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Seeking advice on a the need for a fire-resistant cabinet for Li-Ion battery

MostlyHarmless

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Having a healthy respect for the type of batteries I use for my model airplane pursuits (LiPo, which have been known to energetically combust when not treated right), I am considering fabricating a metal cabinet for my built-up 24V, 3100 Wh Li-Ion battery. The cabinet would be vented to the outside to ensure any smoke/combustion is not released within my garage. For even more protection, I am even considering suspending a large plastic bag of sand over the battery -- in the event of a battery fire, the plastic will melt, dropping the sand onto the battery (another trick learned from charging LiPo's).

I am using one of the recommended BMS's from eBay, as well as carefully managing my charge controller settings.

Am I being overly paranoid or cautious? Is there a huge concern given that I have a BMS to protect from over-charge or -discharge? Or is this a prudent precaution?

One side benefit: an enclosed cabinet would make it easier to maintain battery temps above freezing, since it is located in my unheated garage.

Thanks!
 

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Am I being overly paranoid or cautious? Is there a huge concern given that I have a BMS to protect from over-charge or -discharge? Or is this a prudent precaution?
You know more than I do about Lipos. A BMS will not prevent or put out a battery fire as you found out with your Lipo fires. I think you are being prudent.
 
Fire rated cabinets are pretty expensive. Just speculating here, but maybe a steel cabinet bounded by sheetrock or Durock might be adequate. May be worth some homework.
 
I thought I read somewhere that if Li-Ion batteries catch fire that nothing will contain them or put them out. Perhaps that was relevant only or primarily to the Tesla units' chemistry? EDIT: Just saw this is a pretty old thread.... still curious as to whether that is correct.
 
still curious as to whether that is correct.
Within the general category of Lithium Iron batteries are several sub categories depending on chemistry. The safest chemistry is LiFePO4 (LFP).
That being said, there is a new NEC code being implemented that will put restrictions on how all types of battery storage can be installed.
 
As Ampster said the LiFePO4 are much safer and have seen pics from a lot of people on this forum putting those inside boxes insulated with foam board which is very flammable and has low melting point. I view that as a little bit too risky and used rock wool insulation instead which can withstand 2000F temps.
 
As Ampster said the LiFePO4 are much safer and have seen pics from a lot of people on this forum putting those inside boxes insulated with foam board which is very flammable and has low melting point. I view that as a little bit too risky and used rock wool insulation instead which can withstand 2000F temps.
I was headed the foam direction in my designing here but, it always felt a little wrong. Will def look in the rock wool. Thanks!
 
Within the general category of Lithium Iron batteries are several sub categories depending on chemistry. The safest chemistry is LiFePO4 (LFP).
That being said, there is a new NEC code being implemented that will put restrictions on how all types of battery storage can be installed.
Yes, the LiFePO4's I knew to be substantially safer than Li-Ion but, my understanding is that Mostly Harmless was building a Li-Ion battery and looking for fire-safe cabinet for it.
 
Having a healthy respect for the type of batteries I use for my model airplane pursuits (LiPo, which have been known to energetically combust when not treated right), I am considering fabricating a metal cabinet for my built-up 24V, 3100 Wh Li-Ion battery. The cabinet would be vented to the outside to ensure any smoke/combustion is not released within my garage. For even more protection, I am even considering suspending a large plastic bag of sand over the battery -- in the event of a battery fire, the plastic will melt, dropping the sand onto the battery (another trick learned from charging LiPo's).

I am using one of the recommended BMS's from eBay, as well as carefully managing my charge controller settings.

Am I being overly paranoid or cautious? Is there a huge concern given that I have a BMS to protect from over-charge or -discharge? Or is this a prudent precaution?

One side benefit: an enclosed cabinet would make it easier to maintain battery temps above freezing, since it is located in my unheated garage.

Thanks!
Those batteries will fit inside a 40mm ammo can. Hard to come up with a better enclosure for containing a battery fire than a can designed to carry high explosives around in during a battle.

I was going to use the same cells in my RV, but the thought of trying to sleep with those cells in the same room with me became too much for my piece of mind. I finally bought a set of the 280 AH LiFePO4 cells instead.

