Battery connection method

[Toothless]

Hello everyone

I've reading here for quite some time now and plan on building my own ebike. I'm probably going to use a bbshd as a motor and i'm very interested in making my own battery for it.

So for a bbshd i need to be able to hande at least 30A but i think it might be safer to be able to at least hande 40A. I'm planning on using 21700 samsung 40T(3) cells after studying some threads with cycle life and temperature after a 1000 cycles. I'll be getting these from nkon because i live in the EU and they're recommended in the ultimate spot welding how to guide.

I read the Bluetooth bms thread pretty thoroughly and I think i'm going to buy an ant-bms from ic gogo on aliexpress. Also because this bms can work with the vortecks vbms app that looks rather nice.

Now i'm still debating what way i should be using to connect the battery's (plan on doing a 14S 5P pack) from what it looks like there are a couple of easy options i can use:

1. Spot welding. This is the most common technique used for ebike battery's and a very stable and safe option I think, but there is a problem for me... As i will only be building one battery pack and maybe another one in a couple of years if this first one isn't up to speed anymore, it seems like a lot to spent 200€ on a kweld or a maletronics spot welder.

2. Soldering: doesn't really seem like a great option even though people have proved it can be, I'm not talented in any way with a soldering iron so I think I won't be taking this route

3. Magnets: this seems like a very interesting option and there are some threads to be found about this, but most are old and even though I read them they don't seem to have a very clear conclusion of wether it is actually a viable option.

4. Fuse wires: kinda complicated...

So out of these options option 1 and 3 are by far the most interesting. For option 1 i want to know if using an MOT like some other people have done would be a solid enough option, because i see a lot of contraversy about these and some people get them to work whilst other's don't.

Then for option 3 the magnets seem like the most interesting idea of them all. I've heard of people doing it and running them for quite a while without problems, but the information is out of date. I seem to be stuck thinking that it might not be a viable option.

Any advice/corrections/information is appreciated

Here is a corrected version of your passage:

I've been reading here for quite some time now, and I plan on building my own e-bike. I'm probably going to use a BBSHD as a motor, and I'm very interested in making my own battery for it.

So for a BBSHD, I need at least 30A, but I think it might be safer to be able to handle 40A. I'm planning on using 21700 Samsung 40T(3) cells. I'll be getting these from NKON because I live in the EU and they're recommended in the ultimate spot welding how-to guide.

I read the Bluetooth BMS thread pretty thoroughly and I think I'm going to buy an ANT-BMS from IC GOGO on AliExpress. Also, this BMS can work with the Vortecks VBMS app that looks rather nice.

Now, I'm still debating which way I should use to connect the battery's (plan on doing a 14S 5P pack). From what it looks like, there are a couple of easy options I can use:

Spot welding: This is the most common technique used for e-bike batteries and a very stable and safe option, I think. But there is a problem for me: as I will only be building one battery pack, and maybe another one in a couple of years if this first one isn't up to speed anymore, it seems like a lot to spend 200€ on a KWELD or a Maletronics spot welder.

Soldering: doesn't really seem like a great option even though people have proved it can be done. I'm not talented in any way with a soldering iron, so I think I won't be taking this route.

Magnets: this seems like a very interesting option and there are some threads to be found about this, but most are old and even though I read them, they don't seem to have a very clear conclusion of whether it is actually a viable option.

Fuse wires: kinda complicated...

So out of these options, option 1 and 3 are by far the most interesting. For option 1, I want to know if using an MOT, like some other people have done, would be a solid enough option. Because I see a lot of controversy about these, and some people get them to work whilst others don't.

Then for option 3, the magnets seem like the most interesting idea of them all. I've heard of people doing it and running them for quite a while without problems, but the information is out of date. I seem to be stuck thinking that it might not be a viable option.

Any advice, corrections, or information is appreciated.

 

[amberwolf]

I've reading here for quite some time now and plan on building my own ebike. I'm probably going to use a bbshd as a motor and i'm very interested in making my own battery for it.

