shitty reused lithium cell failure mode? - Page 1
Forum section: electronics / general

author: CopperCone
author_rank: Super Contributor
timestamp: June 04, 2018, 06:56:46 pm
content: If you use these, what does the failure mode look like? Can you detect it with a temperature sensor? Or does it just blow up suddenly?I was thinking that maybe you can make a special fixture that jetisons cells that are about to explode so they can explode in some kind of blast trench. Military trenches have provisions built in so the grenade falls into a little subtrench and minimizes the damage. So if you have alot of em in parallel. I don't really trust the super visor circuits that much, don't try to convince me. I would obviously use them in as a primary saftey but its just not enough to justify using random old shit.I figure if you do your own metal work and make your own springs and find some kind of cheap way to eject em, maybe using some kind of spring mechanical amplifier bonded with low temp solder that melts and throws em out, electrical actuation is expensive unless you use electrically triggered powder charges, I would not want to pay for a bunch of solenoids and shit, tho like putting a fire cracker behind those fuckers set to some kind of single transistor temperature monitoring circuit is not that bad, just wear basic protection when servicing it.I figure I would peel em from the plastic too, so they are less thermally insulated.

author: james_s
author_rank: Super Contributor
timestamp: June 04, 2018, 07:02:16 pm
content: ??The typical failure mode is the internal resistance increases to a point where the cell can no longer deliver the current required by the load, and mAh capacity drops to the point that run time is too short to be useful. They very rarely catch fire, that is more common of a faulty charger that overcharges the battery, which has nothing to do with the quality or age or the cell.

author: CopperCone
author_rank: Super Contributor
timestamp: June 04, 2018, 07:05:13 pm
content: I thought they can explode violently or go into some kind of runaway. Thats the only kind of failure mode I am worried about, electronics can deal with cell isolation and stuff to maintain a working supply, I just can't risk them for whatever reason failing catastrophically.When they do fail bad, for whatever reason, can it be detected with reasonable thermal time constants on the surface?This would be in the interest of maintaining power density and increasing up time. I can envision some kind of cheap solution using conduit segments, but I think the blast radius of each of those fuckers going bad is fairly large, so it really would occupy a wall, unless you do something clever, to maintain operation in worst explosion case.Idon't want a chain reaction or major power failure incase of a unruly runaway cell.

author: james_s
author_rank: Super Contributor
timestamp: June 04, 2018, 07:15:16 pm
content: It's extremely rare. High current LiPo packs like the sort I use in electric RC airplanes can go up in flames if they are physically damaged or short circuited but again the fires typically occur during charging. I've deliberately blown up a couple of worn out packs and what they do is rapidly puff up and then spew flames, there isn't really time to react.If you have a mobile phone, tablet or laptop then you are using a li-ion battery already, how often do they blow up? It does happen but it's very rare.

author: CopperCone
author_rank: Super Contributor
timestamp: June 04, 2018, 07:22:41 pm
content: I don't really care about the frequency, but like, you don't think that a bonded thermistor connected to a powder ejection charge would catch it? Thermocouple maybe?I watched videos on youtube and it looks like the spew quite a bit of flames and rocket around, the C-whatever cylinderical ones, but I have no idea what surface temperature looks like before it happens.I imagine the cells seated in sections of tubing protected by one way rejection leaf springs and some kind of curtain in kao-wool or other high temperature insulator, basically with a normally closed slit over each battery, so if one shoots out, it can rocket around in the trench behind the battery wall with most of its thermal energy being deflected by the high temperature insulation material towards the walls, which would need to be built to withstand quite a blast indeed, I am imagining something like 3/8 inch or more welded steel subsections. The whole box would vent to the outside incase a massive chemical fire ignited in it. I guess it would need to be tested with a few KG of fast thermite (copper etc)It would need to be carefully designed not to function as a bomb, perhaps joule equivalent quantities of black powder can provide a worst case ovepressure event, since powder would burn much quicker then the batteries could explode even with the perfect storm, I think.

author: james_s
author_rank: Super Contributor
timestamp: June 04, 2018, 08:53:54 pm
content: Where do you plan to eject it to? You're not worried about the ejection charge causing injury or damaging something? Perhaps you should just avoid lithium batteries entirely and stick to some nice safe carbon zinc cells, you seem to be excessively paranoid about electrical faults, especially those that are very unlikely. I mean the thought of having some sort of emergency ejection system is frankly absurd.

author: Audioguru
author_rank: Super Contributor
timestamp: June 04, 2018, 11:37:58 pm
content: A lithium battery is damaged if it is discharged too low which causes it to be dangerous if charged. A modern lithium charger IC measures a cell's voltage and will refuse charging it if its voltage is too low preventing an explosion or fire. The modern lithium charger IC will also prevent overcharging which might cause an explosion or fire.

