Fuse-wire for individual cells, DIY Tesla style

[eMark]

Brand New VTC5As
28s20p Pack
Pack will be pushing 600A for about 10 second peaks (30A per cell)
I will be using an expensive "Smart" BMS for constant series connection voltage monitoring, charging and balancing.

My use case is "high performance" but I also want to keep the pack as healthy as possible, safe to use and last as long as possible.

Looks like your VTC5A provides the best of both. According to docware's DCIR tests (posted on BudgetLightForum) your VTC5A choice should satisfy both your performance and longevity needs ALAP ...
<img src="https://i.imgur.com/2qPsTU0.jpg" alt="6"/>
<img src="https://i.imgur.com/FRRahFf.jpg" alt="B"/> (a tad better than my choice of Samsung 30Q for my DIY build)

 

[bik-e-bik-e]

Hope my new design of battery pack will solve your problems.
https://endless-sphere.com/forums/viewtopic.php?f=7&t=103534

 

[john61ct]

I will be using an expensive "Smart" BMS for constant series connection voltage monitoring, charging and balancing.

By Smart do you mean one from

LLT Power, aka SHEN ZHEN LI LU TONG ELECTONIC TECHNOLOGY

specifically, or just in general,

one of the many that are based on bq769x0, compatible with the "xiaoxiang" app?

If so a link would be appreciated. . .

Or, do you mean the completely different "123 Smart" brand BMS from Albertronic BV?

 

[EbikeAus]

Have read the whole thread and tried searching elsewhere but how exactly would you go about deciding which size of fuse wire to use.

Do you know WHY some DIYers use a fusable connection between the parallel cells while other DIYers just as knowledgeable / experienced choose not to use either wire, resistor or glass fuse links between parallel cells?

Is it because some ebikers just love to tinker and any excuse to solder, solder, solder OR because they are using salvaged cells OR is it because the packs they build are performance packs pushed to the limit OR is it because they don't want to invest in an expensive first-class BMS (+$100) OR a combination of all four. If so then WHY do other very knowledgeable DIYers decide not to use fuses? Is it because they see the importance of investing in a first-class BMS OR is it because they use only new expensive reliable cells OR is it because they balance charge keeping a close eye on pack cell condition OR is it because they are more interested in longevity than "raw performance" OR a combination of all four?

Do you really need a BMS, even morese if you can only afford a cheap Chinese BMS? Have you determined beyond a shadow of doubt WHY you're going to use fuse wire between your parallel cells?. Is it because you're using salvaged cells that you've determined are good enuf, but still questionable? Or like flippy are you more concerned in "raw performance" (pedal to the metal) than pack longevity? Like Shawn McCarty, docware and myself i question the need for a BMS when longevity is my objective and keeping a close eye (cell checker) on brand new pack cells and balance charging (when needed) instead of relying on a relatively inexpensive BMS to protect my DIY build.

Maybe, what you need to consider is whether or not to incorporate a couple of these to your pack. Only available up to 8S so need two for my 10S5P build ... https://www.amazon.com/ISDT-Battery-Meter%EF%BC%8CLCD-Capacity-Balancer/dp/B07797N9BG/ref=pd_sbs_21_img_0/139-5157333-5670654?_encoding=UTF8&pd_rd_i=B07797N9BG&pd_rd_r=5ca67aa4-5e4c-44d4-80e8-c807a43b4de3&pd_rd_w=kYKsF&pd_rd_wg=4IMYY&pf_rd_p=5cfcfe89-300f-47d2-b1ad-a4e27203a02a&pf_rd_r=T21BSZXTEF4BZEZV0CF5&psc=1&refRID=T21BSZXTEF4BZEZV0CF5 ... also get a cell checker if you don't already have one. Invest in a good reliable cell checker not one of those cheap ones.


With respect to the disinformation by flippy and john they are poor sports. Flippy's comment apparently reflects his dissatisfaction that i indirectly made a reference to Macho Man (an ebiker more interested in "raw performance" from a pack more so than getting the most longevity lifetime performance from a pack. What's your application ... raw performance or longevity performance? And then how does your application (e.g. raw performance, salvaged cells, personal preference) justify the need for fused connections?

