Spot welder

[DisasterNow]

I often deal with non-functioning 18650 battery packs, where the problem may be just one cell. To access the individual cells, I have to cut the nickel plates. However, I've never replaced a single cell because I don't have the tools to spot-weld a new nickel plate. Does anyone have experience with this type of repair? I've seen that new nickel plates are easy to find. However, I would need a spot welder to do this job, without spending a fortune. Do you have any recommendations on which product to get? (Under €100, preferably).
For example, I've seen the Fnirsi swm-20 model (a brand often discussed here on the forum). What do you think?

https://www.fnirsi.com/it/products/swm-20

Honestly, I'd prefer a non-portable device, but one that can be plugged into the mains...
I also have another question: are these spot welders only used for welding nickel plates? Up to what thickness? Or are they also useful for other materials (copper, etc.)?
Thanks

[KungFuJosh]

More often than not, Fnirsi is discussed for being somewhere between mediocre and dangerous. I imagine a spot welder would land on the dangerous side of things.

[tautech]

Kweld.
The story of Kweld development starts here:
https://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/

[BradC]

This one is a bag of worms. Personally after trying a few different *cheap* products and varying power sources I settled on a cheap product, modified and connected to (relatively) expensive capacitors. Steer clear of the lithium cell based units and look at something like this https://www.aliexpress.com/item/1005006314361461.html

No experience with the unit itself, but for repair purposes, something small and self contained that still packs a reasonable punch is probably where you need to be.

If you were building packs, different story entirely. The issue I see with the lithium based units is longevity of the cell(s). I know KWeld can and does use Lithium batteries, but they're external and can be replaced cheaply. An all in one is a "cell is stuffed, toss it and buy a new unit".

Kweld.
The story of Kweld development starts here:
https://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/

Asks for help selecting an LDV/Chery and gets a link to the Bugati dealer.

[watchmaker]

The one you mention is junk (at least when I tried to use it; forgot for what). Their products area a crap shoot.  Some work well enough, others not so much.

Dewey

[BradC]

The one you mention is junk (at least when I tried to use it; forgot for what).

Context. Who are you responding to, and which product are you talking about?

[DisasterNow]

Thanks everyone for the advice.
I see that Fnirsi isn't very popular.
Mine was just an example from someone who's inexperienced with this type of equipment.
I'd also like to point out that my repairs on 18650 battery cells will only be occasional, so I'd like to purchase an inexpensive spot welder. But that doesn't mean it's unusable, of course.
If anyone has any low-cost equipment of this kind that they're happy with, I'd be happy to hear their opinion. Thanks

[KungFuJosh]

The one you mention is junk (at least when I tried to use it; forgot for what).

Context. Who are you responding to, and which product are you talking about?

I think it's safe to assume he was responding to the OP...though quoting stuff makes it easier.

[wilfred]

The one you mention is junk (at least when I tried to use it; forgot for what).

Context. Who are you responding to, and which product are you talking about?

Even more helpful would be to not simply say it is junk. I don't really find that very useful at all. Better would be to detail what the task it was applied to and what result was unsatisfactory. Then I could match it to what I want to do. Did it fail? Did it not work for thicker strips?

[shooshpah]

review and teardown Fnirsi SWM-10,
audio - Russian only, but video pretty self-explanatory
dzen.ru/video/watch/65ff2d4ae7e5b96a55d42f66

[elektryk]

I personally use AWithZ P20B, you can also consider cheaper UF20B, both are supercaps units.

[KungFuJosh]

Even more helpful would be to not simply say it is junk. I don't really find that very useful at all. Better would be to detail what the task it was applied to and what result was unsatisfactory. Then I could match it to what I want to do. Did it fail? Did it not work for thicker strips?

Some things are just junk and not worth the time thinking about. Sometimes people are too busy to rant about junk, but are kind enough to tell you to avoid something that's...junk. You don't have to believe them.

[gamerpaddy]

Welding copper plates would require different electrodes and much higher currents.
thats why theyre usually welded using ultrasonic or lasers

i personally wouldnt use any spot welder that is a big li-ion battery under the hood, if one of the fets dies, you got a fire there.  im using one of those supercap welders
not the overpriced fancy looking ones but one thats just a small pcb screwed to two 3000F caps in a 3d printed holder
(much like this one but different, https://aliexpress.com/item/1005007523462943.html ) its good up to 0.3mm nickel strip for solid welds.

or go with kweld and the powersupply option, a few hundred bucks but the standard for most cell-repair shops over here
https://www.keenlab.de/index.php/product/kweld-complete-kit/

[BradC]

i personally wouldnt use any spot welder that is a big li-ion battery under the hood, if one of the fets dies, you got a fire there.

