kWeld - "Next level" DIY battery spot welder

It's called galvanic corrosion, and will happen between many dissimilar metals whether there is current flow or not, even without being in an electrical circuit. Faster with some combinations with others, and typically faster with higher humidity.
But it's not that simple. In galvanic corrosion the anode gets all or most of the corrosion.
- anode - washers - zinc plated mild steel
- cathode - fuse - gold plated brass or copper (alloy)
But here the cathode gets significant damage too, probably even more than the anode.

You may be able to minimize it by applying a dielectric grease (like on car battery terminals) to all of the mating surfaces before connecting them, this will prevent humidity from entering the connection and reduce the corrosion problem.
Not advisable. Grease requires large bolts and high clamping forces. But as mentioned above, due to the hardware used, we are way below specs even for dry contacts.

Torque vs. contact resistance goes something like this:
jiky4yR.jpg

But if you apply grease all this graphics shifts up. And also remember - we are way below recommended torque.

The advisable thing is to change the metals being in contact, according to the galvanic series:
kF6buKGl.gif
 
If soldering a crimped contact makes it better, there was air space in it for the solder to flow into, and that's why the crimp was bad. ;)
Better just crimp, or solder. Or if you crimp before soldering, than first apply some flux and crimp very lightly.

Although soldering large cables may seem complicated, it is not. With proper tools it can even be easier than crimping.
Simplest way is a large soldering iron, but you can damage the insulation. Than there is the Resistance Soldering. And most complicated is the Induction Soldering.

kSupply can easily be turned into a Resistance Soldering Unit.
I do not know if tatus1969 sees this potential. But kSupply is super cheap compared to a commercial RSU. They start from $500-$700 and go into the thousands.

A RSU is basically a low voltage high current limited supply. Commercial units use just an autotransformer and a transformer in series. And two carbon electrodes in a free form or in a pliers configuration.

A very detailed and also beautiful explanation and build of a classic DIY RSU:
DIY Resistance Soldering Outfit

A commercial RSU in action:

This one, they say is 1800 W, which is around 250 A at 7 V AC.
But it costs $1700...

kSupply is limited to 70 A, but is still quite powerful.
I had the idea of converting it to a RSU long time ago, but I already have a RSU and also several ordinary large soldering irons.
Since, you see, the RSU in the above video has a weight of over 15 kg...
 
Hi!

I'm looking for the ability to change weld power without using the knob. I have a small CNC-board on which the k-weld is mounted and I'm welding 21700 cells. The amount of power needed is different when welding the minus pole vs the plus pole and I want to automate the "change".

Has anyone done something similar?

Thank

Rikard
 
Hi!

I'm looking for the ability to change weld power without using the knob. I have a small CNC-board on which the k-weld is mounted and I'm welding 21700 cells. The amount of power needed is different when welding the minus pole vs the plus pole and I want to automate the "change".

Has anyone done something similar?

Thank

Rikard
 
Is the knob a digital control, or a potentiometer?

If it's a pot, you can replace it with a digipot, and then automate it by remotely controlling the digipot.
 
Today I replaced the fuse in my welder. With the new one I get again 1.43mR when calibrating. When the original one was still good I got 1.45mR.

Seems the original 300a fuse is very close to this 350a littlefuse.
 

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Hola chicos, sólo quería dar una señal de vida aquí: ¡Feliz Año Nuevo! :) :) De alguna manera, las notificaciones de mis temas van a la carpeta de spam y, por lo tanto, no recibí notificaciones durante mucho tiempo...

Han pasado muchas cosas en este foro desde entonces, si hay algo a lo que deba responder, me alegraría que ese usuario repitiera su pregunta aquí.:confundido:

También tengo una noticia que compartir: estoy trabajando en un nuevo dispositivo "kWeldPro". Las piezas ya se están acumulando aquí (la crisis de los chips significa que necesitas comprar una pieza en el momento en que la pones en tus esquemas...), y debería tener los primeros prototipos a mediados de este año. Algunas especificaciones clave:

- unidad de escritorio lista para usar con entrada de CA
- admite soldadura de cobre (mínimo 3000 amperios)
- Fuente de alimentación de 450 W (impulso de 200 julios, una vez por segundo, en el terminal de salida del dispositivo)
- sistema de electrodos refrigerado por agua (opcional)
- actuador neumático (opción)
- Pantalla táctil de 4,3''
- USB, RS232, interfaz PLC, doble disparador
- carcasa de acero plegada
- precio alrededor de 1000€ (la unidad base, las sondas y la fuente de alimentación serán adicionales)

Saludos Frank
Hola How can I get the pro version of the kwed and how thick can it weld?
 
cutlaszc, If you need thicker buses for high current (such as an electric motorcycle), then read up and consider the "copper nickel sandwich" method. The kWeld can certainly perform the copper / nickel sandwich welding.