As for john he is coming around to the advantages of a DIY Vruzend pack using one or more V2.1 kits (nickel/copper busbars and compression barrel bolts). Previously both john and flippy considered Vruzend "crap" (flippy may still consider it "crap") ...

Is it the consensus here, based on experience, that the Vruzend approach really is "crap"?

No, it's not the consensus. Just ask Erik about his 14S8P Vruzend pack ... https://endless-sphere.com/forums/viewtopic.php?f=14&t=102387&start=150 ... scroll down

As far as parallel groups and series strings i used john's preferred usage in my above reply. john's disinformation post is not helpful (neither is flippy's disinformation comment). They may need a warning to STOP. In other words Get-Over-It guys instead of provoking comments that require a lengthy reply to correct the disinformation / misinformation.

When Ron used "string" in reference to a parallel group he was right because in a rectangular pack both series and parallel cells are in a straight line. Since the use of triangular DIY pack builds the term "group" is correct. A good example of a '"group" of parallel cells (i.e. 8P) is this diagram of Erik's 14S8P Vruzend triangular pack ... <img src="https://endless-sphere.com/forums/download/file.php?id=262283" alt="Wallpaper-IngridMika-Contact-Grid-1-1100x1318 - Copy - Copy - Copy.jpg"/>
It's unfortunate that both flippy and john are still smarting and somehow think by discrediting me (and derailing this thread) they elevate their own credibility. Whereas, determining your pack's application and thus the reason(s) for using wire fuse links between parallel cells is most relevant to this thread.

I diy my own packs because I have access to large quantities of high quality lightly used cells.
I use cell level fusing for added safety.
I also use a BMS, mainly Bluetooth, for ease of monitoring.
If I ever made a pack from new cells, which is unlikely, I would just use a BT BMS for monitoring.

 

[eMark]

I diy my own packs because I have access to large quantities of high quality lightly used cells. I use cell level fusing for added safety. I also use a BMS, mainly Bluetooth, for ease of monitoring.
If I ever made a pack from new cells, which is unlikely, I would just use a BT BMS for monitoring.

The following "fusing" posts are the concluding replies from page 5 of the thread: What battery to choose after your last one burned your house ... that are worth posting on this fusing thread (perhaps the question is: How To Wire A Substantial Pack For Using A Cell Checker and/or Best Way To Balance Charge A Substantial Pack Without A BMS. Instead of any naysayers saying it's too time consuming (yet fusing isn') try instead to post an alternative solution for dogman in lieu of depending on a built-in smart BMS that isn't 100% fail proof so as to prevent a potential fire (like preventive maintenance that's applicable to the pack design/size and ebiking routine.

the people that do DIY cell fusing simply do it because they think it will protect them from damage. it wont. once you reach the point where you pop cell fuses you usually got way bigger problems and you didnt put in the proper protections (like a bms) in the first place.

What if you have balance leads to each cell for a cell checker as well as balance charging ... perhaps the first 30 minutes (if necessary) before bulk charging and then the last 30 minutes before reaching 4.0 or 4.1. Do this as often as necessary which will vary depending on the condition/age of the pack.

still, you can break the fuse wire but that wont stop any short inside a cell. the cell will still heat up and vent and if you have a crappy cell it will also vent flames.

if a cell shorts out it usually does that "gracefully", so no instant fail but you will see it heat up and eat up all the volts in the P group and trigger the bms to fault and killing the output. so you know very fast something is wrong.

unless you have a massive battery with dozens of cells in P you will not pop a cell fuse.

That's even more justification for having balance leads for your cell checker ... preventative maintenance. Yet how many ebikers even consider preventative maintenance when they assume their BMS is sufficient.

