Battery box materials - safety focus

steelmesh

steelmesh

100 W
Joined
Jun 28, 2012
Messages
123
Location
Michigan
Lithium battery fire will burn at twice the melting temperature of aluminum (plz correct me haha). However, aluminum is an amazing heat sink too. Would something like a construction of stainless steel laminated (thin) to aluminum work well...or could the aluminum (like thicker 3/16") survive a couple 5000maH batts killing each other (assuming other batteries are isolated in pairs). It would be designed for rider survivability, so just shielded zones for body parts and no-way pressure could build-up through strategic venting (maybe rocket nozzles so you at least get a little boost).

Anyone ever burn their bike up?
 
It's EXTREMELY easy to make a Kevlar reinforced carbon fiber box (or tube, rectangle, triangle). Too easy to not consider. Just like making a fiberglass part.

after 3 layers, lay two or three layers of Kevlar, and a cuppla more carbon fiber layers. Presto.

A cuppla tips. Don't brush the first layer. It squiggles up the CF lines. Just dab. And don't vigorously stir the resin. Makes bubbles that can screw up end product.

[youtube]Ybyh6Q9MBgE[/youtube]

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Pointless really.

But do put your battery in a stout protective container. The point is, don't puncture the packs in a crash or let them rattle around in a basket or box till they chafe holes in the cells.

Put at least double that effort into being sure you don't build a bike that will short the battery some day. Don't worry about containing a fire near as much as preventing it.
 
As Dogman points out, fireproofing doesnt' matter nearly as much as foolproofing/crashproofing.

Look at Stochastic's (and mine) ammo box battery packs. Ammo cans will protect against a fair bit of impact abuse, and probably prevent a puncture from most crashes you'd still care about anything afterward, anyway. ;) It's partly the material (steel) and partly the way it is put together.

Then the packs are packed tightly and padded so they won't be able to rub on each other or the casing, to cause pouch failure or wire shorting. I havent' done it yet, but tying down the wire harnesses inside so they cant' vibrate and rub would be a really good idea, too, including and especially the balance wires, if any.

As long as the cells and wiring cant' short out or be punctured, then you're as safe as you can get. At that point, only a cell failure from something internal (chemistry, defect, etc) or electrically external (overcharge, overdischarge, etc) is much of a hazard, and you can't do anything about the former, and only be cautious about the latter--unless you manually charge each cell individually while standing there the whole time watching the current and voltage meters, there is no way to guarantee nothing can happen, evne with the best protection electronics--stuff fails sometimes, usually in a way unplanned for by the designer.
 
Re the burn the bike up question,

I fail to recall who it was in all examples. One lipo fire I remember was a bike with the lipo packs bouncing around loose in a front basket. A pack got rubbed and punctured, and the pack went up. The battery was at least able to be dumped out to burn.

Another one was way back. An early lifepo4 "duct tape" pack had a sharp metal edge on the battery box rub a hole in some cells. That one burned a converted cushman.

Lyens had a lipo( I think) pack catch fire while discharging. In that case, I believe he'd done something previously that broke the "lipo rules" .

You pretty much have enough time to get off the bike before you flame your balls.

No way to put the fire out, unless a front loader with a yard of dirt is handy.
 
Somebody brought a used battery in the used section from Dirtdaddy and it caught fire and burned his bike down. About 6mos. ago. Lifepo4.
 
dogman said:
No way to put the fire out, unless a front loader with a yard of dirt is handy.
Click to expand...
Yeah, it's not really a fire. No oxygen needed, but it does need heat. It's a reaction. Like epoxy. It's gasses that shoot out. 1500 degree gasses. Thus the flame.

This is why I mention Kevlar/carbon containers.

Every one of the very cool fiberglass containers I've seen on this site, could have been
made from Kevlar/carbon. Just as easy. These will contain several 1500 degree out-gases,
whilst picking their teeth... So to speak. :)

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Not knocking the carbon box idea. I strongly support a stout protection from puncture, abrasion, and just damage from rattling around loose and naked in some bag.

It can be metal, glass, carbon, even leather saddlebags make good protection.

But actually containing a fire? Thing is, if you haven't seen this picture, this is what you are talking about containing.Lipo fire grange.jpg

This one was accidentally dead shorted as it was being readied for a race.
 
No way to contain the outgassing, and no way to save a a frame on a burning bike. The heat would likely melt, aneal, and warp the frame. the fire is going to be too hot and too big. Its the equivilent of building a gas tank on a car that can burn without hurting the car. Not going to happen. Prevention is the only practicle method

The best thing to do is prevent the fire from ever starting. Ammo boxes are a good way. Centeral locations on the frame another.

Just to give you an idea what 1 cell of a lipo can do, watch this video. Try to imagine 40 cells going up. No box, charging bag, or container that could be carried on a bike is going to help once the lipo decides to run free, the same way no gas tank is ever going to controll the explosion once the gas is ignited.

[youtube]NzUla1udKuA[/youtube]
 
Wow, one cell. I have a pile of em waiting for similar treatment, but I never get around to proper disposal. They are sitting in storage at 0v.

Nothing wrong at all with the idea of building a box that redriects the flames away from you just in case. Like an ammo box with holes in the bottom. If the worst happens, fire at least doesn't shoot towards your body.

The vid shows the folly of storing the battery in a completely sealed ammo box. If something happened, you just made a big mistake.

