Xuba Electronics: DEAL - 280AH LiFePo4 cells. Purchase & Review

Ampster

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Normally, the manufacturer will list the suggested torsion on their specification. If not, just ask them.
Yes, this has been thoroughly discussed as anti torsion in the past 100 or so posts of this very long thread. For the LF280 cells which are the subject of this thread the anti torsion of the terminal is LESS than 8Nm. Most people have concluded that 4 to 5 Nm is sufficient for the torque of the terminal bolts.
 

PeterBC

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I would disagree. The clearance between the roll (or accordion stack) and the case is negligible. If you try to compress the center of a cell, it doesn't move appreciably, even with 20lbs of force. This tells me that the electrode/separator roll is tightly packed inside the casing. Also the fact that the spec lists 0.5mm of expansion during charging shows there is little or no free space inside. This makes sense of course, as movement between the two is likely to cause damage long term. The layers are as thin as possible to maximize energy and material density. The case itself is quite thin, and even the short sides would buckle if they were carrying significant load. Thus the majority of the clamping load is carried by the roll itself. Obviously the roll isn't crammed into the corners though. If memory serves, when they manufacture the cell, a tool expands the cell casing slightly, then the roll is inserted. A series of dies compress the casing and roll until its square ensuring a tight fit. Then the electrolyte is added, and the cell is capped.

The attached excerpt briefly discusses how pressure is needed in wound cell designs.

X ray photo of an jelly roll from a lithium cobalt cell.

View attachment 22187

Sorry to open up this bit after such a delay, but I've reread these 'compression' threads from the beginning and are deeply interested in the best way to setup my 2 packs of 24 cells.

I find the picture above very instructive. If a cell tries to expand when charged and is resisted by the case and any clamping pressure, what happens ? I can imagine that if the pressure is too high that the growth will force the 'roll' into the corners of the rectangular case. This would put significant strains on the layers etc in these corners. At an extreme it would create very tight bends, approaching right angles. That cant be good for the longevity of the cell. Are the cells filled to make curve geometry in the corners to support the jelly roll ?
Ignoring the corners, as the roll tries to expand with charging the centre of the cell , if unclamped, will have significantly less resistance to expansion than the edges. It will bulge (a bit). Yet the edges wont as much as the case will more vigorously resist the expansion there. Again over time that cant be good for the consistency of the cell. The centres will repeatedly flex and contract considerably more than edges. I would imagine the pressures on the edges would cause material to migrate to the less pressured centre areas over time.

Is this the mechanism that the suppliers have discovered contributes to earlier failure than if the cells are compressed to limit the about of growth and contraction (but not too tightly so as to cause issues elsewhere) ?

The initial concave shape of cells is also interesting, and as I noted elsewhere makes simple clamping only effective at the edges initially till the concave bits become flat and touch the neighbouring cell. Or is one expected to put some non flat compressible (at what pressures ?) fillers between 2 concave cells so that the expansion is resisted in the middle immediately not after a 0.25mm unresisted move before contacting the neighbour cell ?

So many questions .. Given we are talking a possible 30% increase in lifespan this is fairly significant.

I suspect this is why much effort goes to making cylindrical cells which dont have many of these concerns, and naturally contain a reasonable symmetrical compression on expansion attempts and minimise flexing.
 

HRTKD

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Hello
can I also install the EVE 280AH LIFEPO4 cells horizontally without problems?

thanks


What we heard is that EVE said it's OK to orient them on the long side, not the short side. You'll end up with a vertical column, not a horizontal column if you use the long side down.

This topic is not covered in EVE's specification document.
 

fatfash

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Wonder where they get those holders from....makes a neat job of stringing 8 cells together.

4.5nm it is then... well spotted.
do you mean this?

 

Solarfun4jim

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do you mean this?

Thanks for the link, but i now wonder where the compression of the cells comes from with this set up?
 

Just John

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Thanks for the link, but i now wonder where the compression of the cells comes from with this set up?
My personal theory is that these large cells are primarily aimed at bus use. Thus the objective of the fixture mentioned in the data sheet is to prevent terminal movement and the accompanying loss of connection and power. I also suspect the torsion measurement of the terminals means how much the terminals are rated to withstand before damaging the cell internally. I certainly could be wrong, but so far it seems like a fixture won't prevent a cell from bloating, and the torsion measurement certainly isn't the correct torque spec for terminal connection.
 

Solarfun4jim

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My personal theory is that these large cells are primarily aimed at bus use. Thus the objective of the fixture mentioned in the data sheet is to prevent terminal movement and the accompanying loss of connection and power. I also suspect the torsion measurement of the terminals means how much the terminals are rated to withstand before damaging the cell internally. I certainly could be wrong, but so far it seems like a fixture won't prevent a cell from bloating, and the torsion measurement certainly isn't the correct torque spec for terminal connection.
Yeah, all my terminal connections are only torqued to 4nm. Using flexible busbars, should keep all the stresses/vibrations off the terminal posts.
 

AussieInSeattle

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I've now started assembling an EVE 280ah 8s battery inside one of my custom battery boxes from Amy.


I chose custom larger dimensions because of my enormous 200A BMS, and because I wanted to mount a bluesea fuse on the positive terminal.


I still need to crimp connectors to the Anderson cables and wire the case voltmeter to the terminals. Probably a separate common battery positive and negative busbar would be the cleanest.
View attachment 29607

I also haven't bound the cells or BMS yet. The MDF boards are 10mm each and were originally used to compress the cells between hose clamps outside the metal box. As it turns out 10mm MDF is too flexible for the task.

Happy Australia Day (here) :). I have to buy a couple of extra cells from XUBA and was going to get them to build a custom box for me - I was going to spec it 1/4" or so larger on the interior (my BMS will be external). Anything you would have done different when speccing the box that I could learn from? All I really need is the box and none of the other stuff they show on their site for anderson connector etc.
 

AussieSim

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Happy Australia Day (here) :). I have to buy a couple of extra cells from XUBA and was going to get them to build a custom box for me - I was going to spec it 1/4" or so larger on the interior (my BMS will be external). Anything you would have done different when speccing the box that I could learn from? All I really need is the box and none of the other stuff they show on their site for anderson connector etc.

Regarding extra space, you can either use the walls of the box for compression (Not advisable for Lishen cells), or have space for external compression (straps, plates, planks), space for the BMS and overhead room for the cabling and a battery fuse.
 
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