Containing a battery pack meltdown.

Short_Shot

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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

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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 :)
 
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Short_Shot

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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.
 

ken morgan

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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

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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.
 
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the_uglydog

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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

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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.
 
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MattiFin

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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.

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:
 

Bluedog225

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If sand is non-conductive, why not cover the cells with sand after build? That is, no need for a fancy release system, just embed the whole deal in sand from the outset. It would have a dampening effect on the whole arrangement.
 

Short_Shot

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If sand is non-conductive, why not cover the cells with sand after build? That is, no need for a fancy release system, just embed the whole deal in sand from the outset. It would have a dampening effect on the whole arrangement.
Heat I would imagine. Lithium cells can get pretty warm and thermal runaway is an issue. Insulating them would be a big problem.
 

OffGridInTheCity

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Heat I would imagine. Lithium cells can get pretty warm and thermal runaway is an issue. Insulating them would be a big problem.
My 18650 cells average charge/discharge is <200ma/cell and they don't get warm at all.

If sand is non-conductive, why not cover the cells with sand after build? That is, no need for a fancy release system, just embed the whole deal in sand from the outset. It would have a dampening effect on the whole arrangement.
This might be one of those ideas either so obviously wrong ( because no one has done it that I know of ) OR maybe so brilliant because its outside the box for sure.

Thinking out loud a bit... Sand would block access to the cells... and I do occasionally need to do maintenance on my DIY 18650 packs. For and EV the weight would be a no go. The sand might gather moisture? and result in some rust or conductivity?. Maybe something sand like but not sand? - interesting idea.
 
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Short_Shot

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My 18650 cells average charge/discharge is <200ma/cell and they don't get warm at all.


This might be one of those ideas either so obviously wrong ( because no one has done it that I know of ) OR maybe so brilliant because its outside the box for sure.

Thinking out load a bit... Sand would block access to the cells... and I do occasionally need to do maintenance on my DIY 18650 packs. For and EV the weight would be a no go. The sand might gather moisture? and result in some rust or conductivity?. Maybe something sand like but not sand? - interesting idea.
It's heat.

Yours don't get hot maybe but with high c rates they do, can, and will runaway.

Moisture wouldn't be an issue in a dry environment but might in a damp basement.
 

thegoogler

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In a thermal event water is your friend....
Sort of. Water is your friend if you have a lot of it available to drown the pack and dilute the lithium-to-water ratio. To the OPs original question I wouldn't try to drown a lithium battery fire with a (melting plastic) gallon of water. Water will cool the pack but will react to lithium so you need enough water to counteract that reaction. You also need to vent the gas or you risk that exploding.

Personally if concerned about a meltdown scenario I'd look for a way to monitor and alert you as soon as the temp spikes and then a way to safely control it
  • bags of sand would be cheap. If you're suspending them above the battery use plastic bags, which will melt easily but are otherwise sturdy. That's apparently how some self-contained charging stations work.
  • fire suppression designed to deal with lithium chemistries would be better.
That said according to the article below in LFP batteries (not LI) the amount of lithium is fairly low and water probably will work OK, but a dry or CO2 (or a class D even better) extinguisher would be preferable. This short article below is absolutely worth a read for all DIYers

 
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