Well designed fuse links won't hurt anything and may protect against certain types of faults, but I have seen many cases where they wouldn't help. If a single cell shorts internally (or externally) and vents with flame, just the heat alone is often enough to set off the adjacent cells and it propagates until the entire pack burns up. I have also seen Tesla pack fires where there was a big short somewhere and a large section of the pack goes off at the same time with a huge fireball.

Not all cells have PTC devices, but i think most have a CID, which will open the circuit when the cell pressure gets too high. This rarely comes into play unless you overcharge a cell.

Let's face it that most ebikers aren't up on all that goes into preventive maintenance of a DIY pack (except those reading these ES threads.

My assumption has always been that in my fire, the bms failed, a cell overcharged, and vented flame. This dominoes to all the other cells.

Fuses are great at protecting from shorts. a fuse type connection between each parallel group of cells in a bike pack seems like a good idea to me. Every cell, I don't know if that would be enough better or not. In any case, a bms that fails and lets a pack overcharge is not something a fuse would help you with.

So, why use a BMS if even an expensive BMS can fail? Why not have balance leads at least for a cell checker, if not for periodic balance charging; especially as the pack ages. Isn't it less labor intensive to install balance leads for cell checking and occasional cell balancing instead of fuse-wires that restrict current flow?

Spinning Magnets has yet to post some concluding remarks that sum up this "con-fusing" thread when it comes to whether or not to even fuse new cells and if so under what conditions (application) when fuse-wiring individaul cells is recommended.

Would appreciate Ron's concluding remarks (in lieu of fuse-wiring) on balance charging without a BMS. Or better yet if someone would start a thread on wiring a pack for "Balance Charging Without A BMS" as it's dogman's assumption that it was a failed BMS. If even a smart BMS isn't 100% fail-safe a fire may still occur. Seems worth the time to have balance leads for checking the condition of each cell, especially as the pack ages with more and more charge cycles and disimilarity among cells.

 

[flippy]

dont follow exactly how a cell checker is some kind of magic bullet here.
if you have a decent bms they are EXTREMELY unlikely to fail and if they fail they fail "safe". so if it craps out or just errors out your whole battery basically dies and you know something is wrong. depending how you programmed it it can also give audible warnings or display a potential issue on its lcd screen.

i fail to see how a cell checker will do anything to add to this exept a lot more wires and connectors that can give issues.

KISS still apllies, and right tool for the job.

problems mentioned here are usually simply a cause of massive underspeccing of components like driving a 4P battery at 100+ amps some something stupid like that.

ps: checking individual cells in a pack that is 2P or more is impossible.

 

[john61ct]

if you have a decent bms they are EXTREMELY unlikely to fail

Links to examples of models you consider that reliable would be appreciated

 

[flippy]

if you have a decent bms they are EXTREMELY unlikely to fail

Links to examples of models you consider that reliable would be appreciated

for most people here a tiny would be sufficient: https://www.energusps.com/shop/product/tiny-bms-s516-150a-750a-36

just remember cables are sold separate wich is really stupid and they are a bit on the short side, expecially for the price.

 

[john61ct]

I personally agree that cell-group level leads should be brought out from the interior of the pack. The same wires can be used for multiple purposes,

including the BMS, which IMO should be easily removed / replaced,

or balancing chargers, or whatever else you choose for restoring any imbalances that may appear.

Or an occasionally-connected known-accurate cell checker, if you doubt the BMS' readings.

If external access to literally every cell is desired, only then do the above issues have anything to do with per-cell fusible link wiring.

KISS is indeed important for safety and reliability. But being able to test for changes in capacity and resistance of each group or even each cell, without decomposing the pack, would be an important capability.

With the **only** wiring to each cell being one pair for all purposes, can"t get simpler than that!

The intra-bank connections may even be wired in a "pod" located toward the outside the pack itself.

Giving the ability to rewire the pack's xPyS on the fly, build in some spare cells to easily replace failed ones, or just "weak link" ones as they are revealed.

 

[john61ct]

for most people here a tiny would be sufficient: https://www.energusps.com/shop/product/tiny-bms-s516-150a-750a-36

Thanks for the confirmation, often reco'd. Not much more expensive than some crap ones either.

