Spot Welding Copper Strips to 18650 Battery Cells

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Re: Spot Welding Copper Strips to 18650 Battery Cells

Postby Joachim » Fri Apr 21, 2017 11:55 am

0:57 https://www.youtube.com/watch?v=yIWmjIF6i6w looks like bosch already use a copper spotwelding machine for the powertoolpacks
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Re: Spot Welding Copper Strips to 18650 Battery Cells

Postby parabellum » Fri Apr 21, 2017 1:24 pm

Joachim wrote:0:57 https://www.youtube.com/watch?v=yIWmjIF6i6w looks like bosch already use a copper spotwelding machine for the powertoolpacks

He says, they use laser welding at 1:40, but it looks like normal spot welding for me.
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Re: Spot Welding Copper Strips to 18650 Battery Cells

Postby kdog » Sun Apr 23, 2017 2:42 am

Macribs,
I did extensive research on copper alloys for battery use. There are some awesome copper alloys out there.... You just can't get them anywhere. I looked for months, sent dozens of emails and scoured the world. Unless you want tons of the stuf your out of luck. :(
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Re: Spot Welding Copper Strips to 18650 Battery Cells

Postby kdog » Thu Jun 08, 2017 6:48 am

so a while ago now, my efforts at finding a nickel alt in copper alloys proved friutless (mostly bc of the volumes i wanted, not bc they dont exist), so i have come up with a DIY version of some high power commecial designs.
i'm building a 20s10p 30q pack that needs to be able to discharge at 120a (peak), even if i used broad sheet .2mm Ni id be required to do a lot of beefing up with solder and copper. As batteries get more and more powerful, ni is going to become increasingly inadequte, and its freaking expensive, but it remains the best welding material so far.
so im working on a different hybrid Ni:Cu spotweld only soultion. this technique isnt new, but im not sure if its been done it has a few benefits, and a few draw backs,
pros:
dual current exit for the Ni means effectively twice the nickel amount per cell
Very short path for the nickel- less loss
all copper-nickel welding is done off the cell with opposing electrodes , also this allows for using thicker copper (i welded 0.2mmNi to 0.15mmCu with ease)
can accomodate any arrangement of cells
uses far less nickel than a broad sheet alternative reducing cost substantially

cons
time consuming
requires setting up with a hole punch and opposed electrodes

The process is to cut out a piece of copper to do the parallel and series connects between adjacent groups.
Punch holes directly over the cell ends
Weld nickel over holes
Weld nickel through holes to battery

I can imaging alot of people saying why bother... and for low power packs this would be overkill, but i think its a good solution if broad nickel isnt going to cut it.
here are some pics to explain
IMG_1789.JPG
test of .2Ni to .15cu
IMG_1789.JPG (68.57 KiB) Viewed 623 times

IMG_1796.JPG
.1mm copper template
IMG_1796.JPG (126.65 KiB) Viewed 623 times

IMG_1799.JPG
instu- not complete obviously
IMG_1799.JPG (96.62 KiB) Viewed 623 times

FullSizeRender.jpg
crude but effective opposing electrode
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IMG_1792.JPG
DIY hole puch- works amazingly well
IMG_1792.JPG (118.34 KiB) Viewed 623 times

im pretty sure ill use this technique for my current build
i can punch out a copper sheet in about 5 mins (which is copying the template), for the unique shapes it takes about 15mins. this incudes shaping and punching.
the welding of copper to the nickel is super easy and takes about 1min for a strip.
all up itll take quite a few hrs, and im still testing as i go so probly even more time there.
not sure if ill use .1mm cu or .15mm. ill order both to see if i can get consistent welds with the .15mmCu
its definitly stronger than the .1mm so i think ill try and use it.
ill update with some more pics when i get the chance
k
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Re: Spot Welding Copper Strips to 18650 Battery Cells

Postby vex_zg » Thu Jun 08, 2017 8:24 am

well done kdog. Was thinking (dreaming) of something similar, good to see how it looks in reality.

