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Oil immersion?
Good evening everyone,

Long time since I posted, but on the background I keep following everything. I'm also still building and collecting cells.

In the long run, I want to go off grid with my entire house and fire safety is a big concern for me.

I plan on putting the 14s powerwall outside but I also plan on immersing it in vegetable oil. I would be testing it with a small cell I built but I reason that a setup completely immersed in oil would avoid thermal runaway if one 18650 would go thermal.

Is my reasoning correct? Anyone ever tried this?
Here's a clue to help you decide if your concept is flawed, or not.

Amish_Fighter_Pilot likes this post
Even if the oil is absolutely non-conductive, the problem is "if" a thermal even occurs. If a cell goes all sparkler, it will be FAR higher temps than the flash point of the oil. In the end, you'll have a whole container of oil on fire and no way to put it out. And it doesn't matter what kind of oil you use, all oil is flammable at some temperature, and that temp is lower than what lithium will burn at.

Now, if you want to help make the inverter/charger a little more efficient under loads, then these could potentially be put in oil.

But, overall, I would recommend against oil submersion.
100kwh-hunter and Amish_Fighter_Pilot like this post
Proceed with caution. Knowledge is Power! Literally! Cool 
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If you do plan to use oil, it has to be mineral oil. Organic oils will eventually go rancid. Apparently the smell of rancid oil is horrendous.
Thx all for the advice!
Amish_Fighter_Pilot likes this post
It would be better to arrange the battery in such a way that cell fires remain isolated and that cells are immediately disconnected from the pack. I'm still pretty new to the world of battery building, but these things burn very hot if they ignite. Maybe some sort of ceramic separators between cell groups? Perhaps even better would be to cast sodium silicate into all the voids between cells(but definitely not blocking the positive end of the cell!). Really, any castable refractory would be good as long as it isn't a conductor or semiconductor(so no silicon carbide!)
I wouldn't do oil immersion for similar reasons as Korishan's post above.
Also any kind on fault fixing, measuring, maintenance, etc becomes a total nightmare.

There's several threads about fire proof battery boxes, etc:
Separate building, eg a garden shed &/or 19 inch equipment racks &/or steel cabinets are a good start too.
Amish_Fighter_Pilot and 100kwh-hunter like this post
Running off solar, DIY & electronics fan :-)
Thermal runaway for an 18650 cell can start between 120C and 230C (1) so the cell has to be hot enough to burn your fingers and some spacing with an air flow would eliminate cell to cell thermal runaway (1), however typical powerwall builds are relatively tightly packed along with some battery packs with zero cell to cell spacing typically where nickel strip spot welding is done, hence the examples of a full thermal cascade of every cell in some packs.

Air spacing can be enough on it's own (to prevent a cascade) with adequate cell spacing then you only need to consider what the short duration flame from the valve gas release can set fire to nearby..

1. EnerSys 2016 test data for NASA
Korishan likes this post
If you can't quantify how much they cost, it's a deal, I'll buy 5 of them for 3 lumps of rocking horse ......
I agree on strongly against the idea of oil...
I am busy with some experiments for the case of a thermal runaway.
So far i have 3 setups for sand.
Even a setup is in the make with a sprinkler system, one filled with water and the other one i want to fill it with a special kind of fire extinguishing fluid, fairly new stuff, especially designed for li ion fire.

AAAAND  i can not find the link anymore.......

its called f-500

My link had 3 9 and 500 liter, was a store in The Netherlands, closer to you btw.
Agree with all the comments. And in particular, the 'practical aspects'... as I fool with my packs all the time. Not every day but every couple of months I'm adding a few cells to or swapping out a pack or building new ones or increasing the wiring size or 'something'. The message is that you want your battery bank as easy to access/maintain as you can within your design parameters!.

@competelycharged said
>some spacing with an air flow would eliminate cell to cell thermal runaway
I've used the standard 4x5 plastic 18650 cell holders. Just out of curiosity - does this qualify as adequate 'air flow' system to match your comment?

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