Just a suggestive note:

If cost of the tools and parts to build the battery is an issue, it's likely to be a cheaper to buy a well-built battery from a reputable vendor like EM3EV, etc. than to build your own from lots of small cells.

If you are willing to work with used EV-grade large-format-cell packs, like those Batteryhookup and the like often have, then you can build a pack for much less, since most of the work has already been done for you.

Typically, as long as the physical format/size/shape of the module you get is usable as-is on your build, all that's needed is to break one/some of the series connections, and either remove the extra cells (like if you need a 14s pack and you start with an 18s module, or whatever) or then parallel those cells with the others (like if you need a 14s module and start with a 28s or 30s or whatever). If the physical format needs modifying, it gets more complicated, depending on the starting format and the required end format.

Then you can install whichever BMS you prefer to it, but with these large format cells it's much less likely to have balance issues until the cells age quite a bit, since most of them can easily handle the loads an ebike middrive would put on them (since they are not being pushed to their limits like many ebike-battery-cells would be, won't be stressed by that either).

 

[amberwolf]

That said, if you're set on building a cylindrical-cell pack, some thoughts about connection methods:

--the magnets are least likely to damage cells during the build process, but will probably have the highest interconnect resistance, and so the lowest current delivery capability and highest voltage sag.

--soldering is the most likely to damage cells during build process.(you might not detect the damage initially, either).

--If buying a spotwelder for the one job isn't cost-effective, building one from a MOT can certainly work, the catch is like all other spotwelders creating the current-pulse control system so that it works reliably to correctly control the pulse(s) length, timing, and strength, without blowing up the power-control devices, or causing weld blowouts, etc. (and making or getting electrodes that don't melt or stick even when the current is right). There's at least one good big thread here with various control methods and hardware in it, some with test results.

If time isn't an issue, the MOT design/experiment process to get a working system for your build could cost less than a prebuilt known-working spotwelder, as long as you don't have to buy too many sets of FETs or SCRs or whichever power-control device you want to use with it, due to failures during the process. If there's a known-working MOT design that does what you need, you can just straight up build it, and that may cost a lot less in time and money.

There is a potential other connection method, but it isn't known to be as reliable or low-resistance, and that's pressure-contact, like springloaded, or compression, etc. There are kits for it, of which most have had reported problems. I have forgotten the name of it but there's one here on ES that is done in small segments with endcaps, then you string those togehter series/parallel as needed. Probably ends up physically larger but might be better than Vruzend and the like.


Fuse wires not in themselves a connection method. They still have to be installed to the cells using one of the available connection methods. (ultrasonic welding equipment like that used by OEMs for the purpose is probably not an option, so you're still stuck with soldering, magnets, or spotwelds, compression, etc.) If you're using cells well-within their limits, the fuses are probably not necessary, but there are detailed discussions about that sort of thing in the various fusing threads. They wouldn't prevent a thermal runaway in the event of a failed cell that's already gone that way, but they would stop other cells from draining into a shorted cell and starting such an event in the first place, as long as they are sized to blow at pretty low currents. The problem with that is that low-P packs are likely to require more current from a cell than the fuses-sized-to-prevent-that-problem could allow.




As for "out of date" information...that's never really the case with methodology/testing. If something has been tested and posted about, even if it was a hundred years ago, then as long as you are doing something the same way as was tested, then your results would still be the same as theirs. As long as those results are the results you are after, the info is perfectly usable. It doesn't have to be a thread currently being posted to, for instance, to be useful.

The only way info is "out of date" is if something has changed that makes the information irrelevant, such as a price change, or some critical thing used in it being no longer available in any form, etc.

 

[Toothless]

Thank you amberwolf for the quick and detailed response, I am indeed set on building a pack and have taken a look at the prebuilt packs. Now that I think about it I never really took a decent look at the prices on prebuilt battery's. When seeing the prices I think that building my own and just buying a spot welder or try building one it will still result in about the same price(maybe a bit higher). I really do want to build the pack myself so considering everything I think that I might just buy a spot welder as the price is not that much. I will most certainly do some more research on the MOT way and because they're so cheap to make like that I might just try that first.

