Car fire started by button cell battery? - Page 1
Forum section: electronics / general

author: tchicago
author_rank: Regular Contributor
timestamp: August 28, 2024, 02:31:19 pm
content: There was a report of a car fire that started from "button battery". Sounds really doubtful to mehttps://www.usatoday.com/story/news/nation/2024/08/27/childrens-book-minivan-fire-north-carolina/74974685007/Would be interesting if Dave can experiment with various kinds of coin / button cells to see if there is enough energy in them to start a fire.

author: Phil1977
author_rank: Frequent Contributor
timestamp: August 28, 2024, 02:50:09 pm
content: As always it depends...The rechargeable LIR2032 button cells can easily let a thin wire burn.But how are the chances that a thin wire starts a car fire? Of course, if it´s embedded in thin paper or anything really easily inflammable then it works out. But if the resistance of the wire is too low or too high then nothing happens at all.On the other hand, if you go to a also not uncommon 2450 size, things get more dangerous.

author: temperance
author_rank: Super Contributor
timestamp: August 28, 2024, 04:35:45 pm
content: I don't know and never tried what would happen if you try charging a non rechargeable lithium coin cell. But I do know that UL has strict requirements on charging non rechargeable lithium cells.

author: AVGresponding
author_rank: Super Contributor
timestamp: August 28, 2024, 05:03:31 pm
content: The article is confusing in that it talks about a "button battery" in the header and the third para, but then goes on to refer to it as a "lithium battery", then mentions advice from the US Fire Administration about "lithium-ion batteries".I suspect it was actually a lithium pouch cell, Li-ion or Li-polymer.Quote from: temperance on August 28, 2024, 04:35:45 pmIt will explode, but it will do it in the charger while being charged, not afterwards in the appliance.

author: edavid
author_rank: Super Contributor
timestamp: August 28, 2024, 05:30:51 pm
content: Quote from: AVGresponding on August 28, 2024, 05:03:31 pmNo, these books are powered by disposable batteries.The one that was mentioned in the article uses 3 AG13/LR44 (alkaline) cells. I've never heard of those catching fire or causing a fire (but I've never tried shorting one). Of course, the fire department unhelpfully did not say if that's the actual book that was found.

author: SiliconWizard
author_rank: Super Contributor
timestamp: August 28, 2024, 08:47:01 pm
content: Never heard of a small primary Lithium cell catching fire either. Sounds fishy if that's what is claimed.

author: AVGresponding
author_rank: Super Contributor
timestamp: August 29, 2024, 11:09:38 am
content: Quote from: edavid on August 28, 2024, 05:30:51 pmThey don't, the internal cell resistance is far too high for that kind of current. It's a relatively cheap and easy experiment to do yourself.There aren't any primary cells, whether lithium, silver oxide, or alkaline, of this genaral size, that are capable of starting a fire by means of a short circuit. Any wire small enough to be fused by the currents these can produce would be too tiny and have too little thermal mass and therefore energy to ignite anything besides possibly black powder or something similar. Certainly not plastic tat cases.While you can get these cells to explode by applying unreasonable V and I to them, these explosions are small, and again, of insufficient energy to ignite adjacent materials other than those that are designed to be ignited easily.

author: themadhippy
author_rank: Super Contributor
timestamp: August 29, 2024, 11:37:38 am
content: Quotetry a bit of wire wool,makes a for great 1 use emergency cigarette lighter

author: ejeffrey
author_rank: Super Contributor
timestamp: August 29, 2024, 01:52:42 pm
content: It's really hard to tell. It would require very particular circumstances, such as a thin metal shaving left over from manufacturing accidentally shorting out, and happening to be in the place to catch the paper on fire. It's theoretically possible but extremely rare. On the other hand, there are probably hundreds of millions of these type of books and out there so an extremely rare failure mode might be observed.On the other hand, there is no further explanation of what the fire department found or what other possible ignition sources exist. Given that we had fire departments sharing photos of car fires warning that hand sanitizer could spontaneous catch fire that turned out to be just made up stories, I don't put too much faith in their claims unless they make a formal investigation and release a report with all of the details.

author: AVGresponding
author_rank: Super Contributor
timestamp: August 29, 2024, 02:00:43 pm
content: Quote from: themadhippy on August 29, 2024, 11:37:38 amA well known ignition material. You need the finer stuff for this to work with a button cell, and I don't ever recall seeing any products that had a wad of steel/magnesium/etc wool inserted that weren'tspecifically intendedto be an ignitor.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 29, 2024, 02:07:38 pm
content: Quote from: AVGresponding on August 29, 2024, 11:09:38 amByshort circuit, probably not, but do we know there was a short circuit (near-zero resistance) involved? I'm quite sure that if my life depended on it, I could demonstrate setting something on fire with a small button cell. With zero-ohm load (short circuit), total power dissipation is indeed at highest, but it's fully on internal ESR, and thus dissipated by the full cell surface area (and slowed down by cell's thermal mass) - it won't be easy to get it hot enough.But try with non-zero load, say load resistance matching ESR which produces maximum possible power to theexternal load. Now make the external load tiny, say a small piece of nichrome wire, and wrap it around something very flammable, and maybe you can have a fire.