Idea behind the ammo can is if there is a fire, I would very much like it to stay inside the box. The box is made out of 11 gauge (1/8") thick steel and the lid is very solidly constructed and attached, plus there is a very heavy duty, high temperature, rubber gasket on the lid. If anything is able to stand up to a LiNMC fire it will be this box. I really wouldn't want to drop it on my toe.

BatteryCan.jpg

I was planning on using a pair of bit-miner cold plates (one on each side of the cells) plus redundant water cooling systems so the battery enclosure could remain completely sealed (no air flow in or out).

PXL_20210129_030835715.jpg

Want to buy some water cooling parts that are a perfect fit for your cells?

Just kidding, I will probably build a portable power station with these next year after I am done with the van conversion.
 
Putting the batteries inside a small fire rated gun safe could be a very good idea. Be sure to pull out the carpeting first. Hate for the smell of melting nylon to detract from the bouquet of burning lithium.

I was going to set mine on top of a piece of refractory blanket.

 
The issue is if they ignite no steel box will stop them from melting out the bottom and moving to whatever is below. Burning lithium cells are like the Xenomorph blood in Alien......

So the best way to de-risk is to work to ensure they never ignite, and have a plan on what to do if they do.

Interesting YouTube video from one of the powerwall guys with a 80P pack that had a couple run away cells and the way to stop the melt down was to drop the entire 80P string underwater. That stopped it but destroyed the string obviously.

This is why LTO is interesting as pretty safe just the power density sucks.
 
Good point, lithium batteries contain their own oxygen so a fire rated cabinet will not help to extinguish the flames. I would install fire sprinklers to cool the batteries, and suffer potential flood damage instead of burn damage.
 
My 2 cents.....

A metal cabinet will not do a good job of containing a LiIon fire. The intense and localized heat will make quick work of sheet metal. You need a large mass (like the mentioned sand) to absorb and dissipate the heat long enough for the fuel source to be exhausted.

This is pretty far outside my area of knowledge, but I would put a rather thick layer of sand under the system so that when it burns through the primary metal enclosure, it meets sand which will do a pretty good job of absorbing the heat before getting to anything else.
 
Burning metallic lithium can reach 2000 degrees C which is above the melting point of steel. If we get that far, I think I will be calling my insurance agent and asking about coverage for a total loss.

Throwing water on burning batteries can cause a hydrogen explosion so that doesn't sound like a great idea either.


Sand, lots and lots of sand sounds like a good idea.

Glad I gave up on the idea of using LiNMC cells in my RV and switched to LiFePO4 cells.

I mean we all have to go sometime, but burning up in a completely preventable RV fire is not my idea of a good way to go.
 
Am I being overly paranoid or cautious? Is there a huge concern given that I have a BMS to protect from over-charge or -discharge? Or is this a prudent precaution?

One side benefit: an enclosed cabinet would make it easier to maintain battery temps above freezing, since it is located in my unheated garage.

Insufficiently paranoid or cautious. Unless the garage, its contents, and any attached structures are all expendable, I think you're better off making a detached bunker to hold the battery. Add whatever insulation and climate control necessary to keep battery happy.

Considering the Probability/Consequences matrix we use to evaluate risks, you should take steps to reduce worst possible consequences to an acceptable level.

It appears future building codes in the US will require a UL listed (in the case of lithium) battery, but make an exception for things like repurposed EV batteries if they are separated from buildings by 5'.
 
Insufficiently paranoid or cautious. Unless the garage, its contents, and any attached structures are all expendable, I think you're better off making a detached bunker to hold the battery. Add whatever insulation and climate control necessary to keep battery happy.

Considering the Probability/Consequences matrix we use to evaluate risks, you should take steps to reduce worst possible consequences to an acceptable level.

It appears future building codes in the US will require a UL listed (in the case of lithium) battery, but make an exception for things like repurposed EV batteries if they are separated from buildings by 5'.
I got an idea. How about a catapult held down by a very flammable rope. Battery pack catches fire, launches them in an arc aimed at the backyard pool.

This sounds like a product we should be able to buy from Acme.

 
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