Tips needed for building a wooden box for prismatic cells

[s0larcuriosity]

I want to make a wooden box to house 8 * 100AH LiFePo4 cells. Each cell weighs ~2.2KG and their dimensions are 220mm(W) x 118mm(H) x 41mm(D).

I would like some suggestions on the following from people who've already done this.

- Which type of wood is best for this and how thick should it be? Is plywood good?
- Each cell has a depth of about 40mm. So along with 1mm epoxy sheets in between the total space occupied would be ~327mm. To achieve a good amount of compression force how many millimeters shorter should be box be?
- Can the box be tightly sealed or should it have holes for ventilation?

This box will be inside my house and the ambient temperature round the year is between 20-40 degree Celsius.

 

[OffGridForGood]

- Which type of wood is best for this and how thick should it be? Is plywood good?

I use plywood.
if your box will rest on a full supporting surface the bottom doesn't need to be very thick (to support the cells) and could be 10-12 mm
if your box will be suspended in a rack style support then the bottom should be thicker 15mm material is sturdy.

- Each cell has a depth of about 40mm. So along with 1mm epoxy sheets in between the total space occupied would be ~327mm. To achieve a good amount of compression force how many millimeters shorter should be box be?

zero "shorter" the cells will normally expand with charging, I allow a few extra mm to ease installation of the cells. Compression is not really important for a stationary battery storage system.

- Can the box be tightly sealed or should it have holes for ventilation?

I don't add any ventilation holes - no place for insects to get into the box.

This box will be inside my house and the ambient temperature round the year is between 20-40 degree Celsius.

I suggest you check on the recommended cell temperatures from the manufacturer - the ones I have indicate they will degrade in 40C temps. I believe you will want to keep them below 30C for best long term operation. Check with your manufacturer to confirm.

Last note: I build the battery boxes with a 'double front' - an inner one to support the cells, and about 80mm space to the exterior front - this space allows room for the BMS, fuse, breaker, through-wall battery terminals, general wiring. Also, if you build your 8s set in two rows of 4-cells, putting a fuse between cell #4 and cell #5 may be a good way to protect your pack from over-current event. I use a simple ANL fuse in the battery case for this in place of one bus-bar, if over-current ever takes place, the fuse will cut off the circuit and reduce voltage by half in each row of cells.