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Kweld spot welder

45J, 0.2mm nickel, 0.15mm copper

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@taz That’s the theory. kWeld calibrates system resistance when you set up, and actually measures the energy going into each weld. I think it’s a little flawed, as it’s energy over time that makes the heat, right? But it’s still doing a lot more than just timing.

kWeld is also built quite tough by design and testing. Hard to kill. Everything (probes, wires, battery pack) gets hot before the welder.

Some notes I have for weld energy using HK Graphene 3s 6000mAh 65C:

official chart
0.1mm   20j
0.2mm   50j
0.3mm   100j
deucesdown testing with utility knife blades and dirty used cells

1 x 0.20mm nickel to steel: 20-35 joules (35 gets hot)
2 x 0.20mm to blade:
  45j sticks okay
  50j very good stick, hot
  55j very good stick very hot
1 x 0.25mm 20-40j
1 x 0.30mm 70-120j (120j was best, but 100j+ was HOT)

@tatus1969 thanks for joining here. Really enjoyed the thread as it was going on ES. Since you’re here I’ll throw you right into the fire. :wink:

I know on ES you’d helped revive some early kWelds that broke, so was surprised to read this. Can you shed any light?

@magharees thanks for making the thread and badgering the maker to come over. Maybe add “Next Level Spot Welder” to the title? That name has been used in a few places, and adding it to the title or first post might help reduce confusion.

EDIT size comparison kWeld vs Boss



That’s exactly the idea behind kWeld. It calculates the instantaneous power that it delivers into the weld spot (not to confuse with the power that it draws) and accumulates it during the pulse, in order to determine when to stop. Keeping the amount of energy/heat dumped into the weld spot constant makes the results more consistent, and mostly independent of mechanical pressure, dirt/corrosion, and the battery voltage. I’ve also recently added an arc detection feature that interrupts a pulse with an error in that case. Arcing can easily puncture a cell can otherwise, when it happens. It’s resistance spot welding, not arc welding in our case :slight_smile:

I’ve actually once used kWeld as a magnetizer, by mounting an air coil instead to its output. It doesn’t make coins jump however, you apparently need more voltage for that.

Good point :slight_smile: And, yes and no. As long as the mass that you deposit the energy into is kept constant, then you’ll get a constant temperature rise. As we are heating up a small spot underneat the electrodes, this is a good approximation when we can keep the pulse duration short. Once that gets longer, then heat starts to spread out form the spot to nearby metal. I could implement an algorithm that estimates this heat spreading, but that would need to be configured for parameters like metal thickness and type. As long as everybody reports me that the repeatability that kWeld produces is good then I don’t think that it’s worth the effort.

At the beginning of our conversation, I was convinced that he overtorqued the current trim pot as these are quite delicate, and didn’t see this as a warranty case. What had worried me much more is that the used Maxwell caps are not intrinsically safe when being overcharged and can apparently go wild in such a case. Therefore I immediately started developing a protection circuit that will be added to a next gen kCap module. It doesn’t matter whether the overvoltage is resulted from a user error, a bad trimpot, or some kind of fault, kCap has to be safe to use. I have the first prototype of this on my table right now. This got me distracted from my communication with this guy, and although I wrote him that I would treat the kSupply fault as a warranty case despite not being entirely convinced, I forgot about the bad kCap that he also has on his table. I just checked my email history, he didn’t ask any further and also didn’t send the kSupply for repair yet. I’ll contact him again to resolve this.


Currently away from home on a job in Glasgow I get back on Monday haven’t shipped it back as It’s at home will get around to it next week.

More interestingly I’m having issues with 0.3mm Nickel
0.15 with slots I’m using 7 Jules with out slots 9 jules. I’v tryed up to 175 on 0.3mm and it’s not welding very well with 2 6ah 3s Turnigy Graphene in parallel XT90 gets hot after a couple of welds battery’s start warming up. I fined some pic

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may be a good idea to try recalibration and taking pics of the calibration screens achieved with this pack

175J, is that possible to achieve? :thinking: If I can weld 0.2 nickel to copper with 45J is’t probably not more joules needed. That 3s2p pack should pack a lot of current.

Start with calibration and then take some test welds? keep your foot on the pedal to see what the results are, maybe share pictures of these welds and of course the weld info (keep foot on pedal)in order to get the best advice

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This is what I was playing with before. Was expecting to blast holes in the cell at them settings

Can you measure the amps delivered and resistance met with a test?

Some batteries appear to have aluminum cans. I have had a customer who had sent me a few samples for testing, and I could confirm that it is not possible to weld nickel strips to these with kWeld, even when cranking up the current to 1700A. You’d probably need laser welding for these.

And, as magharees suggested, keep the foot pedal down to tell the amperage. That’s the best indication of a problem with the setup. Also make sure to calibrate properly: make sure the electrodes are clean, and press the (conical areas of the) tips together hard during the SHORT step. You shouldn’t see any sparks, otherwise repeat. Make sure that all nuts and bolts are tight. Also check the electrode set screws, but don’t overtorque because that is all copper.


No worries, I’ll wait and repair/replace the modules as soon as I have them. (No need to send the kCap as that is broken beyond repair.)

Will do when I get back home from what I can remember the calibration was prity good bottom 1/4 of resistance.

I was thinking about using some thing like this
But the results looked prity good so I didn’t

Is it not worth salvaging the PCB? Even if it’s only for testing? (The acid from the caps got every were still not got on rid of the smell :nauseated_face: even hit the ceiling)

On some step down buck converters you get a display with voltage and amp would be a nice little extra module you could develop in the K weld line later on.