I experimented with .1mm and .2mm copper and really the .1mm is too weak mechanically.In my opinion. I would go with .2mm. It requires around 180Ws per weld, in my experience.
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Re: Spot Welding Copper Strips to 18650 Battery Cells

Postby kdog » Thu Jun 08, 2017 10:38 am

yeh .1mm is really weak. i easily welded some .2ni to .15cu on the test piece so id like to go with that- mechanically its much stronger, but ill have to be able to consistently weld it to use it. i reckon .2Cu will be a bit thick for me
ive ordered a meter of both .1 & .15 so in about 3weeks ill be able to test it out.
is it here yet?!
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Re: Spot Welding Copper Strips to 18650 Battery Cells

Postby vex_zg » Thu Jun 08, 2017 11:36 am

kdog wrote:yeh .1mm is really weak. i easily welded some .2ni to .15cu on the test piece so id like to go with that- mechanically its much stronger, but ill have to be able to consistently weld it to use it. i reckon .2Cu will be a bit thick for me
ive ordered a meter of both .1 & .15 so in about 3weeks ill be able to test it out.
is it here yet?!


where did you get .15mm copper? The .2mm is tricky because it needs rather high weld energies (challenges: battery can damage, blowouts, electrode wear)

I am clueless as to who and what are you asking with "is it here yet?!"
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Re: Spot Welding Copper Strips to 18650 Battery Cells

Postby kdog » Thu Jun 08, 2017 3:40 pm

I just ordered it on aliexpress
https://m.aliexpress.com/s/item/1895592146.html?spm=a2g0n.search-cache.0.0.FtWy6j
They've got a range of thicknesses
I was just making a joke about whether it had arrived yet having only just ordered it... Is it here yet? Ha! Lost in translation.
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Re: Spot Welding Copper Strips to 18650 Battery Cells

Postby vex_zg » Thu Jun 08, 2017 5:29 pm

kdog wrote:I just ordered it on aliexpress
https://m.aliexpress.com/s/item/1895592146.html?spm=a2g0n.search-cache.0.0.FtWy6j
They've got a range of thicknesses
I was just making a joke about whether it had arrived yet having only just ordered it... Is it here yet? Ha! Lost in translation.


Thanks for the link. Just ordered a sheet to test.
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Re: Spot Welding Copper Strips to 18650 Battery Cells

Postby kdog » Thu Jun 08, 2017 9:20 pm

I've had a bit more of a go at testing the through weldability of .15cu to .2ni. I'm pleased to see that I can get consistently good welds. Interestingly, it requires gentle pressure on the electrodes to create a bit of heat via poor contact. If I clamp them together it welds poorly. I'm going to fix up the electrodes cause they are a bit scrappy.
I will use the .15mm cu as it is stronger and carries 50% more current.
I'm working on 20a/mm^2 of copper.
The Cu template has 50mm width of copper ( at its thinnest given the holes) so at:
.1mm that's 5mm^2 = 100amps max
.15mm is 7.5mm^2 = 150amps max
I wonder if it would take more do there being no holes at the point of max current. It's hard to conceptualise but I think it would.... Anyway the other series connect configurations in my pack won't allow for such broad copper as easily, so I'll have to tackle them as I go.
K
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Re: Spot Welding Copper Strips to 18650 Battery Cells

Postby ridethelightning » Fri Jun 09, 2017 8:14 am

kdog wrote: Interestingly, it requires gentle pressure on the electrodes to create a bit of heat via poor contact. If I clamp them together it welds poorly.


this is the resistance that makes tungsten good to weld copper i think. the resistance in the tungsten tip, which will endure very high temps and stay hard, produces the heat that copper will not easily produce, because its too darn conductive. that heat is what melts the copper to make the weld..
id say it might be time to test some tungsten tips with the 0.15, through welding eh?
i have a couple meters of 8mm cu rod, if youd like to make some electodes with it...
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Re: Spot Welding Copper Strips to 18650 Battery Cells

Postby okashira » Fri Jun 09, 2017 8:43 am

tungsten and copper tungsten electrodes are recommended because the electrodes themselves heat up in lieu of the weld material hopefully enough to melt the copper and form the weld.

this is in contrast to welding nickel - where you don't want the electrode to heat at all --- and ideally you want the interface between the two nickel interfaces to heat just enough to melt and fuse in the presence of massive electrical current.

If you can understand this difference you might be able to understand why welding copper is so much more difficult.
Think of it like this - you need to heat the two copper sheets enough to melt the contact between the two copper interfaces so they fuse. This means all of the copper interface that the electrode is contacting must melt because the heat source is coming from the electrode...

Also consider that copper is much more chemicallyreactive then nickel

Basically I think it ends up working like this,
Image

It is certainty more complicated then that, and I don't have any scientific references, but this give a good idea -- for nickel welding you want most of the heat generated between the two nickel interfaces -- where as for copper welding you end up with more heat generated from the electrode - this leads to more melting of the top copper layer and poor welds, mechanically.