author: themadhippy
author_rank: Super Contributor
timestamp: August 29, 2024, 02:45:14 pm
content: Quotebrillo pads? or maybe one of the parents was a plumber or painter.

author: BrokenYugo
author_rank: Super Contributor
timestamp: August 29, 2024, 03:43:16 pm
content: I'm almost curious enough to get out 3x LR44 and some low value cheapo resistors, it's going to be very difficult to start a fire with ~600mW* in a few seconds with no serious accelerant but I'd assume it's possible.*https://www.duracell.com/wp-content/uploads/2023/07/LR44_Datasheet.pdfsee 5 Ohms line on last page.That said I think it's more likely something else started the fire and everyone blamed the book.

author: BrianHG
author_rank: Super Contributor
timestamp: August 29, 2024, 04:35:05 pm
content: Quote from: temperance on August 28, 2024, 04:35:45 pmNothing. After a charge for 24h at ~4v, you literally need to short them out for a few seconds before they will give you something like 2 additional months of capacity compared to the original 5+ years.If the cell isn't designed to be charged, it probably wont be able to be charged.1.5v button cells charge better. They will last ~1 year after a 1.8v charge at 24h.Quote from: AVGresponding on August 28, 2024, 05:03:31 pmWrong, I tried it. Nothing happens. The battery ERS is already too high once drained and it just goes even higher, way too high for any meaningful current required to make it explode.

author: thm_w
author_rank: Super Contributor
timestamp: August 29, 2024, 09:43:24 pm
content: There are more photos here:https://ca.news.yahoo.com/childrens-book-blame-fire-inside-145911725.htmlIt seems unlikely that whatever started the fire would be identifiable at all. Look at how much of the seat burned.There are also paper books under the carseat itself? Or were those on top and the fire started at the bottom, hard to tell.

author: coppercone2
author_rank: Super Contributor
timestamp: August 29, 2024, 10:03:17 pm
content: cow says boomHere is the facts of these cheap devices (button cell devices are the cheapest of the cheap, usually there is a form of respect for even AAA batteries, i.e. battery contacts)1) the contacts are mega shit, often a point contact with a cell. Guess what happens if that bends, it gets jammed between the cell pos and negative. They just stick a sharp bit of spring wire out of a hole and jam it into the cell. Its whatever the designer "figured" might work because its just 'pressure'. With a better device they try to make some 'leaf' contacts that are marginally less shady. Usually the alloy is crap for a spring, and it can fracture off. Then you have a thin piece of metal rattling around in the battery cavity waiting to get stuck in the crevice between positive and negative on the crimp seal. Try a bend test on a legitimate vs alibaba battery holder and you will see what difference the choice of alloy and hardening does. I have seen 300% difference in durability.... and thats for a engineered battery holder. If they crack some shit out on a spring making machine good luck. Oh yeah and this mystery contact is going to go get mystery plated afterwards too (maybe)2) the wiring is counterfeit. Expect copper clad aluminum or copper clad copper (electroplated) or copper clad steel. Usually wire resistance is 3-6x the resistance of a equivalent copper wire (electrical copper). If you strip it and flick it, it s basically like spring wire. Often might not have wire, just "bus bars" made of whatever (steel).3) the switches are jury rigged from stampings with no ingress protection etc. Likely to get dirty and over heat and they can spark too.. many battery devices suffer from these bullshit switches. they get dirty and run hot and melt easily. Steel stampings that press into each other = switch. Forget about a spring load or contact rivets or anything half decent.4) for LR44 and such, the battery cavity is often creative and ambiguous. I have some flashlights that use it, you can put 3, 4 or even 5 cells into it. It will work with all configurations (I expect when its over loaded that LED is cooking but the cells are pretty weak). They don't have a cavity sometimes, its just how much can you fit between some creative stamped metal with maybe a spring. They could engineer a stop into the battery holder, so you can't jam as many cells as you feel like, and are limited to the correct amount, though likely this will be a piece of shit plastic post that breaks off.5) what reverse insertion protection? A good cavity will be strong, add reverse insertion protection and also have a solid stop to prevent you from adding as many cells as you think. When you start requiring more then 2 cells, the springs are so compliant you can end up fitting 3-4 in there. At 4 you deform it and might notice you did it wrong, maybe. I am pretty sure I can get 6 LR44's into this "advertisement" flashlight I found. I wonder if the die is going to glow like a ciggarette lighter.Not to say there is not decent LR44 devices, I have seen some with solid cavities, nice contacts, good switches etc. But usually these things cost like $1

author: MK14
author_rank: Super Contributor
timestamp: August 29, 2024, 10:10:38 pm
content: Could the button cell be incorrectly manufactured, and end up with raw potassium metal or something, which can then easily catch on fire, if it gets wet?Maybe something acted as a magnifying glass, such as a water filled bottle, in bright sunlight, could have ignited the pile of paper books (at least one seems to have mentioned, in this thread).What about the car wiring, between the boot, and front of car, could it have shorted out, under the rear seat?If anyone smokes in the car, they could have put it (when still lit), inadvertently, by that child seat, when removing the child, when leaving the car.

author: coppercone2
author_rank: Super Contributor
timestamp: August 29, 2024, 10:14:15 pm
content: the metal will rather quickly oxidize in the air and the cell will smell if the seal is bad. Its more likely they are too cheap to replace and fix the dies on the presses and it does a bad seal... you typically don't have lithium ribbon sticking of a cell, i never seen it get that bad.

