18650 spot welding -how to- ULTIMATE REPOSITORY

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ChicagoJohn   10 µW

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Re: 18650 spot welding -how to- ULTIMATE REPOSITORY

Post by ChicagoJohn » Jan 09 2018 9:36am

fechter wrote:
Dec 25 2017 9:50pm
ChicagoJohn wrote:
Dec 25 2017 3:26am
Could you tell me the CCA rating of your graphene battery and what the shape of your electrode tips is?
These are Turnigy RC Lipo batteries, mine is a pair of 2.2Ahr in parallel. It is 3s. These don't have CCA rating, but are rated for 130C discharge rate. Not cheap, but very lightweight and small.
Img_0571.jpg

My electrodes are semi-rounded and have about a 2mm dia contact area.
I thought I'd follow up on my status with respect to fechter's method. My 3S graphene Turnigy 5000 mAh battery arrived and in preparation for a trial with my delivery system (based upon a small engine starter relay) I wanted to get an estimate of where my current would be at relative to the manufacturer's stated "burst" rating of 130C = 650A for a 5Ah pack. At 11.39VDC charge, I connected the pack to my delivery system using the XT90 connector supplied such that all connections and cabling remain the same as in the welding scenario, including the use if nickle strip as the electrode contact surface to the load. For a load I used a 3.2 Ohm 25 watt resistor.

Open circuit voltage before and after the test was 11.39 and 11.38VDC, respectively. Using a separate 12VDC source to activate the solenoid, I measured voltage across the resistor load at 5 and 10 second intervals at 11.32 and 11.31VDC respectively. So with the 3.56A current under load, the combined drop for internal R, cables, and contact resistance was 0.07V yielding a combined "rig-resistance" of about 20 mOhm and an associated maximum burst current during spot welding of 578A, about 10% lower than the burst rating of 650A.

I'm now proceeding to evaluate via scope the relationship between Arduino interval setting and the actual pulse interval delivered by the Turnigy battery which will likely involve a latency due to its use in powering the solenoid as well. For the car battery this was a constant 8 ms -- delivery of 60 ms pulse required the Arduino interval to be 68 ms, for example. Once I get that, I'll do a test starting at 8ms and see what happens. After thinking about it, fechter's comment makes sense -- lower current requires longer pulse time and due to thermal conductivity of the strip and substrate this results in more total heat transfer to the cell. The higher the amperage, the shorter the pulse and the more quickly melting temperature is achieved at the weld contact area, reducing total heat transfer.

======================================
Results: Pulse width testing showed the same 8 ms difference between Arduino setting and delivered pulse. I think this is probably a function of the solenoid coils and would have to be evaluated for each specific set of parts. So with the info on likely current limit, I finally decided to try it. It makes very nice welds at 8 ms delivered pulse (16 ms Arduino setting) without sparking. For about $50 for the graphene lipo, not to mention its small form factor and weight as fechter mentioned, this looks like it could be a viable option for spot welding. For testing purposes, I've been using a steel paint tray, probably nickel coated, of about the same thickness of the bottom of an 18650 can with a wood support under the weld location and 0.1 mm pure Ni strip. Previously I was seeing relatively huge black char spots along with smoke, and had to turn the tip on my soldering station up to 700 - 800°F to duplicate it. With this current source, the discoloration of the wood under the weld spots is only barely visible light brown, indicating a very substantial reduction in heat and resulting temperature versus the 325A LA battery and 30 / 60 ms double pulse minimum required for a good weld.

I'm still trying to get the Vruzend system optimized by changing out the stainless steel across the board with phosphor bronze spring temper, brass bolts and nuts, and copper parallel bus bars. But if that doesn't pan out, I now have an alternative to further explore.

