Fuse-wire for individual cells, DIY Tesla style

[Altaowner]

It’s been speculated that this is exactly what they did on their endurocross race packs, except they would have built the packs 5P and saved the weight of 84 cells with only minimal decrease in range.

 

[ENNOID]

Hi,

I have been playing around the idea to create my own battery pack with 18650 cells and I realized that my design is very similar to Alta's pack with fuse wire, PCB on top for fuse wire & plastic case all around the cells.

Just a few pictures to show the idea of my PCB intended design for fuse-wire :

Here is PCB layout version 2 for max 11P3S block (PCB size is limited to 100mm x 100mm for cost reason):


Here is Version 1 PCB mounted on 3Dprinted case (There was not enough space on top holes for spotwelding the fuse wire so I ordered V2)

 

[Altaowner]

Nice work! Could I ask what spot welder you are using and what size and type wire have you been successfully able to spot weld?

Thank you.

 

[ENNOID]

I'm still working on it. I'm using kweld kit. You can choose the wire gauge you want depending of the individual cell max current that you want.

I am using this AWG 28 wire :
https://www.amazon.ca/gp/product/B01BDA7DO6?pf_rd_p=5a1aedcb-634e-416c-9e4d-99f483cdfe00&pf_rd_r=RGTR6ZZ4F7DBXAXRR8N5

According to fusing current column from wikipedia AWG page, it should be able to withstand approx 10amp per cell for a few seconds. Still untested though...

https://en.wikipedia.org/wiki/American_wire_gauge

 

[Altaowner]

Thanks for the info. I'm trying to determine if there is any reasonable way for people to rebuild Alta packs when we start seeing dead packs come into play. Alta appears to be using an aluminum 24 awg fuse wire for both connections, so we'd have to determine what size tinned copper comes close to that as far as "blow" characteristics. I'd love to hear your progress on your DIY pack, so please keep us posted.

Thank you

 

[ENNOID]

Yeah sure, I will post update on endless-sphere and on my github page were all my design files are located:

https://github.com/EnnoidMe/ENNOID-PACK

Thanks

 

[krlenjuska]

Question is this: how to know when some fuse is broken? Battery will keep running without 1 cell in parallel...

 

[ENNOID]

exact, not easy to know which cell doesn't work in the lot.. but the whole pack will still be functionnal and the pack won't burst into flames. the main idea behind fusing all cells is for pack security if one cell get damaged by unwanted event... maybe a sofisticated bms could detect a failure after a short circuit and after a sudden drop in capacity... the fused fuse should be easy to spot thought...

 

[krlenjuska]

Only way is to use transparent battery case

 

[ENNOID]

or easy to remove top case plate & also a removable bottom plate as well for changing the damaged cell... not really a problem there I think... but, how do you see a non-functionnal/shorted cell on another kind of battery pack anyway? I don't see any other way.

 

[krlenjuska]

or easy to remove top case plate & also a removable bottom plate as well for changing the damaged cell... not really a problem there I think... but, how do you see a non-functionnal/shorted cell on another kind of battery pack anyway? I don't see any other way.

So what kind of wire is best to use here?

 

[spinningmagnets]

I recall seeing a device with several DC circuits that had a blown fuse alert. On the current input side, when the fuse would blow in the lower-resistance circuit, a short parallel circuit had a tiny bulb and a high-Ohm resistor. Normal current took the "path of least resistance".

As long as the work circuit was functioning, almost no current would flow through the bulb. Once the fuse blew, there was no other avenue for the current, and the bulb would light up.

I'm not saying it's a good idea, I'm just saying that something similar is possible for anyone that doesn't want to visually check each "wire fuse" once a week. I'm sure there are also other methods to draw your eye to a bad cell.

A burnt fuse suggests a burst of current that would have likely made the bad cell hot for a moment, perhaps a heat-sensitive tape that changes color once activated?

 

[EbikeAus]

Only way is to use transparent battery case

That's why I use clear heat shrink

 

[fechter]

It's going to be challenging to detect a single blown fuse element. Like the one in the Alta pack that just broke and didn't really blow. If a single cell shorted, you'd get smoke out of the pack if not have the whole pack go off.

One possible approach is to use the existing battery current and voltage data to calculate a IR value for the pack and keep track of that. If a cell disconnects, the IR number will suddenly increase. Even if all the fuse links are intact, if a cell is starting to go bad, this measurement might catch it early. This approach is probably easier said than done, as IR depends on a bunch of other things like temperature and state of charge. The hardware would be simple but the software would need to be complex.

