6pence Resistance Spot Welder

[spinningmagnets]

Brass would be a better conductor for the probe holders, so they would run cooler than steel. Copper would work fine, but it is softer and easier the strip the threads when you tighten the screws onto the cables and probes...

edit: yeah, (post below) brass is made specifically to machine easily, among other attributes...

[Storapa]

Brass would be a better conductor for the probe holders, so they would run cooler than steel. Copper would work fine, but it is softer and easier the strip the threads when you tighten the screws onto the cables and probes...

Good point about running cooler. I hadn't thought about that. Copper is also a pain in the A to machine.

[sudsy7]

The demo video shows 2 car batteries in parallel for power. Is that really required for this to work or just provides extra capacity for more welds?

[spinningmagnets]

In order to keep the welder simple, the amps are adjusted by changing the amount of the battery amps. You can use one small battery, one medium, one large, two medium, two large.

The amount of amps you need is dependent solely on the thickness of the strips you are welding, and the results you are getting with "X" amount of battery. Once you have settled on a combination that provides good results, just stick with the same battery combo and the same nickel bus thickness.

[sudsy7]

In order to keep the welder simple, the amps are adjusted by changing the amount of the battery amps.

So would the CCA of the battery be a better indicator of "weld power" than Ah? Most of the car batteries I have seen don't even have Ah ratings.

[fechter]

So would the CCA of the battery be a better indicator of "weld power" than Ah? Most of the car batteries I have seen don't even have Ah ratings.

Generally, yes. A physically larger battery will have more. "Deep cycle" or RV batteries are not as good as they have less plate surface area.

[spinningmagnets]

Lead/acid is a different world than lithium (or capacitors)...The amount of "Cold Cranking Amps" (CCA) is directly related to how much surface area is available for the chemical reaction between lead oxide plates and the lead DI-oxide plates (with a sulfuric acid 50% electrolyte solution).

A "deep cycle" battery has thick plates (about as thick as your little finger), because as the battery is charged and discharged...each plate is dissolved a little bit. This limits the physical volume of the total battery pack.

An automobile engine "starter battery" needs to provide a LOT of CCA on start-up, but...it is re-charged up immediately by the cars' alternator. Therefore, the way to have the maximum CCA is to have as many as possible THIN plates in the electrolyte bath as possible.

For the purposes of the "pocket spot-welder" designs...definitely use a car starter battery, do NOT buy an expensive "deep cycle" battery...

[The Mighty Volt]

In order to keep the welder simple, the amps are adjusted by changing the amount of the battery amps.

So would the CCA of the battery be a better indicator of "weld power" than Ah? Most of the car batteries I have seen don't even have Ah ratings.

Car batteries provide more wallop for far less time, as SpinningMagnets said, they have more and thinner plates, designed to provide more wallop per turnover.

Leisure batteries have fewer but fatter plates, designed to provide less initial current but longer,deeper discharge cycles.

So a 100Ah 12v car battery would, all other things being equal, weld thicker strips than a 100Ah leisure battery...........but the leisure battery would weld more of thinner stuff.

It's all about getting a few batteries and testing.

With the old capacitance discharge welders, it was a question of getting good Caps and then adjusting the voltage for the material you were welding. 3 Farads at 12v did nothing. 3 Farads at 17v atomised the nickel.

[Valld]

Just a small update to confirm that I'm able to weld 0.2mm nickel to a battery tab with my single 72Ah car battery. I tested a few different settings and settled on 1.5 - 1 - 10 ms on the controller. Tried with 8 and 9 ms pulse, not strong enough, with 10ms I cannot pry the nickel strip from the tab without damaging it, so I guess a good weld. I believe I'm reaching my battery limit with the 0.2mm nickel. For 0.3mm I guess I would need a second battery I also experimented with split strip, just used my proxxon rotary tool to cut a slid in the middle of the strip about 6mm long. I can confirm that the weld is better and you need less ms, but didn't try this on a battery tab.

I made new cables with the 5mm copper electrodes sent from Paul - see the photo below. This was extremely easy to make, I just grind the two sides on a bench grinder and hammered about 4 cm directly in the middle of the cable, then grind the outside tip again to remove the damage from the hammering and finally polished the tips with 1000 grit sandpaper. This last step turned out very important, with a rough tips I had very strong sticking of the electrodes to the nickel strips, after polishing the tips no sticking anymore. Took me 10 minutes for both cables including the cable lugs on the other end.

