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.
[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.]
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.)
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.
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.
2 ESPs and a 4” color LCD screen (and a keyboard).
Depending on how bright the backlight was, that could eat through battery. And if they were using the wifi for any active communication, that increases power too.
I suspect they wanted it to last the entire weekend with the display always on. The original design probably only had one cell (maybe even smaller battery with built-in protection) and they hurriedly switched to two 18650 cells at the last moment.
They probably went with parallel because that seemed easier, no need to switch to another voltage regulator and charge controller.
That is highly dependent on the exact ESP32 model and current power state. They can use in excess of 500mA with peaks of 800mA, and can easily use >250mA constant at 3.3V. Some draw much more than that.
A board with a few bits and bobs on and a single 18650 cell might only last, say, 8 hours on a charge.
Now, a well optimized board with a low-power ESP32 and proper use of sleep states would make that number go from 8 hours to over a week, but that does take a lot of extra effort and may not be worth it over just slapping on another cell.
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.
> 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.
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].
WHY2025 orga has been a shitshow on the social & interpersonal level. The badge team was one of the casualties. (And triggers, from what I've heard they weren't paragons either, but that's even more hearsay.)
(Source: I'm in c3noc/Internetmanufaktur, though not attending WHY. TBH I saw the shitshow coming and decided I don't need it in my life.)
But surely two 18650s are just overkill. I might understand switching from the recommended LiPo cell to a single 18650 for cost cutting reasons (even though that's still probably a bad idea safety-wise), but why two?!
> 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).
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.
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.
That's not obvious from the comment and logically inconsistent with parts of it; if the trace between the cells is small it would act as an auxiliary fuse, and there is that balancing resistor (whose value I can't read because whoever drew that schematic didn't bother repositioning overlapping labels.) I'm also a bit confused about the 2 polyfuses.
That said you're right and I was focusing a bit too much on my reading/interpretation of the GGP post. I'm not sure I've ever seen a 1S2P LiIon configuration with individually user swappable cells. In the 2-cell design I did, I specifically decided to go for 2S1P and have the balancing circuit, to avoid this exact issue. It does have the downside that you need both cells, the WHY design works with only one populated... (which is what I'd recommend doing in any case.)
[ed.: the balancing resistor seems to be 200Ω. The polyfuses are 15mΩ. So I guess it's designed to trip one or both polyfuses if the cells are imbalanced. That's an... "odd"... design.]
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?
I don't know about the rest of it, but I think this is just an idiosyncratic translation of "LED will light when battery wrong way round" - IE it's a warning LED.
Putting the protection circuit* on the battery's negative pole is standard best practice (due to NMOS efficiency, and it not being a problem in the slightest), and the 50mΩ actually improves balancing. Please avoid making comments like this based on half knowledge.
[*] I do wish it were an actual full protection circuit. It isn't. Then again a run of the mill protection circuit commonly doesn't cover reversed polarity [between protector and cell], which is rather important for this specific appliation.
Look at the reference circuits, it's a pair of antiserial NMOS on the negative pole.
(Those 2 protection circuits are at the opposite ends of complexity & features)
To be clear, using 2 PMOS on the positive pole is also quite common, my choice of words with "standard best practice" might be a bit misleading.
> use bus bars to minimize wiring resistance.
Those come after the protection circuit, there should always be 2 MOSFETs in series with the individual Li-Ion cell in a design like this (specifically: user swappable cell).
(Protecting paralleled cells together is kinda nonsensical because you also want to protect them from each other, I don't think I've ever seen a 2P combined protection circuit.)
> Those datasheets show creating a series pack/cell.
You seem to only have looked at the TI one, the Diodes one is for a single cell.
& if the cells are "permanently" connected in a pack, you wouldn't have individual cell protection and just have them properly balanced before connecting them in factory.
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.
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.
There has been some controversy surrounding the use of 18650 Li-Ion cells in the design of the WHY2025 hacker camp badge and questions have been raised whether it is safe to hand out badges to participants including children starting from age 7.
Sorry, but I was not aware that the text with the submit (which I wanted to keep short) appears as a comment, otherwise, I would have given more details or left it out.
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.]
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.
I did indeed totally miss that, thanks for pointing it out!
Sure, that means the idea of using unprotected cells was already there when the holders were selected :)
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.)
Ah yea then I misunderstood. That's right you can't easily switch out the cells for protected cells yourself :(
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
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.
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.
Quite oversized amounts of power for 2 ESP32s running, last I measured a ESP32 board I have running it would consume some 120-180mA.
2 ESPs and a 4” color LCD screen (and a keyboard).
Depending on how bright the backlight was, that could eat through battery. And if they were using the wifi for any active communication, that increases power too.
I suspect they wanted it to last the entire weekend with the display always on. The original design probably only had one cell (maybe even smaller battery with built-in protection) and they hurriedly switched to two 18650 cells at the last moment.
They probably went with parallel because that seemed easier, no need to switch to another voltage regulator and charge controller.
That is highly dependent on the exact ESP32 model and current power state. They can use in excess of 500mA with peaks of 800mA, and can easily use >250mA constant at 3.3V. Some draw much more than that.
