hyperair

I did some amount of research (read: googling) on the topic during the months leading up to the great Singapore EUC ban. Some of the useful resources I'd found were: https://www.youtube.com/watch?v=1wcLVfwd8mk (an hour-long lecture about fighting li-ion fires at what looks like a fire-fighting conference of some sort) https://www.youtube.com/watch?v=vS6KA_Si-m8 (practical evaluation of various approaches to extinguishing laptop battery fires, which are relevant to EUCs because they share similar characteristics (battery is not easily accessible even when it catches fire, etc.) https://www.sciencedirect.com/science/article/abs/pii/S2405829716303464 (Thermal runaway mechanism of lithium ion battery for electric vehicles: A review) Not everything was relevant, but these were the highest quality content I'd come across for dealing with Li-ion fires. My takeaways from going through these were: Li-ion batteries undergoing thermal runaway generate their own oxygen, so smothering/depriving the battery of oxygen does not stop thermal runaway Smothering potentially traps heat, which raises the temperature of the battery pack even more, which causes the thermal runaway to be more likely to spread from one or a couple of cells to the whole pack. If you use a fire blanket, then what you'll do is prevent the fire from spreading to other things, but prolong the fire. The best way to stop thermal runaway is to remove the heat. This means that you either let it completely burn out (heat dissipates to the environment anyway, and no new heat is produced because fuel runs out), or you actually manage to cool each cell down back to room temperature. Water is great at removing heat and also great at getting into the battery, or at least close enough to draw heat out of the pack. Some of the difficulties involved with putting out a Li-ion fire are related to the fact that the cells are buried inside a battery pack, which is itself buried deep inside the wheel. So, If you can get it out of the wheel, do so, then pour water into the battery compartment. Otherwise, find a large body of water, and drown your flaming wheel in it. Watering a wheel doesn't really work because you can't get deep enough (EUCs are kinda splash proof anyway). Extra notes regarding water and Li-ion cells: Li-ion cells do not contain much elemental lithium and will not react with water to create a huge explosion During a thermal runaway, you've got an internal short circuit with much lower resistance than water inside your cell anyway, so don't worry about the water creating a short circuit and making things worse The risk of electrocution from this is very small as long as your wheel is not plugged into the charger because you're unlikely to close the circuit with the wheel. TL;DR for a fire: Get the wheel outside, away from anything else that can burn. Get access to the battery if you can Drown the battery, or the whole wheel if you can't get access to the battery Leave it until the fire is out, and then leave it for another day or so

Wouldn't disconnecting it from the main pack and charging it independently usually reset the auxiliary BMS's charge and discharge stop circuits?

What @meepmeepmayer said is mostly correct, but don't forget that our hub motors are permanent magnet motors. They can go into thermal runaway: Internal motor temperature rises Magnets get weaker at ~100°C (I think, not sure about the actual specs of our motor magnets) Magnetic field gets weaker, motor constant (KV) rises RPM per volt increases (higher top speed, yay!), current per Nm of torque increases Motor now draws more current for the same torque Go back to step 1 and repeat in an upwards cycle until your magnets are dead. Also, a motor is a relatively massive thing (relatively huge mass) and takes a lot of energy to raise its temperature. Motor windings may generate quite a bit of heat energy, but because of the huge thermal capacity of the motor, the motor temperature still takes a long time to rise. In that time, most other components (e.g. MOSFETs which are tiny) would have failed from the high currents.

I got mine for a decent price ($200+ for 50x Sanyo GA) at batterybro.com. Rebuilt my V8 battery pack and range-tested it at 49.15km according to EUC World from 100% to 0% battery tiltback.

Ay, it's great for visualizing tiltback characteristics and I wish more manufacturers report this information. Here's an old graph I made from one of my old WheelLog dumps while trying to figure out why my V8 was tilting back so early (tiltback began at 20km/h even when the configured tiltback speed was 30km/h).

@Seba I noticed that tilt in the CSV is now reported as an integer rather than a float. This gives very little resolution for analyzing the tiltback behaviour of a wheel (they only tilt by ~0-4 degrees after all). Could you revert it to a float please?

Learn how to dismount gracefully from a tilted back wheel. Don't brake hard when you feel it, keep your balance centred on the wheel, and try to just let it coast to a stop in a straight line, then step off and grab your wheel by the handle to prevent it from running away or tipping over.

I think Strava had something like private areas, and all parts of any ride that entered the area were either automatically redacted or just not shown to the general public. I think that would be a pretty nice feature to have in EUC World as well.