"Copper/nickel sandwich" buses for series connections"
 
My kweld has arrived. For the power supply of the kweld I can use LithiumWerks 26650 lifepo4 2s8p cells. I just found this on Facebook:



My goal is to solder copper 0.15mm nickel 0.15mm Sandwich method with infinite groove only on nickel
 
Hello,
I'm about to start spot welding with the KWELD, but I've encountered a problem. Initially, I tested the internal resistance of my Bosch AGM S5A11 800CCA 80AH battery using the RC3563 tester, and the result was 2.8 milliohms. The voltage reads at 12.7V.

Then, when I connected the KWELD to the battery, I measured the internal resistance at the positive and negative terminals of the KWELD, and the result was 4.8 milliohms.

I'm using 8AWG wires with a length of 33+33cm for positive and negative connections (the electrode 8AWG wires are 40+40cm long).

My concern is that my current calculation is approximately 12.7V ÷ 0.0048 ohms = 2645 amperes! However, the KWELD can only handle up to 2000A. I really don't want to risk damaging the KWELD. Unfortunately, I don't have another battery, and I can't afford to spend money on a solution right now.

Do any of you have any suggestions on how I can safely reduce the current to stay just below 2000A?

Thank you for your help.

P. S i already posted this message on secondlifestorage forum then i discovered this thread dedicated to Kweld.
 
First thing you need to do is to set the total cable length to 1.5m and this will limit your kweld maximum current to 1500a

My concern is that my current calculation is approximately 12.7V ÷ 0.0048 ohms = 2645 amperes!
Wrong, you have to add also the resistance of the kweld internal switch, the resistance of the wires after kweld and electrodes and also the resistance of the welded parts.
With your setup and 12.7v on the battery you will probably reach 1700-1800A but will be limited to 1500 because of the cable length.

Edit.
it is possible to get overcurrent error when you calibrate the system because then the resistance of the “welded parts” is very low. If this is the case try to decrease the battery voltage below 12.3v
 
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First thing you need to do is to set the total cable length to 1.5m and this will limit your kweld maximum current to 1500a


Wrong, you have to add also the resistance of the kweld internal switch, the resistance of the wires after kweld and electrodes and also the resistance of the welded parts.
With your setup and 12.7v on the battery you will probably reach 1700-1800A but will be limited to 1500 because of the cable length.

Edit.
it is possible to get overcurrent error when you calibrate the system because then the resistance of the “welded parts” is very low. If this is the case try to decrease the battery voltage below 12.3v
Hello @Schultz , thanks for your advice. I discharged the battery to 12.1v and made a calibration. The current was 1560A. My cables length total 140cm. So i guess everything is fine now👍.
 
Great!

Did you set the total cable length accordingly(1.4m)?

Your system total resistance seems ~7.7miliohm. If you add to this the resistance of welded parts which is approximately ~0.5miliohm results in a total resistance of ~8.2miliohm. If you multiply 0.0082r with 1600a you will get the voltage at which you need to charge the battery ~13.1v
 
Hola How can I get the pro version of the kwed and how thick can it weld?
I wasnt able to progress as fast as I wanted, because we had to do firefighting for weird firmware bugs in a customer project, literally for several months in a row. Conclusion: Wireshark does not see everything bad happening on USB, but thanks to the makers of the Beagle USB sniffer we managed to find a solution (also, thanks to Microsoft for making USB things different since Win11...
|O
).

At the moment, I am close to ordering a first batch of maybe 30 preproduction boards. Firmware development will take quite a bit more time, and therefore it is my idea to do the most important stuff first and then publish a number of firmware updates. For example, remote control via USB will come later, among other not so mission critical features. The GUI development is going nicely, attached a short clip of what this looks like at the moment. Last week I have started the enclosure design, which will be done by a fellow mechanical engineer who is mindblowing in SolidWorks. The enclosure will be punched, embossed, bent steel with powder coating, so there will be a sampling batch followed by a larger one. These processes require tool manufacturing, so that might become the bottleneck towards my goal of having the first smaller batch of units ready before this Xmas :)

https://www.keenlab.de/wp-content/uploads/2023/09/VID_20230818_194152340.mp4
 
I ordered a Kweld, but none of the recommended batteries on their website are available at Hobbyking. Can you recommend an alternative LiPo battery? Or any of these Acid batteries should work?

---

In the end I decided to use the car battery, I hope not badly (Exide 95Ah, 800A).
 
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kSupply is limited to 70 A, but is still quite powerful.
I had the idea of converting it to a RSU long time ago, but I already have a RSU and also several ordinary large soldering irons.
Since, you see, the RSU in the above video has a weight of over 15 kg...
sorry, just seeing this now. kSupply can be paralleled, so upping the current is quite easy. Two to three of them in parallel, with a server power supply for each of them, would allow for maybe 250 amps short time. Might actually be an interesting approach.
 
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