Containing a battery pack meltdown.

[Short_Shot]

I actually like his( @justinjja ) thought process and it is getting us all to think about what we are dealing with and how to minimize the potential of a fire. Actually water isn't very conductive my itself and most batteries are under 60 volts which is safe to touch. Water with salts in it get more conductive but not a tone.

Someone needs to settle down. This is a great thread.

Pure distilled water isn't conductive.

Literally any other water is conductive enough to be a problem. It doesn't need to be salts specifically. Basically any impurities do the trick. Like tap water that's been sitting in a container for months growing who knows what bacteria.

Source: I have to measure conductivity weekly in my chiller system at work. Conductivity is a function of total dissolved solids for practical application. Salt counts as a dissolved solid, but it's not the only thing that will increase said conductivity.


Never mind the previously pointed out aspect of needing to boil the water out of the container before the container will melt and rupture in the first place.

 

[justinjja]

15Kwh will heat up and completely boil out around 21 liters of water.

Thanks, at some point I mixed up gallons and litters...
I'd say I'm an idiot, but I'm pretty NASA crashed a spaceship due to a similar problem :D

 

[justinjja]

If the battery is properly fused and temperature monitored I don't see why such extraordinary measures would be useful. Certainly vehicle manufacturers aren't doing anything similar.

While the chemistry isn't not nearly as safe as lifepo4, proper cooling, fusing, voltage, current and temperature monitoring, venting, and containment are sufficient.

Well the news articles that pop up from time to time about Teslas going up in flames,
despite cell level fuses a good BMS and active cooling.

Make me think that my extraordinary measures could be useful.
At the very least for peace of mind.

 

[dweick]

Google says 0.6g of lithium per 18650.
so there is something like 720g of lithium.
Burning lithium is 43.1MJ/KG so thats an extra 31 Mega Joules of heat.

I mentioned there would be a hole in the lid with a fan, so no pressure.

Imagine how much hydrogen is in 8oz of water

 

[justinjja]

Pure distilled water isn't conductive.

Literally any other water is conductive enough to be a problem. It doesn't need to be salts specifically. Basically any impurities do the trick. Like tap water that's been sitting in a container for months growing who knows what bacteria.

Source: I have to measure conductivity weekly in my chiller system at work. Conductivity is a function of total dissolved solids for practical application. Salt counts as a dissolved solid, but it's not the only thing that will increase said conductivity.


Never mind the previously pointed out aspect of needing to boil the water out of the container before the container will melt and rupture in the first place.

It's a problem in the sense that the pack will be ruined if I have a fire that is extinguished by this system.
Which isn't a problem. Now if I have a leak that ruins the pack, that is a problem.

But as far as making the problem worse, not at all.
My 48V potential points can stay 1 inch apart.
Even even in very dirty water, 1 inch is going to mean less than 1 amp at 48v.

 

[justinjja]

Imagine how much hydrogen is in 8oz of water

Weird to think about the fact that we use water to put out fires,
When water is built from 2 elements that burn like crazy together.

 

[dweick]

I've heard of some people on here talking about putting sandbags above groups of cells on like a mesh grate. I don't think lithium and water mixed too well.

That would be true of elemental lithium but there isn't any of that in lithium ion batteries, they use a lithium oxide.

 

[newbostonconst]

Pure distilled water isn't conductive.

Literally any other water is conductive enough to be a problem. It doesn't need to be salts specifically. Basically any impurities do the trick. Like tap water that's been sitting in a container for months growing who knows what bacteria.

Source: I have to measure conductivity weekly in my chiller system at work. Conductivity is a function of total dissolved solids for practical application. Salt counts as a dissolved solid, but it's not the only thing that will increase said conductivity.


Never mind the previously pointed out aspect of needing to boil the water out of the container before the container will melt and rupture in the first place.

