Kweld spot welder

Having run into problems with Boss welder (link) I was stumped on how to carry on building my battery packs for my ATBs. It’s still my go-to soldering iron, there is much to love even though I would like to bring back it’s welding capability.

I suspect FET damage but there are no errors or visible signs, apart from weak welds even with high settings. It wasn’t always this way, I was very happy and able to weld nickel on top of copper even with a 3s 3Ah 65c Graphene which is ever so slightly swollen now.

A switch to 4S via 4 x 2s high discharge Turnigy hard case 5Ah 60-120c packs did not help. Nor a Turnigy Nano-Tech 4s 3.3Ah 70-150c…so it’s the welder(*) but do not know how to diagnose and fix.

Here’s the full kit along with my own not-so-great 3D print of the stl available, out of sight is a foot pedal which is included.

It was a fun, easy and relatively quick operation to put together with helpful documentation. One gotcha is that you should have a crimp tool to mate the 8AWG electrode wire to the electrode, I was lucky enough to have this one from Amazon which did quick work of it

The electrodes are a thing of beauty btw. You can keep your foot on the pedal which allows you to inspect the values of the weld you just performed such as energy used in the pulse in Joules, weld duration, amps used, resistance of weld, FET temp.

I’ll build up on this post some more in the coming days

Here is some 0.15 pure nickel @30 joules using the Nano-Tech, I’m still fine-tuning it. What I really love is the calibration and measuring of discharge, that is distinctly an advantage for consistency and problem tracing.

20190827-154736-719 20190827-155326-657

Here is a range of weld on a 5J range using fresh 0.2mm nickel on 0.15mm copper

Lets look closeup at the 45J weld as a deep but sane welding energy level20190827-164624-27 20190827-164651-283

You can get this spot welder here, I think Frank may be able to work in a small discount code if someone need a push.

  • Frank kindly provided a spare set of electrodes to perform a like-for-like test using the same electrodes/battery, more on this to come.

So you run the kweld with 4s?
I wanted to buy the kweld too and asked if it’s possible to use with my 6s lipos (have some and the specs say it would be in range).
According to the guy who sell them it’s best to go low voltage. 3S is good, but probably 2S even better.

Here the official answer:

the voltage at the weld spot is only in the region of a few volts, all the extra voltage needs to be dissipated into heat elsewhere. This means that your batteries will either run very hot, or bring the system into overcurrent (2000A max). That’s why I don’t recommend 6S. It is better to build a 2S to 3S pack with more cells in parallel.


It supports 6s according to the manual but you have the caveat from the designer, so I think try it but budget for a lipo which suits


I believe it throws an error if your current exceeds specs

I can’t get a Kweld as of import regulations.
Went with the maelectrics which works well too for me and a 3s graphen 75c pack.
It was more a thought for you as you run 2x 2S if I understood right. So might be working better to wire them up in parallel than in series. Just a thought.


It’s making super welds already on 4s1p with this new pack so no need! Sorry to hear about your embargo

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Here is the calibration results with this Turnigy nano-tech 4s battery

The battery can supply 1338A to the welder, anything over 2000A will not pass calibration, the resistance value is a low value of 2.22, I did a good job on the electrode assembly it seems :slight_smile:
For the standard kWeld cable / electrode holder / electrode assembly, the value should range between 2.5and 3.0 milli-Ohms

Now we’re close up you can see just how bad the case print quality is, I printed it this way to avoid much support use but I forgot to block the logo, being PETG is does not really want to come off there and I don’t care too much…

If you care and don’t even have a 3d printer, you can buy a very nice case cut from acrylic but I haven’t tried it yet as it is not included in the kit due to wanting to keep the price as low as possible.


magharees invited me to join here. I’m the developer of kWeld and run the website. I’ll do my best to answer all your questions in this thread :sweat_smile:

Sorry for that, but the system uses some “dual use” components that could also be used for bad stuff like railguns and alike, which is why I have to do that.

Haven’t used the coupon feature of my webshop system yet, but there’s a simpler way: PM me through here and mention your keenlab order number, and I’ll make a 10€ discount on an order of 100€+.


I have a question regarding the operation of all these arduino welders.
They all work by short circuiting a battery and the differences between them lie in the way you make the various adjustments and the robustness of their construction?
So for eg the malectrics you adjust the welding duration whereas with the kweld the welding energy.
Meaning that as the battery voltage drops or there is a difference in pressure the kweld will provide more consistent results?

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@tatus1969 don’t worry I fully understood the reason. Sure sad for me, but better like this than to get troubles with the customs. It’s not good for any of us :wink:
Nice to have you here, ready to answer our questions!

we’re going to need a guide on this mod :innocent:


What energy you using and nickel thickness?

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.)