author: MK14
author_rank: Super Contributor
timestamp: August 29, 2024, 10:39:37 pm
content: Quote from: coppercone2 on August 29, 2024, 10:14:15 pmMaybe a battery pack (USB high capacity), or something (electronic with lithium batteries), in the rumored stuff/junk, below the car seat.Here is an example, of a somewhat small battery pack (USB), getting damaged and causing a fire.

author: Someone
author_rank: Super Contributor
timestamp: August 29, 2024, 10:45:43 pm
content: Quote from: AVGresponding on August 29, 2024, 11:09:38 amSaft make primary lithiums with rated discharge current (pulsed) greater than 20A. That would easily start a fire, so you'll need to walk back the bold claim of all primary lithium to something significantly smaller like: consumer button cells.Even energizer will happily point out the significant short circuit currents available in their consumer AA's:https://data.energizer.com/pdfs/lithiuml91l92_appman.pdfA few dozen joules? yep that's some significant hazard.

author: coppercone2
author_rank: Super Contributor
timestamp: August 29, 2024, 10:50:25 pm
content: they have PTC in primary lithium cells for energizerI had one that shorted out on me recently, it was 70C for a good hour when I left it outside. It was in a stupid mouse that uses 2 parallel batteries. Don't use them in parallel. However, it did not rupture, rather scary though.Usually the problem is when the battery is drained too low. If you have 3 good battery and 1 dead battery, the device will keep drawing current through the dead battery until something goes for series.... because they have higher voltage, the cutoff will not engage in the device to stop drawing current at the normal point where batteries go bad (in smarter circuits). In parallel I am not sure what happened exactly, but obviously it got a internal short.That is why its so important not to mix and match cells to try to get things to work. When you put them in a device it should be cradle to grave, not retrofitting. I think its safe to use those partially depleted batteries in a simple device that only uses 1 cell though. Its all nonlienar so you can't get great results even if you try to match them by measuring voltage... sorry cheap skates... its more complicated then rolling up a tube of tooth paste.

author: Someone
author_rank: Super Contributor
timestamp: August 29, 2024, 10:58:16 pm
content: Quote from: coppercone2 on August 29, 2024, 10:50:25 pmYes, as they happily explain in their public documents, such as the one I linked above. That doesn't stop it being possible to pull dozens of joules out of the battery in a short timeframe, which can be more than enough to start a fire.

author: coppercone2
author_rank: Super Contributor
timestamp: August 29, 2024, 11:00:12 pm
content: that is their main use, high current camera flash charging and stuff. Thats what these cells were all used for up until the 2000's.Its not appropriate to put energizer lithium into a cheap piece of crap device like my mouse. It used to go into hundreds of dollars cameras.They kinda redid their marketing without changing the design too much, since AA flash cams died... keep the lines going.I think the main problem in general with all this stuff is that a mechanical engineer does the electronics because its simple component wise and the circuit ends up being literal crap. Plus its all avante garde "circuits", that is plastic on metal, press fit, using mechanical components unrated for electricity, for electricity, 'figured' stampings, etc. I saw art students doing a electronic lighting fixture and I thought wow, thats how its designed! (jam foil into a wedge to make a 'interconnect"). And when you add malfunctioning assembly lines and realistic design tolerances to the equation, it ends up being really fucking bad. ALso, atrocious solderingIs putting a steel wire into a hole on a nickel strip and then jamming it full of plastic considered a good interconnect?

author: Someone
author_rank: Super Contributor
timestamp: August 29, 2024, 11:31:33 pm
content: Quote from: coppercone2 on August 29, 2024, 11:00:12 pmWhy not in cheaper/smaller devices? I put those buggers in anything that needs a long shelf/off lifetime such as rarely used wireless keyboard, mouse, remotes.You post that it has a PTC is moot, because a) no-one is suggesting it doesn't, but more importantly b) that PTC does not prevent fire in all circumstances (only some circumstances). Those energizer lithium batteries are capable of making a fire.

author: coppercone2
author_rank: Super Contributor
timestamp: August 29, 2024, 11:35:38 pm
content: and what point are you making, because a regular alkaline battery can start a fire too. their comparable because of the PTCthey even have that trick where you use a gum wrapper to make a AA battery work with a smaller cell. wow that can be a bad idea huh

author: BrianHG
author_rank: Super Contributor
timestamp: August 30, 2024, 12:02:20 am
content: Nile red opens an AA lithium battery: (Yes, it burst into flames and even explodes when he drops it in water...)https://www.youtube.com/shorts/yGDkiUAwxRs

author: AVGresponding
author_rank: Super Contributor
timestamp: August 30, 2024, 09:29:05 am
content: Quote from: Someone on August 29, 2024, 10:45:43 pmRead what Iactuallywrote.

author: AVGresponding
author_rank: Super Contributor
timestamp: August 30, 2024, 09:57:59 am
content: Most of what has been posted since my post reply #9 has NO relevance to this subject.Siwastija mentions "a small piece of nichrome wire, and wrap it around something very flammable, and maybe you can have a fire."How is this relevant? This scenario is a deliberate attempt to cause a fire, not an accident. You think these e-books have nichrome wire wrapped around flammable materials in them?!?Other people talk about large, specialist primary cells or AA's or AAA's. None of this has ANY relevance to button/coin cells. The internal cell resistance and capacity is different by orders of magnitude.