This might work: https://www.aliexpress.com/item/32905014845.html?spm=a2g0o.productlist.0.0.4573b3dcSspMF5&algo_pvid=433e8a97-c882-42de-8d3f-e129f202c5d8&algo_expid=433e8a97-c882-42de-8d3f-e129f202c5d8-4&btsid=1e0c7cdc-d1d4-4413-8f2b-232fbcfbe343&ws_ab_test=searchweb0_0,searchweb201602_8,searchweb201603_55 Or this: https://www.amazon.com/Metric-Spanner-Tubular-24mm-27mm-Fitting/dp/B07WDQ4K2T

I think Ninebot hammers some metal shims into the gap between the six nut side faces and the cylindrical wall of the pedal hangers, which prevents it from unscrewing. It's a workable system until you want to replace the motor, because it damages the pedal hanger every time you install that shim. Inmotion seems to just use threadlock as far as I can tell. I suspect that the only difference between Inmotion and Gotway in this regard is how tightly they install the nut (whether they use a torque wrench for repeatable torque, or whether they just use a normal wrench and tighten by feel), and whether or not they use threadlock. Another thing is that none of the other vendors using the wheel nut system have wheels above 16" in diameter (I think), and the torque requirements on the axle go up linearly with an increasing wheel size. It might simply be that this system fails on wheels with larger torque requirements, or that the wheel nut needs to be installed with more torque on these larger wheels. Also, did Gotway increase their axle size? I suspect that an increase in thread size requires a corresponding increase in nut tightening torque.

Inmotion uses the same system as Gotway, and IIRC, so does Ninebot, and this is before we even get into the various off-brand wheels on the market. The only EUC manufacturers I've seen using the King Song pedal arm clamp system are King Song themselves and the Rockwheel (specifically the GT16).

If you need the stuff to reapply it, look for a neutral-cure Silicone, e.g. Kafuter K-705. Like @Seba said, don't use the acetoxy stuff (the stuff you use on sinks), because it can corrode the metal parts that the fumes touch. Otherwise, if you're in a pinch and need something real quick, hot glue works too. For removing them, drip isopropyl alcohol over the joint between the gunk and the substrate -- hot glue will pop right off, silicone will get softer, but still require digging to remove.

@Aneta Where'd you find the Rockwheel BMS photos? I can't seem to find any, and I've been looking for a while. Almost -- GT16 has 4x 10S2P BMSes, of which there is some communication going on between series packs (there seems to be a 3-wire connector for communication here), and potentially communication between the parallel packs (I've not been able to verify this as my vendor replaced the packs on one side with a third-party set after it shut down on me at 23km/h). Many wheels with parallel BMSes have a wire to synchronize the charge/discharge cutoff MOSFETs to mitigate the explosive rebalancing issue (one pack at 100% charges another pack at 0% explosively) documented in https://us.reddit.com/r/AskElectronics/wiki/batteries#wiki_increase_the_capacity_with_batteries_in_parallel. The KS18L, which has 2x 20S2P packs with independent BMSes, has this wire. I think the GT16's battery packs are potentially one-of-a-kind, and I'm rather curious to see what the BMS looks like. Additionally, I don't see a charge-cutoff-sync wire connecting the parallel packs, so I've been slightly concerned that the issue mentioned above could happen to an aging GT16 battery pack. No, some BMSes don't balance the cells, but simply stop the charging process when any one cell hits the max voltage of 4.2V. I left my Inmotion V8 battery plugged in for days (cumulatively, I unplugged it when I left the house), but the battery was pretty far out of balance and not fixing itself. Manually balancing that pack by charging up the low cells helped buy some cycles until the battery pack fell out of balance again. The Inmotion V5F, V8, and GT16 packs, at least, still cut power when cells dip below the minimum allowable voltage. I don't think output protection was current-based as much as it was a per-cell-voltage thing. The V5F and V8 packs at least had a smart connector that could signal errors to the motherboard so that it could enter deep tiltback instead of violently dropping the user. The discharge-cutoff bypass (aka shunt) was a rather dangerous thing that exchanged the risk of a BMS cutoff for an increased fire risk, because that discharge cutoff MOSFET is the only thing preventing a battery pack from being over discharged to the point of voltage inversion. And you wouldn't even know you had a dead cell until you charged it up again and it set your house on fire instead. I wouldn't even be surprised if the e-scooter fires in Singapore were caused by something like this.

Some things I picked up while working on battery packs: You can't turn off a battery, so be very careful with exposed leads -- shorting a battery pack can spray vapourized metal 84V DC can shock you pretty hard, so think twice before picking up a fully-assembled battery pack with exposed leads (I picked up an assembled V8 battery pack with left hand over the B- connection and right hand over the B+ connection -- fun times). Consider adopting the one-hand rule wherever possible, and being extra careful when you need to bring both hands in. Watch where your solder wire goes -- if it drags over another part of a battery pack, you can short it while soldering a joint. Silicone wires have fragile insulation. The insulation can crack easily if kinked and get scraped off if pulled through a small hole.

@Seba I tried out the new EUC World update today and it looks great. One issue though -- battery percentage estimation on my Rockwheel GT16 no longer works. Did you rebase my GT16 detection fix out?