kWeld - "Next level" DIY battery spot welder

[frnandu]

In that last pic it looks like someone touched the brass with one of the electrodes.

If you get it fixed and still plan on lending it to people then I recommend getting a case for the welder.

I'm not lending it to people, we just bought it together 3 people and shared the cost, since we don't need it all the time fulltime

And we have a case 3d-printed, but there are some situation when someone might need to open it to change the battery cables for their specific battery or something like that.

[Headrc]

I have moved over to the recommended Turnigy nano-tech 5000mah 3S 65~130C Lipo Pack for my Kweld. But I still cannot get good welds for the thicker .3mm nickel. The highest Joule I can get at this time is 62.5 ...after that I get an undercurrent message. Has anyone tried these Turnigy packs in parallel ....essentially doubling capacity and C rate? Thanks, Richard

[john61ct]

Doubling capacity halves the C-rate for given current, or doubles current at the same C-rate.

[Headrc]

Ok ...I stated that wrong ...it is about doubling the current that I am interested in. So again has anyone tried this?

[BVH]

Same idea but different battery. I use two, 3S/6000 Panthers and it welds fine. However, I was not able to initially calibrate the Kweld with both batteries run in Parallel due to too much current available. I'd get an error when trying to calibrate. So at the mfg's recommendation, I calibrated using only one of the Panthers and once calibrated, actually weld with both in Parallel.

[Headrc]

Thanks ...have you found then that your are able to weld thicker nickel strips?

[BVH]

I've not had the need for .3 strips. Most I've needed is .2.

[spinningmagnets]

If you need more current from each cell than can be provided from a 0.20mm thick nickel strip, consider adding a copper strip under the nickel, attached to the series connections. The parallel connections never carry high current.

[tatus1969]

I have moved over to the recommended Turnigy nano-tech 5000mah 3S 65~130C Lipo Pack for my Kweld. But I still cannot get good welds for the thicker .3mm nickel. The highest Joule I can get at this time is 62.5 ...after that I get an undercurrent message. Has anyone tried these Turnigy packs in parallel ....essentially doubling capacity and C rate? Thanks, Richard

With a nanotech 5000mAh you should get at least 1400A of current, and be able to produce pulses of way more than 100J. Please keep the foot pedal down after the OPEN and SHORT calibration steps and post all the info that is displayed. I suspect that either the battery, the welder, or something with your setup is wrong (maybe post a picture that shows everything, also the cables). 0.3mm pure nickel is definitely doable with this setup.

[tatus1969]

Doubling capacity halves the C-rate for given current, or doubles current at the same C-rate.

That's right but doesn't show the full picture. kWeld does basically short circuit the battery when pulsing, and the amount of current is directly given by Ohm's law: voltage stays constant when paralleling two batteries, but their combined internal resistance is half of that of a single one. But still current does not double, as there are more electrical resistances in the loop: cabling, the welder switch and fuse, and also the weld spot itself. Using one nanotech 5000 gives 1400A typical current, and using two in parallel will likely exceed the 2000A current limit of kWeld and is therefore not recommended.

[john61ct]

A right size resistor to limit current?

[eee291]

A right size resistor to limit current?

Hello no.

[ossivirt]

A right size resistor to limit current?

Longer avg6 batteryleads and or smaller and worse connectors . Not recomended mut if you keep them under max allowed lenghts if will loose some current..

Edit: meant 8 or higher awg..

[john61ct]

Same difference.

[tatus1969]

A right size resistor to limit current?

Longer avg6 batteryleads and or smaller and worse connectors . Not recomended mut if you keep them under max allowed lenghts if will loose some current..

Adding resistance in whatever way isn't recommended as it only produces more heat. Adding cable neither, as this adds unhealthy inductance. The only proper way to reduce current (if you don't want to reduce the battery capacity) is to lower the voltage, i.e. use a 2S Lipo instead of 3S.

[flippy]

A right size resistor to limit current?

that would be hillarious to see a regular resistor take 2500 amps without being atomized back into its base elements.

[john61ct]

So assuming an unlimited amps capacity, but with adjustable current limiting as well as voltage,

what is the ideal input to get maximum safe and effective welding, being conservative about not damaging cells nor reducing their longevity?

[john61ct]

HEADWAY 38120 HP 3.2V 8AH LIFEPO4 LITHIUM BATTERIES 25C 200A
..
Boston Power Swing 5300's

those are shit batteries so expect poor results.

That is not my understanding.

I can look past obnoxious tone if the actual expertise is solid, but this flippant comment is a big red flag.

Hmmm, flippant, is that why the flippy handle? or more like "flipping a bird"?