author: Someone
author_rank: Super Contributor
timestamp: August 30, 2024, 10:33:54 am
content: Quote from: AVGresponding on August 30, 2024, 09:29:05 amReading would be easier if you didn't use a low contrast font colour....Quote from: AVGresponding on August 29, 2024, 11:09:38 am3 x LR44 or AG13, so a 1/3 to a 1/4 of an AA which is still in the plausible range given the aboveconsumerAA's have more than enough energy to produce fire (despite protection).

author: MK14
author_rank: Super Contributor
timestamp: August 30, 2024, 10:41:39 am
content: It seems that the experts are saying those AG13 batteries, can be a fire hazard.From the link below:QuoteSource of picture (publishers of the book, involved with this fire incident):https://www.wbtv.com/2024/08/28/batteries-childrens-book-that-caused-burke-county-minivan-fire-arent-lithium-publisher-says/

author: AVGresponding
author_rank: Super Contributor
timestamp: August 30, 2024, 11:42:35 am
content: Quote from: Someone on August 30, 2024, 10:33:54 amPeople read what they want to read and disregard the rest.Quote from: Someone on August 30, 2024, 10:33:54 am"X can start a fire, so 1/4-1/3X can also start a fire". This is nonsensical.Quote from: MK14 on August 30, 2024, 10:41:39 amWhat experts? Give links to published, peer reviewed research.

author: MK14
author_rank: Super Contributor
timestamp: August 30, 2024, 12:08:01 pm
content: Quote from: AVGresponding on August 30, 2024, 11:42:35 amWell that linked to article, seems to also say, something on the lines of, they are continuing to investigate the cause of the fire.So, I'm happy that the American system, has chosen appropriate expert(s), and are professionally investigating the cause of the fire.If on the other hand, that is not good enough for others, such as yourself. Then feel free to reach out to the American authorities, and/or other people involved, in this case, and argue the point with them.I'd suggest at least giving them the time to complete their work, and publish or announce their results, rather than hassling them, at such an early stage of their inquiries.

author: MK14
author_rank: Super Contributor
timestamp: August 30, 2024, 12:25:18 pm
content: I have a new, super wild, possible theory, of what might have happened. Partly based, on something I read on the internet.The battery set ran out, then instead of replacing all three AG13 batteries, they tried replacing ONLY 2 of them, leaving one old cell in place. The device (book) appeared to work ok, so they stopped adding any more batteries (or had run out of new ones). Alternatively, a battery was the wrong way round, assuming it could still make contact, with the battery terminals, in that case? (off-hand, I don't think it would, but maybe it had flimsy battery contacts, which can connect in both orientations?)The run down, old remaining AG13 cell, then became super discharged, and within its sealed cell, built up a big pressure of gases (possibly Hydrogen).At some point, the gas pressure was too much for the sealed and expired AG13 battery, which then exploded. The release of a high percentage of compressed Hydrogen gas, then found an ignition source (possibly via one of the remaining two good batteries, during the explosion), which then ignited stuff, causing the fire.

author: tszaboo
author_rank: Super Contributor
timestamp: August 30, 2024, 02:34:15 pm
content: Quote from: AVGresponding on August 30, 2024, 11:42:35 amI cannot find UN 38.1 documents for AG13 batteries after a quick search. That would describe the short circuit conditions of the batteryNor ESR. I found one claim that it's ~5 Ohm, so let's work with that.4.5V 15 Ohm source means that there is 337mW power available for the electronics. I can make electronics safe with this much power, it's very low. Meaning I can design you eg. a sensor that's mounted inside a gas tank, and it's going to be safe. But let's work from the other way.It's a children book with built in battery. Paper's autoignition temperature is ~230C. Probably they just chucked the electronics in between paper pieces, with some loose wires, and it's made from single side phenol PCB. And made a mistake while assembling it, wire is not properly isolated. Take a small part, like an 0402 resistor, apply 300mW to it. It goes from 70C to 150C with 63mW, about 1.2K/mW, suddenly your part is over 400 Celsius hot, enough to set paper on fire.

author: tom66
author_rank: Super Contributor
timestamp: August 30, 2024, 02:46:44 pm
content: Quote from: tszaboo on August 30, 2024, 02:34:15 pmYou are neglecting the thermal loading of the paper on the resistor. I would be surprised if the paper could itself get to 400C in a local spot to support combustion with that resistor alone.

author: Andy Chee
author_rank: Super Contributor
timestamp: August 30, 2024, 03:04:03 pm
content: I would've thought this battery fire would've been relatively simple to replicate by someone on YouTube by now.