It's not just that. Anecdotally in a short circuit scenario pouch cells degrade much faster than caps, so limit the life of the device. Then you have the issue with making sure the cell is kept with enough charge, but not so much as to speed its degradation. In a "once in blue moon" repair scenario it could be sitting there for months untouched.

I love the fact when I put the welder to bed I can put it in the cupboard for a year or two, pull it out, charge it up and get welding without having to worry about the thing being over-discharged or whether it's going to work at all. In my case, I've got one of the 6 cell 16V 500F packs, so I can also charge it up from the bench supply and use it to jump start the car. Multi-purpose

[DisasterNow]

review and teardown Fnirsi SWM-10,
audio - Russian only, but video pretty self-explanatory
dzen.ru/video/watch/65ff2d4ae7e5b96a55d42f66

Interesting, I understand it can weld one type of material and not others. The stability of the device, however, is embarrassing. Could we say it can weld thicknesses of 0.2 at most?

I personally use AWithZ P20B, you can also consider cheaper UF20B, both are supercaps units.

I watched a video of the UF20B model, and I have to say that these models with capacitors seem to have much more power compared to those with the 18650. This model doesn't seem bad, of course maybe I wanted to spend a little less honestly.

Welding copper plates would require different electrodes and much higher currents.
thats why theyre usually welded using ultrasonic or lasers

i personally wouldnt use any spot welder that is a big li-ion battery under the hood, if one of the fets dies, you got a fire there.  im using one of those supercap welders
not the overpriced fancy looking ones but one thats just a small pcb screwed to two 3000F caps in a 3d printed holder
(much like this one but different, https://aliexpress.com/item/1005007523462943.html ) its good up to 0.3mm nickel strip for solid welds.

or go with kweld and the powersupply option, a few hundred bucks but the standard for most cell-repair shops over here
https://www.keenlab.de/index.php/product/kweld-complete-kit/

The one on aliexpress is quite cheap, I think it could do what I need, while the kweld, even though I know it's a good product, costs too much for my needs.

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I'd like to add a few more considerations, since this is a new topic for me:
-To achieve a decent welding power, you need a device with capacitors.
- My goal would be to solder the tabs on 18650 batteries. I measured some tabs from 18650 batteries that power tools, and they're only 0.1mm thick. Besides this job, what other uses could a spot welder have?
- I'm not sure what material would be best for the 18650 battery laminations, for example: are they nickel? Or steel? Which materials does the spot welder weld best, and which ones can't it weld? (I mean with a maximum thickness of 0.2/0.3mm).

Thanks

[gamerpaddy]

those strips are allways nickel, steel has even less conductivity and isnt corrosion resistant.
plus, you can solder nickel!  after welding you can lower its resistance quite a bit by soldering copper wick for desoldering onto it.

you can of course spotweld anything with it not just batteries
i repaired car back-lights where a contact broke off. it was stamped steel molded in plastic, you cant solder on steel and even if, before you can get it hot enough the plastic melts.  so just welding a few strips onto it makes it enough of a thermal bridge to be able to solder.   saved me 100+ bucks.

[elektryk]

- My goal would be to solder the tabs on 18650 batteries. I measured some tabs from 18650 batteries that power tools, and they're only 0.1mm thick.

Good quality battery packs from cordless tools often have nickel plated copper 0.25mm thick, weak spot welder won't even touch it.
0.1mm may be good for notebook batteries, but beware that most of the ali stuff is nickel plated steel not pure nickel.

[BradC]

those strips are allways nickel, steel has even less conductivity and isnt corrosion resistant.

Plenty of nickel plated steel strips out there in non-critical applications and all over the cheap marketplaces.

Good quality battery packs from cordless tools often have nickel plated copper 0.25mm thick, weak spot welder won't even touch it.

I've yet to personally see copper in a battery pack and I've rebuilt quite a few. Pretty much everything power tool I've worked on has been 0.15 Nickel and low power packs 0.1. The power tool packs just use more area (wider strips). I believe some of the new high power packs with "tabless" cells have been seen to use copper, but they're also laser welded.