Thank you, Mr. fecter !! :)
===========================
RISK WARNING: In the event anyone decides to attempt something like this, they should be thoroughly familiar with the potentially dangerous, life/property-threatening consequences associated with short-circuiting lipo packs; which this could easily become depending upon the system used to deliver and control the pulse to the weld areas. I think the risk is considerably higher using a graphene lipo, even though it is "rated" for 130C burst current, than it would be with a lead-acid battery as the current source in this regard. From my research on this topic, it appears there are no recognized and accepted criteria for burst current rating and many maintain that every excursion beyond continuous use current rating causes additive damage to a pack and could be catastrophic. Proceed at your own risk !!!

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Re: 18650 spot welding -how to- ULTIMATE REPOSITORY

Post by DasDouble » Feb 14 2018 5:10pm

I have just tried out a spot welder of a friend of mine who has built it by himself with the help of a 3€ timer from Amazon and an old microwafe + some AWG2 wires. I can tell you, I have never felt such a nice spot welder in my hands before. The microwave transformer is 230 : 1,5 and works perfeckt at 0,1 seconds.
I know thats a little bit of topic maybe. Just wanted to tell my short experience with it. I have also built myself the same one in the old box of my old Sanyo 779 Spot welder which gave its job up lol but the one of my friend looks nicer and cleaner. Just don´t have a pic of it right now

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Re: 18650 spot welding -how to- ULTIMATE REPOSITORY

Post by bigbore » May 08 2018 8:27am

What do you think about this method of using copper strips soldered to nickel strip? This is a test with scrap cells then I will make a new 20S14P battery with these copper strips.
What I do is solder copper and nickel with a soldering jig and then spot weld the nickel strips on battery terminals.
Nickel strip are 0.2mm thickness 10mm x 18mm and copper are 0.2mm thickness 8mm x 64mm

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Re: 18650 spot welding -how to- ULTIMATE REPOSITORY

Post by flippy » May 08 2018 9:56am

i expect a lot of oxidation when the nickel, copper and solder/tin are going to have a reaction. dont know by memory but one metal is going to be the sacrifical one.

it also looks REALLY labour intensive. there is nothing to be gained by this method compared to just spotwelding the proper nickel strip or even copper if you can do that.
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Re: 18650 spot welding -how to- ULTIMATE REPOSITORY

Post by bigbore » May 08 2018 10:44am

flippy wrote:
May 08 2018 9:56am
i expect a lot of oxidation when the nickel, copper and solder/tin are going to have a reaction. dont know by memory but one metal is going to be the sacrifical one.

it also looks REALLY labour intensive. there is nothing to be gained by this method compared to just spotwelding the proper nickel strip or even copper if you can do that.
I want to spot weld nickel strip on battery terminals and I do not find a good one that can carry 22A continuous.
Where did you find the info about the oxidation? I need to check the soldering points of the balance wires on my current battery that was built in 2014.

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Re: 18650 spot welding -how to- ULTIMATE REPOSITORY

Post by flippy » May 08 2018 11:22am

Google sacrifical metals and start from there.


Does each cell actually carry 22A continous?
If that is the case then most batteries are drained in under 10 minutes.
For peak loads of 22A a 8x0.2mm strip would be enough, 8x0.3mm if you can weld that thick is well enough. Your cells will die before that strip does.
You can also double up on 0.2mm if you use 3 welds on the first layer.

Also, dont focus so much on the parralel current strip. That is almost zero amps, its just to keep the cells balanced. It does not need to handle any current. Start with the series strips and after all those are done you can weld the parralel strips and make the pack whole. It is also a lot safer when working on the battery as you only short 1 series string instead of the whole pack.
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bigbore   1 kW

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Re: 18650 spot welding -how to- ULTIMATE REPOSITORY

Post by bigbore » May 08 2018 12:24pm

flippy wrote:
May 08 2018 11:22am
Google sacrifical metals and start from there.


Does each cell actually carry 22A continous?
If that is the case then most batteries are drained in under 10 minutes.
For peak loads of 22A a 8x0.2mm strip would be enough, 8x0.3mm if you can weld that thick is well enough. Your cells will die before that strip does.
You can also double up on 0.2mm if you use 3 welds on the first layer.