2 things worth noting.

Pressure on the probes makes a huge difference. Heavy pressure seems to make the welds weaker. Light pressure seems to make them stronger. This is worth experimenting/practicing with. I suppose I should add, keep the tips clean – something I too often neglect.

The negative herminal is the whole cell body, so can take a lot more heat. The positive terminal is a tiny piece of steel, and cannot dissipate as much heat. The terminals may also respond differently to the amount of energy.

:thinking:I was thinking the total opposite I was applying more and more pressure trying to get the current to go down in to the cell thanks need to try this.

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After the claims of 175J earlier & just out of curiosity, I tried to pull 75J and released the white smoke from my 2 week old 4s lipo which now reads a few mA and us toast, alas nano-tech I knew thee barely.


Eek! 120j is the highest in my notes. Everything got hot in like 1-3 welds. The graphene pack is still happy.

My notes are rough, but I think I had 75ms for a 100j weld. Amps were in the 1100-1200 range.

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There’s a reason most builders use 0.15 or 0.2mm strip - any thicker and you need a very short, high power welding pulse to get fusion, which these style of welders can’t provide. If you need the extra current carrying ability, I’d suggest doubling up on thinner strip rather than trying to weld armor plating to your cells.


I made an RMA with a couple of multimeter readings and whammie HK credited my a/c. Glad it happened within the 1mth warranty window tbh

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I don’t think this is quite correct – the welder is providing the energy (granted it gets hot quick), but the amount of energy it takes to weld 0.30mm nickel seems beyond what’s healthy/safe for the cell and the process.

I do not think a stronger welder will make the 0.30mm process better. I wanted .30mm to work – stupidly I bought a 1kg roll of the stuff.

Sorry to pick at your post, but when I tested, I really did not like the adhesion I got with nickel to nickel welds. It seemed so weak and inconsistent even at high power. So me personally, I prefer one layer, and adding copper, or skipping right to soldering copper, if called for.

As stated in other threads I was using 2 turnagy grapine 6amp 3s in parallel

the battery’s were warming up but ok the xt90 was getting to hot that’s why I stoped and didn’t push the jules any higher. I think my weekest point seemed to be the XT90. If I remember right the battery’s are rated to 6amp *2 at 150c peak so 1800 amp but I’d expect that to be over ambitious as always with Lipo rating. The lith ion cells were getting to hot for my liking even tho these ones were cheep eBay crap I was going to throw away so I was pushing it higher than I would be comftable to weld a pack. I came to the conclusion that the .3mm nickel was too conductive and way to hot to touch after trying to weld and the only chance I had was to fined slotted stuff to aid the current passing in to the battry instead of along the nickel.

I was thinking of swoping the xt90 on the unit to XT150 and making a XT150 to dule XT90 but I don’t think that will be enough. I think the k Capps are the only real option that might work on .3 I could have a cold weld on my XT90 splitter as it’s with AWG8 cable that’s difficult to keep the heat in the cable as it wicks it away so quickly and is a little to large to fit in a XT90.

As fare as I’m aware a supposed peak manufacture rating of 1800 amps is one of the highest I’ve seen on esk8 forums and think this is why I’m seeing the XT90 issue that no one els is reporting.

I have been unsusefull in welding 0.3 mm nickle so fare but that doesn’t mean that this unit can’t do it. I have gone back to using 0.15mm to finish my current pack until I work out and refine how to use .3mm.

The issue I keep finding is people say it’s a power issue or the welders not powerful enough but thay have never used more powerful units and are just guessing.

I’m weld 0.15 sloted nickle consistently with jules as low as 6
I’m weld 0.15 nickle consistently with jules as low as 9
Iv tryed to weld 0.3 nickle with jules as high as 175 to a low standard at that point I’m having overheating problems of XT90, cooking the nickle and leaving to much heat in the cell.

That’s double the thickness at 20 times the energy I think that proves stronger power supply’s and heavy duty welders are not the answer on there own. I’m convinced 0.3mm nickle is to conductive to weld in the same way as 0.15. And if that’s not enough try sanwidging electrode craftblade 0.3mm nickle the electrode with a setting of 30+ jules then rip it apart

I try to pick up some more cheep battery’s so I can post the energy delivered in to the weld at them settings when I get home. Sloted 0.3 nickle will aid in the issues I’m having but I can’t fined any to try so fare if any one knows a place I could get some. 0.3mm nickle plated steel would have a higher resistance so wondering if that’s how people have welded 0.3mm in the past.

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Things iv yet to try that in theory could help.

Reduced pressure as sergested by @deucesdown
Sloted 0.3mm nickle
Changing out XT90 to XT150 (to reduce resistance for higher amp delivery).
Super capacitors
Cleaning my welder tips again (thay were new replacement ones when I started playing with 0.3mm)

For me, IIRC, the order of things that get hot are:

  • probes OUCH OUCH 1 weld at 100j and it’s really hot
  • XT90
  • lipos where all the wires go in
  • lipo and probe wires
  • screw terminals
  • lipo cells

Remember kweld protects itself at 2000amp. You’re tickling that limit. Improving the connectors and wires might push you over. :slight_smile:

@jeffwuneo I remember you mentioned you can do custom nickel? Would you be able to do something like 0.30mm thick, 25mm wide (double wide for foldover), 62mm long (span 4 cells), slotted over the cell contact points? Something like this?


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