In most cases, you would simply notice the capacity was less than expected first.

 

[john61ct]

Fusible link wiring has special insulator to handle the fire/sparking when it burns.

Color coded by AWG, should also be clearly labeled as fusible link.

There are no "ampacity ratings" as such, they do not react in the same way as more precise CB/fuses.

Tradition is, to "protect the wire", go 4 numbers up, so a #16 power wire get protected by a short segment of #20 fusible link.

But for protecting a cell, I would do actual testing within as realistic a production setup as possible.

And remember, you are adding resistance, you are designing for a little fire in there, might be cheaper but but be careful.

 

[c70r]

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

For example I'm intending to use VTC5As and push them to 35A peaks for about 10s.
I saw this for example: https://www.ebay.co.uk/itm/5-6-6-7-5-9-13-18-20-24-27-32-35-45-65-100-Amp-Tinned-Copper-Wire-50g/123838091172?hash=item1cd5534fa4:m:mO0-ob6ZLr1WT2nBLBLVxcg

They claim that 1mm of the wire can handle 35A continuously and act as a fuse to about 80A. Would this be a wise decision or should I go for something a little smaller to reduce the fuse value but that would then reduce the potential continuous rating (essentially increasing resistance/temp). The only reason I thought of using 35A continuous wire for a 35A peak load is to avoid any further resistance/voltage sag and temp increase when pushing the limit.

 

[john61ct]

Get a bunch of different AWG, "bracketing" a bit above and below what you think might be the possibilities, and test for **your** real-life infrastructure and scenarios.

 

[eMark]

They claim that 1mm of the wire can handle 35A continuously and act as a fuse to about 80A.

This site is also helpful and supports your 1mm copper fuse wire that melts at 80A ... (18 awg, 1.023mm dia., 82 amps) ...
https://www.powerstream.com/wire-fusing-currents.htm

If the paralleled sub-pack is a 5P and one cell-fuse melts, that string will suddenly become a 4P sub-pack, but...the pack will still run, with each of the other four cells having 20% more amps pulled from them. I have a few ideas about how to flag a blown cell-fuse right away, but...the important thing is for an internally shorted cell to stop thermal-runaway immediately, so the entire pack doesn't go up in flames.

When one cell in a 5P group becomes disfunctional is it the series string of that bad cell that suffers most? For example if the 5 strings were 10S one of the S strings now becomes 9S (although it's in parallel with the other four 10S strings) that 9S string with the dead cell may be further degrading what was once a 10S string? In such a scenario would a BMS shut down the entire pack? Are there BMS' that sound an alarm or buzzer when (for instance) a cell in a 10S string becomes disfunctinal or does the BMS automatically shut down the pack?

Would appreciate any recent idea(s) about how "to flag a blown cell-fuse right away" to prevent further pack degradation.

 

[Hillhater]

When one cell in a 5P group becomes disfunctional is it the series string of that bad cell that suffers most? For example if the 5 strings were 10S one of the S strings now becomes 9S (although it's in parallel with the other four 10S strings) that 9S string with the dead cell may be further degrading what was once a 10S string? In such a scenario would a BMS shut down the entire pack? Are there BMS' that sound an alarm or buzzer when (for instance) a cell in a 10S string becomes disfunctinal or does the BMS automatically shut down the pack?

You seem to be mixing your groups of parallel “P” cells ,..and your strings of series “S” cells (and groups of cells).

 

[john61ct]

Yes you're confused. 10S means a 36V pack, a string of 10 cells, by definition a "string" means in series; use "groups" for paralleled cells.

Sub-pack modules perhaps when strings are paralleled.

This
> For example if the 5 strings were 10S one of the S strings now becomes 9S

is meaningless.

All the paralleling should ideally be at the lowest 1S level, say 6P group of cells, so if one cell goes off line, capacity is reduced by under 20% and thing keep ticking along at the normal voltage

Paralleling same-size 1P sub-packs would be the worst possible design.

And those Powerstream ratings are not real life, rather just super conservative, real life testing in context is required.

 

[eMark]

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.

 

[c70r]

Not really sure why I was quoted but my scenario is as follows.

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. The fuse wires purpose is just to solve one of the potential hazards of such a pack. I've even been looking at the potential use of a suppressant gel for example. The example I saw involved a pack of 18650s with one of the cells being pierced to ignite it and with the suppressant gel the surrounding cells did not ignite.

I can't really comment on why some DIYers do and don't cell fuse but I would assume one of the reasons is that the cell fusing is much more time consuming than just spot welding long nickel strips.

