Again, knowing what the expansion force at HOL (half of life) sure would be helpful, but my general sense is that it’s going to be practically impossible to design a rigid fixture that remains rigid under 5000kgf(!).
I doubt any EV battery out there will not deform under 5000 kg of force. So first, batteries are unlikely to be used for anywhere close to the service life needed to generate 5000kgf of expansion force, and second, even if they did, the metal box is unlikely not to deform a bit and hence apply less than 5000kgf.
I think you underestimate how rigid metals are. Say I wrap my battery in a 10mm steel box, similar to what EVE seem to be doing when welding. Having 250mm height and 130mm width I get 2 x 250 mm x 10 mm + 2 x130mm x 10 mm = 5000mm² + 2600mm² = 7600 mm² cross-section area.
Or, let's use aluminium instead of steel, since it's not even half as rigid at 69 GPa.
If we apply 50kN over 7600mm², that gives 6.579 MPa. That creates a stress of 6.679 MPa / 69 GPa = 0.0000967. Over the length of 8 of my 36.35mm cells, a total of 290.8 mm, that gives 0.0000967 * 290.8 mm = 0.02mm of elongation if I'm not messing up my calculations. Or, 0.0035mm per cell.
Using 6 M16 rods of 200GPa steel we get 6 * 125mm²= 750mm². Applying 50 kN we get 66.67 MPa. Stress = 66.67MPa / 200 GPa = .00033. Over 290.8 mm we get 0.097mm elongation. Or 0.012 mm per cell. We can continue calculating how much this would decrease the pressure, but I don't think it would be that much..
So I take this new datasheet to mean that enclosing these cells in a rigid metal box such as that used for an EV battery will be fine.
If I had seen this datasheet before building my 300kgf clamping fixture, I would not have bothered.
For the LF280K it doesn't seem to be necessary, no. I'm not sure whether you have LF280K or LF280 though.
On the other hand, if you are not using a ready-made box for the purpose and are already going the route of rigid end plates secured by threaded rod, the additional cost and effort to add calibrated springs to apply 300kgf is modest.
Yeah, It's partly an exercise in welding too. Might be useful to learn.
If I’d seen this data and wanted to go to the trouble of building a clamping fixture, I would have had no concerns using a shorter calibrated spring (though the only advantage would have been slightly shorter overall dimension, since spring cost would have been about the same…).
Indeed. In my case I have the width of a 19" rack to work with, and I can't fit 16 cells from side to side, so it becomes 2 rows of 8 and thus have plenty of room for springs and bolts. I considered using LF280K and placing them from front to back instead, but 16 cells in a rack would become impossible to handle.
[regarding monitoring cell expansion]
Been there, thought about doing that, decided it wasn’t worth the trouble and wouldn’t even consider it after one year of experience with my battery now.
I might get sidetracked with other projects before adding this, but it seems like fairly easy data points to add to indicate a possibly severe issue with the battery. The cost of adding it is nothing compared to the cost of the possible consequences of an issue.
Setting SCC and parameters set up to correctly charge and discharge cells within target voltage ange is a much bigger concern to me than anything to do with expansion or clamping force at this stage.
In my case I'm trying to add this to a lead UPS where much of the battery handling is a black box I have to work around.
The BNS is there as a fall-back safety device but when the BMS cut-off kicks in, it causes a fault to the overall system requiring a manual reset.
In my case I don't trust the BMS fully, especially since it can't communicate with the UPS.
‘Leakage’ does not occur until over 100,000 kgf (before which I suspect the battery box would burst).
100 000 N, or 10 000 kgf. Looking at a data table this is within what two M12 (½") rods can hold before starting to deform permanently.