kWeld - "Next level" DIY battery spot welder

[Fraser]

I have just placed my pre-order. I went for the partially unassembled PCB, two 300A fuses (one and a spare) plus the raw bus bars. The rest I can sort out for myself.

This design is exactly what I have been searching for Perfect !
I know the parts for the PCB were not cheap so thanks for the hobby friendly pricing.

There was mention of a programmer for updating the firmware on the unit. Some details of the required programmer would be appreciated.

Best Wishes from the UK

Fraser

[Kjelt]

I'll order tomorrow, have to figure out what to get, are those high current connectors shown in any video already?

[tatus1969]

I have just placed my pre-order. I went for the partially unassembled PCB, two 300A fuses (one and a spare) plus the raw bus bars. The rest I can sort out for myself.

Got it! Thanks!

I know the parts for the PCB were not cheap so thanks for the hobby friendly pricing.

Yes, especially the MOSFETs. But I decided pro robustness and to accept a higher price for that. Also the microcontroller had to be a bit beefier because it has to do the entire energy calculation algorithm and all safety measures in a 10µs cycle.

There was mention of a programmer for updating the firmware on the unit. Some details of the required programmer would be appreciated.

It's very simple, a FTDI RS232 adapter and a cable. The red socket on the welder is a combined UART / JTAG interface. The firmware will run a dedicated in-application-programming code. I cannot show this part yet because it is not ready yet. That will take some more days to implement, the framework and the theoretical design is finished.

[Fraser]

Wonderful news on the programmer. Thank you for keeping it simple. I have lots of FTDI RS232 converters 

I shall start planning my version of the probes, case and power source. I have plenty of time to source the required parts.

Best Wishes

Fraser

[tatus1969]

Wonderful news on the programmer. Thank you for keeping it simple. I have lots of FTDI RS232 converters 

You need one without level shifter that uses 3.3V TTL levels. The pinout of the red connector is here in the thread:

https://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/msg1240839/#msg1240839

Not to forget: the schematic there is not up to date anymore, nor is it working like that

[Fraser]

Many thanks. I have 3V3 types as well as 5V so all sorted on that front
Will the documentation that comes with the unit contain a schematic and brief theory of operation please ?

Best Wishes

Fraser

[Fraser]

I have now ordered the following via eBay:

1m Red 8AWG Turnigy Silicone coated cable
1m Black 8AWG Turnigy Silicone coated cable
Ten 100mm Brass tubes - 6mm with 1mm wall
300mm x 4mm copper rod
Ten high quality solder/crimp lugs. 10mm2 / 6mm

I wanted more parts than are actually needed to enable me to experiment a little. The cost mounts up though. The kits offered by the OP are very good value and recommended for most users of the unit.

With regard to terminating the cables with the large lugs. There are two options open to me, Soldering or Crimping. Crimping can be a reliable connection, but only if a quality crimp is made. This normally requires an expensive high quality crimper. The crimp needs to be sit tight to avoid oxidation issues. Where such a high quality crimp is not possible, soldering is the preferred method, even in high current applications. The solder fills the voids and provides an excellent connection to all cable strands. The down side of soldering is that the solder can travel down the cable making the area adjacent to the connector stiff. I am going to so,dear mine with my high powered soldering iron.

Fraser

[TheAmmoniacal]

Great little device you've made 

I'm just curious, would it help to use flux? Common solder one or plumber type? Sure it will just burn into smoke rapidly, but will the surface finish/oxidation, and color look better? Any difference in the quality of the weld?

[tatus1969]

Will the documentation that comes with the unit contain a schematic and brief theory of operation please ?

Noted, I'll include that.

This normally requires an expensive high quality crimper.

I've ordered one of these, they are not as expensive as you might think. They develop huge force and should make reliable, gas-tight crimps.

Great little device you've made 

I'm just curious, would it help to use flux? Common solder one or plumber type? Sure it will just burn into smoke rapidly, but will the surface finish/oxidation, and color look better? Any difference in the quality of the weld?

Thanks 
Its welding not soldering, the temperatures are way higher here, maybe 1000degC. I think that flux will just vaporize or burn.

The welds actually look better than many of those which I showed in the videos. That was letting you participate in me experimenting, and of course to discover the limits. A typical weld of 0.1mm nickel strip to an 18650 cell typically does not produce any coloring.

I just made these welds on a dead battery to show how a regular weld looks like: this is 0.2mm 0.1mm nickel strip, the energy is set to 30J. It can probably still be lowered.



EDIT2: Okay, I'll have to take back everything that I said about using flux. The below welds are with 0.2mm nickel strips, and you can see the coloring which cannot be prevented when doing it as usual. Except both leftmost welds per cell, where I added a drop of flux! Awesome, I can definitely recommend that to everyone! The used flux was Chipquik SMD291.

[TheAmmoniacal]

Those welds do look great, no improvement needed! Maybe try a few with flux for fun?

[tautech]

Those welds do look great, no improvement needed! Maybe try a few with flux for fun?

I don't see any point, if you watch the vid there's an attempt to tear the spot welded strip off and to apply additional force than what was shown would only tear the strip or the battery.
This IMO gives the same result as professionally welded battery packs and you never see flux on them.