I think welding copper is a great idea - if you have a nice 10k pulse arc welder. If you have a spot welder, stick to nickel and optimize your design for current flow. You're missing almost nothing.
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Re: Spot Welding Copper Strips to 18650 Battery Cells

Postby vex_zg » Fri Jun 09, 2017 5:09 pm

i tried tungsten, molybdenum, 30-70 copper tungsten. Tested for welding copper, nickel, copper-nickel.

pure copper electrodes still work best for me. Tungsten/molybdenum cause more sparks and blowouts and stick much more.

I have not yet tried zirconium copper (the electrodes I bought are quite big in diameter so need some machining first)

Anybody willing to experiment can get cheap on aliexpress/ebay.

Beware though - machining tungsten and molybden is quite hard. Those are hard materials. Eats grinding stone like it was cake.
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Re: Spot Welding Copper Strips to 18650 Battery Cells

Postby vex_zg » Fri Jun 09, 2017 6:20 pm

vex_zg wrote:i tried tungsten, molybdenum, 30-70 copper tungsten. Tested for welding copper, nickel, copper-nickel.

pure copper electrodes still work best for me. Tungsten/molybdenum cause more sparks and blowouts and stick much more.

I have not yet tried zirconium copper (the electrodes I bought are quite big in diameter so need some machining first)

Anybody willing to experiment can get cheap on aliexpress/ebay.

Beware though - machining tungsten and molybden is quite hard. Those are hard materials. Eats grinding stone like it was cake.


oh yes, I have a CD welder, and my pulse lenghts are typically in range of maybe couple of miliseconds.
If some slower discharge welder or pulse timing was used maybe tungsten/molybdenum would work better since there would be more time for the heat to transfer from electrode tip into the weld. Still it is best if it is created in the weld. Would be interesting to see how a MOT welder copes with molybdenum/tungsten when welding copper. I have a nice MOT but no time to start yet another project.
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Re: Spot Welding Copper Strips to 18650 Battery Cells

Postby kdog » Fri Jun 09, 2017 6:39 pm

Ah time.... I'd give my left one for some of that :lol:
I'm going to try really short tungsten electrodes for this type of welding. I had zero success with them last time but never say never!
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Re: Spot Welding Copper Strips to 18650 Battery Cells

Postby Matador » Sat Jun 10, 2017 7:13 am

I wonder if cellman's welder could do it... the copper. He does use copper, but not directly on each cells post...
Warning, This is some serious battery porn :

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Re: Spot Welding Copper Strips to 18650 Battery Cells

Postby Matador » Sat Jun 10, 2017 7:23 am

okashira wrote:I think welding copper is a great idea - if you have a nice 10k pulse arc welder. If you have a spot welder, stick to nickel and optimize your design for current flow. You're missing almost nothing.


10000 $ Orion Pulse 250iEV is way too expensive.
With all your experience Okashira, could we build the same pulse arc welder with less ultrasophistication to bring the costs down ?

Could we build a reliable enough puls arc welder for 1000 $ instead of 10000$ if we get rid of the bells and wistles ?
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Re: Spot Welding Copper Strips to 18650 Battery Cells

Postby vex_zg » Sat Jun 10, 2017 4:39 pm

Matador wrote:
okashira wrote:I think welding copper is a great idea - if you have a nice 10k pulse arc welder. If you have a spot welder, stick to nickel and optimize your design for current flow. You're missing almost nothing.


10000 $ Orion Pulse 250iEV is way too expensive.
With all your experience Okashira, could we build the same pulse arc welder with less ultrasophistication to bring the costs down ?

Could we build a reliable enough puls arc welder for 1000 $ instead of 10000$ if we get rid of the bells and wistles ?


Probably. But what I have read is that pulse arc welding is a level up in complexity over the CD welder, and to perfect a CD welder it took me like a year and hundreds of night hours after my dayjob (transients and inductance required quite some rethinking and investigating). Unless I get laid off with a severance package to have undisturbed few months I don't see I can do a pulse arc welder it in reasonable amount of time.

If we team up - I can do stuff (write code@atmel/c/java/arduino, test, have a 4ch scope and soldering/hot air station).

