kWeld - "Next level" DIY battery spot welder

[crevettedragon]

Your bench power supply can be used, but there's one possible caveat: some power supplies don't like being backfed into their output when they are turned off, and can get damaged in the worst case. Many don't have a problem, but you should check that.

kCap has two 6mm holes to mount ring cable lugs coming from the power supply, but soldering them directly is also possible. The kit doesn't include connecting material for the power supply side, but everything else is included to start welding after assembly.

Thanks for the answers.
Good to know for the bench power supply backfeeding risk, I guess I will test and see, got the classic cheap Uniroi UC305.
As for connecting the power supply side, after examinating the part list of the kCap, your 6€ "kWeld – mechanical parts" should allow me to screw a m6 ring cable to the I+/I- of the kCap. I tend to avoid soldering when I can.
Thank you.

 

[BVH]

Did anybody tested the kWeld against a Sunkko 709A?
I'm looking forward to buying a spotwelder and like the possibility of the Sunkko devices to just run them off a socket. No need for a LiPo battery and just plug&play, comes with a soldering iron too. The prices are about the same for the Sunkko and the kWeld, so what's better?

If you want real spot welder you choose kweld or something similar. But only one is the best :wink: I have 1sunkko and would not recommend it. It's 220v version so it's better than the version for 110v but it can just barely weld 0.15mm nickel. It also trips my house breakers all the time so be aware if you have "new" kind of fuces that you just flip on and off. With older style fuse that is single use it worked better.

If you don't have a soldering iron just buy one hakko clone for 20 dollars.

I am not fan of lipos and had lead acid battery just gathering dust so now I am using it but it's real pain to carry around..

Ps I have sunkko welder on sale if anyone is interested

Same here. My Sunkko 709A is on Craigslist. It's just not as tune-able as the Kweld. Had to use double pulse or more and high power to get a descent weld. Welding with the rigid arms was difficult with all the upward travel necessary before triggering the pulse.

 

[Marv1337n]

I'll get the kWeld then. Any information about how long the linked 3S 5Ah LiPo battery life is?
I don't wanna pause mid build because the LiPo is dead.

 

[eee291]

I made 2500 welds @35J and it used about 15Ah on a 3S battery.
I checked the capacity afterwards and didn't see any degradation.
So with a 5Ah battery I expect it to last 700-800 welds @35J per charge.

 

[ossivirt]

I don't have experience but I have assume that with little use the calendar life of the lipo cell will be what kills it eventually. I don't even remember how long that would be but if you store it at right voltage and temperature it should last many years

 

[Marv1337n]

I don't have experience but I have assume that with little use the calendar life of the lipo cell will be what kills it eventually. I don't even remember how long that would be but if you store it at right voltage and temperature it should last many years

I'm not talking about the lifetime, I'm talking about how long one charge lasts.

 

[ossivirt]

I don't have experience but I have assume that with little use the calendar life of the lipo cell will be what kills it eventually. I don't even remember how long that would be but if you store it at right voltage and temperature it should last many years

I'm not talking about the lifetime, I'm talking about how long one charge lasts.

OK I misunderstood you. Someone once said something about user needing more to recharge more often than battery..

 

[BVH]

The Hobbyking Grapheen Panther I linked to before is a 6AH so you could possibly get another 20% more welds than with the 700-800 estimate graphed above. They make larger capacity, up to 10 AH but those might provide too much current and cause the Calibration Over-current issue I was having. Of course you can buy a second battery. They were cheap over the weekend but not sure if the code would still be good.

 

[fechter]

I'm using a little 3s 4.4Ahr Graphene Lipo with my welder. I charge while welding with my bench supply set at 12.3v. Keeping the battery voltage constant maintains consistent weld results. I was worried about big transients backfeeding my supply so I placed a large inductor in series with the charger to stop any spikes. I can weld until my electrodes get too warm for comfort.

 

[spinningmagnets]

What's a cheap and easy inductor that the average builder could add between their battery and power supply?

 

[fechter]

What's a cheap and easy inductor that the average builder could add between their battery and power supply?

I have very large selection of inductors in my junk box so it's easy for me. The one I used I think came off an old microwave oven magnetron. The input choke from an old computer power supply or any switching supply should be good. The inductor has to handle whatever your charging current is (around 3A in my case). The more turns the better.

Those ferrite rings that go on video cables could be used by winding a bunch of wire through it.

I just used one inductor in series with the bench supply. It shouldn't matter much which wire it goes on.

 

[tatus1969]

I'm using a little 3s 4.4Ahr Graphene Lipo with my welder. I charge while welding with my bench supply set at 12.3v. Keeping the battery voltage constant maintains consistent weld results. I was worried about big transients backfeeding my supply so I placed a large inductor in series with the charger to stop any spikes. I can weld until my electrodes get too warm for comfort.

That sounds like a good idea. Inductive kickback reaches approximately 55V for 20 microseconds at the welder. The battery will significantly dampen this, but I've actually never measured that with my batteries. I did though with kCap, and found that it is only a few volts and doesn't require additional protection there.

