Little tiny wires welded to the cells that act like fuses if a cell goes rogue
I just checked their Instagram for the first time in a while and it seems like they made some advancements. Still not up to date with the build standards here but definitely better than a few months ago.
I still donāt really like the cell level fusing. I guess it will probably be fine with the onewheel packs since they draw relatively little current.
3 Likes
Batteryhookup has the same sort of nickel thatās āfusedā for sell
But like @JoeyZ5 said it could cascade and be very dangerous if you end up with no braking
Iām torn when it comes to esk8 cell-level fusing.
If a cell shorts internally and there is no fusing then it will take out the all of the cells in the p-group. Iām ignoring any possibility of thermal runaway for now.
If there is fusing (and it blows) then the remaining cells will be stressed harder but not nearly as hard as they would be without fusing. Yes, this p-group will drop its voltage faster than the other p-groups but not as quickly as feeding a shorted cell.
Both scenarios result in a dead p-group but the fused p-group will not be feeding a shorted cell (increasing the possibility of thermal runaway) and will probably drop its voltage slower than a shorted p-group without fusing would.
If you notice the issue and stop then the blown fuse will prevent any further problems. But without fusing the internally shorted cell will still be fed the energy from the entire p-group and thatās a real good way to force it into thermal runaway.
But I have a concern with the Chi method of fusingā¦
The fusing elements are free to bounce and vibrate. Iām wondering if metal fatigue could become an issue?
4 Likes
Iām curious, does cell level fusing make any significant increase to pack resistance or voltage sag?
4 Likes
Mooch will likely have looked into this more than I have, but Iāll give a tentative no. Apologies if you know bits of this, itās just for completeness
Resistance of a conductor is (Length) x (Resistivity)/ (Area), where resistivity is a property of the material that determines its resistance. Resistivity is like density in that it doesnāt actually tell you the total resistance of a body, just the amount of resistance per amount of material - water is 1g per ml, but knowing that doesnāt tell you how much water is in a container it just lets you work it out without having to weigh it.
Power converted to heat in a body is (current squared) x (resistance). Power is energy per second, doesnāt necessarily tell you how much energy is in a body it just tells you how quickly or slowly itās entering or leaving.
The wire is very thin (small area, high resistance per unit length). So doesnāt this make it a big resistor and therefore lose a load of power? Not quite, because itās also very short. This comes out to mean that if thereās a big current then thereās a lot of power converted to heat relative to the size of the conductor in that little strand. That wire generates lots of heat power, doesnāt have any way of expelling it at a rate that would match the input, so it heats that tiny mass of wire up a lot. The total amount of energy converted to heat (and therefore robbed from the system) is low, but itās concentrated enough to still act as a fuse to heat up and break the conductor.
The manufacturer has to balance making the fuse long enough that the voltage canāt arc across when the fuse blows, while still being short enough to not waste excess energy by adding total resistance and mass of metal to melt. Theyāve also got to make it thin enough to act as a resistor to melt itself, but thick enough that normal operational currents can pass through without a huge sag.
As usual, plese correct any inaccuracies
1 Like
TBH, I donāt know.
Of course the fuse element has some resistance but how large that is compared to the cellās internal resistance, the resistance of the spot welds, and the resistance of the metal strip is important.
If the fuse adds, letās say, 5% to the overall resistance thatās not a big concern. If it adds 25% then we have to seriously consider its effect on pack performance.
But since fuses are a safety feature then performance could be secondary and the resistance wouldnāt really matter. There are some real benefits to cell-level fusing for some failure mechanisms. Tesla doesnāt waste money on useless fusing. 
If fuses have a measurable, and unacceptable, effect on performance then the pack can be reconfigured to compensate for the sag. Otherwise the performance loss can just be accepted as part of the tradeoff for a āsaferā pack.
So much of what makes cell-level fusing a good or bad idea will be up to our own personal preferences and priorities for the packs we use. But that should be based on the most likely cell failure scenarios, and their likelihood, and I donāt know if we have enough data to know that.
