Please rate/ advise me on my soldering

I have been trying to make a DIY spot welder from car batteries and Arduinos for weeks and have had no success. As a result I’ve opted for soldering. I know the basics: don’t short, hot soldering iron and small contact time to reduce heat. However this is my first time and would appreciate any advice or help this community can give! I’m using nickel strip and 60 year-old lead roof welding tool as it has a huge thermal mass.

N.b. Video is completely unedited

[Video of soldering ](

Some screenshots from the video: image image image image image

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I can’t say anything about how you’ve done because I probably know less than you, But Thanks for giving photos as an option here!

@darkkevind makes and sells Soldered battrey packs here, maybe he could give some input.

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Nickel is not the easiest to solder on. Guess you would go better by using a copper wire or bar. Where are you located? Maybe somebody here can rent you a spot welder


Weld the solder to the cell first. Then weld solder to the conductor. (nickel in this case) Then weld them together.

Also, everytime you solder anything you should always try your best to pull them apart after cooling. If you can pull it apart, it was a bad weld and needs to be redone anyway. This kind-of applies to 18650s also. You want to do that, but you don’t want to accidentally short things out, either.

You should keep a piece of metal handy so that after you remove the iron you can press it on the end of the cell to suck the heat out faster and keep the heat from going as deep into the cell.

Also, protip: the positive connections are the most difficult, so it’s better to troubleshoot those ends

Also if you’re soldering, you may as well use copper and not nickel.


The nickel strip has been nice to me so far, I think it grips easier with the scuffs. I live in London. I’ve tried to find people but no luck so far…

What form of copper would you recommend, strip? Bar? Braid? Thanks for all the pointers.

Maybe @moon can help you. If i‘m not wrong he is from somewhere there and was looking for a spotwelder too (or he own one idk)

Sorry I don’t want to be a dick, but just my 2 cents, this soldering work is awfull. Better bring your cells to someone with the right tools and skills, this batteries can burn down your house easily.


I am like 2hrs away from london and building my 2nd spot welder. Soon I will be moving even further away from London :sweat_smile:

2 hours … by esk8?

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2hours for Russia it’s normal way to work :point_up: :joy: ok it was worth a try… Thought you maybe just can recommend him somebody local who could help him.

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More like 10 months because I am still waiting for stuff to arrive


Nothing in soldering is referred to as welding, so keep that in mind.

  1. It appears that you are using a pipe-soldering, soldering iron to do the work. That can work, but it takes lots of practice and skill. If I were you, I’d use the big soldering iron to tin the nickle strip, then use your other iron that I can see in the back which appears to be temperature controlled, to do the actually soldering of the nickel to the cell.

  2. Prep your surfaces. Scuff your battery and nickle strips with sand paper to lightly turn the surface matt. Then clean the surface with isopropyl alcohol.

  3. Put a bit of flux on each surface to be soldered and then use your temperature controlled iron with a well tinned tip at ~450c or so to quickly touch the battery surface and then add just enough solder to get a little blob to stick. The little blob of solder should be shiny when it cools, and well adhered to the surface. This will take practice.

  4. This process of sticking a bit of solder to the surface before soldering things together is called tinning and is vital. Use the same process to tin the nickel strip at where you intended to join it to the battery.

  5. With both surfaces tinned (battery and nickle strip), put the two tinned surfaces in contact and clamp them so that they won’t move when soldering. You can now use your still well tinned and clean soldering iron to heat the top of the nickel strip such that the tinned solder on the bottom melts, the melted solder from the nickle strip, should then melt the solder on the battery terminal and the nickle strip will sink into the top of the battery cell. When it sinks, remove the soldering iron and let it cool.

Spot welding is better, but if you must solder, do it as above for good results.



Maybe in this thread can help you find a spotwelder

I second this. This is the most important bit of all the advice in all the posts above


I did this in the video but only to the battery side, the nickel strip was only scuffed and had flux applied.

Yes, I’m well aware of the risks. Can you elaborate on why you think this is so bad?

Really useful instructions- thank you.

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I THIRD this. Tinning is everything in soldering. makes solder absorb and require less heat when joining two parts

edited. I can’t type for :poop:


I saw you melted solder onto the top of the cell but it didn’t appear to be stuck/welded/tinned. Just physically touching. I bet if you took a straight screwdriver, you could pop it off…

But then again prying on the end of an 18650 with a screwdriver is a very bad idea in general