A board with a few bits and bobs on and a single 18650 cell might only last, say, 8 hours on a charge.
Now, a well optimized board with a low-power ESP32 and proper use of sleep states would make that number go from 8 hours to over a week, but that does take a lot of extra effort and may not be worth it over just slapping on another cell.
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.
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.
> 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.
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/
Why was that advice ignored?
WHY2025 orga has been a shitshow on the social & interpersonal level. The badge team was one of the casualties. (And triggers, from what I've heard they weren't paragons either, but that's even more hearsay.)
(Source: I'm in c3noc/Internetmanufaktur, though not attending WHY. TBH I saw the shitshow coming and decided I don't need it in my life.)
Often it is the case that safety concerns are overruled by less technical savvy managers for some lesser critical reason.
But surely two 18650s are just overkill. I might understand switching from the recommended LiPo cell to a single 18650 for cost cutting reasons (even though that's still probably a bad idea safety-wise), but why two?!
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?
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/
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.
Rechargeable safe(r) chemistries. Alkaline batteries are insta-e-waste. Like the common form-factors of AA/AAA Ni-MH that are acquirable locally.
> 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).
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.
Li-Ion chemistry is pretty happy with 1S2P configurations. (That doesn't necessarily mean you should do it.) 2S1P is where the fun starts.
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.
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.
That's not obvious from the comment and logically inconsistent with parts of it; if the trace between the cells is small it would act as an auxiliary fuse, and there is that balancing resistor (whose value I can't read because whoever drew that schematic didn't bother repositioning overlapping labels.) I'm also a bit confused about the 2 polyfuses.
That said you're right and I was focusing a bit too much on my reading/interpretation of the GGP post. I'm not sure I've ever seen a 1S2P LiIon configuration with individually user swappable cells. In the 2-cell design I did, I specifically decided to go for 2S1P and have the balancing circuit, to avoid this exact issue. It does have the downside that you need both cells, the WHY design works with only one populated... (which is what I'd recommend doing in any case.)
[ed.: the balancing resistor seems to be 200Ω. The polyfuses are 15mΩ. So I guess it's designed to trip one or both polyfuses if the cells are imbalanced. That's an... "odd"... design.]
> That's not obvious from the comment and logically inconsistent with parts of it
I agree, but personally I decided to go with the most charitable interpretation, and that's the one that made the most sense to me.
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...
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?
"LED will burn when battery wrong way round" .
I don't know about the rest of it, but I think this is just an idiosyncratic translation of "LED will light when battery wrong way round" - IE it's a warning LED.
With floating grounds due to those MOSFETS adding 50 milliohms or so (on the order of the internal resistance of the batteries!)!
YIKES!
Putting the protection circuit* on the battery's negative pole is standard best practice (due to NMOS efficiency, and it not being a problem in the slightest), and the 50mΩ actually improves balancing. Please avoid making comments like this based on half knowledge.
[*] I do wish it were an actual full protection circuit. It isn't. Then again a run of the mill protection circuit commonly doesn't cover reversed polarity [between protector and cell], which is rather important for this specific appliation.
> Putting the protection circuit* on the battery's negative pole is standard best practice
Pointer? Especially since LiPol paralleling seems to want to use bus bars to minimize wiring resistance.
Admittedly my experience is all about avoiding parallel LiPol batteries ...
https://www.ti.com/lit/gpn/bq77908a
https://www.diodes.com/assets/Datasheets/products_inactive_d...
Look at the reference circuits, it's a pair of antiserial NMOS on the negative pole.
(Those 2 protection circuits are at the opposite ends of complexity & features)
To be clear, using 2 PMOS on the positive pole is also quite common, my choice of words with "standard best practice" might be a bit misleading.
> use bus bars to minimize wiring resistance.
Those come after the protection circuit, there should always be 2 MOSFETs in series with the individual Li-Ion cell in a design like this (specifically: user swappable cell).
(Protecting paralleled cells together is kinda nonsensical because you also want to protect them from each other, I don't think I've ever seen a 2P combined protection circuit.)
Those datasheets show creating a series pack/cell. They don't show the circuitry to then parallel the packs together.
I guess I need to do more research on this.
> Those datasheets show creating a series pack/cell.
You seem to only have looked at the TI one, the Diodes one is for a single cell.
& if the cells are "permanently" connected in a pack, you wouldn't have individual cell protection and just have them properly balanced before connecting them in factory.
> parallel the packs together
You parallel cells, not packs.
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.
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.
There has been some controversy surrounding the use of 18650 Li-Ion cells in the design of the WHY2025 hacker camp badge and questions have been raised whether it is safe to hand out badges to participants including children starting from age 7.
Please don't post LLM summaries without any additional context. If I wanted one I'd ask my nearest LLM for it.
You're replying to the author/submitter of the post. I don't think this is LLM-generated.
Sorry, but I was not aware that the text with the submit (which I wanted to keep short) appears as a comment, otherwise, I would have given more details or left it out.
Fair enough, I didn't realise you were the original poster and that's what happened.