So, do you mean that these decent-quality cells are just not well suited to a particular type of use case?

[flippy]

That is not my understanding.
I can look past obnoxious tone if the actual expertise is solid, but this flippant comment is a big red flag.
Hmmm, flippant, is that why the flippy handle? or more like "flipping a bird"?
So, do you mean that these decent-quality cells are just not well suited to a particular type of use case?

yes, these cells are not suitable for this, they are light duty at best. they sag, have quality issues and short lifespans by comparison to their price and inconsistent power delivery. and i have tested enough (and had to warranty a couple batteries with headways that ate all my profit margin) to support my claims to never recommend headway-type cells or akwardly sized off-brand cells nobody ever heard of or without testing them to destruction to actually map their performance.

yes, these cells are probably " fine" in a pure DIY setup and to tinker with, but trusting them with your life and the lives of others on public roads is a different matter. there is better -and cheaper- alternatives for that.

i sent you a PM about the personal stuff, it does not belong on this thread.

[john61ct]

Fair 'nuff, I could give a shit about feeling myself, not calling you names at all.

But just sticking to the whole point of helping out in a public forum, from a utilitarian / functional POV

just flipping off an unqualified "those batteries suck" without any explanation is the opposite of a constructive contribution.

Especially with two cell types that are actually very high quality

but maybe just don't happen to meet the needs of your particular use case.

Why assume high discharge rates?

What have "public roads" got to do with anything?

Are you saying for use cases where LFP is ideally suited, Headway sucks compared to say K2? Would only last 5000 cycles rather than 7000?

[frnandu]

Is this "REMOVE SHORT" error cause only possible if this diode is somehow damaged (even if it looks ok)?
If so, can it be easily replaced with an ordinary soldering iron?
I need to order from you new electrodes, so if indeed I should replace this diode for stopping the error, maybe you can send me a replacement together with the electrodes?

It is not always easily noticable when these components crack, sometimes the black top only lifts up very slighlty above the large metal tab at the one end. There are other possible reasons for this message, but I now realize that I haven't read your initial post correctly. You say that you had removed and connected the fuse and that it then worked. I somehow had read that you had removed the TVS diode, which is why I gave that warning. This is a completely different situation, and I am thinking about this right now as I haven't had this before... A few questions:
- you actually removed and replaced the fuse while the system was powered from the battery, right?
- are you sure that you have never accidentally touched something on the logic board with one of the electrodes?
- are you sure that you haven't applied external voltage to the electrodes?
- can you once measure the voltage across the electrodes, a) hafter having powering the system, and b) after you have removed+replaced the fuse?

Hi Frank,
For a few weeks the "Remove short" problem somehow went away (didn't do anything, just several times disconnected and connected the battery and it just stopped appearing), but now it again shows up (simply by reconnecting the battery), so I did measure the voltage across the electrodes as you asked.
The voltage is 8.37v (when it shows the "remove short"), and after I disconnect the fuse and reconnect it (the error goes away) it is 8.19v.
Here's a short video showing the error and voltage:

https://photos.app.goo.gl/TQ9F8TB8yWynGr4j6

and pic after reconnected the fuse:

20190908_103706.jpg (293.42 KiB) Viewed 689 times

Can you figure out what might be wrong?
Thanks

[frnandu]

Let me just add that this is something that since the very begining we (me and another guy you bought the kweld together) have been having, check the very first time in January we posted here about this problem:

viewtopic.php?f=14&t=89039&start=525#p1440919

So, even before we started using the kweld this error was already appearing. But then it went away and we didn't tough anymore about it.
It might be that we somehow made an error while assembly, but we can't figure out what exactly. We tried to follow the assembly manual carefully.

[tatus1969]

Can you figure out what might be wrong?

The voltage is absolutely okay, and if the welder makes consistent welds as well then I suspect an entirely different problem. Do you have the firmware updater so that I can send you two different firmware images for testing? I'm varying the 'short' detection parameter so that one firmware should always fail, and the other should always pass. If my theory proves true, then there will be an easy fix for this.

[Headrc]

I plan to give a more lengthy response at a later date on this ...primarily because I am still experimenting with my battery power for the Kweld. But I can state this ....the battery connections to the Kweld, including the internal ones on the battery itself are absolutely critical. That and the cable length setting will have an impact on whether the battery will prove successful in powering the Kweld. Plugging and unplugging connectors has proven to be a big part of the problem for me ...and it does not matter if they are Anderson,XT's or any other connector. A high power battery disconnect switch is what I am currently experimenting with.

[john61ct]

Blue Sea makes very robust bank isolation switches designed to handle interrupting some darn high currents.