Realiable spot welder, need some advice

I notieced that the welds are much better with cool mosfets they probably switch better cold Mine was heatsinked with a pc fan as well 7ms 2x 2ms 0.15 pure nickel for first layer 9ms second I used 2 5ah 75c graphene so currents shouldnt be a problem unless the batteries have got weaker over time Since the welder probably did like 12-13k welds

That’s how to tell that the weld is done correctly If the strip breaks too easily why blame the welder? Just get thicker material…

You can make a welder out of microwave transformer, budget under $200 and gets you welding current of 1500A. Also powered from mains so no fokin with batteries as a source.

But will need quite a bit of work, needs some basic handyman skills and tools. . . . . .

Wait this stuff is actually even better from Mr Deu:


Do u have any pics of what ur welders have been handling? And of ur welder set up? Cuz it seems like ur pushing the small welder past its heat handling but dont want to asume

I made a simple welder using a timing circuit from AliExpress and a 1400w microwave transformer. The strips tear before the welds come off. The wires do seem to get a little warm/hot tips after about 30-40 welds but using larger tips and thicker wire will solve this issue, I opted for cheaper 21mm^2 wire instead of 35mm. Total cost was about $40 and I’ve made one pack so far

1 Like

I was considering this option At the moment I do not have the time for this But great to know someone who has made a good welder so I can just copy the design :smiley:

At the moment, I can not take a risk to receive a bad welder like the last time I managed to get unlimited power through my main cable box and the only limit is the wires and fuses basically, I installed a 40A C breaker fuse for the welder, but sadly it didn’t make the welds. @taz Its on my list to try some time soon, but hopefully I will be happy with the Kweld

Also I just got an idea to power these welders with a portable car starter like this

1 Like

Have you considered using a cheap TIG welder?

They usually have controls between DC and AC. Most have current and voltage control. A quick search turned up a 20-200V DC and up to 200A at the electrodes. 37A at the wall socket.

You’d just have to hook up an Arduino to control the foot pedal. You probably could spring the foot pedal and hook it up between the pedal and the welder to control the timings.

Only problem I see is the welder may not have good ramp up and ramp down time. I’m sure you could find that spec somewhere though.

Any idea how kweld is controlling the amount of energy? Is he just measuring voltage and voltage drop on MOSFETs?

Yeah he’s actually measuring the current. There’s actually a calibration routine built in. Once you assemble, you go into calibration and short the leads together. kweld measures the total resistance of the circuit. Then it can measure current, convert to joules, and use that to control the amount of energy going into the weld spot. With the idea that using joules, you can keep the welds consistent throughout your lipo’s state of charge.

After each weld, you can keep the pedal down, and it’ll tell you measured resistance, time, and current.

IIRC the goal is to tune the resistance of the whole circuit including the lipo, so it can deliver between 1000-1500amps.

The thing is like a horse. I don’t think you can kill it. Everything gets hot before the mosfets. If you watch his youtube videos, there’s a mode where if you make contact with both probes, the welder will discharge within a set time. In the videos, he’s talking, and accidentally shorts the leads together while in this mode, and ZAP! More than once, no issues. I scared the shit out of myself doing the same with my unit, also no issues. He added audibles after that video lol, so you know when it’s getting ready to fire.

1 Like


I’m asking because although the design is excellent, I would rather have like 5kA as I already have a 1kA welder and I’m limited in terms of thickness of material I can use. This would mean I have to go 5x all the power components. But I actually have found the schematics so perhaps after I finish building my esk8 I will start working on it and make a 5k version compatible with his firmware.

Oh and also I want to supply it from ultra capacitors, charged by some CC/CV LED driver PSU so I don’t bother with lipos.

1 Like

He talked about his design a lot, with some specifics at eevblog. But it’s not open source, so you might have trouble cloning his design.

What are you gonna do with 5kA?


At his website there were urls to EEVBLOG and endless sphere, first one not working second has schematics so how not open soruce? Or you mean the code is not open source? Well that shouldn’t be much of a problem, he would have to be pure evil to not send me modified version of the firmware with just bumped up max current/joules settings. And even if not then decompilation and then change of the matching numbers, right? :stuck_out_tongue:

Well as I said I would like to use decent thickness materials to weld the cells together not some paper-like nickel plated steel shyte :smiley:

1 Like

haver you tried the sunkko 788H? I used it for years before i got my sunstone 150.

1 Like

When you say they failed on you, did the screen turn off and a red light appear any time you try to turn it on?

Everything works, but the mosfets dont work as good, even when i turn on the ms lenght, probably the got cooked from the heat, and the welder before this one the mosfets on it completely died, and it displayed fet error on the screen which is fixable for like 20$

If you want your boss level welder to last, weld every 3+ seconds and dont stay above 30-35celsius for long time, with cooling especially, since the temperature sensor is not located on the mosfets but instead on the copper wire of the power out wire, and its temperature is not really important.

No I did not, honestly I would like to stay away from sunkko because of my bad experience with them, also I just got a quote from sunstone for a welder and they want 4500$ with a welding pen, which is atm out of my budget…

Where did you go to get it repaired?

You can sent it to @aulakiria or replace the mosfets yourself, its not that hard if you have some soldering skills

Did you managed to run your welder with this power supply?

Also what spot welder did you end up getting?