That being said you are right about out of date information, it still holds up today and I think I was just a but uncertain about the methodology because it was old and I thought "well if nobody has done it recently it must be a pretty bad method".

 

[amberwolf]

Regarding the threads "dying":

Sometimes the development of something stops because once the research reaches a certain point where it "works" well enough, and you can replicate it reasonably easily vs further developing it, things tend to just sit like that, and only get posted to when someone either has a question or if they are showing off what they built with the info.

Also, good DIY spotwelders like the Kweld, etc., have gotten cheap enough and reliable enough and easy enough to use, and easily available, so that their cost can be comparable with working out the rest of a MOT welder, etc., and are much smaller and more portable, more programmability for different usages, etc.

So that tends to dampen the enthusiasm for something that essentially has to be built from scratch just to use it to build something else from scratch...when one has to build major tools to then build the project pieces, to then build the project it greatly lengthens the time and effort to get something done. For those that just love the whole process of building things, that's not really an issue (if time is available), but most people, even most DIYers, are trying to accomplish some specific goal, to end up with something that does something they need to use or do, and anything that shortens the path to that goal that isn't excessively costly may be helpful in this.

There was a time when I was much younger that the building was more important than the using, but these days I have a lot less energy (and time) for the building part, and tend to use existing stuff already made for the purposes as much as possible...I might be getting them used, but at least I don't have to fix them or build them first, in multiple levels of construction, to get done what I need done.

(Honestly, these days, if I had money to pay someone else to custom-build things for me, and fix them when required, at this point I'd do that rather than building them myself, so I could use what time and energy I do have for creation on my music and other art instead.)

 

[ZeroEm]

Biggest thing about building your own is you know what you have. most pre built batteries have cheap and some times bad cells. You have the chance to only put quality cells in and get a longer lasting battery. set it up where you can test the battery for balance.

 

[goatman]

30 amps from 5p is only 6amps
a 10mmx1mm ring magnet would work on the 21700 cells with some 0.07mm copper. the 0.07mm copper works better than the 0.1mm copper, its more flexible.

you sure you want 40T3 instead of 50e?
is it cold where you live?

im still using the magnets but i have to breakdown and buy a k weld spot welder so i can easily repair spot welded packs
alot of bad batteries are from bad spotwelds so get a good one.

 

[99t4]

More "pressure contact" battery constructions for you to consider (#5 in your list?):

The Barncat Battery- No weld/no solder
https://endless-sphere.com/forums/viewtopic.php?f=14&t=115074

N.E.S.E. the no solder module
https://endless-sphere.com/forums/viewtopic.php?f=31&t=88051

 

[Toothless]

goatman, I did some more research about the magnets and also I will fully read the thread you have about the plastic dip. I've seen the thread before but just quickly scrolled through it. I think magnets are the most interesting way of making a battery pack so I'll look into it a bit more.

Also will take a look at the 50E, it's not particularly cold where I live so they might be a better option.

 

[Toothless]

99T4, I've already checked those threads before and they're indeed really cool options. I think the barncat battery is pretty hard to build though, but I won't rule it out because it is a very cool design(unlike I've ever seen).

I also have taken a look at the NESE before but ruled it out because the cost of these would be about the same as just buying a spot welder instead. BUT, a good friend of my dad's has a job that involves 3D printing and the design of the module is open source so I might ask him for some help/advice on this. If it would be possible to do that I feel like this is a very cool option as it is very stable because of the sort of rubber used to make sure the battery does not lose contact.

 

[agniusm]

I also have taken a look at the NESE before but ruled it out because the cost of these would be about the same as just buying a spot welder instead. BUT, a good friend of my dad's has a job that involves 3D printing and the design of the module is open source so I might ask him for some help/advice on this. If it would be possible to do that I feel like this is a very cool option as it is very stable because of the sort of rubber used to make sure the battery does not lose contact.