[tatus1969]

Those welds do look great, no improvement needed! Maybe try a few with flux for fun?

did that, updated my previous post 

[Fraser]

Regarding cell surface condition.......

OEM's would reject any cell that showed oxidisation or corrosion on the welding surfaces. I have bought many new Ni-Mh cells at discounted prices because they have suffered some level of corrosion on the end caps. Such cells are easily 'recovered' by cleaning the surfaces before spit welding. An OEM does not want such hassle and does not use flux as a result.

Cleaning of cell end caps is a good idea, especially if they have been sitting around for a while. Oxide layers do effect the way the weld forms as they have to be burnt off. This MAY be the true reason behind the double pulse protocol used by some battery tab welders.

I so no problem with using electronics rated flux when welding, it burns odd and cleans the surfaces in the process.

One matter that needs consideration when welding cells is heat. If too much heat is present on the cells surface, damage can result. This is especially so with button cells. Plastic seals can melt or boiling of the cells electrolyte can result.  The minimum weld current and duration should be used in such cases to avoid cell damage. The thin nickel tabs can be discoloured by the very high temperatures and I would be a bit careful about seeing that if working with fragile cell constructions, such as button cells. When using my Chinese Tab welder the cells surface does not get too hot to touch and the tag rips before the weld breaks. There is no discolouration around the welds but they are a lot smaller diameter ! I do prefer the welds produced by this DIY version. Far more in keeping with those I have seen on commercial batteries.

Fraser

[tatus1969]

hmmmm. Fraser that's very interesting, but I'm not sure if you have understood me correctly. I haven't added flux between battery and tab, but between tab and electrode.

[Fraser]

Ooooh, I had not thought of that. Interesting.

Fraser

[Kjelt]

Also placed my pre-order (see your pm)  .
Just wondering where do you order those metal strips that you use for the batterypack assembly ? Link ?

[tatus1969]

Also placed my pre-order (see your pm)  .
Just wondering where do you order those metal strips that you use for the batterypack assembly ? Link ?

I got them from ebay, the search term is Hilumin strip, or battery spot welding nickel strip. For example http://www.ebay.de/itm/2m-Solid-Pure-Nickel-Strap-Strip-Spot-Welding-battery-12mm-x-0-15mm-12x0-15-40A-/263057602801

[Fraser]

I have several types of strip that I bought from eBay. Some are described as pure nickel whilst others are nickel plated steel. I am uncertain whether the nickel plated steel is any good as I have yet to use it. I do know that it is important that the strip is not TOO conductive as that can present a very low tab resistance path to the probes. This may reduce current flow into the battery cap, and may result in a lower quality weld. That is why you do not see copper battery tabs on welded batteries.

Fraser

[tatus1969]

I forgot to mention, I recently tested these ones:

http://www.ebay.de/itm/10-St%C3%BCck-Hochstrom-L%C3%B6tfahnen-L%C3%B6tbr%C3%BCcken-Akkuverbinder-zb-f%C3%BCr-18650-27x9x0-3/162191637024?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

Their advantage is that they are 0.3mm and can carry higher battery currents, and they can yet be welded with low energies because of their pre-shaped spots. Just make sure not to repeat my silly mistake and always probe pairs of contacts with the slit inbetween.

[Fraser]

 This article caught my eye. How to check what strip material you have been sold ...... pure nickel or the cheaper plated steel.

http://www.ebikeschool.com/how-to-differ-between-pure-nickel-strip-battery-tabs-vs-steel-core/

It looks like for my battery applications, steel tabs will be fine. I am not working at high currents where small resistive losses become a factor.

Fraser

[Fraser]

A crude but still interesting test of battery connection strip.......

http://www.electric-skateboard.builders/t/carbon-steel-strip-vs-stainless-steel-strip-vs-pure-nickel-strip-fake-nickel-strips-tested-practical-performance-test-results/18633

Fraser

[tautech]

hmmmm. Fraser that's very interesting, but I'm not sure if you have understood me correctly. I haven't added flux between battery and tab, but between tab and electrode.

What was your rationale for doing this ? 

[tatus1969]

What was your rationale for doing this ? 

curiosity. to see if that helps reducing coloring. it does

This article caught my eye. How to check what strip material you have been sold ...... pure nickel or the cheaper plated steel.

http://www.ebikeschool.com/how-to-differ-between-pure-nickel-strip-battery-tabs-vs-steel-core/

I can make another proposal: measure up a reasonable length of your strip material, press the electrodes of my welder against the ends of that, trigger a pulse of lets say 50J, and take the ohmic resistance that it reports to determine the material 

[tautech]

What was your rationale for doing this ? 

curiosity. to see if that helps reducing coloring. it does

In my mind it's just acting as a coolant then so other liquids could have the same result........could you try some others to further satisfy curiosity ?

[tatus1969]

What was your rationale for doing this ? 

curiosity. to see if that helps reducing coloring. it does

In my mind it's just acting as a coolant then so other liquids could have the same result........could you try some others to further satisfy curiosity ?

I'm a bit hesitant to use other liquids like water, because I am afraid of eruptive vaporization. It is just that advantage which flux has that it just crumples instead.