Spot Welder - Weld is not strong enough

Hey there fellow eskaters, I made an Spot Welder using a 600W Microwave and an Arduino and Relais. But when I want to weld a 0.15mm Nickelstrip onto an 18650 battery it doesnt really hold well, its not strong enough.

I am measuring about 1.5V on the secondary winding (using a 35mm² Wire). Also here are some pics if that would help.

Any help will be appreciated!


What pulse time did you tried? Can we see the welded nickel? Are those electrodes copper?


Tried from 50 ms to 450 ms and yes its made from copper. Will post pics soon

@Zentaria I had exactly the same issue, I had the pulse set to about half a second and would see the nickel glow but the weld was crap. I added another loop to the secondary winding, voltage went up to 3.5 or something and now I need a pulse with of 0.01s to get a nice strong weld.

So try adding another winding to the secondary coil. image

Who me? Here’s mine prior to the new timer board and case. Three windings. IMG_20180715_150620

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It has 1 1/2 windings, cable is to thick for another winding

Sorry, old timer of what?

I do will PM you

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Sorry i am confusing things. Sorry

Ignore me

Should I try an thinner cable?

Are you pushing hard? I had the same problem and almost exactly the same setup. No matter what time I put in welds were weak. Than I read somewhere that force that you use is very important. Now without changing anything I’m making welds that won’t let go (have tear nickel strip) and my time setting is 0,25s. I’m just touching nickel with electrodes and it works perfect almost zero pressure.

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Tried it while pushing hard and just laying down, same effect sadly

Try to barely touch it. When I do that I have big spark and it burns through. You are welding nickel not copper strip right?

yea I am welding pure Nickel, will try later with just laying down

In commercial spot welders there usually is a double pulse weld, the first short pulse like up to 10ms if im not mistaken is meant to soften the material and the second completes the weld. And yes you better be pushing hard on that weldspot. Also, try adding a small cut with a dremel or something in between the electrode touching points on the nickel, makes more current go through the cell casing, ergo better welds. You can see this on all of the chinese premade battery pack nickel strips as well. Also for trying another loop you might just strip that fat ass insulation and wrap the wire in kapton or somehing, I bet you will have plenty of space left.

@LukePL 0.25 s welds are insanely long my dude :smiley: you need moar powaaa I bet your cells get rather toasty.

I actually built a dual pulse spot welder, a short activation and then the time i selected on my menu.Where should I cut it?


You see that tiny cut in the nickel? One electrode goes on one side of the cut, another …well, on the other side.

ah thank you, can try tomorrow, but shouldnt it work without the cut too?

How can I do that? My microwave transformer is 700w. They don’t get so hot I think but for sure I need to learn more and have more practice,

Yes it should, if your welder has the balls or it. But this thing can help a lot. I was surprised to see the difference with and without that cut.

@LukePL hell man, idk, rewind the transformer like @JonathanLau1983 mentioned, use some fancy mosfets for activating your welder as relays usually have some “bounciness” to them, not sure, but it could compromise the current output to the weld spot. And if you are going full balls to the wall making many battery packs, you might just go ahead and get a k-weld

We have this at work, powered by 5 supercapacitors in series (2.7 V and I think 1200F each), god damn that thing can weld anything. I personally love it. The darn thing decides on the weld time on its own, because you set the power output in joules. Yea, its smart

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