Boss level custom spot welder

I think thin tips work better but that’s just my opinion. I know nothing about that thing.

I’d agree and defer on that to your experience, solely tabling the idea that it’s possible to diy it & use use the idea: use 3.5mm bullets or smaller with copper rod

Basically steal the inventory list from that site to make a elegant solution

Personally happy enough with Lee’s

The blue electrodes (last) of the video are more or less like that. I’m not sure about the size. Well, i never use them, the welds are way worse. But again i’m not certain about those you posted because i do not own them. In my experience thinner were way better.

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All sorts of spank material in my mailbox today! I wouldve lost my shit if my batteries from nkon had been there too! =P


What size are those adaptors? I have some but mine look smaller

That’s kweld. I agree with rojitor, I think the thin one hand electrodes are easier. But no doubt the kweld one is beefy and tough. XT150 connectors crimped onto thick copper rod. I think it’s the 3rd iteration of kweld’s electrode design. I need to try shaving the tips down.

Here’s a photo because the scale is funny.


Nope. I think yours are bigger. I used the smallest of the store.

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I’ve only tried Lees I can’t imagine a two handed affair and I have a pedal

I found this at my local harbor freight today!

At $13 its the bomb!


Amazing price!!!

Harbor freight always cheap. But stuff is cheap so… I only buy certain things from harbor freight.


Its not #buyitforlife, but for certain things its amazing.

I wanted to post the results of my research and experiences in case someone can benefit from it. Though I am an engineer, these results are not necessarily proper test results, partially since the tests are not complete or performed under proper controlled conditions, so please keep that in mind. Also as you will see, some of my research is still completely inconclusive. Part of the reason why I wanted to publish early though is because I have tested three S2s and many cells to failure (partially due to my ignorance and haste), and figured some of you might like to spare yourself that expense and also be wary of the potential for serious bodily and other harm. Below I talk about welding copper, but as aulakiria says, the machine was not designed to weld copper, and as rojitor says, IT IS DANGEROUS to both you, your property, and your machine, so proceed at your own risk. I only mention the below for those of you who will experiment on copper regardless of my post. I am not advocating it, and I bear no responsibility for what could happen. You could literally burn your house down, or seriously injure yourself, even mortally so.

Some of the below is applicable to quality, consistent welds with nickel, too.

Firstly, what does a good weld look like? To answer that question, I think you need to look at welds at about 200x magnification as in the following pictures. If you can’t, the key is to:

  1. Use the minimum flux time and repeats (e.g. 2x or maybe 3x) needed to make the metal strip tear away from the battery leaving two holes (with no/minimal burning of the metal), AND
  2. Ensure you have enough battery power and cooling to keep it that way. Settings one day, or settings after things heat up or battery voltage drops will not be the same as settings another.

Here is a picture of a decent weld, but I think a little too hot at the upper right side of the weld:

I’m personally not concerned about heat to the battery since I beleive it trivial (though i only make one or two welds per cell then allow the cell time to cool), but it is likely that the dark brown/black part is where the metal is burned away. Where there is no metal, no current will flow, potentially resulting in excessive voltage sag and other problems. Here is an exaggeration to show it (really bad weld, this one partially off the + button of the cell):

Concerning my recommendation #2, above, cooling and consistent battery power is critical to consistent good welds since they tend to get worse over time during the weld series. In my experience to produce consistent welds when welding 0.1mm copper, you need at least 10Ah of high-quality 4S cells. 5AH will give you a small number of good welds (maybe 25 welds?), but then you have to let things cool for 45 minutes or more. As a result, I use 20Ah of 4S cells, which produce far more reliable welds for copper.

For cooling when welding copper, you will need to add a heat sink and 12 volt or higher fans. I use this heat sink: You can use 3/4" #4 wood screws to hold the fans on (assuming 10mm deep fans). Wood screws mean you don’t have to tap the holes–just screw them in. Mine looks like this, where one fan is pushing and one is pulling air, and I use tape to seal the heat sink to make a duct.

Perhaps one fan would be sufficient, but you should have the fan(s) push air toward the batteries since they will normally get hotter than the welder. Though it looks huge compared to the machine, this heat sink barely keeps the FETs cool enough at 75 degrees F ambient temperature.

Since pressure on the welding tips is important, I also like to modify Lee’s design by removing most of the (typically blue) heat shrink that holds the two tips together. The result is easier-to-accomplish even-pressure contact, kind of like an independent rear suspension on a car rather than a solid rear axle. Here is how I modify them–you will notice only one little 1/8" band of heat shrink holding the tips together:

As others have pointed out, the tips get very hot when welding copper. They also get worn down quickly. As a result you will need at least two sets. It seems Lee uses 14 gauge half-hard copper to make the tips.

Speaking of tips, here are some particularly important results from research, though testing is short since I am awaiting replacement FETs. In an effort to increase weld consistency, I made some new tips using 6 gauge copper leads and 12 gauge half-hard copper tips. Using the normal settings, I tried them and blew a large hole in the battery! Needless to say I was quite surprised by the difference in performance. After turning flux time way down I made some successful high-quality welds but then got the fatal “FET error!!!” message. I made a few more welds on a different S2, then tried to weld two strips of 0.1mm copper together. I turned flux time up to 5ms, pressed my foot pedal switch, and proceeded to blow a 1/4" hole in the copper, PLUS the welder would not shut off and burned out the FETs on my last (third) welder. As a result, research on the upgraded leads and tips is inconclusive.

Last tip on copper: a switch or foot pedal is required rather than using automated welds. It is too dangerous and error-prone without a manual switch. I recommend a foot pedal since it is convenient to use.

Please read the above 800+ posts to get more information on the things that I have not discussed in detail.

So why all of this danger and effort to weld copper? I would love for someone to convince me otherwise, and assuming manufacturer claims of 70A/3,000W per e-skate motor are accurate, engineering theory would suggest that nickel as we use it cannot transfer 140A (70A x 2) without very significant voltage sag. Significant voltage sag means performance (e.g. skateboard acceleration) is significantly reduced.

I’d love to hear advice or corrections from others.

Thanks to @aulakiria for creating such a great and inexpensive machine (immensely better than my Sunkko, which was unusably bad). Thanks also to @rojitor to bringing the S2 to our attention and for all of the tips and instructions. Both are sincerely appreciated.

I hope this helps someone. Good luck, and stay safe!


Thats 1800 apache box doesn’t feel cheap at all using it for a 10s6p battery with bms and also building a 12s5p with my trusty spot welder but still looks really good for storage it even looks to have more space for other things to fit

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Payment sent. Next step is 18650 batteries now. Also can this lipo work for this spot welder ? Or do I need the 5000mah ?

You need a large lipo. From others trying to use small lipo it doesn’t work very well. Long ms times and Multi-stage. I’m using an 8k mAh nanotech lipo. It works great.


You are right. I guess at least 5000 is needed, 8000 mah is perfect. Saving cash on the lipo is not a good idea.

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I will take your advice and get a 8000mah one instead. Thanks for clarification

Im gonna try my spot welder today, but when i plug it with tue battery and turned on, there is a fast beeping sound, so i didn’t pursue to test( dont wanna screw up), any one knows what’s happening with this?

Anything on the screen?