Also, dont focus so much on the parralel current strip. That is almost zero amps, its just to keep the cells balanced. It does not need to handle any current. Start with the series strips and after all those are done you can weld the parralel strips and make the pack whole. It is also a lot safer when working on the battery as you only short 1 series string instead of the whole pack.
Not peak! CONTINUOUS. I want to ride for 4-5 km at 90-100Km/h
Each cell will deliver 11A continuous so each strip in the middle section will see 22A continuous
Image

Also I forget to mention that I think that hot glue (also the Bosch) sticks very badly on the cells wrap but it sticks much better on Kapton tape. So for that reason and for added cell to cell protection I'm gonna wrap each cell in a turn of Kapton tape. I got the 30 and 35mm wide.

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Re: 18650 spot welding -how to- ULTIMATE REPOSITORY

Post by litespeed » May 08 2018 5:04pm

I can’t find where it is but search for pictures of maddin88’s battery builds.....NO ONE builds a better 18650 pack then he does.

Battery Hero even.....

Tom
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Re: 18650 spot welding -how to- ULTIMATE REPOSITORY

Post by Allex » May 08 2018 5:12pm

Yep to much labor and problem with oxidation.
Use double strips of 0.2x10mm on top of each other, like so(well you cant actually see that they are doubled).
IMG_4591.jpg
In fact I have a better suggestion to you about your layout where you only have 1cell instead of 2 together like your pack today while maintaining the same measurements. With this layout you can even quadruple nickel strips - plenty enough to run your currents without even getting to the body temps.
Lets see if you can solve this puzzle :mrgreen: Its a 20s10p but hey, how is the rest of 5p connected? :wink:
IMG_4553.jpg
IMG_4553.jpg (113.36 KiB) Viewed 1834 times

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Re: 18650 spot welding -how to- ULTIMATE REPOSITORY

Post by bigbore » May 09 2018 10:28am

Yeah :D The lower picture is the way to go ..... with that setup there will be 14 nickel strips for series connection instead of the 7 that I actually have. Then each strip will carry 11A that is a great improvement.
In the upper picture instead I do not understand how did you connected the series cells.

About the oxidation problem is it not present also on the soldered end of the balance wires on nickel strips?

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Re: 18650 spot welding -how to- ULTIMATE REPOSITORY

Post by Allex » May 09 2018 11:33am

Well you can still have 14 strips with your current layout where you have 2pairs of cells, just weld the strips on top of each other. But the lower picture is a better layout because you have a better current distribution with only 1cell in a row instead of two.

The upper picture shows a pack with 11p where I have 14 strips in total. 7 + another 7 on top of them.

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Re: 18650 spot welding -how to- ULTIMATE REPOSITORY

Post by SilverLine » May 13 2018 3:56am

Sorry if this have been asked before.

But i`m going to spot weld my first li-ion pack, so i want to be sure i understand the Amp draw correctly, so i build my pack the right way with the right nickel stribs for the current.

Lets say my ESC draws 20 amp from my battery pack ( in this example a simple 4s1p pack) How many amps is going through the circuit in point A, B and C ? When all the 4 cells is giving 5 amp each to the total 20 amp. Thanks...


BTW. Where do people buy copper strips ? I`m from EU, but have a hard time finding a supplier. There is one on eBay, but he is on vacation until July :-(
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Re: 18650 spot welding -how to- ULTIMATE REPOSITORY

Post by izeman » May 13 2018 5:19am

20A through all the serial connections. almost nothing through the parallel ones.
no need to buy copper strips for 20A. 0.1mm nickel will be fine.

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Re: 18650 spot welding -how to- ULTIMATE REPOSITORY

Post by SilverLine » May 13 2018 5:28am

Thanks :-)

This was just an example...

But now i know how to calculate the currents..... thanks again.