My lipo carries in an open top box right between my legs. It's front and center, I'm seeing it, smelling it, and I'll be off the bike long before flames shoot out. I kid myself I might be able to remove a hot pack in time but I won't. I might be able to snag out a few undamaged packs before the bad one pops though. Hopefully the aluminum wall between the pack and the frame will help save the bike. It won't burn the motor, but it might take some wiring on the controler. A fireball will be directed mosty up and away from the frame.

I'm sure I can dismount if the pack pops off and suprises me. It won't be fun to dismount at 30 mph, but it's a manuver I first learned to do 45 years ago.
 
So that's the photo of the event at granger race thanks Dogman. l went there this year and the guy is still a legend he would like to forget. Legend Ha Ha
 
Okay so prevention of a lithium fire event through proper mounting, monitoring, and storage is key, #1... then after that I guess is where this thread comes into play, as the secondary fire control method. They don't put FIREwalls in cars for nothing, which is just piece of sheet metal between the passenger compartment and the engine bay. This is the analogy, having a basic firewall to allow a rider to safely demount (buying time to stop and evacuate).

A philosophy of mine, the worst possible thing that could happen, could happen (its great to laugh off my major follies, because I already knew it could happen and content if it did, everything is a blessing in disguise). Maybe you let a friend, amature ebiker, or investor ride your bike one time, and it happens to "blow up", the rider's logic may go out the window in a stressful situation, like riding it back to you as if it weren't a major issue or pure laziness (again, no logic present), but ends up grilling himself. However, if the box could contain the fire properly long enough, they would ride back and then could laugh together about how they almost just died.

ht_Fisker_Karma_fire_nt_120530_mn.jpg

Fisker Karma, cremated
 
If you have a box that allows venting of the gas in a direction other than towards you, you'll have plenty of time to get off before the next stage happens (if it does).

There are vids (jeremy harris posted one a while back) of RC LiPo packs/cells being deliberately overloaded to cause rupture, venting, and fire, where if they were contained in a vessel allowing venting of the gases but not allowing in-drawing of air for oxygen/etc., no actual fire occured, even though it should have under normal circumstances.

the untested theory behind my vented ammocan is taht the hot gases will vent, and the pressure will both blow the air out of the can and prevent any from being allowed back in until the venting is done.
http://www.endless-sphere.com/forums/viewtopic.php?p=536242#p536242


I have some dead cells that still need to be used for pyro testing, and as soon as I can actually remember to do it, I will use them to test this theory, to see if I can get flames out of the can or if it stays unignited, and what temperature it reaches inside the can (using a BBQ thermometer if I can get the one I have to work in there "remotely"), and what temperature the can itself reaches. I already verified that my high-current overvoltage overcharge method on identical dead cells can cause venting and flame, so it should ignite them the same way inside the can. I'll use as many as I can at once to verify it works, and video it at night with no other lighting to see if I can see any flames. If I can find someone to borrow a thermal imager from for the test I will, but this is highly unlikely. Probably will just be my Sony digicam with basic video, like my other tests were done with.

http://www.endless-sphere.com/forums/viewtopic.php?p=605878#p605878

[youtube]UjtGYUt_XgQ[/youtube]
 
Defiinetly, the strategy needs to be to seperate the fire from the rider, by venting it the other way. Containing it simply isn't going to work. Firewall is exactly that, not a box trying to contain an engine fire in a car completely. Just keep the burning gasoline from spraying the passenger compartment.

So you want to have holes in the bottom, that aren't blocked by the cells themselves, then some kind of tape over the holes so they can blow out when they need to, yet not let water in all day.

Or a battery box top, that can gather the gas, and redirect it down a pipe perhaps, to the safer location of your choice for the venting.

I just rely on being able to see the tops of my batteries, and smell any hot plastic before she goes. So far that's all I've had, a stink of hot shrink wrap warning me to check what's going on. Plenty of time to stop and jank out the good batteries to save em.

My entire approach to RC lipo hinges around very quick and very easy removal of packs, removal immediately after every ride so I notice a pack that got hot instead of merely warm, safer storage and charging off the bike. A bit more pita, but it lets me sleep well.

Sealed in a box, buried in the bike, I'd want at least a thermometer in there, so I can see if the pack heats up more than normal.
 
Imagining out loud here: Was looking into building a battery pack some more, then creating mini-packs of cells (12.8v lifepo). Based on the carbon fiber suggestion and looking at people wrapping up their packs with tape...could you just finish the pack's casing with carbon fiber (semi-permanent, epoxy filled) with a maybe 1/2" thin walled stainless vent tube to release pressure, and -at the least- create a stress riser at the tube joint.

Or take a RC pack, then wrap it with carbon fiber (again, instead of a complete seal, it would have a high temp stainless vent tube). Is this feasible? Does it fair well on the cost-benefit chart :p
 
The larger the area you give it to expand, the more comfort zone you have.

I would make a box big enough to hold everything. Wall off and ventilate the electronics, and line the battery compartment with sticky sided rubber foam. And vent it down.

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From what I have seen with carbon fibre parts in fires, the resin melts and you are left with a piece of carbon, ready to be re-used. :lol:
 
Talked to these guys (http://lithfire-x.com/) exhibiting at The Battery Show, they are also our neighbors in the same building I work at. They showed me some graphite powered they had on display that could be sprayed on like a coating, can withstand 3000F, he suggested that would work well in the ebike applications. He was also telling us about the military wanting to isolate the battery packs to improve redundancy, he showed a pretty simple system that reacts to heat. Above the batteries is a single tube that goes through all the battery compartments, if one battery goes it burns a hole in the tube then sprays in the neutralizer. They also mentioned additional packs that burst, under the batteries when they reach a certain temperature.
 
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