safety and fully enclosed/embedded packs?

WalkerYYJ

1 mW
Joined
Jun 1, 2020
Messages
18
Location
Left Coast, Canada
Hey all,

Working on a project that will have 12x 25Ah LiFePO4 prismatic cells https://www.electriccarpartscompany.com/Fortune-25Ah-Aluminum-Encased-Battery (12S) built underneath the frame of a cargo bike's cargo bed
The concept I’m rolling with at the moment is to use 2”x1” Tslot https://www.mcmaster.com/47065T107 to outline the battery bay which will exist as a void space bellow the floor of the cargo bed. I’m going to use aluminum plate (1/8”?) for the cargo bed floor, (access hatches cut out), and another plate to accommodate the floor of the void space (if that makes sense.) T slot grooves, and the edges of the 2 plates will be sealed with RTV silicone/similar.
The end result will be a fully sealed aluminum box containing ~1000 Whrs of batteries. I’m assuming I should add some provisions for pressure relief in the (hopefully) unlikely even that a LiFePO4 cell were to have a runaway. How have others approached this? I’m thinking of adding 1-2? Rupture disks to the bottom plate ?? https://www.mcmaster.com/rupture/ but not sure if there’s some other best practices on this… Also not sure how quickly one could expect a pressure build up to occur….

Would love any suggestions or guidance.
 
I am not sold on these cells not requiring compression plates.

capkart04.jpg

So I would make that part of the heavy-plate part of the design.

The other sides of the enclosure can be lighter gauge.

Sealing right up airtight is IMO pointless, unless you're thinking the whole rig is going to end up submerged?
 
WalkerYYJ said:
Hey all,

Working on a project that will have 12x 25Ah LiFePO4 prismatic cells https://www.electriccarpartscompany.com/Fortune-25Ah-Aluminum-Encased-Battery (12S) built underneath the frame of a cargo bike's cargo bed
The concept I’m rolling with at the moment is to use 2”x1” Tslot https://www.mcmaster.com/47065T107 to outline the battery bay which will exist as a void space bellow the floor of the cargo bed. I’m going to use aluminum plate (1/8”?) for the cargo bed floor, (access hatches cut out), and another plate to accommodate the floor of the void space (if that makes sense.) T slot grooves, and the edges of the 2 plates will be sealed with RTV silicone/similar.
The end result will be a fully sealed aluminum box containing ~1000 Whrs of batteries. I’m assuming I should add some provisions for pressure relief in the (hopefully) unlikely even that a LiFePO4 cell were to have a runaway. How have others approached this? I’m thinking of adding 1-2? Rupture disks to the bottom plate ?? https://www.mcmaster.com/rupture/ but not sure if there’s some other best practices on this… Also not sure how quickly one could expect a pressure build up to occur….

Would love any suggestions or guidance.

I have just welded a box out of aluminum sheet to stuff all in.
o8hmhvo.jpg


Zw6ErEo.jpg
 
WalkerYYJ said:
Working on a project that will have 12x 25Ah LiFePO4 prismatic cells https://www.electriccarpartscompany.com/Fortune-25Ah-Aluminum-Encased-Battery
Don't forget to setup compression plates on them, so they cannot expand during charge and discharge. If you don't, they'll expand internally, the layers will come apart, and the cells will increase (dramatically in some cases) in inernal resistance and decrease in current-delivery ability and increase in voltage sag under load.

The end result will be a fully sealed aluminum box containing ~1000 Whrs of batteries.
I don't think you'd need to worry about a pressure relief vent, per se, but if you use one I'd use a Goretex valve, at the lowest corner(s) of the box, screwed in, so that you can remove it and drain accumulated moisture from the box that gets in thru the wiring over time, and thru the gaps in the access hatch seals (there will be gaps, if not now, as it ages).

If you are in a very dry environment like I am here in Phoenix, you likely don't have to worry about moisture, unless the wiring gets submerged whenever it does rain.


If you can, please post the build itself, as I (and I'm sure others) would like to see what you're building (step by step if possible. :)
 
Batteries you link to have a Aluminum Shell.
https://www.electriccarpartscompany.com/Fortune-25Ah-Aluminum-Encased-Battery
25Ah EV Lithium LiFePO4 LFP Aluminum Shell Battery Pack
thumbnail.asp

Don't think a sealed box is necessary. I would drill some holes in the bottom of the box so that if water gets in. It can get out.

Don't think compression plates are necessary because batteries already have a aluminum shell. For a better answer to this question. Ask Electric Car Parts Company people.

Do take all electrical precautions, fuses, BMS, etc. so that hopefully fire don't happen. Make sure nothing can rattle around.
 
I would still use compression strapped plates for aluminum enclosed cells.

Vendors will tell you what you want to hear to make the sale
 
marty said:
Don't think compression plates are necessary because batteries already have a aluminum shell. For a better answer to this question. Ask Electric Car Parts Company people.
AFAICS they don't have a thick enough shell to stop from swelling, without compression.
 
Back
Top