author: Daixiwen
author_rank: Frequent Contributor
timestamp: June 05, 2018, 06:01:59 am
content: I don't think you can catch a thermal runaway with temperature sensors on the surface of the cell. When a cell is overcharged the internal temperature and pressure increase rapidly inside and the reaction has already started long before you could measure a high temperature on the surface.As others said the best you can do is to monitor the cell voltage and never allow it to be under- or over charged.

author: CopperCone
author_rank: Super Contributor
timestamp: June 05, 2018, 03:01:21 pm
content: I might try one i have an old one that was getting particularly hot from charging which i put out of service.I know my idea sounds stupid but if you have say 2000 of these to make a home storage, the chain reaction from burning would be intese. They cant be supressed with oxygen and i can easily see a high temperature fireball capable of setting stuff across the room on fire from radient heat. If you eject em through a one way firewall you can hopefully eliminate some failure modes.Just making it capable of withstanding the fire means you can still loose the whole bank due to 1/2000 components failing possibly.

author: metrologist
author_rank: Super Contributor
timestamp: June 05, 2018, 03:37:40 pm
content: It builds pressure - it will self propel if you just mount it in a blind chamber. An 18650 in a shotgun chamber and applying 12V would be an interesting test (you could use your conduit idea). I think the vents are always on the positive side.

author: CopperCone
author_rank: Super Contributor
timestamp: June 05, 2018, 04:39:44 pm
content: I am scared that it could wedge in there and explode worse. My idea was to make a pyrotechnically actuated piston that basically pushes it out of a loose collet.The gas physics behind this are simple and i think something can be mass produced using emt conduit or copper pipeI had batteries basically jam up in flash lights. I had to beat em out with a stick.If they swell it might be possible to make some kind of collet yhat is spring loaded and drops it like a bomb by opening it up if it swells but the mechanical sensitivity would need to be high, i suspect that it would be difficult to manufacture and that each little holder would need to be carefully tuned.And of course if the battery decided to bottle rocket around it would likely smash into the other battery holders and open them unless it got pushed out forcefully which would make it even more mechanically complicated, so some kind of textured one way valve can be usedIf you watch the youtube videos you will see that they can behave like high powered jumping jacks if they vent in a particular space.

author: james_s
author_rank: Super Contributor
timestamp: June 05, 2018, 05:17:26 pm
content: If you're scared of a Li-ion battery the answer is simple, don't use them, either that or seek professional help with your irrational phobia. To any rational person the idea of using a pyrotechnic charge to eject a battery that by some crazy chance might catch fire sounds absolutely ridiculous. Stored energy is potentially dangerous no matter how you look at it. A properly designed battery is going to be safer than a freaking pyrotechnic ejection charge though. Put the batteries in a concrete bunker out back, or hide in a concrete bunker to protect yourself from them.

author: CJay
author_rank: Super Contributor
timestamp: June 05, 2018, 06:15:40 pm
content: So to mitigate the chances of a cell exploding you're going to homebrew a bomb?Can't see that going wrong in any way shape or form at all.Let us know what Homeland Security say when they come calling, we'll wait 'til your trial and any sentence is over.

author: metrologist
author_rank: Super Contributor
timestamp: June 05, 2018, 06:30:42 pm
content: You could have the cell in a sealed sleeve and use the pressure build-up as an indicator to a solenoid to eject the entire pod.

author: CopperCone
author_rank: Super Contributor
timestamp: June 05, 2018, 07:11:39 pm
content: Quote from: CJay on June 05, 2018, 06:15:40 pmhttps://images-na.ssl-images-amazon.com/images/I/512hAfzK%2BXL.jpgmaybe you are over taken with shock and can't read properly because you don't realize disciplines like explosives engineering, fire engineering and ballistics engineering actually exist and its not mephistopheles banging fire sticks together?

author: CopperCone
author_rank: Super Contributor
timestamp: June 05, 2018, 07:12:39 pm
content: Quote from: metrologist on June 05, 2018, 06:30:42 pmThe idea is to make it safe if it all catches on fire, to redirect the hot gasses and flame elsewhere, but to also prevent a cascade failure or explosion ripping out of a bunch of wiring/protection circuits.I would say this is a good solution for an airplane though. Or a submarine, ship, space station, etc, where you can't afford the weight of heavy shielding and fire is more of a concern then up time.That would be a good yarn though, if a giant ass battery bank engulfed in a fire ball was shot out from someones ham shack yea

author: metrologist
author_rank: Super Contributor
timestamp: June 05, 2018, 07:47:57 pm
content: I meant just eject the single cell (pod). As a matter of fact, perhaps it, the pod, could sprout fins (wings) and fly like a model rocket, and you will design a GPS navigated MCU solution to have it safely piloted to the extinguishing pool. Or rather, a more passive solution.