author: tszaboo
author_rank: Super Contributor
timestamp: August 30, 2024, 03:10:43 pm
content: Quote from: tom66 on August 30, 2024, 02:46:44 pmI'm ignoring a lot of things here, because not many things are known about the construction or the battery itself.I'm only pointing it out that it's not impossible.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 30, 2024, 03:28:51 pm
content: I just measured the short-circuit current of a new LR44 at 0.7A - not totally implausaible that this ( or 2-3 of them) could start a fire

author: 55pilot
author_rank: Newbie
timestamp: August 30, 2024, 05:39:35 pm
content: Quote from: mikeselectricstuff on August 30, 2024, 03:28:51 pmThat is an ESR of about 2 Ohms, which is almost exactly what the graph on Page 2 of the Duracell spec, posted earlier, predicts.Some people are incorrectly quoting the graph as showing an ESR of 5 Ohms. What that graph is actually showing is the voltage when loaded by various resistors, the smallest of which is 5 Ohms. The 0.45V drop across the ESR and 1.1V across the 5 Ohm indicates an ESR of about 2 Ohms.

author: tszaboo
author_rank: Super Contributor
timestamp: August 30, 2024, 05:49:39 pm
content: Quote from: 55pilot on August 30, 2024, 05:39:35 pmWhat datasheet?

author: MK14
author_rank: Super Contributor
timestamp: August 30, 2024, 05:53:25 pm
content: Over on a Chemistry related forum, there seem to be a large number of reports, of these types of batteries, exploding. There are so many reports by different posters, it makes me wonder if there is something to it.So, if as I mentioned earlier, the gas is mainly Hydrogen (I'm NOT sure), that could explain a fire, as Hydrogen, can very easily ignite and then potentially set fire to stuff.I discount one of the reports, where the battery exploded when they were soldering to it.Here:https://www.reddit.com/r/chemistry/comments/a63dy3/lr44_just_exploded_2018/

author: Siwastaja
author_rank: Super Contributor
timestamp: August 30, 2024, 06:14:19 pm
content: Quote from: tszaboo on August 30, 2024, 03:10:43 pmI agree. It's entirely possible that the button cell batteries are the cause, but it is more probable that the cause is actually something else.It would be most interesting to hear about why anyone thinks the cause is the battery and not something else. Do they have any basis for it, or is it just an assumption "battery was present, and batteries are dangerous, therefore must have been the battery"?

author: Phil1977
author_rank: Frequent Contributor
timestamp: August 30, 2024, 07:02:47 pm
content: Quote from: MK14 on August 30, 2024, 05:53:25 pmInteresting reports... But these batteries seem to have exploded without fire, probably they just build up pressure until the housing popped.Hydrogen is usually not a big danger - yes it easily ignites but it also diffuses away from its source in no time. And if a small volume of hydrogen burns then it´s just a very short flash, very hard to imagine that this lights up a book. Lead acid batteries generate quite a large amount of hydrogen/oxygen mixture, and its danger is much more spraying around the sulphuric acid than setting anything on fire.I think its not common but also not impossible that an overloaded 0402 resistor wrapped in paper sets something on fire. Heated paper really is a good fire starter.

author: MK14
author_rank: Super Contributor
timestamp: August 30, 2024, 07:23:02 pm
content: Quote from: Phil1977 on August 30, 2024, 07:02:47 pmThanks, that is a very thoughtful and good post!Unfortunately, I think we are (or at least me), like back seat drivers, or it is all too easy to comment, when sitting at ones couch.If any entity gets serious about investigating this fire incident. They would need to process all the available evidence and information.As regards the batteries, being involved.There are lots of possible ways (many already mentioned in this thread). Such as electrical over-heating, setting fire to something, a Hydrogen explosion (as you said, the vast bulk of the time, it does not set anything on fire, but there is a small or tiny risk, that maybe it could or did), even theories that the same Chinese battery factory, handles (makes) Lithium batteries as well, and such material ended up in the fire starting battery cells.There are also many other causes of car fires, including its electrical wiring, fuel leaks catching fire, a fire underneath the car for some reason (almost certainly would have been noticed and caused different fire effects), the owners setting the car on fire for reasons (such as insurance fraud), etc.Hopefully and if necessary. The investigators can get any research professionally done by experts, as necessary, if they deem it necessary.As regards this thread, my gut feeling (I could easily be wrong), LR44 batteries are too weak and low capacity, electrically speaking, to readily (ignoring a super-rare accident), heat stuff up (or itself), enough to pose a serious fire risk.On the other hand, (as already mentioned), 700 milliamps, is more than I was expecting, from such a tiny cell, especially with it being Alkaline. Even much bigger Alkaline cells, don't seem to have anything like as high short-circuit currents (IIRC, I managed to get around 5 .. 10 Amps, from a fresh Alkaline C cell, of decent brand), compared to most rechargeable battery types, such as Lead-acid batteries, which give out crazy amounts of current, if necessary.EDIT: Much editing, lots of typos and made shorter.

author: MK14
author_rank: Super Contributor
timestamp: August 30, 2024, 07:59:32 pm
content: Here (at end of the post) is a tear-down and demonstration video, of around 6.5 minutes long, of what seems to be a similar type of electronic button/sound toddler book.Apart from the possibility of the somewhat flimsy looking metal battery tabs, perhaps being able to short out, the battery(s). I can't see any immediate/easy fire risk.The only real component, is a black epoxy blob style chip, on a PCB, no resistors, just a speaker and the buttons, on some kind of flexible PCB style setup. Maybe a small decoupling capacitor, I didn't see it, but it was on the hand drawn schematic, later in the video.But it is possible, the actual book, was significantly different inside, I don't know.