> just remember cables are sold separate wich is really stupid and they are a bit on the short side, expecially for the price

No worries, used to crimping my own harnesses, and also happy to learn to solder too if necessary.

 

[eMark]

dont follow exactly how a cell checker is some kind of magic bullet here.

Don't follow your thinkng that you think i think a cell checker is a magic bullet (gross exxageration).

ps: checking individual cells in a pack that is 2P or more is impossible.

Remember way back when john said there's an advantage to DIY pack design in which cells can be easily disassembled (e.g. Vruzend V2.1 kit). John later said he is even contemplating his own such pack design for easy disassembly of cells. Also whether 2P or 4P a cell checker is able to alert you to a P Group that is suspect. It's possible to further determine which cell(s) are inferior with pack design.

You've got to admit that in the right hands and application Vruzend has it's advantages as well as other such ingenious designs that have appeared in these battery threads ... and a "decent bms" is mandatory when building a pack with recycled cells.

if you have a decent bms they are EXTREMELY unlikely to fail and if they fail they fail "safe". so if it craps out or just errors out your whole battery basically dies and you know something is wrong. depending how you programmed it it can also give audible warnings or display a potential issue on its lcd screen.

Agree, but how many packs in use today (DIY and/or commercial) have a "decent bms" ??? Isn't this why Shawn McCarty and even docware question the need for a $40 BMS in favor of occasionally balance charging (e.g. such as with a smaller pack size such as 10S5P).

i fail to see how a cell checker will do anything to add to this exept a lot more wires and connectors that can give issues.

Very true, especially if it's a larger spot-welded pack (e.g. 14S8P). So, it comes down to spending $159 for a "decent bms" or if a smaller pack wired for some occasional balance charging (as needed) before bulk charging and after bulk charging (as needed) during the final stage to 4.05v to 4.10v. And just to be clear ... a decent cell checker and a half-decent $40 BMS(maybe, maybe not) haven't decided yet, but am not going to spend $160 on a BMS.

Even with a $40 BMS it's not wasted time to periodically check cell voltages ... thus one viable reason for assembling your own friction-fit pack and taking into account occasionally balance charging especially as the pack ages for cycle life longevity. As for me and my 10S5P Vruzend pack i would never fuse-wire it, but i would wire it for occasional balance charging as needed (preventive maintenance).

Correct Me If Wrong: Isn't the bottomline of this thread that fuse-wire isn't necessary with a "decent bms" and a DIY custom pack in the hands of a conscientious responsible builder and responsible ebiker that knows the limitations of his pack :thumb:

 

[john61ct]

ps: checking individual cells in a pack that is 2P or more is impossible.

whether 2P or 4P a cell checker is able to alert you to a P Group that is suspect

I hope you did not mean to imply that I agree with this idea. If you think this is possible yourself please explain how, in detail.

I don't, unless by "cell checker" you mean a dummy load at 1S voltage, isolating the group and putting it through a timed CC-load discharge test to get a precise measure of current Ah capacity.

I know of no "cell checker" that has that feature, but would love to find one.

Could you specify (link to) which cell checker device you are talking about here?


> It's possible to further determine which cell(s) are inferior with pack design.

Sorry but again I have no idea what that might mean, please explain.


> a "decent bms" is mandatory when building a pack with recycled cells

A BMS is never "mandatory". Yes if you choose to use devices that provide whatever subset of the functionality implied by that term, they should be of good quality, accurate and reliable, and ideally with a safe failure mode.

With recycled cells, I never advocate using those, but if you do, I would suggest using only those that test out meeting condition criteria so that they can safely be used without any "a BMS" functionality at the per-cell level.


> pack wired for some occasional balance charging (as needed) before bulk charging and after bulk charging (as needed)

Balancing should only be done at/to a single specific SoC point. Doing so at more than one is a pointless counter-productive waste of time.

The primary goal in choosing that point (bottom balancing vs top vs mid-point) should be a result that - given the SoH of your cells, and your chosen pack cycling profile - minimizes how often balancing is needed.