Have you considered getting 3D printer instead of a spotwelder? You could get decent ender 3 printer for less than kWeld and use it not only for battery but around the house, on bike builds.
Here is a photo of a bikes i did for kids, makita battery converter with integrated esc on red one:


12V battery with 3D printed connector holders and Meanwell led supply feet and handle:

Bike tail light:

Around the house spice rack:

This greatly reduce cost of my system

 

[tomjasz]

NESE isn't expensive when it comes time to rebuild a pack. You have everything you need except new cells. I've had KWeld and another welder from Croatia sold here on ES. Welding is a pain. After the welder you'll need nickel ribbon, kapton tape, solder and soldering device, case and/or shrink-wrap. Add the real costs.

I've had the magnet kits, Vruzend kits, and more. N.E.S.E. remain the best and easiest to use for me. Also the most responsive reseller of battery kits ever. And even paying to have someone else print I'm still not spending what I did on welding.

 

[jas67]

You could probably recover 50-75% of the cost of the K-weld by selling it when you're done making your pack.
I'm sure there are some here who would happily purchase a lightly-used K-weld for a discount. I know that I would've (I bought one new recently).

The K-weld is a brilliant piece of kit. I had a Sunkko briefly. It wasn't up to task for anything thicker than .1mm nickel. The K-weld does .2mm with ease, and very consistently. It also produces very good results for .08mm copper with .1mm nickel on top.

 

[ZeroEm]

by jas67 » Jan 25 2023 6:21am

You could probably recover 50-75% of the cost of the K-weld by selling it when you're done making your pack.
I'm sure there are some here who would happily purchase a lightly-used K-weld for a discount. I know that I would've (I bought one new recently).

The K-weld is a brilliant piece of kit. I had a Sunkko briefly. It wasn't up to task for anything thicker than .1mm nickel. The K-weld does .2mm with ease, and very consistently. It also produces very good results for .08mm copper with .1mm nickel on top.
Top

Second that, would resale quickly one would think.

 

[tomjasz]

Sure, my KWeld sold rather quickly. Sadly I jumped in to early and it needed significant upgrades. And then I was warned it wasn't pacemaker friendly.

So do you buy another KWeld every time you need a new pack or need a repair? Reusable kits are sustainable.

https://endless-sphere.com/forums/viewtopic.php?t=95865

 

[Toothless]

Okay so over the last few weeks I've been researching a lot more...
Even having seen about a 100 different methods, I still keep coming back to the N.E.S.E. modules, which I believe is the best option for me(and also the safest). It is also sustainable and I can reuse it in a couple years if needed, so the price isn't really an issue
Thanks all for the advice!

 

[Hummina Shadeeba]

--the magnets are least likely to damage cells during the build process, but will probably have the highest interconnect resistance, and so the lowest current delivery capability and highest voltage sag.

Have you seen evidence of the magnet method having higher resistance? I thought it would have the least resistance. It would be good to see resistance testing of all the connection methods. Someone said each weld is good for 5 amps but seems hearsay

 

[docw009]

I spent over twice that on the learning curve to get here, but what I use now is a $20 welder from china running of a RC drone battery, 10.8V-5AH Lipo with 600A pulse rating, The RC charger and Lipo pack are about $120, It has enough power for my needs, which is .15 nickel. Should have bought a kweld, but they were unavailable in late 2021.

Everyone is right though, It's also a cost to buy cells. For a BBSHD, I would like at least 13S-5P with Sanyo/Samsung cells. Those would cost $6 each, so it's $400 for cells, Add $100 for case, BMS, and supplies. I believe UPP sells that in a G70 case for $500-600.

On the other hand, someone like me would take a flyer on the $1 Samsung 30Q's that BatteryHooklup recently sold. These cells supposedly date back from 2019, but have not been used in the field. They may even be older, I recently built a 13S-4P with those cells in a hard Dolphin style case. We;ll see how this $120 battery works when Spring comes. It's nominally 48V12AH and my load tester says 10,9 AH pulling 3A down to 42V LVC.