author: tszaboo
author_rank: Super Contributor
timestamp: August 30, 2024, 08:10:44 pm
content: Quote from: MK14 on August 30, 2024, 07:59:32 pmHint: One of them is black, the other red. They go directly to the battery.Also these things get chewed on, thrown around, and who knows what else.

author: MK14
author_rank: Super Contributor
timestamp: August 30, 2024, 08:29:18 pm
content: Quote from: tszaboo on August 30, 2024, 08:10:44 pmBut they would have to break through the plastic case, break the insulation of both wires, then the wires would need to contact each other. Even then, I'm not sure such a modest current (maybe 0.7 Amps), could readily cause a fire.On the other hand, a 200 milliamp bulb, at perhaps 4.5 Volts, can glow almost white hot, inside its sealed glass envelope.

author: SiliconWizard
author_rank: Super Contributor
timestamp: August 30, 2024, 08:40:16 pm
content: I haven't followed the latest posts but there seems to be a lot of guesses and maybes.In the end, I am unsure of exactly what type of "button cell battery" this is all about.I have personally never seen or directly heard of a standard Lithium primary button cell battery exploding.But - I certainly have for Zn-air batteries (the ones used in particular in hearind aids) which are a completely different chemistry and hold a lot more capacity too.

author: thm_w
author_rank: Super Contributor
timestamp: August 30, 2024, 11:11:19 pm
content: Quote from: SiliconWizard on August 30, 2024, 08:40:16 pmAG13/LR44 as was explained above.QuoteThey absolutely do and I've mentioned it here a few times, I've seen it myself twice on major brands (Renata). Its just incredibly uncommon on quality brands (this was 2 out of 10,000+ cells).https://www.google.com/search?q=cr2032+blown

author: Someone
author_rank: Super Contributor
timestamp: August 30, 2024, 11:28:42 pm
content: Quote from: AVGresponding on August 30, 2024, 11:42:35 amThat would be engineering, on you know, an engineering forum where you are choosing to post. How much energy can a AA dump? dozens of joules, is 1/3 or a 1/4 of that enough to make flames? yes.Perhaps you'd like to claim maths is forbidden?

author: 55pilot
author_rank: Newbie
timestamp: August 31, 2024, 02:44:42 am
content: Quote from: tszaboo on August 30, 2024, 05:49:39 pmFrom reply #13 above:https://www.duracell.com/wp-content/uploads/2023/07/LR44_Datasheet.pdf

author: IanB
author_rank: Super Contributor
timestamp: August 31, 2024, 03:02:41 am
content: Quote from: AVGresponding on August 30, 2024, 11:42:35 amAVGresponding does not wish their posts to be read. I comply accordingly, and skip over all posts in that funny colour and font without looking at them.

author: coppercone2
author_rank: Super Contributor
timestamp: August 31, 2024, 03:04:41 am
content: you know if a battery cover falls off and a hamburger aluminized wrapper gets in there I can see it causing a problem

author: amyk
author_rank: Super Contributor
timestamp: August 31, 2024, 06:46:55 am
content: Quote from: tom66 on August 30, 2024, 02:46:44 pmDon't forget that combustion also requires oxygen. Also, in my experience regular book paper is difficult to ignite with things other than an actual flame, especially if the heat source is small; it tends to just carbonise instead.On the other hand, if the paper was soaked in something like ethanol-based hand sanitiser...

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 31, 2024, 08:23:36 am
content: Quote from: MK14 on August 30, 2024, 08:29:18 pmOr just a strand of a stripped end shorting at the PCB end. These wires will be crazy thin to start with.

author: tszaboo
author_rank: Super Contributor
timestamp: August 31, 2024, 08:27:21 am
content: Quote from: 55pilot on August 31, 2024, 02:44:42 amThank you, I was perfectly able to read the datasheet. It's a datasheet for a LR44 battery, while the article states the book has an AG13 battery in it. Which is different chemistry.

author: AVGresponding
author_rank: Super Contributor
timestamp: August 31, 2024, 09:41:56 am
content: Quote from: Someone on August 30, 2024, 11:28:42 pmI'd like to claim that you haven't proved it, you've just guessed at it. That's not engineering.Quote from: tszaboo on August 31, 2024, 08:27:21 amIn counter-argument, they are the same size, and the average person is likely to replace dead ones with the cheapest option they find on/in Amazon/ebay/a local shop, so we don't know if the ones in the e-book in the fire were alkaline or silver oxide.Quote from: mikeselectricstuff on August 30, 2024, 03:28:51 pmOver what duration?

author: Siwastaja
author_rank: Super Contributor
timestamp: August 31, 2024, 10:21:58 am
content: Quote from: AVGresponding on August 31, 2024, 09:41:56 amWe can guess that Mike did not use an oscilloscope and pulse generator for the test, but instead just shorted the battery with a multimeter and looked at the screen. Which makes it in ~1 second timescale where the AC (capacitor) effects of the cell are irrelevant. Actually cells heating up reduces their ESR so current would even rise higher for some time - seconds, tens of seconds(?)0.7A * 4.5V = 3.15W and this in timescales of at least tens of seconds.I do agree that terms LR44 and AG13 are widely and synonymously (even if incorrectly) used to describe the form factor, most probably the chemistry would be either Alkaline or some of the lower-voltage primary lithiums like lithium iron disulfide.

