24 volt 280ah compressed..isolated studs...fire

wiseacre

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..and now for something completely different
If you can't prevent a fire - contain it and make maple syrup.

My small maple sugaring arch could handle the heat. Fully lined with full size firebrick with a triple wall stainless chimney that will handle at least the 3rd level of Hellfire.
arch.jpg

The 1/8th inch steel plate on top is used to heat the Maple Room (the sugar shed) in winter so we can use it as a sitting room.
During sugaring season there's an evaporator pan with an inch of roiling boiling sap in it.

It would make a hell of a fire safety battery box.
I wonder how many LiFePo4 cells would equal a cord of wood?
 

Short_Shot

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..and now for something completely different
If you can't prevent a fire - contain it and make maple syrup.

My small maple sugaring arch could handle the heat. Fully lined with full size firebrick with a triple wall stainless chimney that will handle at least the 3rd level of Hellfire.
View attachment 66740

The 1/8th inch steel plate on top is used to heat the Maple Room (the sugar shed) in winter so we can use it as a sitting room.
During sugaring season there's an evaporator pan with an inch of roiling boiling sap in it.

It would make a hell of a fire safety battery box.
I wonder how many LiFePo4 cells would equal a cord of wood?
You can replicate a similar setup with a pile of old drywall and some angle/sheet steel. Would need to be a fair bit thicker though.

That's how cheaper fireproof gun safes are made anyways. Lots of drywall.
 

Supervstech

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I have been brought into this thread from reports.

I am bothered by the way members are treating each other in this thread.

Why all the arguments focus on the technicalities, and argue that point?

Extinguishing a fire makes sense. Options existing to do so exist. Arguing semantics make no sense…

ANY battery chemistry with Lithium in it is a lithium ion…

The question shouldn’t be why are we discussing lithium ion options, it should be, is this option applicable to LFP…

Don’t make the point pivot on if LFP is Lithium Ion… of course LFP is Lithium Ion… the point needs to be what is best for LFP specifics…

In a Tesla fire, it’s not the car the fire department is concerned about, it is the surrounding area… it is very unlikely in a home battery fire situation, for the house to be in a mall parking lot, or at a school, or other places where an uncontrolled fire breaking out would pose risk to bystanders… so, 30K gallons is the FASTEST containment for that situation… in a house LFP fire… the wiring, and the home, and occupants are the immediate concern…


Best fire prevention for LFP? Fuses. Preventing shorts, and failures from causing combustion temperatures in the wiring… because in a home setup… it’ll be the wiring that starts the fire… protect it at every point.
SOMETHING WILL FAIL. Make sure that WHEN it fails, there is a fuse protecting the wiring from becoming a tinder starter… and make sure as little tinder as possible is available…

Focus people! This forum is about discussion and helping.., not browbeating semantics…

I had to delete a LOT of posts today. Quips are easy… intelligence allows us to discuss topics, or argue pointlessly… I have to delete pointlessness…
 

Surferdudemi

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Those of us that are compressing our cells are trying to avoid cell swelling lol
There's a nuance here. If you use an insulating layer that compresses at about the force you want to maintain, then as the battery tries to swell, the foam will give only once your target pressure is reached and then exert more pressure until it's flattened between adjacent cells. I think that's what you want, right? And the corners and edges which don't swell as much will not be affected. I.e., the foam would exert the force you want in the areas of the surface where you need it until it's fully compressed (at which point the force would increase a lot more). A hard, non-compressible plastic would not conform to the surface, and would transfer whatever force you're placing on the pack to the points on contact on the surface. That force could be more or less than what you intend, depending upon (a) what state of charge you clamp them at, and (b) whether the pressure is from a spring-loaded rig. If you use a spring-loaded rig, then can't the cells move and put stress on the terminals as some have expressed concern over?
 

Short_Shot

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There's a nuance here. If you use an insulating layer that compresses at about the force you want to maintain, then as the battery tries to swell, the foam will give only once your target pressure is reached and then exert more pressure until it's flattened between adjacent cells. I think that's what you want, right? And the corners and edges which don't swell as much will not be affected. I.e., the foam would exert the force you want in the areas of the surface where you need it until it's fully compressed (at which point the force would increase a lot more). A hard, non-compressible plastic would not conform to the surface, and would transfer whatever force you're placing on the pack to the points on contact on the surface. That force could be more or less than what you intend, depending upon (a) what state of charge you clamp them at, and (b) whether the pressure is from a spring-loaded rig. If you use a spring-loaded rig, then can't the cells move and put stress on the terminals as some have expressed concern over?
There is a whoole other thread discussing the various methods of compression and their merits. The best seems to be springs but I can't afford the space so I'm using poron foam.
 

RayfromTX

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Jul 17, 2021
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120
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.


  • View attachment 61581
  • View attachment 61584 View attachment 61585
  • 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
All that metal surrounding those cells gives me the heebie jeebies but not as much as the braided cable. Use a Mohm tester and use it to test the variation and also just the discreet resistance in those cables. Please report back your results. I think you will be surprised. I tested some cheap busbars and got .17 Mohms I tested a short 4awg cable with excellent crimped terminals and to .27 Mohms I'm going to guess you will be nearly an order of magnitude higher than that and your delta between cables may be as much as 50% different from one to another. You seem to be focusing on trying to get this right and avoid risk but I think you are looking at the wrong things. fhorst made demonstrable mistakes that are very easy to avoid. Try not to find the wrong takeaways. It isn't the chemistry that was the danger it was the chemist or in this case the technician. Reading the threads on this site about fires makes me rest easy because the mistakes made are pretty obvious and easily avoidable. I will say though that for sure, not everyone should be attempting this endeavor.

It's a good thing we aren't building cars from scratch because the lengths some would go to in avoiding the dangers of gasoline and component failures would create vehicles that would never leave the garage.
 
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S Davis

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Sep 25, 2021
Messages
48
So my question is what is the distortion to the cells from having alternate support between them going to do?

I have mine compressed at 640lbs which is about 11.8psi @ 50%soc and I can see the expansion and contraction in the springs.

I would bet the cells will bulge in those spots stressing the cells even more than them being able to expand and contract as one, all those little bend points between the strips. Maybe the space will keep the pack from being over compressed at 100%soc?

I might be way off base but I wouldn’t do it that way, from what I read over compression is bad too.
 
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