The inductance doesn't need to be high, if we assume at least 100uF at the output of the charger, then a 100uH inductor should already provide enough damping. But I strongly recommend to also add a resistor in series with the inductor, if its own resistance is very low, otherwise you have created a resonant circuit that will oscillate. According to LTspice below, a 0.1 Ohm resistance would be enough for this circuit. Quick check at Digikey: https://www.digikey.de/product-detail/de/kemet/SBC6-101-172/399-18931-ND/5819271

 

[sevillano1982]

Hello my friend @tatus1969

I have placed an order in your store (# 4923) for europe spain, do you know when you can send it to me? Thank you very much and my most sincere congratulations

 

[tatus1969]

Hello my friend @tatus1969

I have placed an order in your store (# 4923) for europe spain, do you know when you can send it to me? Thank you very much and my most sincere congratulations

Our next packing&shipping session is planned for next Monday. If you need yours urgently, then I can process that individually. Please let me know.

 

[bobmutch]

How about a larger version of this? You could use the same pattern but make it 20S 8P.

This pack is using parallel busbars, current travels serial, don't copy this poor design.

 

[eee291]

It's not a poor design unless tela engineers are idiots as well

It fused to protect the other cells in parallel in case one shorts internally.

 

[ossivirt]

I tested some nickel plated copper with the kweld. Difference is not huge compared to bare copper but at 0.1mm I noticed that it made it just slightly stiffer when I ripped the strips off. Copper is so soft that when it stars to tear it just keeps going and my plating reduced this effect a little bit. At 0.2mm the plating means less joules but in my opinion still too much for it to be safe for cells. It is most likely a lot better still than soldering but.. In my opinion plated +slotted 0.2mm copper still needs 140joules at least

At 0.1mm sweet spot is around 40-45joules and not much difference if plated.
View attachment 3 When ripping off plated tears little less and because of that it it's just a tiny bit stronger weld I think.View attachment 1 0.2mm you can see that plated welded with lower energy levels.
However welds were not strong..

Nickel is just too easy with this welder because you can use any value between 10-100 and difference is pretty much how dark and burned looking it gets. :lol: Copper needs just the right amount of energy or you don't get weld at all or burn hole through the strip and make it weak

Ps: I hope this is not too much off the topic. I have not seen much this kind of test numbers around this welder.

 

[frnandu]

This is very usefull information.
Where did you get nickel plated copper?
And what are you using for power?

 

[ossivirt]

This is very usefull information.
Where did you get nickel plated copper?
And what are you using for power?

I just got my copper from ebay and plated it myself. I have not really find any sellers online that sells plated copper https://www.instructables.com/id/High-Quality-and-safe-Nickel-Plating/

It's not really that difficult or require anything special.

I have this huge 110ah lead acid battery which was taken from 24v wheel loader when the other battery died.. Its probably not 100% like new but gives me 1500a on kweld. It's very inconvenient but as long as I don't need to move it around its just fine..

 

[tatus1969]

Ps: I hope this is not too much off the topic. I have not seen much this kind of test numbers around this welder.

I find this very valuable! I have some ideas:
- can you try slitting the strips, because this will help current guidance
- your razor blade is probably thicker than a battery can would be, can you try welding the copper strips to a 0.2mm nickel strip?
- it would be interesting to see how a battery can that gets this amount of energy will look from the inside, as you don't want to burn chemicals or the separator

 

[ossivirt]

Ps: I hope this is not too much off the topic. I have not seen much this kind of test numbers around this welder.

I find this very valuable! I have some ideas:
- can you try slitting the strips, because this will help current guidance
- your razor blade is probably thicker than a battery can would be, can you try welding the copper strips to a 0.2mm nickel strip?
- it would be interesting to see how a battery can that gets this amount of energy will look from the inside, as you don't want to burn chemicals or the separator

I have done some tests with slitted strips. There is some difference but it needs more testing.
Razor blade is pretty thick, I think it is around 0.5 or 0.6mm. I have no idea how thick cell end is. It is stainless steel if I am not mistaken? Maybe I need to make some welds with different energy levels and then cut open couple cells. That is probably stinking bad idea but it's for science :lol:
My nickel is 7x0.15mm but I can't test welding copper to it.

EDIT: Probably just "regular" steel with maybe some plating..

 

[frnandu]

ossivirt, did you use standard copper electrodes or other material?

 

[ossivirt]

ossivirt, did you use standard copper electrodes or other material?

Standard kweld electrodes.

 

[Acido]

I need a power supply for my kCap capacitors, which one do you guys use?
And if you made one can you link the parts used please?

 

[tatus1969]

I need a power supply for my kCap capacitors, which one do you guys use?
And if you made one can you link the parts used please?

I've been working on a solution for that in the past, but had to pause this in favor of design projects for customers. The kCap power supply project got "lucky" now because a customer needs it as well. I'm very close to making a first series production order and add it to the shop, and have a few prototypes on my desk that I could sell.