kekk k7 pro spot welder?

[markifi]

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i'm thinking of buying this, but i'll ask for advice here first. do you guys see anything wrong with it? first i would use it for repairing powertool battery packs and an old headlamp that needs a 3s lithium ion pack, but once i know i can do that properly i'll build an ebike and i would use it to also build a larger pack or two. i know kweld exists but for that i'd need car batteries which would make it cumbersome because i'd need to take them out of family members' cars to use the welder, or i'd need a welder to make a pack for the welder, if that makes sense. for this reason a ready-made kit makes more sense. i see there's along history of the now open source JP welder here, and that's nice, but i don't think it's available as a kit nowadays? is it? that would be my preference if it is available, simply because it's open source, but i can't find it. if anyone has a used one in east europe, i'm up for it

 

[docw009]

They're rating it for .20 mm nickel. If your tool battery packs uses .30mm nickel, you'll want something bigger.

 

[jonyjoe303]

I bought one of the cheap 30 dollar welders, it didnt last me long before it was smoking, maybe 5 welds total. I bought as a spare to use when I didnt have to do too many welds. I have no confidence that the inexpensive welders will last long from my experience.
My go to welder is the malectrics welder (made in europe) which I owned for about 5 years, it is similar to the kweld. Both run off 12 volt car batteries but can also run off a lipo RC pack.
If your going to be serious about building packs, you need a malectrics or kweld, they are expensive but will last you years. You don't need a car battery, I've use the smaller 16ah agm batteries (found on jump starters) to power it.
The one on Aliexpress might work or it might not, I don't like the thin wires on the probes. On my malectrics I have to use 6 gauge pure copper wire for the probes to get good welds.

 

[gromike]

It's probably a junk welder, meaning you'll soon throw it away. Though, you are most welcome to buy it and prove me wrong.
I'll hazard a guess that quite a few people here have burned up several cheap welders. I have, but some people do report good results.

 

[markifi]

thank you all for the replies. i won't buy it. the malectrics is a bit above the budget, but i'll think about it. the whole thing isn't urgent. another one that's very interesting to me is converting a stick welder, but it's a very involved project with building it's own timing board and re-coiling it's transformer. i've seen a video about it (

) and happen to have that exact same welder i'm not using. this is less "buy it now" and more of a "maybe one day" projects though, i'm afraid. not cheap either.

 

[Daijoubu]

I bought it and did a couple of test welds, seems to deliver, getting solid welds with 0.2mm pure nickel.
Has 9x Infineon 4N04R8 300A FETs, FET driver instead of an optocoupler, however all the FETs gates are connected in parallel. There's one TVS diode but I'm not sure they put it in the right place between +/-, should have been between the FETs drain and source afaik and a schottky diode between +/-.

Seller were very responsive and adamant on not replacing the leads with thicker gauge and/or longer when I asked them about buying a welding pen, stock leads are 7AWG 35cm.
Larger gauge results in higher current, longer cables result into higher inductance/kickback/avalanche, both of which can fry the FETs.

Powered by a pair of repurposed/used Maxwell 2.7V 3000F super capacitor connected in series.
Charged via USB-C (max 5V) or 9/12V 3A (caps are charged at constant current of 3.66A)

Posted about it on Reddit

https://www.reddit.com/r/18650masterrace/s/nlGKvgi9Cs

https://www.reddit.com/r/18650masterrace/s/Hx1ntgLbIS