Fire hazard of WHY2025 badge due to 18650 Li-Ion cells

https://wiki.why2025.org/Badge/Fire_hazard

by fjfaase • 12 months ago

107 102 12 months ago

wiki.why2025.org

That's a lot of juice for a trinket. Shorted a 'mitigated' battery of these in a charger once, was enough to reconsider vaping entirely

pjc502• 12 months ago

Given how much torch you can power off one of these, I'm not clear why you'd need two of them for a badge, since any conceivable use for that much current is going to start heating up the badge PCB fairly quickly. They're usually sized for >1A each, and you can get >10A off them for short periods, which is very lively for a badge pinned to flammable clothing.

arghwhat2• 12 months ago

Assuming decent cells with low ESR (say, <30mOhm), one such cell will deliver hundreds of amps when shorted, making things a little bit more lively than your estimation. :)

(A few hundred amps isn't a lot for a shorted battery, but these are tiny cells so that's what you'll get.)

Two cells was probably selected for one of: Voltage to avoid boost converters, capacity to avoid having to do extensive power optimization to make it run the whole event, balance to make it hang even off your neck.

bsder4• 12 months ago

The WHY2025 badge was designed to be powered by 2 Li-Ion 18650 battery cells connected in parallel.

Wait, what?

I was under the impression that Lithium batteries were really difficult to put in parallel without a LOT of engineering work.

The discharge curve for Lithium batteries is super flat. If you put them in parallel, even a small differential between the two means that one battery will completely discharge simply trying to bring the voltage of the other up to match. This is very different from the discharge curve from alkaline which has a nice slope and the batteries can equalize without burning up very much of their capacity.

These don't look like they're matched in any way. The connection between them doesn't like very big--I suspect a non-trivial voltage drop if one battery tries to empty into the other.

If you need the power, it's much better to put them in series and use a buck converter to bring the final value where you want it.

This seems more like a fundamental engineering flaw rather than a fault in the boards (although, to be fair, the creepage and clearance don't look great).

exmadscientist3• 12 months ago

Li-Ion chemistry is pretty happy with 1S2P configurations. (That doesn't necessarily mean you should do it.) 2S1P is where the fun starts.

rollulus• 12 months ago

It’s what I thought as well, but I’m not too much into electronics to hold an opinion. It looks like there’s a balancing resistor between them: https://gitlab.com/why2025/team-badge/Hardware/-/blob/main/C...

bsder4• 12 months ago

With floating grounds due to those MOSFETS adding 50 milliohms or so (on the order of the internal resistance of the batteries!)!

YIKES!

pjc502• 12 months ago

Is it just me or is that schematic hard to read due to bits of text being on top of each other? Also "LED will burn when battery wrong way round" .. how about fixing this problem which you have acknowledged? What happens to your balancing resistor when you put one battery one way round?

eqvinox10• 12 months ago

It doesn't matter what happens in the 10 to 90% range, if one discharges before the other, it's perfectly fine. It's not like this is an application that needs the combined current capability of both cells. What does matter is that neither cell is overcharged nor deep discharged, and the [dis]charge curve is absolutely not flat in those areas.

stavros3• 12 months ago

The GP is talking about the case where you plug in two batteries of varying charge levels or health, which I agree is not an amazing thing to do.

jacquesm• 12 months ago

Paralleling 18650's is relatively easy. You need to match voltage to within a few mV and make sure the connection is really solid (welded) to ensure they stay paired perfectly. Flaky connections, putting cells in series, impact damage, bad chargers etc are the risky bits, a solidly connected pair of 18650's is to a close approximation just as safe as a single cell, but it does have twice the short circuit current so you are going to have to be more careful around them. But at least the casings will be at the same potential.