IMO all this should have nothing to do with BMS functionality, nothing attached to the pack while it's in use being discharged.

Yes periodic preventive maintenance, but nothing to do with regular charging for daily use.

To me BMS **protective** functionality is essential, but that is separate from balancing.


> Isn't the bottom line of this thread that fuse-wire isn't necessary

Did anyone claim it is necessary? I thought it already clear that per-cell fusible link wiring was a preference.

But even so, there is no alternative for the functionality it delivers.

The decision whether or not to do so, IMO has nothing to do with weld-vs-no-weld construction.

Nor BMS usage vs cell-checker usage.

 

[eMark]

Spinningmagnets, john, flippy and others possibly think this thread is getting derailed with my belief that the use of a cell checker and balance charging with a DIY friction-fit kit (e.g. Vruzend V2.1, Nishi, or other ingenious designs) is a poor substitute for incorportating a decent BMS with Tesla style fuse-wiring in a spot-welded pack.

According to Shawn McCarty he believes the use of a cell checker with balance charging will triple the cycle life of a new pack. Maybe he's exxagerating or maybe not depending on other variables including the ebiker's need for speed, quick charging, a half decent BMS, etc, etc. I'd be happy if i get double the life or even 50% more cycle life and being a little nerdy helps :thumb:

On another thread docware commented that he sees the merit in McCarty's logic. Thus because my pack cells are easily accessible and i'm a little nerdy, patient and interested in giving something a try unless someone can convince me that McCarty is all wet and docware is deceived by the youtube presentation posted below.

I already have one balance charger from my RC Lipo flying days many moons ago and bought another used one. So, the following may not be john's, flippy's or spinningmagnets cup of tea, but i'm going to give it a try by doing the following with my Vruzend 10S5P pack ... https://www.youtube.com/watch?v=pljSZcEwc8Q&list=LLwENr3DwzrICzdPmRan_fkg&index=1699

Now will john, flippy and spinningmagnets be able to convince others watching this youtube that a decent BMS and Tesla style fuse-wiring is the way to go; whereas McCarty's is an example of what-not-to-do (i.e. KISS). So, am especially interested in john and flippy proving their convincing reasons why McCarty's logic is inferior to a decent BMS and Tesla style fuse wiring on my 10S5P pack (and no side-stepping the comparisons as Vruzend V2.1 has its advantages in DIY pack building).

Here's another Youtube using cell checker and balance charging a pack of recycled cells without a BMS ... https://www.youtube.com/watch?v=E2laf30KYyU ... those two connections hanging loose when riding is well ...
I included this youtube with those hanging loose connections near the tire as incentive that nerds using a cell checker and balance charging their packs are not the norm and therefore a decent BMS and Tesla style fuse wiring is still the way to go. Also, when McCarty says "triple the life" he is basically referring to charging a pack to only 4.0v instead of 4.2v and NOT because of the use of a cell checker and balance charging.

 

[john61ct]

Please stop putting words in my mouth, bit over the top drama creation there.

I am not in any way opposed to using a cell checker, but then I have no idea what you think it does, or why it is an either or choice

nor does that issue have anything to do with Vruzend

nor with fusible links.

Cycle life does not result from these choices but in how the cells are treated, and for each of the many factors there are many ways to accomplish your goals.

I'm not trying to convince anyone of anything, wrt your imagined debate I'm just confused.

Leave whoever McCarty is out of it, I'm not watching YouTube videos, hate that medium big waste of time.

Just lay out the logic of your points, as clearly and succinctly as you can, ideally one point at a time not mixing up with unrelated issues.

I raised specific points above and asked specific questions, trying to engage in actual constructive discussion.

 

[eMark]

Leave whoever McCarty is out of it, I'm not watching YouTube videos, hate that medium big waste of time.

That's about as narrow-minded as it gets. It's just another example of how little you regard my posts which you follow up with subtle or not-so-sutble belittling, demeaning or otherwise putting me down. What is your problem?

