diy,
Your assumption about my perceived assumptions is not correct. I do not assume anything more then that profesionals have put a lot of thought and experiments in problems with lithium batteries.
I did not state that they were putting fires out with water, only that they used water on smoking and burning vehicles and that only to fend of someones opinion that water and lithium batteries would end up in a catastrophe.
I realize that often people do not want to take the time to get the whole gist of the thread and just jump in.
To avoid further complications i will repost my first post in the hope that further confusion can clear.
Post#1
Please comment on this proposed build.
-A-After reading thru some of the fire / burn threads I changed my design to
incorporate space between the battery that can be flooded with water in case of an emergency.
-B-The frame is welded from bed frame angle iron. 3/8" wood in the bottom and 1/16" pvc sheets on the side to prevent the cells to contact the steel frame..strips of 1/16" rubber roofing glued with pieces of double side tape to separate the cells from each other.
-C-To avoid mechanical stress on the terminal I propose two layers of braided tinned copper in diagonal. Thought is here larger distance/ surface allowed for better thermal separation between cells and at the same time allows more flexibility.
-D-Used stainless studs without starter threads as to give maximum resistance against pulling out the aluminum thread.
To avoid or better limit current thru the stud I want to use an insulating washer between the top of the braided wire and the compression nut. This I hope will limit potential heat generation in the stud.
-E-My other thought is that the flat braided strip will make multiple contacts with the aluminum battery terminal.
The stud that is supposed to carry no current will have the bms wiring on top thru the red ring terminal.
--The idea with the rubber roofing strip is to allow space between the cells to insert temp sensors and in an emergency the ability to cool the cells with pouring water over them.. emergency only!
The steel frame is a tight fit, the last cell will have to be pushed in. There is no space for the cells to expand.
Please give me your thoughts about the proposed approach.
The next one I would like to build in an aluminum or even stainless box that can better contain a thermal runaway event and also that I can flood the box with water to reduce the chance of more cells getting affected.
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- Lets first try to discuss A
- Murphy is always there so design for the worst imaginable situation.
- something bad happened, a vehicle roll over, some one shoots a bullet, a cell is internally damaged and starts to heat up. people are trapped in the vehicle.
- The adjacent cell is not damaged but gets heated by the now smoldering damaged cell. A potential the whole pack heats up, o much heat is generated and sets the vehicle on fire.
- ASSUMPTION......By continually dousing the battery with water the heat from one cell is absorbed in the water and so the adjacent cells stay cool, or cooler. And so a potential vehicle fire is diverted. The cells have the rubber strips glued on so that can not make direct contact between the casing and can allow water to flow between the cell as to have more surface contact to absorb the heat. the rubber strip are 1" wide and the spacing is about 3/4". So a channel is created 3/4 wide and 1/16" deep where water can flow thru....AGAIN, this is only an emergency, Not just cooling hot batteries.
- QUESTION.....Does anyone know the thickness of the aluminum casing of these batteries so that i can calculated if 17 psi will bulge the casing in the 3/4" between the rubber strips.
- Please do not discuss the other bullet points, only this point A.. The assumption and the question
- Thank you Johan