There is quite little info online on how pulse arc welding works so some reverse engineering would be needed.
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Re: Spot Welding Copper Strips to 18650 Battery Cells

Postby kdog » Fri Jun 16, 2017 9:43 am

so after i ordered my .15mmCu on line RTL gave me a tip on where to get it locally. $40aud (~30us) got me 600x1000mm- sweet! about 10x cheaper than broad sheet Ni from aliexpress
about two hrs of work produced this (some havent been punched yet)
thumbnail_IMG_1816[1].jpg
thumbnail_IMG_1816[1].jpg (25.17 KiB) Viewed 449 times

the main time consuming part is trimming the copper to exactly the right shape, i might try tracing paper or the likes to speed it up.
the multiple parallelogram like shape is easy to bang out a few in quick succession, but the odd shapes take longer being unique. ive test welded this super soft 0.15mm Cu so i know thats no problem.
its kind of satisfying even if its a bit slow.
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Re: Spot Welding Copper Strips to 18650 Battery Cells

Postby spinningmagnets » Fri Jun 16, 2017 9:51 am

I am seeing more info posted about high-end cordless tool packs that use copper bus-plates, and they are nickel-plated for the corrosion resistance. The high-amp tools have been doing it this ways for years...just didn't know it was copper because of the nickel-plate.

EDIT: after some research, I do NOT recommend zinc-plated copper [disregard the paragraph below]

I now believe that zinc-plating is an acceptable option, maybe cheaper than nickel, and more easily available locally around the globe? "Galvanised" nails that are intended for outdoor use (your roof shingles?) Are simply steel nails that are zinc-plated. The zinc is not as shiny or pretty as nickel, but it will remain cheap in my lifetime, where-as nickel is projected to double in price soon...the electrical resistance of a thin zinc coating is roughly the same as nickel...
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Re: Spot Welding Copper Strips to 18650 Battery Cells

Postby Hummina Shadeeba » Fri Jun 16, 2017 11:02 am

does it really need to be plated if it's spot welded? the rest of the tab may get tarnished if not protected but I'd think the actual connection is sealed to any possible chemical reaction that would destroy the conductivity.
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Re: Spot Welding Copper Strips to 18650 Battery Cells

Postby kdog » Fri Jun 16, 2017 12:15 pm

I opened up my first pack I did with copper a few days ago to inspect -its almost two yrs old. It's done with copper on nickel in the standard spot welding way, 20s5p. Apart from a small amount of corrosion in the HAZ of the welds it's fine. Hardly tarnished on the rest of the tab. At the time when I was welding it, I noticed the current would leave a heat mark on the tab (0.1mm), this is where the corrosion has started. I've used that bike for about 5000ks now and it hasn't faltered once. With this technique, the HAZ is much less so I'm hoping the corrosion is correspondingly reduced.
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Re: Spot Welding Copper Strips to 18650 Battery Cells

Postby ridethelightning » Sun Jun 18, 2017 7:08 am

kdog wrote:I opened up my first pack I did with copper a few days ago to inspect -its almost two yrs old. It's done with copper on nickel in the standard spot welding way, 20s5p. Apart from a small amount of corrosion in the HAZ of the welds it's fine. Hardly tarnished on the rest of the tab. At the time when I was welding it, I noticed the current would leave a heat mark on the tab (0.1mm), this is where the corrosion has started. I've used that bike for about 5000ks now and it hasn't faltered once. With this technique, the HAZ is much less so I'm hoping the corrosion is correspondingly reduced.

you know how ridiculously easy it is it Ni plate copper...
id be tempted to leave the copper pieces AFTER spotwelding the stips on, in a bath of the ol' salt 'n vinegar w/Ni anode, just to keep the sceptics at bay if nothing else :lol:
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Re: Spot Welding Copper Strips to 18650 Battery Cells

Postby spinningmagnets » Mon Jun 26, 2017 7:22 pm

Here is a recent high-amp cordless tool battery pack. The busses are verified to be copper (with a nickel-plate for corrosion and to help make spot-welding easier). Notice how much longer the slot is, compared to the more common pure nickel strips in the past...

Image

2017 Bosch "Core" 18V packs with Panasonic high-amp 20700 cells. Copper busses, no nickel

Image

Doctor Bass with Makita packs, 2011...no slot at all

Image

Here's a link with info on various tab connection methods, including dissimilar metals, like welding copper busses.

http://www.todaysmedicaldevelopments.com/article/medical-device-batter-welding-primer-miyachi-america-9214/
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Re: Spot Welding Copper Strips to 18650 Battery Cells

Postby vex_zg » Tue Jun 27, 2017 2:33 am

good article covering all we know so far.

the makita pack without slots was not resistance-welded I think. Notice no pressure dimples, but instead what looks like melted-pool remnants on weld joins. That would suggest microTig (pulse arc) or laser welding.

Bosch pack has slots because resistance welding was used
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