I've built a 17P10S pack which was a pretty interesting (and scary) effort but it has been working flawlessly for years now with just one inspection of the guts after two years to make sure that nothing was coming loose (it's on an s-pedelec e-bike). In a big pack like that it's the spaces between the alternating blocks of cells and on top where the interconnects are that the real risk lies, besides the fact that the short circuit current of that pack is just shy of a kilo ampere so you really don't want to drop a tool or a piece of interconnect strip on that.

Eduard3• 12 months ago

Paralleling 18650's is relatively easy. You need to match voltage to within a few mV and make sure the connection is really solid (welded) to ensure they stay paired perfectly.

These requirements are already not easy, and there are still plenty of things to consider for using LiPos in parallel (e.g. identical health, preferably batteries from same batch, to increase chance they age identically)

ajsnigrutin• 12 months ago

Many devices have parallel lipo cells, from powerbanks to electric cars, nothing special here.

If one cell is weaker, the other provides more current, there is no "one discharging/emptying into the other" during normal work (read below). No real need for any proper matching either, if you only care about capacity (if you care about current, you don't want to get into a situation where any of the cells has to provide more current than designed for and safe.

The only "problematic" part of parallel batteries is making the first connection, where one might be at a much higher voltage than the other. Usually this is mitigated by equalizing voltages (either dis/charging to a fixed voltage, or do a parallel connection through a proper resistor), and after they're safely connected in parallel, it doesn't matter.

On the other hand, two cells, user removable and replacable can cause exactly this issue, where the user removes one, recharges it in an external charger and replaces it (while the other, empty one, still stays inside)... but maybe there's a diode somewhere that prevents reverse currents.

Dylan168072• 12 months ago

These don't look like they're matched in any way.

How would you tell?

The problem you're describing is real, but it's only when installing the batteries. And you can avoid it by only inserting batteries that are both empty or both full.

exmadscientist3• 12 months ago

The WHY2025 badge was designed to be powered by 2 Li-Ion 18650 battery cells connected in parallel. The cells provided to visitors are of the "unprotected" kind

...I am going to put on my "client-facing consultant" hat for a moment, which means skipping the expletives, and just say that not only is this a Very Bad Design, it is such a Very Bad Design that someone should really have noticed this and not let it happen.

Because this really is a Startlingly Bad Idea.

fjfaase3• 12 months ago

An earlier design by Badge.Team [1] did not use these cells and Badge.Team (no longer associated with WHY2025) strongly advised against the use of these cells.

The earlier design has been matured into Konsool [2] and is available as Tanmatsu [3].

[1] https://badge.team/

[2] https://badge.team/docs/badges/konsool/

[3] https://nicolaielectronics.nl/tanmatsu/

stavros3• 12 months ago

Why was that advice ignored?

slacktivism123• 12 months ago

What's with the mock-security-advisory with logo for the 'vulnerability' (Heartbleed, anyone?)

Why is the important safety advice buried in a bunch of interpersonal drama and administrivia?

Juerd• 12 months ago

Author here. I didn't add the logo, but it's a wiki so others can theoretically change things.

I think the logo is cute though, so let's keep it. I think it was made with the WHY2025 logo generator at https://design.why2025.org/

eqvinox10• 12 months ago

I'm confused that noone is pointing out most protected 18650 cells won't even fit in those holders, since protected cells are generally in the 18690…18700 pseudo size range. That's too long to get into those holders.

Source: the holders are likely Keystone 1042 [https://www.keyelco.com/product.cfm/product_id/918], which I've worked with before. For a protected cell, cf. for example https://imrbatteries.com/products/panasonic-ncr18650b-3350ma... - note 69.41mm length.