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Re: 18650 spot welding -how to- ULTIMATE REPOSITORY

Post by flippy » May 13 2018 6:05am

divide the current between the P. so 20A draw with a 5P pack means 20/5=4A per cell. it does not matter how much series cells there are, 20A is 20A.

also: make the serial connetions first. after those are done you can make the parrelel connections to make the pack a whole. there is almost no current across that parralel strip so just use one and put on top of the serial strips. those serial strips carry the current so they need to be on the cells directly.
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Re: 18650 spot welding -how to- ULTIMATE REPOSITORY

Post by SilverLine » May 13 2018 6:26am

That makes sense

Thanks

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Re: 18650 spot welding -how to- ULTIMATE REPOSITORY

Post by Spongeworthy » May 14 2018 9:51pm

I've welded all my parallel groups, but due to the geometry of my pack and about a 50A current draw, it'll be hard to get ideal current sharing using just nickel strips for series connections. I'm thinking about using copper wire but soldering only in between the parallel cells ontop of the nickel strips connecting them so with a 5P pack I'd have 4 series connections. Should I be worried at all about the current flowing through the parallel nickel strip since the series connections aren't ontop of each cell?

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Re: 18650 spot welding -how to- ULTIMATE REPOSITORY

Post by bigbore » May 15 2018 10:20am

Kapton tape and sand paper are the best friend to glue the cells together with hot glue. :shock:
Yesterday still playing with some scrap cells after wrapping them in a loop of Kapton tape I tried to make the surface rough with 180 grit sandpaper and then glued the cells with hot glue. The result is amazing, it is almost impossible to detach the cells from each other by pulling with your hands.

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Re: 18650 spot welding -how to- ULTIMATE REPOSITORY

Post by flippy » May 28 2018 4:24am

flippy wrote:
Dec 14 2017 6:51am
i orderd this one:

https://www.aliexpress.com/item/0-15-x- ... 96871.html

8mm wide and costs 59 USD. the 8mm fits better on most square spacers and if you need to overlap. it can also carry 15% more current.
when i get it i will fo the test and report back.
follow up: its'the good stuff.
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Re: 18650 spot welding -how to- ULTIMATE REPOSITORY

Post by eSK8r » Jun 12 2018 2:26am

Grrrr- It is so frustrating, I bought strips from Germany (NKON.NL genuine, but 0.3mm and too thick for my welder) and some off eBay and AliExp. Guess which is which. Grind then salt water test. :cry: Ideally I want some 0.2mm x 12mm but hard to find.
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Re: 18650 spot welding -how to- ULTIMATE REPOSITORY

Post by flippy » Jun 12 2018 10:05am

eSK8r wrote:
Jun 12 2018 2:26am
Grrrr- It is so frustrating, I bought strips from Germany (NKON.NL genuine, but 0.3mm and too thick for my welder) and some off eBay and AliExp. Guess which is which. Grind then salt water test. :cry: Ideally I want some 0.2mm x 12mm but hard to find.
try here: https://www.aliexpress.com/item/1kg-0-1 ... 66249.html
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Re: 18650 spot welding -how to- ULTIMATE REPOSITORY

Post by kdog » Jun 13 2018 7:20pm

0.2mm is where it's at. Perfect for welding, good current capacity. I'll see if I can find the AliExpress seller I used last time.

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Re: 18650 spot welding -how to- ULTIMATE REPOSITORY

Post by bigbore » Jul 02 2018 1:54pm

Last weekend I finished the assembly of my new 20S14P battery.
What do you think of the termination cables I made?
These are 14 18AWG cables soldered to a 8AWG one.
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Re: 18650 spot welding -how to- ULTIMATE REPOSITORY

Post by litespeed » Jul 02 2018 6:30pm

I guess it COULD kinda act as a fusible link if all goes to hell in a hand Basket?

I would think you need a whole bunch more of parallel connections? Looks like only a thin piece of nickel at each parallel run?

What cells and what is total draw from pack?

Tom
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Re: 18650 spot welding -how to- ULTIMATE REPOSITORY

Post by bigbore » Jul 03 2018 8:25am

Parallel strips are 0.2mmx5mm and they should be good for 5A that in my opinion is more than needed.
The battery is made with 280 Sony VTC6 and in the worst case I will draw from each series 11,5A peak and 10,5A continuos.

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