Just lay out the logic of your points, as clearly and succinctly as you can, ideally one point at a time not mixing up with unrelated issues.

That youtube is related to this thread (clearly and succinctly) as another option to consider other than Tesla-style fuse-wiring, but unfortuately you're unwilling to even watch it. Do you really think others buy into your excuse that watching informative, instructional youtubes is a waste of your time? Instead they are just as likely to think you're closed-minded or that you think it's a waste of your time that i'd have another option worth considering (as preventive maintenance) instead of Tesla-style fuse wiring.

I raised specific points above and asked specific questions, trying to engage in actual constructive discussion.

So, have i, but perhaps the real reason you don't want to watch that youtube is because you may find it difficult to refute and that McCarty makes some points worth consideration instead of using Tesla-style fuse wiring in favor of balance charging and cell checker.

OK, your turn to rip into me again, which you seem to relish, as you think any informative, instrutional youtube as another option besides Tesla-style fuse-wiring isn't applicable to DIY pack building ... if for no other reason that i suggest it. Even though docware thinks McCarty's balance charging rationale has some merit. Perhaps, even more merit than Tesla-style fuse wiring of a DIY spot-welded pack.

dont follow exactly how a cell checker is some kind of magic bullet here.

Going to paint my cell checker silver and enclose it in the shape of a bullet :wink: "Hi O, Silver Away"

ps: checking individual cells in a pack that is 2P or more is impossible.

Not so with my Vruzend pack that is easy to partially disassemble (if necessary) and using a DMM to check individual cell voltage ... may not even need to disassemble. You might find this informative youtube worth watching ... https://www.youtube.com/watch?v=pljSZcEwc8Q&list=LLwENr3DwzrICzdPmRan_fkg&index=1699 ... unless like john you're of the opinion that any youtube i'd recommend can't possibly be a viable option (balance charging when necessary) for any DIY pack build instead of / inplace of Tesla style fuse wiring (even with a $159 BMS).

 

[eMark]

Further Clarification: Actually john may have previously watched that youtube months ago so why does john think it's a waste of time. Well for one reason because using a BMS is the industry NORM for ebikers that don't do and don't want to do preventative maintenance like balance charging when needed (don't worry be happy) ... just as using fuse wiring in a Tesla is the NORM (don't worry be happy). The problem is that many of the BMSs in 18650 packs are at best only half-decent; whereas Tesla style fuse wiring and balance charging is FIRST CLASS (even above and beyond decent).

So, why is john bad-mouthing that video by Shawn McCarty when it makes so much sense? Because BMSs are an industry NORM even if only half-decent. Also john can't refute McCarty's basic premise that balance charging (WHEN NEEDED as the pack ages) is a good thing and a better option than Tesla style fuse wiring for the majority of 18650 pack applications for pack longevity. If your application is road racing with the pedal to the metal pulling most of the available amps ... then a very decent BMS is mandatory (IMO) and Tesla style fuse wiring may be just the ticket :thumb:

What really woke me up to the pathetic (half-decent) BMS in most packs is that they don't balance charge until the cells voltage is at or near 4.2v. Here's an extreme example (or maybe not so extreme): The manufacturer of my 10S4P 18650 pack gives the following instructions to owners ... "Once a month leave the 2.5A charger plugged in overnight for 16 hrs" and "Give it a full charge before storing over winter so it will be ready to go in the spring." I told this owner/CEO what i thought of that and of course he tried to defend himself. I actually got so frustrated that i told him i'd rent the nearby boxing club rink, drive several hundred miles and we'd see who's standing after a couple rounds with boxing gloves.

And what is john's and possibly flippy's reason for supposedly not watching or commenting ... BECAUSE using a BMS, even a half-decent one is an ebiking NORM (don't worry be happy) to the extent that the first words out of Shawn McCarty's mouth is like blasphemy to ebikers and for good reason ... EXCEPT the vast majority of BMSs don't balance charge until the cells reach 4.2v so that once a month a less expensive (cheap) Chinese pack needs to be balance charged overnight at 4.2v/cell for sixteen hours -- YIKES!
If that isn't a red flag what is and yet for many occasional recreational ebikers they just do what the instructions say and follow the rest of the sheep (be happy, don't worry).