Conductivity (Electrical Conductance) and Water | U.S. Geological Survey

Water and electricity don't mix, right? Well actually, pure water is an excellent insulator and does not conduct electricity. The thing is, you won't find any pure water in nature, so don't mix electricity and water. Our Water Science School page will give you all the details.

www.usgs.gov

Might want to read this....

Also, you wont have to boil the water out of a water bottle before it explodes from the pressure. Keep it sealed and it will open on it own faster and spread water over everything.

Also most car manufactories have there packs in coolant that is likely 90% water.

 

[justinjja]

Conductivity (Electrical Conductance) and Water | U.S. Geological Survey

Water and electricity don't mix, right? Well actually, pure water is an excellent insulator and does not conduct electricity. The thing is, you won't find any pure water in nature, so don't mix electricity and water. Our Water Science School page will give you all the details.

www.usgs.gov

Might want to read this....

Also, you wont have to boil the water out of a water bottle before it explodes from the pressure. Keep it sealed and it will open on it own faster and spread water over everything.

Right my assumption is that it would open.
But I have seen videos with people boiling water over a camp fire inside a plastic water bottle.

 

[justinjja]

My test was simple, stick a coupler alligator clips in my nasty Texas tap water,
Crank volts up to 48, observe current at 1in
result: 20 Milliamps

 

[Hedges]

Thanks, at some point I mixed up gallons and litters...
I'd say I'm an idiot, but I'm pretty NASA crashed a spaceship due to a similar problem :D

And I helped give them the flight computer to do that.

https://trs.jpl.nasa.gov/bitstream/handle/2014/33518/94-1363.pdf

Previously, I read that NASA was going to require all providers to work in the metric system. But they discovered they could save something like $10 million or $100 million by letting vendors use whichever system they preferred, so not excluding those with equipment having English units.


A couple months after that little units mix-up, NASA then relied on input from a single sensor to make critical flight decisions.

My test was simple, stick a coupler alligator clips in my nasty Texas tap water,
Crank volts up to 48, observe current at 1in
result: 20 Milliamps

No problem then!
It's not enough to stop your heart, just enough to make sure you can't let go!
??‍

 

[Short_Shot]

Conductivity (Electrical Conductance) and Water | U.S. Geological Survey

Water and electricity don't mix, right? Well actually, pure water is an excellent insulator and does not conduct electricity. The thing is, you won't find any pure water in nature, so don't mix electricity and water. Our Water Science School page will give you all the details.

www.usgs.gov

Might want to read this....

Also, you wont have to boil the water out of a water bottle before it explodes from the pressure. Keep it sealed and it will open on it own faster and spread water over everything.

Also most car manufactories have there packs in coolant that is likely 90% water.

Yeah. It says salts make it more conductive. So much so that sea water is more conductive than humans are.

Your statement was originally that water isn't very conductive at all 'unless salts are added' (to paraphrase a bit). You stated that salts wont be present, so conductivity isn't a concern.

I refuted the claim that water isn't particularly conductive without salts by simply stating that salt is not the only dissolved solid that can, and does, increase conductivity.


Again, source: My calibrated conductivity meter at work that I use every single week.

Our system uses no salts. In fact, its tested for such things specifically to avoid the corrosion problems associated with them. And yet, the conductivity is typically rather high from other non-salt dissolved solids.


Regarding getting it to open sooner, yes. You could use a thin film over the port leading to the battery. However, you still have to have a sufficient amount of water to put it out. You would need the water container to be built into the lid of the system to transfer as much heat as possible and honestly, by the time the fire is large enough to boil a few gallons of water - the system is already ruined and chances are the fire has spread.

But if everything is perfectly designed, and everything is sufficiently isolated from other flammable stuff (typically via distance) and you can heat your water up reasonably fast via a fire in your battery box and the stars align nicely. Sure. The water might help.


However, all of those things combined would mean the battery could just burn itself to the ground before anything else catches fire.