Personally, the only thing that made me decide to cell fuse is that Alta does so and I have yet to see any of their packs face major failure, sure there's a few cases of the fuses breaking but that seems to have been a manufacture fault. Again, not saying that fusing is the solution or reason why their packs seem reliable for a "high performance" application but it is a level of precaution that should be taken if you're not lazy.

 

[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. The fuse wires purpose is just to solve one of the potential hazards of such a pack.

Personally, the only thing that made me decide to cell fuse is that Alta does so and I have yet to see any of their packs face major failure, sure there's a few cases of the fuses breaking but that seems to have been a manufacture fault. Again, not saying that fusing is the solution or reason why their packs seem reliable for a "high performance" application but it is a level of precaution that should be taken if you're not lazy.

You may rightly deserve the Macho Man (28S20P) DIY build of 2019 . Your application definitely calls for fused links between your Mucho parallel cells. Your peers would think you "lazy" (maybe, maybe not) if you don't use fused parallel group connections with your triangular (customized shape) monster pack. PLEASE do post some photos of your build progress with parallel fusing.

Flippy is possibly the ONE most knowledgeable and experienced in recommending what kind of fused parallel connections to use with your performance pack ... as well as his smart BMS brand preference, balance charging (how often - when needed), etc. You definitely came to the right place and flippy's advice (fusing, etc) is invaluable :thumb:

This is the image in my mind of your BIKE (looks like 21700 or bigger instead of your VTC5As 18650 cells ... <img src="http://www.plugbike.com/wp-content/uploads/2009/06/ttxgp-kingston-university-naked.jpg" alt="Image"/> ... although from what can be seen what type of fusable connections were used on the parallel groups ??? When the cells are exposed as they are in this photo then thin 1mm copper wire fuse connections aren't a practical application (?more of a hazard?). Can't really make out the type of fusing.

 

[john61ct]

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.

Ridiculous poppycock.

String means in series, period, it is an electrical term, nothing to do with physical layout. Same with group for paralleled cells.


I have no desire to undermine your "credibility", just trying to increase it by correcting your mistakes, you should be grateful not lashing out.

Your logorrhea does not help your cause.

Most packs have no fusing at all, because fuses increase resistance, reduce efficiency and complexity reduces reliability.

And 99.99% of packs are spot-welded, for good reasons, but not conducive to rebuilding after individual cells fail.

Fusible links don't add as much resistance as fuses, but 99.99% of pack builders have never even heard of them.

It takes experience, skills, judgment and special gear to size them right.

 

[eMark]

Frankly, i value flippy's 4 posts in this thread (with respect to fusing parallel cells :thumb: ) as much or more than all the others ... sometimes it helps if you can read between the lines. For example why only the following 4 posts by flippy in this 5-page fusing thread when he's a seasoned 18650 DIY Pro ...

you need to use proper cell holders, proper sized nickel strips and make sure the balance wires dont touch or cross and glue/tape everything down so nothing can move. Then put the battery in some shock absorbing foam and strong case that can endure being thrown around a mountain.

that way you wont get a short. i built dozens of mountainbike batteries and never had a single issue in the past years.

One of several questions i'd like to sit down with flippy and listen~listen to his explanation is: How many of your mountainbike battery pack's parallel groups were fused and for those packs that weren't - Why Not?

Would a layer or 2 of shrink tubing over the glass provide enough protection?

1 is enough. Prefrably heat shrink with glue.

One layer is enough, especially if you use glue. That will keep the glass in place when it shatters and absorbing the force. They also do this in regular commerical stuff where they just have a fusable resistor or something.

what cell was that shorted? all name brand cells i use have protection for overpressure built in and those trigger way before the plastic melts.

That's good to know. In this case it was a samsung cell being soldered, so the heat was not generated within the cell.

Don't take flippy's last reply and Addy's reply the wrong way. Flippy is by no means in favor of DIYers soldering directly onto the ends of an 18650 cell.

As another seasoned and tactful DIYer once commented about a thread photo of a DIYer using thin wire fuse links -- "I know why you are doing it, but i question why you need to do it." (paraphrased)

If i was trying to get top prize with my ebike speeding down the Brainerd International Raceway Dragstrip for 15 seconds of glory i'd do whatever necessary to prevent one blown 18650 cyclinder from starting a chain reaction. Even if i just liked to put the pedal to the metal, feel the need for speed and the wind against my face i'd do whatever to prevent as little damage as humanly possible to my expensive 28S20P LoL (Labor of Love) should one of the cylinders suddenly decide to have a mind of its own