That kind of leaves it at being a personal choice without any real science to back it up? 
Should the community be working on some way to get the data we need to make educated decisions on fusing vs non-fusing?
1 Like
IMO, the data gathered kind of needs to be done on a per-cell or per-configuration basis, and therefore not as useful for us because thereās so much variability. I think a conclusion made on data gathered from one setup isnāt very transferable.
The two exceptions I can think of are if someone like @DRI wanted to create a āreferenceā pack design that gets studied in detail and replicated, or if someone were to buy power modules from EVs where they are already heavily integrated mass produced devices where BMW/Tesla/whoever does the intensive testing for us. Even then thereās flaws because our deployment doesnāt match a car perfectly
1 Like
Iād love to get a statement from ChiBatterySystems on their fusing and why they did it. Is this just a marketing tool to increase sales or have they done testing that shows increased safety? What is the science behind their decision? LOLā¦is there any science or is it just a bunch of guys around a table wondering how to boost sales since āTesla does it so we should tooā?
1 Like
Agreed. Determining the fuseās usefulness needs to be independent of the packās configuration. Which I donāt see, right now, as being a show-stopper.
1 Like
I think we might be saying something a bit different, I was thinking more that some differences in setups (especially number of P groups, how close to the limit of the cells theyāre operating, level of vibration dampening) mean that cell level fusing could go from making a load of sense in one configuration to being very dangerous in another, in a way thatās not immediately obvious. Say two 12S3P P42A packs, both sound the same but A is exposed to much more vibrations than B. For B, the safety benefit of avoiding catastrophic fires makes it a no brainer but for A the fuses are actually an extra risk if they vibrate themselves to pieces and take a P group with them.
Basically unless someone was making (or sharing the info to make) a standardised pack with known limitations, that fusing data couldnāt feasibly be collected with any certainty
1 Like
Just a thoughtā¦
Iām wondering if having an exposed Chi-style metal-strip fuse that can bounce around, that has undefined I2T characteristics (current vs clearing time), and that could leave metal free (after blowing) to bounce around and short the cell is a good idea.
For a powerwall, Iām not too concerned since thereās no shock and vibration. But for esk8ā¦.
I have done zero testing to back up my concernsā¦.just wondering.
2 Likes
Unless you live in San Franciscoā¦
3 Likes
I feel that a scenario like that can be tested at the cell level though, independent of pack configuration. Part of the testing of different fusing methods would be vibration and shock related.
The pack builder would consider the operating environment and choose the fuse type that bests fit their requirementsā¦or realize that no fuse method is viable for the intended use for the pack.
2 Likes
Yeah I think that makes sense now that I think about it? I feel like Iāve confused myself into a corner a bit
1 Like
LOLā¦
Yea, the mind reels at all the different directions this leads to all at once.
1 Like
I see how this could be good but I need my breaks, and I have yet to slide stop this ride.
3 Likes
The Onewheel world is one of the weirdest, fickle yet stubborn, and generally confusing spheres Iāve come to know.
From what Iāve seen (and itās a lotā¦Iām really deep in the OW world at this point), Iām inclined to believe itās the latter. A lot of the āadvancementsā posted to social media are solely things that make for easy marketing copy and to continue to keep the market share. The language used to address issues has never actually admitted a flaw in a pack, only shifted blame to the end user.
Iām very skeptical of the intentions of a lot of OW based aftermarket folks. Not all, but thereās a seedy underbelly that exists and I kind of regret going down that rabbit hole. There are many reasons why Iāve kind of relegated my involvement to YouTube, where itās all on my channel and my terms, and I donāt have to trudge the muck.
Anyway, Iāve seen enough aftermarket OW batteries literally grip-clamped into a battery box to know that safetyā¢ is a very loose term in Stokeville.
8 Likes
ok but why do pink wheels look so good 
4 Likes
Unfortunately that is a question that they probably wouldnāt answer in a public face lol
2 Likes