 

[newbostonconst]

https://allstarce.com/wp-content/uploads/2016/12/2017-NEC-Code-Ch-7-Article-706-.pdf

So stationary storage is limited to 60 volts without engineering and testing.

NEC and Osha have a 60 volt DC limit for touch proofing and safety. Thus 60 volts DC and under is implied as safe to touch and doesn't require shielding.

 

[justinjja]

https://allstarce.com/wp-content/uploads/2016/12/2017-NEC-Code-Ch-7-Article-706-.pdf

So stationary storage is limited to 60 volts without engineering and testing.

NEC and Osha have a 60 volt DC limit for touch proofing and safety. Thus 60 volts DC and under is implied as safe to touch and doesn't require shielding.

 

[brewmatic]

Pure distilled water isn't conductive.

Exploded cell will leak enough electrolytes to make distilled water conductive.

 

[Short_Shot]

Exploded cell will leak enough electrolytes to make distilled water conductive.

Also a valid point.

 

[Short_Shot]

You can run 150 thousand volts through a chain of toddlers with nothing more than their hair standing on end too, under the right circumstances of course.

Doesn't mean DC is inherently safe at all voltages, so they limit it to be sure and provide large safety factor.

 

[brewmatic]

It's very hard to be killed by 120V AC if your skin is dry. I was many time zapped by 220V and couple times I was stupid enough to accidentally touch one 220V wire by one hand and another wire by another hand. Still alive

 

[Short_Shot]

It's very hard to be killed by 120V AC if you skin is dry. I was many time zapped by 220V and couple times I was stupid enough to accidentally touch one 220V wire by one hand and another wire by another hand. Still alive

I've eaten 480 hand to hand once and lived. Not sure how. I suspect the cabinet paint saved me, offering up just a bit more resistance.

220, same deal one hand to the other. Still here.

120? Used to touch it for fun as a kid because I'm stupid.

But while 120vac is "safer" than 220, it can kill you under the right circumstances.

 

[Daddy Tanuki]

I am a little late to this love fest but I want to point out one thing.... at 54.4 volts my 20kw (400 A/h) battery bank give me a shock through the skin of my hands if I present a ground to it. I found that out when I was building it... something my AGM 600 A/H battery bank never did. the lithium batteries being able to dump their current at a much higher rate makes and prior data about DC volts vs amps and danger something that needs to be looked at again. It literally shocked some sense into me.

While it was only a tingling feeling (which my dumb ass (due to surprise) turned around and tested by touching the terminals and it was enough to make my finger twitch and jerk off the terminal) so we are in the realm of danger.

I had the discussion with someone here about DC power, danger etc. and at that time I was probably kind of ambivalent about it, well I was wrong... it can zap you, at least with LiFePo4 batteries.

 

[justinjja]

I am a little late to this love fest but I want to point out one thing.... at 54.4 volts my 20kw (400 A/h) battery bank give me a shock through the skin of my hands if I present a ground to it. I found that out when I was building it... something my AGM 600 A/H battery bank never did. the lithium batteries being able to dump their current at a much higher rate makes and prior data about DC volts vs amps and danger something that needs to be looked at again. It literally shocked some sense into me.

While it was only a tingling feeling (which my dumb ass (due to surprise) turned around and tested by touching the terminals and it was enough to make my finger twitch and jerk off the terminal) so we are in the realm of danger.

I had the discussion with someone here about DC power, danger etc. and at that time I was probably kind of ambivalent about it, well I was wrong... it can zap you, at least with LiFePo4 batteries.

There is some misunderstanding of basic V=IR here.

Here is a fun experiment for you,
Daisy chain 6 little alkaline 9v batteries and touch the 54v,
!Side note, never short a voltage from one hand to the other, even if you think you are sure the voltage is low enough to be safe.
Touch both + and - with the same hand.

You will feel the same shock from the 9v batteries as you get from your lithium cells.