author: tooki
author_rank: Super Contributor
timestamp: August 31, 2024, 10:29:37 am
content: Quote from: AVGresponding on August 30, 2024, 11:42:35 amI’ve been asking you for years to stop using your stupid custom font and color, which reduces legibility by overriding the defaults. (Which means that when the user adjusts their browser to make the default readable, your settings override it to an extent.)I’m glad someone else has called you out on this nonsense. I don’t understand why you can’t just leave the damned default text formatting. (In the past you’ve said it’s to improve legibility, but it does the exact opposite.)

author: Someone
author_rank: Super Contributor
timestamp: August 31, 2024, 11:20:43 am
content: Quote from: AVGresponding on August 31, 2024, 09:41:56 amI checked some standards for safety limits on energy and some battery data sheets, and presented the maths. Engineering building upon the established methods and standards. You think 10 joules cannot start a fire and is benign? Perhaps show us the supporting documentation that says so.

author: MK14
author_rank: Super Contributor
timestamp: August 31, 2024, 11:38:56 am
content: Quote from: mikeselectricstuff on August 31, 2024, 08:23:36 amOn reflection, I agree with you. That is a very good point. That sounds very plausible.Now, is that 0.7 Amp back of envelope, ball-park measurement, enough to potentially cause a fire?Looking into, the minimum current needed to cause an electrical fire, finds the following, professional/academic looking, interesting (free/open) paper, on the subject:https://www.mdpi.com/2571-6255/5/6/201Which seems to mention (but it refers to another person or source of information), that as little as 4.5 Volts (coincidentally the nominal battery voltage, of this threads situation, 3 x 1.5 Volt AG13 batteries = 4.5 Volts), and 300 milliamps (which seems plausible, since you already measured a short-circuit current of 0.7 Amps), may be able to cause sparking (maybe even arcing), and hence be an ignition/fire risk.Also, on reflection, I've realized that my assumption, that the wires were pure copper, plastic insulated ones. Could be wrong. The Chinese (other countries could have been just as bad), may have cheaped out on these wires, possibly being a different metal, or copper coated metal of some sort.Hence the wires, could, unlike copper, have higher resistance, be more susceptible to breaking (brittle, hence sparking/arcing etc), possibly even being flammable (aluminum comes to mind).So, I now think, that it has become more plausible, that those 3 x AG13's (or LR44's, if that is what they were replaced with), may be able to be the cause of that fire.Practical demonstration. This video, less than 2 minutes long (if inpatient, at around 38 seconds into the video, it is shown), seems to show a low voltage and current, set fire to the ends of some thin wires. I'm not sure of what PP3 battery type they were using, or how much more current, it can make, as a result.

author: Someone
author_rank: Super Contributor
timestamp: August 31, 2024, 12:24:44 pm
content: Quote from: MK14 on August 31, 2024, 11:38:56 amSure is, having some time to play around I tested this directly.4.5V 0.7A supply, connected to a 10ohm resistor with very fine copper wires.0402 glowed bright red and let off a puff of smoke as it desoldered itself, still measures in the ballpark0805 glowed bright red and let off a puff of smoke (the characteristic ceramic/resistor smell) but stayed attached much longer.SET PAPER ON FIREcase closed

author: Someone
author_rank: Super Contributor
timestamp: August 31, 2024, 12:29:31 pm
content: Only needed 300mA

author: Psi
author_rank: Super Contributor
timestamp: August 31, 2024, 12:51:57 pm
content: You don't need much energy to start a fire if you have the right conditions.I can totally see a toy made of flammable plastic catching fire from coin cells.The size of the hot spot can be very small if everything is aligned perfectly.Usually you wouldn't get that alignment which is why this sort of fire from coil cells is so rare.You'd need exactly the right placement to get the tiny hot spot to catch the plastic alight combined with enough air through the inside to keep the fire growing.Maybe a tiny sliver of 'flash' that's against a component on the PCB right next to a speaker grill that's full of holes. The sliver catches on fire, and that manages to couple to the plastic between all the holes in the speaker and that spreads to the entire device.

author: Monkeh
author_rank: Super Contributor
timestamp: August 31, 2024, 01:26:08 pm
content: Quote from: tszaboo on August 31, 2024, 08:27:21 amLR44 and AG13 are the same chemistry - don't get confused with the silver-oxide version.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 31, 2024, 01:32:44 pm
content: For example, manufacturer might have decided to save $0.001 each by specifying any plastic for injection molding, instead of some UL94 (or whatever, I don't remember the standards that well) rated material. It is also well possible that the relevant legal standards allow doing this because they consider available power level small enough. (See PIS (potential ignition source) and their classifications based on available power.)But as Someone demonstrated, even power levels below such requirements pose fire risks, just that the risk is probably smaller but still non-zero. So even if you have a totally standard compliant, legal device, a "freak accident" can still happen, that's life.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 31, 2024, 01:41:36 pm
content: Quote from: Someone on August 31, 2024, 12:24:44 pmWhere's the peer reviewed scientific publication???

