# LIFePO4 - Safe, but crash safe?



## Ziggythewiz (May 16, 2010)

If you get hit by someone doing 100 you'll be lucky to survive no matter what kind of Chinese car you're driving.


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## lithiumlogic (Aug 24, 2011)

Well, the point i'm driving at, is is it ok to put batteries in the crumple zone? Trouble is, in most EV conversions you don't have a choice.. inside the engine bay or under the boot floor are your only options.

Maybe a pickup conversion, a 2 seater coupe, van or flat bed conversion allows you sufficient room, otherwise you're looking at a completely custom build car from the ground up!


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## Ziggythewiz (May 16, 2010)

Many people do. I wouldn't if it could be avoided, not for safety reasons but because I wouldn't want the most expensive part of the car damaged in a fender-bender.

As you mentioned, placement options are limited, my car is just 1 big crumple zone, but I like to have some heavy lead in front of me to break the impact a bit.

If you want a difinitive answer, too bad. Every chemistry is different and every accident is different. A lump of any material will burn if you hit it hard enough, and anywhere you put it someone will find a way to hit it.

Keep in mind, in this accident a tree ripped past the trunk and through the back seat. What if the tree had gone through the front, or the side? You can't protect against that.


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## Roy Von Rogers (Mar 21, 2009)

There are many accidents on a daily basis were ice vehicles burn, its expected, after all it has gasoline in the tank, thats why most times you will see the fire department on a scene. So why are EV's so different, why is it there such a hoopla when an electric car burns, for whatever reasons.

Whenever you have a large amount of power packed in a dense package, stuff can happen. As far as I can see the lipo4 batteries are no more, or no less dangerous, depending on the circumstances. The biggest dangers I see in this technology is not crashes, but how to put the energy in, in a save manner without burning the batteries.

The emphasis should be on perfecting a charging system that is super reliable, cause it seems that were most fires are occuring.

Roy


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## swoozle (Nov 13, 2011)

The sinopoly destruct testing. 

http://www.youtube.com/watch?v=aQs7L5LmEss


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## rwaudio (May 22, 2008)

In a crash a 12v lead acid battery can start a fire from a short circuit/damaged wiring. There is no reason to assume that the fire was started "chemically" vs "electrically" from a shorted wire.

The only extra hazard would come from how LiFePO4 reacts in a fire that was started elsewhere in the car. I would consider it like a gas tank, unless you drive a Pinto it's probably not going to explode on impact, but there is a chance the vehicle could burn to the ground given enough time.


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## piotrsko (Dec 9, 2007)

+1 everybody ^^^

That is why Halon fire systems were invented.


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## SandRailEV (May 11, 2012)

So, if you're so afraid of a battery catching fire in an accident, are you also afraid to drive or ride in a gasoline powered car?


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## jeremyjs (Sep 22, 2010)

SandRailEV said:


> So, if you're so afraid of a battery catching fire in an accident, are you also afraid to drive or ride in a gasoline powered car?


agreed there are many car fires that kill people every year from gas fires after accidents. I don't drive for a living or commute very far to work, but I've seen at least 2 or 3 cars burning to the ground in my time.

You could simulate a severe crush test on one of these cells pretty easily though. Get a big chunk of scrap steel that weight a couple hunderd pounds and drop it on a cell from 10 feet up. seems like it's be a pretty easy test to do if you had an extra cell.


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## Ziggythewiz (May 16, 2010)

That test would do nothing. Your chunk of scrap steel needs to weigh 2-3 tons and hit at 10-20 Gs, so try dropping from 1000-10000 feet up.


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## lithiumlogic (Aug 24, 2011)

To test it you'd need to assemble a load of cells, about the number you'd find in the engine or under the boot floor of a typical ev conversion, up against a concrete wall. Then you have to slam something that weighs 1 ton on wheels or rails into it at 40mph. And do it 10 times, since even Mythbusters had trouble making a gas tank explode with tracer rounds etc.


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## jeremyjs (Sep 22, 2010)

Ziggythewiz said:


> That test would do nothing. Your chunk of scrap steel needs to weigh 2-3 tons and hit at 10-20 Gs, so try dropping from 1000-10000 feet up.


It may not be exact, but it's certainly enough to crush a cell flat plus you'd be putting all of the force on a single cell instead of a whole pack and the car itself; which is designed to dissipate the impact energy during a crash. It would certainly be enough to crush the cell flat, break the case, expose and short all of the internal cells, etc all within a fraction of a second. It should be about 28000 newtons of force concentrated on a single cell. This is as good a way to do it as anything else short of a full blown crash test with a full pack; which would be really expensive and not within the realm of possibility for most of us.

If that's not enough to flatten a cell scrap iron is cheap. Just add more.


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## GizmoEV (Nov 28, 2009)

lithiumlogic said:


> Now, this rather cool lecture
> 
> http://www.ri.cmu.edu/video_view.html?video_id=60&menu_id=387
> 
> ...


Where did you get that the electrolyte is nearly 50% of the mass of the cell? That is definitely not the case as anyone who has dissected a cell can attest.


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