If you felt a difference from 54v agm to 54v lithium,
it's most likely because of different skin conditions to the time of the touch,
Or possibility the distance between the touch.
You will feel a low voltage shock more if you touch both leads with the same hand vs going through your whole body (despite whole body being more dangerous)

There of course are still dangers to 48v systems, like if you short it out with a wrench and the wrench explodes in your face.
And under the right conditions, I'm sure 48v could be dangerous too, like your hands are sweaty, + you ate a bunch of salt the day before.

 

[the_uglydog]

That sounds like an excellent idea! Maybe instead of water bottles get a high volume sprinkler system release. (glass tube that breaks and allows water to flow) and use another 55 gallon drum to store the water at a higher point than the batteries, lots of gravity fed water to drown the batteries, no plastic to make fumes. Also maybe use a larger fan and keep the entire top open so there would be no chance of a pressure spike. That's about it. the dog

 

[OffGridInTheCity]

This was the eye-opener for me - watch (starting @ 3:14) as these 18650 cells in a Tesla pack ignite because of overcharge leading to an all-out roman candle (around 7:21) as this battery goes crazy....

I have 9,000 18650 cells under the house with Batrium BMS and shunt-trip. I've got overcharge/undercharge, ambient temps, pack temps, punctures(physical protection), high-drain/stress avoidance... all in tight control - so I'm not worried about the 'usual things'.

However.... I do not understand the DENDRITE issue. Will dendrites will form as the packs age? or only some badly manufactured cell? or only after they go below XX% original capacity? or just what is the right way to think about dendrites starting a fire. If anyone has info on dendrite/aging fire risk or even 'spontaneous'? fire risk I'd love to hear thoughts.

 

[MattiFin]

Any thoughts on something like this:

15kwh 14s 18650 battery pack,
Put it at the bottom of a 55 gallon steel drum
put a couple 32 packs of water bottles inside the barrel above the batteries.
Cut a hole in the lid and install a cooling fan.

If all the other safety measures failed for some reason,
1. Battery catches on fire, melts the plastic water bottles and gets doused in water.

In theory all the energy goes toward making steam instead of burning down my garage.

2. Does burning an 18650 release more energy than fully discharging it?

15kwh is 54 mega joules, or enough energy to boil only about 5 liters of water.

And if you are wondering about just the steel barrel without the water,
It would only take about 2.5 mega joules to melt the lid on a steel drum.

1. As already mentioned you would need to devise some other mechanism to trigger the water dousing.
If you submerge the battery pack before it is all gloving red hot your strategy should work fine. Just make sure that you went the barrel outside of the garage.
Doesn't matter if you use clear water or salty sea water, both cool the pack down and in both cases your battery pack is going to get ruined. Salt water produces some chlorine when mixed with the electricity but this is small problem compared to the Fluorine components produced in battery fire.

2. Burning li-ion battery releases something like 10x more thermal energy than electrical energy.
Electrolyte is flammable, graphite burns also at enough high temperature, lithium is flammable...
Li-Ion pack fire on Tesla is equivalent or worse than full tank of gasoline. IIRC equivalent to 70-300L of gasoline and it has electrical energy only similar to 10L of gasoline.

https://ec.europa.eu/jrc/sites/default/files/thermal-propagation-in-lithium-ion-batteries.pdf

2. leads to that if you can suppress the burning itself the chain reaction is lot easier to handle: IE enough thick layer of sand on top of the cells that cools down the gases and prevents the cells and escaping cases to catch on fire. Entire battery pack would be destroyed but no fire. You would still have hell lot of toxic fluorine gases. Link above suggest that escaping gases are worse if they don't combust..

More reading on subject:

Battery Fire Safety | RISE

RISE is a state owned research institute collaborating with academia, industry and society as a central part of the Swedish innovation system. Welcome to RISE!

www.ri.se

 

[MurphyGuy]

Mineral oil is not conductive

LOL..

Why don't you think about that for a moment..