[ed.: it's the China equivalent of a Keystone 1042, https://www.lcsc.com/product-detail/C2988620.html - I can't confirm but am 95% confident a protected cell won't fit; if it would, the hold on an unprotected 18650 cell would be quite loose.]

supakeen2• 12 months ago

Sure, that means the idea of using unprotected cells was already there when the holders were selected :)

eqvinox10• 12 months ago

Yeah, I'm just saying, you can't even buy regular protected cells and put them in, because they won't fucking fit. I do think "actual" 18650 protected cells exist, but they would be rare and expensive because you can't build them out of mass manufactured bare 18650 cells (for obvious reasons of where do you put the damn protection circuit.)

unwind• 12 months ago

That is mentioned in the article, although could perhaps be more emphasized since it does mean the "obvious" fix is not possible:

Commonly available protected 18650 cells don't fit in the badge's cell holders because they are slightly longer.

eqvinox10• 12 months ago

I did indeed totally miss that, thanks for pointing it out!

nubinetwork• 12 months ago

FWIW, I have battery holders that deathgrip unprotected cells, so even finding a proper holder for those is a crapshoot.

krekr2• 12 months ago

I’ve worked with the Keystone holders and can confirm that those will hold protected cells, at least some I got from nkon.nl

wkat42422• 12 months ago

That's a good tip for safety conscious visitors because the webshop is in the same country. Probably a good idea to put it on the event wiki. Is the event still going on?

eqvinox10• 12 months ago

Can you please specify the exact type of these cells.

A friend found a 68.8mm cell that fits; the Keystone holder caps out at 68.88mm. Most protected cells are 69.2mm…69.8mm.

leptons• 12 months ago

The Keystone holders are nice but expensive, but they do not fit most protected 18650 cells, and I don't like the PCB mounting options.

I designed my own 3D printed 18650 holder for my project, including a positive battery tab cut-out to prevent reverse battery insertion. I get to decide how big the battery can be, and protected cells are 100% the way to go.

I've never had a problem with a short with the protected cells, and my circuit also cuts off power to the load using a mosfet, if a short ever occurs. It's been working great for years.

giantg2• 12 months ago

Funny, I'm also going with a 3D printed 18650 battery module... for a lepton (FLIR) project.

ryao• 12 months ago

At work, whenever we design hardware that uses Li-Ion cells, I always discuss safety before we even have done the design work so that we build something that is safe. Why did these guys not do that? Did they only learn about videos of li-ion explosions/fires after design this?

By the way, they probably should have used a LiFePo4 chemistry instead. It would not have the same runtime, but it would be much safer in worst case scenarios.

Zak3• 12 months ago

The battery would be less likely to enter thermal runaway and explode with LiFePO4, but this level of short circuit risk is still a significant fire hazard. 3.6V / 0.04 Ohms[0] = 90A.

[0] https://lygte-info.dk/review/batteries2012/LFP18650%201500mA...

burnt-resistor2• 12 months ago

Why the fuck didn't they just use say 4 safe(r) CR2032s or simply have only +5V USB-C power in?

They could've eliminated most of the risk by simply ripping the 18650 holders off the badges and rely on USB power.

Zak3• 12 months ago

You are proposing replacing a ~20Wh battery with a 2.8Wh battery. The maximum current draw from button cells is also likely inadequate for the application.

andrewstuart• 12 months ago

Avoid battery fires: design your boards for alkaline batteries.

They’re safer and in many cases just fine for the job - for example a conference badge needs nothing more than alkaline batts.

Also, alkaline batteries are not an expensive nightmare to ship.

burnt-resistor2• 12 months ago

Rechargeable safe(r) chemistries. Alkaline batteries are insta-e-waste. Like the common form-factors of AA/AAA Ni-MH that are acquirable locally.

rgovostes• 12 months ago

Conference badges are basically insta-e-waste too.

em3rgent0rdr3• 12 months ago

AA/AAA won't fit in a flat conference badge. I've wanted to get coin cell format NiMH, but they only seem to be the more thicker button type (or I don't know the magical term to search for), and I can't seem to find cheap options either. The 40 maH ones seem to be 5mm tall and I can't seem to find many smaller capacity ones that are thinner.

