LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[exMaggieDrum]

Originally Posted by T1 Terry

That is what I was trying to say, yes. As far as the 20mm bulge, is that per cell? 5mm rod is the biggest that will fit between the cells side by side with the narrow edges meeting, in the early days we constructed a pack this way and the pressure stripped the thread out of the stainless nut and distorted the thread on the rod so much a nut could no longer be wound past the damaged area. 4 cells will bend 50mm x 3mm steel strap, so we now use 3mm aluminium plates and stainless band strapping folded over each end cap and screwed through the end plate, 3 up each side. This will hold a pack in normal use but will not stop them from bulging if overcharged or completely drain and heat causes gassing to occurs. Once the cells have bulged a 10 tonne press would not flatten them until the vent cap was released..... that much pressure. I have seen them fitted in a confined space where the owner determined strapping was not required as there wasn't enough room for it and the confined space would act as the case for holding them together. In this case the owner was quite correct, they fitted into the space quite nicely and each swelled to the room available. The down side was he could not remove a cell from the group when he attempted to remove them to swap them to his new RV, they are there for life.

T1 Terry

Thanks for your informative posts!

Do you have a photo of your pack construction with the 3mm aluminum plate. It would be helpful.

I was considering using stainless strap to confine the cells but was concerned there would be too much pressure at the corners. I have also seen pictures of some type of plastic banding used. I was thinking of putting end plates that extended past the ends. The obvious problem with any plans I have seen is that the end cells would be much more constrained but the middle units would be able to push out, like Martin's stress analysis shows (nice!). Some kind of significant construction seems necessary to prevent this deformation at the middles. (If needed)

FYI - I have been quoted US $1.45/Ah by a supplier of cells in BC Canada, plus shipping. That includes end plates and lifting straps for each set of 4 cells.