 

[Aussie78]

The published study “Electrical contact resistance measurements of clamped battery cell connectors for cylindrical 18650 battery cells” by
Christoph Bolsinger *, Matthias Zorn, Kai Peter Birke that appeared in the Journal of Energy Storage in April 2017 shows the following:

Average contact resistance of nickel resistance spot welded to a Panasonic 18650 with 12 spots is about 167 micro ohm. (167 µΩ = 0.000167 Ω)

Clamping Copper, polished with 800 grip paper, clamped with 400N of force, can achieve 50 micro ohm. (50 µΩ = 0.00005 Ω)

Resistance spot welding is used in manufacturing because it’s cheap.

Edited to microohms, not milliohms. Sorry people, was rushing and messed up. Well spotted.

Yes this article is expensive to purchase, I have access to a mates engineering subscriptions, many of these subscriptions run 8k usd a year. Sign up for studocu.com, pick a electrical engineering under grad course and then search for this article. It’s something like $280 usd a year from memory for studocu

 

[Hummina Shadeeba]

Nice find thanks!
How much pressure will a commonly used n52 with .2mm copper between put on a cell though?

https://www.kjmagnetics.com/calculator.asp

I’m math illiterate but seems the pressure from a magnet on a cell is far far from what this study is talking about, no?

 

[agniusm]

The published study “Electrical contact resistance measurements of clamped battery cell connectors for cylindrical 18650 battery cells” by
Christoph Bolsinger *, Matthias Zorn, Kai Peter Birke that appeared in the Journal of Energy Storage in April 2017

Could you link to that article? 400N does not say much. If its on area of the positive contact, that's 40kg per contact.
Thanks

 

[tomjasz]

The published study “Electrical contact resistance measurements of clamped battery cell connectors for cylindrical 18650 battery cells” by
Christoph Bolsinger *, Matthias Zorn, Kai Peter Birke that appeared in the Journal of Energy Storage in April 2017

Could you link to that article? 400N does not say much. If its on area of the positive contact, that's 40kg per contact.
Thanks

Sadly full version unavailable. Requested from authors just now.

 

[Hummina Shadeeba]

https://www.sfu.ca/~mbahrami/pdf/2011/Investigating%20electrical%20contact%20resistance%20losses%20in%20lithium-ion%20battery%20assemblies%20for%20hybrid%20and%20electric%20vehicles.pdf

This study shows a good connection with 2000 ft/lbs pressure on 364mm^2. To get similar pressure on a 18650 with only 10mm^2 contact area my guess at the math is: (2000/36.4 =55).
So 55ft/lbs on a 10x10mm cylindrical cell terminal would get the same pressure as in this study.

But that’s a lot less surface area in contact and apples to oranges

 

[Hillhater]

Average contact resistance of nickel resistance spot welded to a Panasonic 18650 with 12 spots is about 167 milliohm

Clamping Copper, polished with 800 grip paper, clamped with 400N of force, can achieve 50 milliohm.

Is it just me, or is 167milliOhms ..extremely high for a fused metal connection ?
A 10s 1p string would have a resistance of 1.67 ohms ??

 

[Hummina Shadeeba]

Average contact resistance of nickel resistance spot welded to a Panasonic 18650 with 12 spots is about 167 milliohm

Clamping Copper, polished with 800 grip paper, clamped with 400N of force, can achieve 50 milliohm.

Is it just me, or is 167milliOhms ..extremely high for a fused metal connection ?
A 10s 1p string would have a resistance of 1.67 ohms ??

How do u know 1.67 ohms? Isn’t it a pretty simple test w the three wire method? Or an appropriate battery resistance tester? I almost don’t do anything beyond type but isn’t this an easy number to get?

There’s huge threads on magnets n copper or welding .. but where’s the juicy graph w weld number:conductance and magnet size :conductance

And it seems welds are all over the place in wattage n time and all assumed good enough if u leave bits when rip it off.