Eduard3• 12 months ago

citation needed. From mining over production to recycling, NiMH batteries are ecologically inferior to alkaline batteries. A breakeven and superior performance may only set in after many recharge uses which NiMHs may never reach (ageing, rare usage)

ahoka• 12 months ago

Mercury free alkaline batteries are not e-waste, even if they are often handled as such for simplicity (battery bad mmmkey?).

charcircuit• 12 months ago

Hopefully, they get sued to clearly set the precedent that this is not acceptable. Just because it may be a devkit, targeted towards knowledgeable individuals, or amateur made that doesn't mean that they should be distributing unsafe electronics like this because it's cheaper than making a safe version.

seszett• 12 months ago

This is the Netherlands, they obviously (and luckily IMO) won't get sued when there has not even been any incident and they have a clear advisory for the safety problem.

I don't even know on what grounds could anyone sue them.

krekr2• 12 months ago

I've also written up some more findings. They can be found at https://www.krekr.nl/content/why2025-badge-fire-hazard-addit...

1oooqooq• 12 months ago

fireworks in the badge? take that defcon!

1970-01-01• 12 months ago

It's all cute fun and nerding out until the room is filled with smoke. The art of one upping your hackercon badges is clearly getting out of control. Good job on calling it out now.

lysace• 12 months ago

Repost from a previous comment of mine, that sort of applies here:

I get nervous when I see videos of people buying random Li-Ion/Po-battery powered crap from Teemu etc.
My personal policy for buying anything with such a battery: the seller must have a meaningful presence in my country, selling at least like $10M/year.

I.e. they need to have a large enough exposure to handle a catastrophic house fire if something happens due to e.g. a bad design. I figure that at around $10M/year they start caring, even if they are psychopaths or incompetent.

ShakataGaNai• 12 months ago

I love these concept of badges, but almost never are they well executed. Defcon has had TONS of problems with their badges of all types. OpenSauce has tried for the last two years with only middling results.

Don't get me wrong, I'm not trying to say "don't do it" or "These people are stupid". It's just that people underestimate the time and effort required. It's basically bringing a product to market, for 20 to 50k people (depending on the event), in a few months time. But it also needs to be "cool" and "unique" and often "beginner friendly" and extremely cheap. Crazy crazy hard.

Waterluvian• 12 months ago

Engineering is the first 80% of work. But productization is the second 80%. I find that the more nerdy a community or product audience, the more the latter suffers.

fjfaase3• 12 months ago

This is right. But this time that was not the primary reason. From earlier experiences, Badge.Team, started well ahead of time and were on schedule, but things went wrong after some drama with the WHY2025 organization.

richardlblair• 12 months ago

It's almost fitting, isn't it? Given what each of these conferences are all about.

ryukoposting2• 12 months ago

It's worth noting that this kind of thing works great at a smaller scale. Adafruit has been marketing bare PCBs for sew-on applications for years.

On an even smaller scale: I contributed to a beginner soldering class by designing this simple board shaped like the high school's logo: https://postimg.cc/ftwtqHFn (for the record, shorts across the contacts in the exposed metal area are harmless. The transistor never saturates in this circuit)

The key to Adafruit's arduinos-but-for-cosplay, and my keychain photocell thingy is that neither demands two(!) 18650s worth of power. There just isn't a significant hazard in the first place.

brainzap• 12 months ago

we copy paste adafruit pcb to make our own badges

Xss3• 12 months ago

A lot of people pay for pis when all they need is an esp32 at most.

knotimpressed4• 12 months ago

Braving potentially getting spit roasted to ask:

If I'm making my own 18650 USB C power banks, are there any easy to miss risks? I've got the cells in holders, not welded, but the holders are specc'd above the current I need. The cells are unprotected, but the Aliexpress listing for the power management board says specifically to use unprotected cells, as at 6A draw most protection boards don't do well (dubious). The cells are tested and mechanically protected by a thick enclosure. The only EE work I'm doing is soldering 2 high gauge wires from the holder to the board that's doing everything else. I know Aliexpress isn't a bastion of quality, but the seller has good feedback and I checked over the board to make sure there's at the very least a good counterfeit battery protection IC included.

