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

Diysolar123

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Yes insulation all around.


Regarding fire..
Is there documented reasoning why water would be a bad idea to cool cells down and prevent a thermal runaway from affecting other cells?

Sofar:

-Airlines use water
-Tesla says use a lot of water
-The Netherlands drops a smoking BMW in tank of water.

I am hoping for arguments less opinions.

Johan
consider this possibility... you are starting out with a false assumption and then trying to build on that.

First: Your assumption is that "water" will put out a fire due to oxygen isolation and temperature reduction(this is why water is great are putting out almost everything else that is "burning" (oxidation))...this is wrong for the lifepo4 chemistry.
neither oxygen nor external high temperature are needed once the runaway has started

second: Your assumption from tesla/others to use "water" on lithium battery fires is to put it out...this is wrong for life4 chemistry, they are NOT trying to put it out.
The battery discharge is self sustaining once you have reached the point of mechanical failure and internal shorting; water does nothing to stop that. The reason tesla recommends water, and a LOT of water, is just to contain the reaction and not allow it to spread...and by water they mean an insane amount of water, thousands of gallons. It does not stop the failed battery from the runaway reaction which will run until it is spent, anything touching that battery will go up as well.

My lithium batteries are on a cart (harbor freight steel hand cart!) and in the event of a runaway it is unplugged and rolled outside...
 

joeblack5

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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
 

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Smokin

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Pouring sand on a lithium ion fire cools the hot gasses. This removes the flames.
Water is the approved method to respond to a lithium ion battery fire. It cools the mass and stops the runaway effect from spreading to other cells.
 

Short_Shot

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Pouring sand on a lithium ion fire cools the hot gasses. This removes the flames.
Water is the approved method to respond to a lithium ion battery fire. It cools the mass and stops the runaway effect from spreading to other cells.
Yes but I'm still not sure why we're discussing lithium ion in relation to lifepo4.
 

Surferdudemi

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The number 1 cause of heat / fire in any electrical system is a bad connection.
Over time with heating, cooling and vibration and oxidation .... and even galvanic oxidation can cause a bad connection. Any time there is aluminum in electrical wiring, there is a greater chance of a bad connection developing over time. A bad connection + current flow = heat, and that can be run away heat that can cause a fire.
The thread Fhorst posted where his pack caught fire resulted in nothing but disagreement about what may have caused the fire .... given that we have never seen it happen before, I would have a hard time believing it was thermal runaway of a cell.

We had a situation once where a frequency drive we were controlling caught fire and almost burned the building down. Of course they tried to claim it was because we weren't controlling it properly .... which was ridiculous .... It was obvious that the main power terminals was where the fire started and it was a bad connection .... but we had to hire an expert to prove that to them.

There was a thread recently where a guy with a marine installation had a fuse holder melt down and he caught it just before it broke into flames.

People have intentionally mistreated these LFP cells and there is only the one situation I have seen where the cell was repeatedly stabbed with a metal object that a fire broke out one of the holes that had already been stabbed. That fire may very well have been caused by a spark from the metal object igniting the cell electrolyte that had already spilled out ......So, the cell itself just does not have a fire risk .... or a risk so low as to be almost insignificant ... in the case of LFP cells.

In the early days of this forum, there were opinions that there needed to be some circulation between cells, but as people have built more and more packs and observed pack temperatures under different circumstances, the general opinion has changed and this is generally not recommended any more.
Since we started getting an examining the EVE spec sheets, it has become apparent that controlling the compression of a pack is much more important over all.
I could see situations where the pack was always in a hot environment that the priority might change, because higher temperatures will also cause quicker degradation .... but, in that case, it would probably be better to figure out a way to control the environment.
In the video where the guy stabs the cells, he noted that there was red hot material in the first hole. When he stabs it the second time is when flames shoot out of the first hole and, eventually, the second hole. It may just be that the second stab allowed gases to migrate through a layer inside and exit through the first hole, igniting from the red hot metal there. No external sparks needed. Hard to tell for sure, but an ignition source was right there.
 

nonoceb

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I try adding space between cell because if thermal wrap insulation on cell failed there is a short of 10000A @ 3.2V
I chosen to make a litle grid of sikaflex 1mm thin to isolate from next cell and be able to compressing
 

Short_Shot

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I try adding space between cell because if thermal wrap insulation on cell failed there is a short of 10000A @ 3.2V
I chosen to make a litle grid of sikaflex 1mm thin to isolate from next cell and be able to compressing
Or just do what the rest of us do and stick a sheet of stiff plastic between them.
 