author: CJay
author_rank: Super Contributor
timestamp: June 05, 2018, 07:53:09 pm
content: Sigh, yes yes, of course, I can't read and must be stupid because I think your grand idea about adding explosives is a great way to make LiIon cells more dangerous.Hint, adding explosive or pyrotechnic charges to a burning cell isn't going to make it more safe and is going to add a barrow load of liabilities, if you want to eject the burning cell into a fireproof box why the hell not just put it in the fireproof box in the first place?Ejecting a burning battery pack form a 'plane is going to have *huge* liability issues if it's over populated land.If your 'loose collet' is loose enough for the cell to be ejected by the pyro it will be loose enough to eject itself when it explodes, all you achieve by adding a pyro is a higher muzzle velocity cannon that shoots exploding rounds.If it's a handheld device, how many fingers are you willing to sacrifice if your pyro detonates and the cell has swollen up and jammed?There are ways to mitigate the effect of an exploding LiIon cell, adding explosives is not a good one.

author: CJay
author_rank: Super Contributor
timestamp: June 05, 2018, 07:53:43 pm
content: Quote from: metrologist on June 05, 2018, 07:47:57 pm

author: kripton2035
author_rank: Super Contributor
timestamp: June 05, 2018, 07:59:22 pm
content: lithium batteries can inflate 2-5x times their original size, when they come to end of life.then, if their package is too thin, it breaks and they can enter in contact with oxygen, and there they can catch fire.it is the same that happens if you handle them with not enough care, you can damage the package, make a small hole , and it can catch fire there.this is another failure mode that can happens, not only with a too beefy charger.also if you short them with a (big) wire, they can catch fire and melt quite fast.

author: f4eru
author_rank: Super Contributor
timestamp: June 05, 2018, 08:22:53 pm
content: QuoteThat's only for pouch type cellsPerhaps we could modify the pouches so they take a NACA airfoil profile when being ejected of the pack by their high pressure relief valve, transforming the pouch cell in a rocket.All that's left to do is controlling this rocket.An exemple of many pouch cells failing and being ejected can be seen in this video :Don't worry, this was a worst case test, with all cells ejecting. The crew is fine, the plane only had to restart the APU to replace the power from the missing battery.

author: janoc
author_rank: Super Contributor
timestamp: June 05, 2018, 09:04:25 pm
content: Quote from: CopperCone on June 05, 2018, 07:11:39 pmAnd what you don't realize is that all that stuff is heavily regulated, requiring various safety devices and procedures to be put in place before anyone would even consider adding as much as an explosive bolt to something.Seriously, this kind of idea may have worked in StarTrek (warp core ejection - and that wasn't using explosives!) but for a lithium battery it is completely absurd and potentially making a small fire hazard into a lethal projectile/shrapnel/explosion one.

author: CopperCone
author_rank: Super Contributor
timestamp: June 06, 2018, 12:59:11 am
content: don't have time to read the venom right now, but it looks like this might be an option that's more expensive then pyrotechnics but some how more agreeable for whatever reason: (despite the fact that it vaporizes with the same energy as the few miligrams of black powder required)I don't see why you can't use a wire that vaporizes over a spring like this saw-stop

author: station240
author_rank: Unknown
timestamp: June 06, 2018, 03:42:26 am
content: Pretty obvious this is a troll post by OP.Trying to win a bet or something ?Talk of what the failure mode of (reused) lithium cells, seems a normal question.But adding thoughts on pyrotechnics and breakable connections to fire the cell out of the battery if it fails, is just insane.If you can afford all this extra nonsense, you can afford new cells.

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 07, 2018, 07:29:18 pm
content: Keep it simple with a piece of iron pipe capped securely on one end and duct taped over on the other. The idea being that if it overpressurizes, it will fail in a predictable manner.

author: stj
author_rank: Super Contributor
timestamp: September 24, 2018, 04:26:29 pm
content: this is all amusing, but i dont think coppercone has said what type of lithium he has in mind or if they will be charged stand-alone, or in the application-equipment.i use salvaged lithiums (18650's)i charge them to 3.7v at 20ma fixed current - yes it's slow.then leave them 24 hours,them meter the voltage to check if they are internally leaky.then charge them fully at 500mAH,then another 24hours,then a final meter check.i always charge them in an occupied room, and the charger sits on an old pc, so i have a big metal plate under the charger if it burns.not had a problem yet, but i'm ready if it happens.now if we are talking lipo pouches, that's a different matter - i wont touch those things!

author: james_s
author_rank: Super Contributor
timestamp: September 25, 2018, 04:17:15 am
content: LiPo pouches are fine, I have dozens of them from tiny little gumsticks up to 3S 3300 packs. I've done many hundreds of charge cycles, no issues whatsoever. They're no different than a jug of gasoline/petrol, when used carelessly both can and do cause serious fires. When used properly, both are quite safe.