Currently, the concerns I have are: - the holder relies on good contact to deliver 6A without developing hotspots on the terminals - the board from Aliexpress perhaps should not be trusted

If there's anything else anyone can think of, I'm happy to hear it.

Eduard3• 12 months ago

it helps if you give us links and model numbers

knotimpressed4• 12 months ago

Well, there’s only one real part (the cells are interchangeable, and reclaimed) https://a.aliexpress.com/_mKNNnGZ I’ve gone with the purple C and U model.

Cyan488• 12 months ago

As an electronics designer myself, I would find it hard to trust the AliExpress board.

Without the design files, running a failure modes and effects analysis on the board is difficult.

There's also no guarantee that each board you get is built identically. Some parts or the whole design could be changed between orders.

If I was designing a power bank board professionally, I'd be putting it through the ringer - environmental, mechanical, component level short circuit, load short circuit, load power injection, input over-voltage, input transient, RFI/EMI susceptibility, etc. Do you trust that all that has been done on a board that is representative of what you've received?

Panzer042• 12 months ago

There's a difference between acceptable standards for a truly professional product that you'd have to certify and hobbyist stuff.

Beyond short circuit/overcurrent, overtemp, over voltage, under voltage protections, what else would be necessary to ensure safe usage of the cells from an electrical perspective? Ie. What additional protections would a batter management circuit need to be safe in normal circumstances?

knotimpressed4• 12 months ago

Definitely agreed on the lack of consistency between orders and even between boards in the same order. I’m doing very low volume for myself and not giving anyone else the banks, so I’m more than happy to check over all the boards for visually obvious issues with a loupe.

As another commenter said, is there anything beyond short circuit/overcurrent for the load side, and undervoltage/overcurrent protection on the cell side that’s crucial for a non professional bank? I’m happy to pop a few boards testing them myself.

ranger207• 12 months ago

There is a subreddit dedicated to 18650s where people make power banks and the like, https://old.reddit.com/r/18650masterrace/ . Off the top of my head I remember reading about making sure you use the same set of cells together so you don't get unwanted current flow from highly-charged cell to low-charge cell, but I'm sure there's other details too

knotimpressed4• 12 months ago

Absolutely, I’ve browsed that sub a bunch but frankly I trust the opinions here more. I’m using matched reclaimed cells that I’ve tested to make sure they’re still healthy.

aetherspawn2• 12 months ago

Lithium is the wrong chemistry for this novelty throwaway thing. Risks of fire all along the supply and disposal chain.

They could just use a few watch cells. LEDs use no power at all, so lithium not required; and watch cells aren’t hazardous when shorted.

Even the form factor of 18650 seems wrong for this, they would be so bulky compared to watch cells or AAA cells.

stonogo• 12 months ago

Watch cells are also usually lithium. I'd have just gone with LiFePO4 18650 cells.

amluto• 12 months ago

Huh? A little CR2032 or similar cell has minimal short circuit current. A LiFePO4 18650 may not set itself on fire if shorted, but it could still set the rest of the badge or your shirt on fire.

aetherspawn2• 12 months ago

That doesn’t solve the issue because the fire risk is due to short circuit. Any battery that is Li-based has too low IR to self limit.

mfitzp• 11 months ago

The “badge” has a 2.8'' TFT screen, not just a couple of LEDs.

squarefoot• 12 months ago

Most if not all holders I worked with simply can't hold protected cells, which I find shortsighted and stupid as making receptacles and spring contacts that can hold both would be dead easy, but I guess saving fractions of pennies with less plastic, metal and weight is the priority.

Fire hazard of WHY2025 badge due to 18650 Li-Ion cells

Related Stories