OK, I would bet my life that there's no way that thing can do 0.15 copper legitimately. Without a bank of super capacitors, I can't imagine anyone's home AC power being able to provide the pulse of energy needed to do legit copper welds... nickel is hard enough for most homes, and blows many fuses (which is why these Chinese welders were never even an option for me... if my apartments power lines we're ancient, I may have given them a try, but def not for copper). As for handheld spot welders, I've been growing very knowledgeable, and have a few different ones myself.
The first recommendation you were giving is a very solid unit, at a bargain of a price.... the DIY arduino based spot welder: https://www.instructables.com/id/DIY-Ar ... ot-Welder/
You literally cannot beat the price of that, the creator sells the PCBs and machined aluminum nearly at cost (I can't stress how good of a price it is, especially considering 1 of the PCB boards is 2oz copper). It also uses 8 x IRFB7430's.... which are really nice MOSFETs (one of the best for this type of device), and lots of other similar welders use 6, often with weaker fets. This thing is rock solid.... and if you are doing A LOT of welds, it's likely worth going with a car battery instead of a LIPO (the newer, very high discharge Lipos definitely do the trick, but they only last so long). You can also get the pre-built version for a VERY reasonable price (especially considering how much an engineer's time is worth... and how little above the cost of parts it's being sold for). It's also very easy to build yourself.. surprisingly easy. It's got a great design for use with a car battery... so really a solid choice for your needs.
Another welder I own is the "BOSS" spot welder. Another arduino based design, though it uses only 6 fets, the IRF4110's, which are a little weaker than the IRFB7430's, but still very good... a lot of people have used this one quite a bit with good results. I honestly think the above one is a slightly more solid unit at an incredible price.... but this is also a very solid unit... and also at a very cheap price considering what goes into it. It can also double as a solid portable soldering iron with a knockoff hakko handle and T12 tips (better than most soldering irons people have at home). https://m.blog.naver.com/aulakiria/220992039512
The most advanced welder I know of (in this category, I'm sure there are some crazy industrial welders if you spend thousands), that I think has the most potential, is the kWeld. Sadly he just sold out this batch's pre-orders... so might be a little while before you could get your hands on one. It has a unique design concept (with regards to the controlling circuit)... instead of setting pulse times, etc... you simply set the joules per a weld. This theoretically (and seems like the test back it up) makes welds more consistent. It's definitely the most straight forward user interface (IMO).... just 1 value to set. Also, this welder has some pretty serious MOSFETs on it (a decent step up from both the IRFB7430's and IRF4110's). I pre-ordered one, can't wait to finally test it. https://endless-sphere.com/forums/viewt ... 14&t=89039
As far as welding copper goes... while some people have managed to succeed (I've seen it done with the BOSS welder), I think if you really wanted to do this consistently, the best option is to build a bank of super capacitors. BTW, a bank of super capacitors is also likely the best option for powering any of these devices if you want it to last for a long time. Unlike batteries (especially batteries being abused), super capacitors can have a lifetime of 1,000,000 charge cycles, even more (as long as they are used correctly.... overcharging, or worse, connecting backwards are both cases for disaster). But super capacitors used correctly, have the potential to last longer than any of our lives will. But one thing to note is... even more so than the other options... these can 100% be deadly if you are not careful. Of course every option is using pretty high amps, and has the potential to be very dangerous, but a bank of super capacitors has soo much potential, making a mistake is very life threatening (though if you know what you are doing, and are careful, they are relatively safe... generally the only danger is if you make a mistake)... there are plenty of videos of people destroying things with 1 super capacitor... let alone a bank of them. Sadly they are not exactly cheap... especially the ones with insanely low ESRs (in the 0.1-2 mOhm range... usaully in the 500-3000F range.... tho in this case, the ESR is actually more important than the Farads, higher F will give lots more welds before needing a charge, though I'm pretty sure all viable super capacitors are going to give you a hell of a lot... but the low ESR is what's important when it comes to supplying enough power in a short amount of time, especially when it comes to copper). I'm planning on building one of these soon, might even design my own protection board (which I'll release to the public if I succeed)... I think I finally found some that have unbelievably low ESRs, and cost a little less than the other's I've found (usually the really low ESR caps cost min $50, easily $60+ each... and probably need at least 3 to get the voltage high enough). These are the ones I just found, https://www.skeletontech.com/ultracapacitor-webstore
.... sadly need to buy a box at a time (either 20 or 10 caps)... but at those specs, and that price... I think I'm gonna bite the bullet and make this happen finally.
I will be making a comparison of the 3 welders I've mentioned as soon as I have all in my hands. But my current hypothesis is that the kWeld has the most potential, while the first one I listed is the best band for your buck, and still very capable... but all 3 should be able to get the job they were designed for done. But the real goal is to get a setup that'll handle 0.1 copper without a problem (0.15 would even be better, but one step at a time). Been researching welding copper specifically, learning some potential ways to achieve it... also just certain techniques that help with spot welding any metal to batteries. One of the best things I've learned so far is to have a slot in the nickel or copper between your two weld points. This makes t so that path of least resistance for the electricity to follow is through the nickel/copper into the metal top/bottom of the battery, and back out the other side of the nickel/copper (exactly what you want)... without the slot the path of least resistance is gonna be from one of the welders tips through the nickel/copper to the other tip... instead of through the battery.
BTW, there are also other ways to utilize copper without welding it... what I plan to try on my next pack is to rty a technique very similar to what they are doing here (screw to the bottom photos to see the complete design): https://www.aliexpress.com/store/produc ... 57299.html
.... basically build battery holders with knurled insert nuts at the top/bottom between the batteries. Spot weld a layer of nickel to the groups of parallel batteries, then screw down a layer of copper on top to allow for a lot more amps to flow through the whole system. This seems like a very practical technique, and doesn't require anything more than your standard nickel spot welder. They sell different size battery holders, the pure nickel (0.2mm thick) and the copper 'H' by the meter (0.3mm thick)... all for a very reasonable price. AND I can vouch for the company, anything they sell that claims to be pure nickel IS (and good quality at that)... but they do also have nickel plated steel, though it is very clearly labeled (and for that setup specifically, it's pure nickel and pure copper, no steel). The issue for me is, I've been using 20700 batteries, not 18650... so mine wouldn't fit, so I plan on 3D printing my own holders... and imitating there design pretty closely, with my own tweaks.