Also, with a friction-fit pack it takes less than five minutes to remove a few small nuts and a couple parallel busbars to check the voltage of an individual cell that is suspect. Also, a friction-fit pack allows experimenting and other options. For example when my 10S5P pack has aged to the point that some cells are too far gone to be maintain proper balance i may be able to remove 10 of the poorest cells and convert it to a 10S4P pack which may still have close to 10A (12A when new) with the 30Q cells than does my current 10S4P Chinese 9A pack.

"WHAT! ARE YOU NUTS! You can't build a battery pack without a BMS!" ... https://www.youtube.com/watch?v=pljSZcEwc8Q&list=LLwENr3DwzrICzdPmRan_fkg&index=1699

 

[john61ct]

I give up, pretty close to just ban-ignoring. I fully agree with lots you say, but it's just not worth the trouble figuring out the 90% I don't even grok.

I do not claim a BMS is required.

Yes most are POS more dangerous than useful.
Yes if you use one it should be of good quality, but even if costing over a grand, you should not trust it nor rely on it too much.

I am a strong believer in regular preventative maintenance.

I think no-weld solderless is an excellent idea.

I think fusible links are a wonderful idea.

Does not mean I am advocating any specific implementation of either, neither for myself and especially not for others, to each their own as long as not making decisions from ignorance.

I've never seen a protective BMS that I would use for balancing.

IMO balancing should only be done when actually needed, often is not needed at all starting with good new cells, and I prefer a center-balance approach, bottom second, top last. But none at all best of all.

Again, does not mean I am advocating any of this for others, nor am I interested in expanding this discussion into that topic.

If Shawn McCarty whoever he is, comes here I may well be interested in **reading** what he has to say.

 

[eMark]

AWAY with 2019 and IN with 2020 (deleted previous post)

 

[eMark]

No matter how good the QC (zero tolerance for defects) at Tesla's Panasonic Gigafactory it's just a matter of time (120-150K miles?) before cell degradation with thousands of cells (no matter how sophiscated the BMSs?)

It would be interesting to know on average how many (if any) fuse wires are melted at 120K or at 150K (under warranty)? Maybe the BMSs in the Tesla S (7,104 cells with 16 modules in series) are so advanced that overcharging a cell is near impossible? ... http://store.evtv.me/prodimages/IMG_0468_medium.jpg ... Perhaps, the primary reason for fuse wiring the Tesla S battery is in case of an accident and possible lawsuit, that's assuming the sophiscated BMSs in the Tesla S would prevent a cell rupture/fire under normal driving use ... "After the crash, the Tesla's lithium ion battery caught fire, according to a wrongful-death lawsuit" (Oct 23, 2019). How often (if ever) has a Tesla S caught on fire because of a battery malfunction due to routine driving and preventative maintenance?

Large battery packs (hundreds of cells) on electric motorcycles (with 18650 or 21700 cells) may also rely on fuse wiring (e.g. Harley Davidson's electric LiveWire ($29,799). Curious to see what i can find out about the BMS, if cell fuse wiring and battery warranty ... https://res.cloudinary.com/twisted-road/image/upload/c_fill,g_center,h_600,w_900/v1/twisted_api/production/vehicles/igoyhwe2l6jxee3wgctj.jpg

Beijing-based Evoke Motorcycles are testing a newer, 2nd generation 18650 battery. The batteries incorporate new advancements, including a proprietary active thermal management system. The design includes a combination of software and hardware that integrate to precisely control the temperature range of the Li-ion 18650 battery cells.

“We quickly understood that cell surface cooling wasn’t enough to effectively bring down temperatures to a safe range while ultra-fast charging.” Says Chris Riether, VP of Engineering. Additionally, extensive design time went into creating a thermal cooling system that is inexpensive and light for small to mid-scale vehicles. Electric motorcycles and other small scale EVs don’t have the luxury of space like electric cars and busses.”

