like I need to put the 8M rods on the top and bottom (Green) to reduce flexing in the centre rather than on the sides (Blue) or is the amount of pressure so low that it doesnt matter which I choose?

I cant put the two rods on top between the terminals as it will get in the way of my thick cable connectors.

[Dacian Todea (electrodacus)]

You can use my setup as inspiration

Your cells are twice as wide and I think 6mm plate will not be thick enough.

Here is my other battery made with A123 20Ah LFP pouch cells this is 9 years old and still works great. These use 10mm thick plates.

If you will be using PVA foam between cells then you do not need the springs.

Either use thicker plates or add L or C channels and just those 4 blue rods. Also leave space so you can isolate the rods in my case I used clear tubing so there is no chance of cell casing getting electrically connected.

[jedics]

Thanks for the pics, yes will use 10mm plates