[elektryk]

I've yet to personally see copper in a battery pack and I've rebuilt quite a few. Pretty much everything power tool I've worked on has been 0.15 Nickel and low power packs 0.1. The power tool packs just use more area (wider strips). I believe some of the new high power packs with "tabless" cells have been seen to use copper, but they're also laser welded.

Just look at genuine LXT or M18 packs, both use quite thick nickel plated copper even older non tabless models.
I've seen 0.15mm x 10mm nickel plated steel strip that was easily burned used with cordless rotary hammer.

[Cyclotron]

I have a Kweld and this one:  https://www.amazon.com/Capacitor-AWithZ-Automatic-Equipment-P20B/dp/B0CX4BNZQ3
Both do a great job. I think the Kweld is a great design but you must be willing to build it and be a part of it's creation.

The AWithZ is fully functional but I can't tell how safe it is long term. I can tell you it is surprisingly very very powerful. I've spot welded stainless to stainless with it.
I can do that with the Kweld too but again, I build that with the parts and my additions like PSU etc.

[tooki]

I often deal with non-functioning 18650 battery packs, where the problem may be just one cell. To access the individual cells, I have to cut the nickel plates. However, I've never replaced a single cell because I don't have the tools to spot-weld a new nickel plate. Does anyone have experience with this type of repair? I've seen that new nickel plates are easy to find. However, I would need a spot welder to do this job, without spending a fortune. Do you have any recommendations on which product to get? (Under €100, preferably).

FYI, I would advise that you replace all the cells. You fundamentally want all the cells in a pack to be as closely matched as possible: this means you want them to be not only the same model of cell, but ideally be from the same production batch, with exactly the same wear. Mixing new and old is inadvisable.

[guenthert]

Welding copper plates would require different electrodes and much higher currents.
thats why theyre usually welded using ultrasonic or lasers

Now I wished I knew more about metals and material science in general, but why is a higher current needed for welding copper?  I see that the melting point of copper is lower, density about the same and specific heat capacity actually considerably lower than the one of nickel.  So why would one need more energy to weld?

(I'm peripherally interested in welding small copper wires, chiefly in an attempt to avoid Seebeck effect.)

[tooki]

Welding copper plates would require different electrodes and much higher currents.
thats why theyre usually welded using ultrasonic or lasers

Now I wished I knew more about metals and material science in general, but why is a higher current needed for welding copper?  I see that the melting point of copper is lower, density about the same and specific heat capacity actually considerably lower than the one of nickel.  So why would one need more energy to weld?

(I'm peripherally interested in welding small copper wires, chiefly in an attempt to avoid Seebeck effect.)

If I had to guess, it’s because a) copper has better conductivity than most metals, meaning lower I²R heating produced in it as current flows through, and b) because what little heat is generated is conducted away very effectively.

(But I could be totally wrong; I have never looked into the physics of spot welding.)

[Cyclotron]

Welding copper plates would require different electrodes and much higher currents.
thats why theyre usually welded using ultrasonic or lasers

Now I wished I knew more about metals and material science in general, but why is a higher current needed for welding copper?  I see that the melting point of copper is lower, density about the same and specific heat capacity actually considerably lower than the one of nickel.  So why would one need more energy to weld?

(I'm peripherally interested in welding small copper wires, chiefly in an attempt to avoid Seebeck effect.)

If I had to guess, it’s because a) copper has better conductivity than most metals, meaning lower I²R heating produced in it as current flows through, and b) because what little heat is generated is conducted away very effectively.

(But I could be totally wrong; I have never looked into the physics of spot welding.)

You are right. Spot welding is directly using the natural resistance of the metal to generate the heat needed to liquify the metal at the point the two pieces touch.

The electrodes of the spot welder are copper to keep their heat lower. If you want to spot weld copper you can use tungsten electrodes which will produce more heat at the spot weld location due to its resistance and hopefully enough heat will be there to fuse the copper.

The other easier way to spot weld copper if really required is to plate the copper with nickel to create a temporary higher resistance t the two surfaces enough to generate the heat required for fusing.

[gamerpaddy]

also those cheap aliexpress welders usually come with flimsy 1mm electrodes, made of just copper.
you want tungsten copper for that, as it wont deform under the generated heat and they dont stick.
the cable diameter isnt ideal either, mine get quite hot after a few welds.

so if you get one of those capacitive welders, pick up a set of electrodes from kweld or whereever theyre selling that type of alloy. much less of a hassle in the end