author: IanB
author_rank: Super Contributor
timestamp: August 31, 2024, 01:42:04 pm
content: Quote from: Monkeh on August 31, 2024, 01:26:08 pmTechnically, the AG in AG13 should mean it is silver oxide composition (Ag being the chemical symbol for silver), however the market has ended up confusing them, and nearly all such cells of this size are now alkaline, presumably because the alkaline version is much cheaper to produce, and few products really need the special properties of silver oxide.Similarly, SR44 should be silver oxide and LR44 should be alkaline, but once more, marketing has confused the issue, and now you see "SR44 alkaline", which is daft.Nevertheless, silver oxide cells are never going to be found in consumable products like greetings cards or children's toys.

author: Someone
author_rank: Super Contributor
timestamp: August 31, 2024, 01:48:00 pm
content: Quote from: Siwastaja on August 31, 2024, 01:32:44 pmMy reading of standards and papers suggested 10 joules, I ended up in benign conditions with around 5 joules to flame (no forced air/oxygen or diethyl ether soaked paper needed). Always nice when the calculations arrive on target.

author: Monkeh
author_rank: Super Contributor
timestamp: August 31, 2024, 08:09:43 pm
content: Quote from: IanB on August 31, 2024, 01:42:04 pmExcept that's an SG13. I've never once seen an AG marked cell which is silver-oxide. Probably because the A stands for alkaline.. Technically, there is no standard (that I've ever seen) so you're simply assuming there's a correlation between two as good as random letters in a part number and a chemical element.

author: IanB
author_rank: Super Contributor
timestamp: August 31, 2024, 08:37:10 pm
content: Quote from: Monkeh on August 31, 2024, 08:09:43 pmYes, that seems true. The silver oxide cells are typically marked as 303, 357, or SR44. They will clearly say "silver oxide" on the packaging, rather than alkaline.There is a presumed standard that LR44 is alkaline, and SR44 is silver oxide.Here's an actual example of a silver oxide cell:https://www.duracell.com/en-us/product/coin-button-303357-battery/

author: Siwastaja
author_rank: Super Contributor
timestamp: September 01, 2024, 09:13:01 am
content: It's safest to treat these letter-number combinations as physical form factors only, and verify the chemistry separately from the packaging/datasheet.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: September 07, 2024, 09:31:15 pm
content: Just for a sanity check. Under fairly ideal conditions (dry fine tinder etc.) it is possible to start a fire with a single spark from a flint/steel combination. Assuming that the the grit of steel shaved off and heated is roughly a 0.5 mm cube, and giving it white hot temperature, the thermal energy in the spark is on the order of 0.5 joule. I suspect that these sparks are actually quite a bit smaller than 0.5 mm so the estimate is conservative.So any of these batteries contain plenty of energy to start a fire under ideal conditions. The question then devolves into two parts. Can the energy be extracted rapidly enough from the battery and how close to "ideal" conditions are realistic.The first question is half easy. From data sheets and the experiments reported here something on the order of a half watt can be extracted from these cells. How hot that can make something depends on the degree of thermal isolation. Getting from the ambient temperature up to the greater than 200 degree ignition temperature of common materials requires something like 300 deg/watt thermal isolation. High, but not impossible. And there is always the possibility that this is a two factor event. A cell phone, or baby bottle or something else had raised the ambient temperature to quite a bit above the nominal 23 C.The second question is harder to pin down. A list of materials with low ignition temperatures includes quite a few that might be found in such a device. What can't be easily determined is whether any of those likely candidates could have been in a configuration that allowed them to be heated enough to ignite. Anyone who has ever built fires knows that configuration is at least as important as composition.Rubber, Butadiene 155Diethyl ether 160Acetaldehyde 175Rubber, Styrene butadiene - Styrene 24% 182Rubber, Butyl 185Ehtyl cellulose 188Polybutane 188Rubber, Natural - Low refine 191Polypropylene 201Diesel 210Fuel Oil No.1 210Kerosine 210Jet A-1 fuel 210n-Heptane 215n-Octane 220Gun Cotton 221n-Hexane 225Polyethylene 226Polyethylene glycol 226Polystyrene 226Peat 227Wood, Pine - Powdered 232Paper 233Cyclohexane 245Nitro-glycerine 254Fuel Oil No.2 256n-Pentane 260Phosphorous - Amorphus 260Fuel Oil No.4 262Polymethyl methacrylate 265Cotton cloth 267Gasoline 280Rubber, Styrene butadiene - Styrene 85% 280Rifle Powder 288Nylon 11 289n-Pentene 298Rubber, Butadiene - Vulcanized 298Bituminous coal 300Wood 300Acetylene 305Nylon 6 329Polyvinylidene Fluoride 330Rubber, Natural - High refine 331Charcoal 349Nylon 6/9 356Ehtyl Alcohol 365

author: Someone
author_rank: Super Contributor
timestamp: September 07, 2024, 10:25:09 pm
content: Quote from: CatalinaWOW on September 07, 2024, 09:31:15 pmYes, it does require some marginal design but x00 Rth values (degrees C/W) are easy enough to find:https://www.vishay.com/docs/53048/pprachp.pdf

author: ejeffrey
author_rank: Super Contributor
timestamp: September 07, 2024, 11:15:43 pm
content: Quote from: tooki on August 31, 2024, 10:29:37 amYeah they have long since gone into my ignore filter. I only see their comments when someone else quotes them. I'm not interested in wasting time that nonsense.