This thermal management should greatly increase the life of Evoke’s battery packs. Evoke’s 2nd generation batteries are designed as a modular system intended for different applications. The company says they can be daisy-chained together for use in other small and medium-size electric vehicles.... https://electrek.co/wp-content/uploads/sites/3/2018/10/unnamed.jpg

 

[spinningmagnets]

Please avoid personal attacks on each other, even if the substance of the attack is true. Trust the readers to see who has presented the more persuasive argument.

Please stay on subject. Good points that may be vaguely related are certainly allowed, since all threads have a tendency to "drift" a little. However, when a certain line of discussion is consistently on a separate subject, it may be split-off and moved to its own new thread. Such actions are at the discretion of the moderating board.

The subject at hand is DIY individual cell fusing.

 

[obcd]

If one cell in a parallel group behaves badly and starts to have a lower voltage than the others, all the others will pump current into that one cell untill it's voltage becomes equal. On an e-bike, it's usually 3 - 5 cells that will do that. On a tesla pack, you have a lot more parallel cells. This is a possible problem even expensive BMS boards can't solve as they only measure the voltage of the whole group.
I have no idea if the bad behavour (lower voltage) of a cell is something that can happen all a sudden or if it's something that happens slowly. In the second case, you might see a cell group lowering it's voltage much faster than the others during discharge, indicating that one cell of the group is not providing current anymore.
So, to stay on topic, the individual cell fuses of a parallel group do have a function. The more cells you have in parallel, the more important they become.
I watched part of the youtube of using a battery without BMS. A BMS does not only perform balancing. It also protects the cell groups against over discharge (low voltage) and against over charging. They also limit charge and discharge current. (Because there is a limit in how much current they can handle)
In my opinion, a bluetooth BMS does pretty much the same as your hobby balance charger. You also have the option to view the cell voltages of the individual cell groups. If your battery isn't made from a number of scrap cells with a different capacity, the low current used to balance the cells should be more than enough. If your BMS is unable to balance your cells, it's time for a new battery, or at least check your fire insurance. Most people don't care about their battery and simply charge it, use it and charge it again. In their case, a hobby balance charger won't work and a bluetooth BMS isn't usefull either.
A bluetooth BMS has the advantage that it can stay connected to the battery groups. Frequently plugged in and out JST connectors like to release their pins (they aren't really made for frequently plugging and unplugging) And we all know every pin of the connector has a voltage difference with the one next to him.
So, if someone wants to use a hobby balance charger and work without BMS, please do. Just don't promote it as the ideal method for everyone.

 

[fechter]

According to people more knowledgeable than me, the reason Tesla uses wire bonding is not so much to use them as fuses, but to automate the pack construction and minimize thermal damage to the cells. Even spot welding heats up the bottom of the cell to red hot and can cause deterioration of the cells. Thermal decomposition of the electrolyte and insulator material can contaminate the rest of the cell. While there are millions of packs out there that are spot welded and seem to be working OK, apparently there is still a chance of causing cell failure from the spot welding process. This failure may be months or years later.

 

[obcd]

Another thing you might ask is why most commercial e-bike batteries don't have individual cell fuses?
Tesla Model S and Model X batteries are not easy to service.
Maybe the idea with the fuses is that the battery can remain functional, even if some of the individual cells become disconnected.
The battery capacity will drop a little if a cell disconnects, but this also happens when the battery is aging.
I wonder if used tesla batteries are looked at, if they have some of the fuses blown and cells disconnected?

 

[john61ct]

Tesla Model S and Model X batteries are not easy to service.
Maybe the idea with the fuses is that the battery can remain functional, even if some of the individual cells become disconnected.

Exactly.

But there is no intention to "service" the modules, other than swapping the old/bad ones out and scrapping them.

 

[spinningmagnets]

Another thing you might ask is why most commercial e-bike batteries don't have individual cell fuses?

Fuses cost more, and the majority of customers are extremely price-sensitive.