MattiFin

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Please comment on this proposed build.


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.
You limit the current trough the stud but at the expense of total resistance.
In case the braid-terminal connection is getting marginal your terminal or braid is just going to get hotter than without the insulating washer.
Plastic washer would work as intented if you suddenly develop high resistance between terminal and braid. (no current would flow)

And I have to agree with "hightechlab". I'm not fan of the non-terminated braid.
 

Short_Shot

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That puncture test has been discussed here too and your last video is still lithium ion lmao

If you're puncturing your cells you've got bigger issues than dumping sand on top.

Namely a hole in the side of the battery nowhere near your sand, where water could just pour out anyways.
 

Short_Shot

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A LiFePO4 cell is a type of lithium ion cell.
With wildly different behavior when heated or overcharged...

This has also been demonstrated in this very thread and many times on this forum and across the internet that lifepo4 are far and away more fault tolerant and much safer than any other "lithium ion" battery chemistry.
 

mrzed001

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With wildly different behavior when heated or overcharged...

This has also been demonstrated in this very thread and many times on this forum and across the internet that lifepo4 are far and away more fault tolerant and much safer than any other "lithium ion" battery chemistry.

Just a side note:

Technically he is right :)
Lithium ion is: NMC, NCA, LiFePo4, LTO, LiPo, .... all that use lithium ion.
But Li-ion is usually used for NMC an NCA cells only (sometimes LiPo too).

And you are right, the Li-ion behave differently than LFP in a thermal runaway situation.

And @curiouscarbon is right too on that if there is a thermal runaway in an LFP then it is glowing hot inside.
If you can transfer a lot of heat from that cell then you stop the cascade failure where one wrong cell heats up the neighbour cell to thermal runaway ... and that the next ....
Tesla has a cooling pipe around all the little cells to transfer heat.
Toyota uses non conductive liquid to cool the inverters from 1996.
And somewhere I read about someone doing the same with batteries too (sorry, forgot to bookmark it).
Maybe in the Chinese Tesla Model 3 prismatic LFP version ?
 

Short_Shot

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Yeah. It's the distinction that matters. Not the technicality that they're still lithium ion.

The difference in chemistry absolutely changes the debate at a fundamental level.
 

Surferdudemi

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Lifepo4 is Lithium ion
and yet, if you treat it the same as other Li chemistries, you will likely have bad results. So your campaign to convince everyone that soylent green is people ... er ... LiFePO4 is Li-ion is kinda of irrelevant to the discussion at hand.
 

DerpsyDoodler

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and yet, if you treat it the same as other Li chemistries, you will likely have bad results. So your campaign to convince everyone that soylent green is people ... er ... LiFePO4 is Li-ion is kinda of irrelevant to the discussion at hand.
his statement was not wrong (in this case). lifepo4 is lithium ion while not all lithium ion is lifepo4. lithium titanate is also lithium ion among several others.

He needs to be taught the distinction between the different types of li-ion and why lifepo4 is different. Telling him he's wrong when he isn't is self-serving and has no place in the discussion.
 

Surferdudemi

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his statement was not wrong (in this case). lifepo4 is lithium ion while not all lithium ion is lifepo4. lithium titanate is also lithium ion among several others.

He needs to be taught the distinction between the different types of li-ion and why lifepo4 is different. Telling him he's wrong when he isn't is self-serving and has no place in the discussion.
Didn't say he is wrong. Just pointed out that continuing to assert the statement in the face of explanations as to why it's not a useful aggregation of various Li chemistries does not advance the discussion. If you use the Li-ion setting on chargers that don't "know about" LiFePO4 with that type of battery, you may get bad outcomes.
 
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