My GA batteries from tumich are in Capetown, took two months from Poland to South Africa. I hope they will arrive in Botswana in 3-4 more weeks. Then I will have much more to share....

[pguk]

Nice
I'm not quite clear how you attached your electrodes to the ends of your cables?
For myself, I wrapped a few turns of 22awg stranded wire around the electrode and cable, and then soldered this up and covered with heat shrink. The electrodes are normal copper wire - any larger than 5mm and you won't be able to get on the ends of a cell. (I don't carry these any more)

[Valld]

☺ I literally hammered them straight in the middle of the copper core, with a hammer. The isolation of the cable is pretty strong and is holding all together.

[Animalector]

Well spent a significant portion of yesterday and this morning putting this thing together, and it works.. now I need to get some nickel strip, and some cells and go wild...

Still Todo: Find some better probes / copper rod.



Andy

[pguk]

Hey Andy,

Thanks for taking the time to do this neat little video. Looks like you have it nailed on one battery - must be a large one.

Best wishes, Paul.

[Storapa]

Morning Folks,

Sorry about the lack of updates in the last week or so. I had a fair bit of house maintenance to complete to keep the good lady happy. Right, back to the spot welder.

I decided to buy a new tip for my soldering iron, as I only had a couple of smaller ones. The busbars were a bit of a task. I think the issue was that my gas powered iron struggled to maintain a constant temperature. Being a bit of a perfectionist this stressed me. Anyway, they are done now (but not that nicely). I also backed up the battery and spotweld lead points with copper as suggested. If I did this again I would borrow a more capable iron.

IMG_1480.JPG (64.31 KiB) Viewed 3882 times

The rest of the build has been straight forward. I need to finish the soldering of the signal wires and switches and put the complete assembly into a box.

IMG_1481.JPG (87.01 KiB) Viewed 3882 times

The battery I built for the spot welder uses 20Ahr pouch cells. I had these in stock. The completed battery is 2s 3p x 3. The pack will be 8.2v off the charger and 180Ahr in total, so should be more than capable. I've made a copper busbar to go across the top of the pack.

Spot Welder Power Pack.JPG (120.13 KiB) Viewed 3882 times

[Animalector]

Will the 1ms and 5ms settings be too much with a lithium pack capable of delivering mega-uber-huge current? Thats a very pretty pack though i love the interconnects. How did you machine those?

[Storapa]

Will the 1ms and 5ms settings be too much with a lithium pack capable of delivering mega-uber-huge current? Thats a very pretty pack though i love the interconnects. How did you machine those?

Hi there,

I'm not sure I understand your point, "too much". The pack can put out 1800amps for 10 seconds, so hopefully it should have enough grunt. If it's over spec'd I'll reduce it in size. Am I missing something? You can probably tell I'm a mechanical engineer.

The pack was part of a traction battery out of car. I stripped it and used the original interconnectors. The interconnectors are pressed. They are great packs to build up.

[Animalector]

As I understand it, the mosfets are open for short duration in the order of 1ms to 15ms etc. The amount of energy they can deliver in that time is dependent on the source (in my case a car battery in your case a Lithium battery). The weld energy to get a good weld is somewhat constant depending on the material. With a Dodgy old car battery with high internal impedance, and weak current delivery, longer weld times are required to get enough energy to make a good weld..

My feeling is that with a super-duper-mega-awesome-1800Amp lithium, you're going to get nice big bangs as it can delivery way more in the same time window as what a car battery can... Thus I am questioning if we can adjust the on-time small enough???

Perhaps I am not understanding the way these things operate, but that's how i thought it worked.. anyone else care to correct me?

Andy

[Storapa]

Hi Andy,

Interesting. If the battery is a bit too brutal, I'll reduce it in size, to say 2s 3p x 2 or even a single.

Anybody else have any thoughts on this one?

[fechter]

I think the resistance of your weld cables will limit how much you get, especially at 8.2v. If you find it's too hot, you can add some length to the cables.

[riba2233]

This battery will blow your welder instantly. Try with 30 Ah instead of 180 and see if it fits you.

[notger]

Hi,

just ordered the Stuff for a 6pence-welder.
So beforehand some Questions came up.

I would rather use a PSU and HIFI-Power-Cap instead of a Car-battery.

That would make up the chance to play around with different Volts too.
Sure Pulse duration and delay will make most difference still?....

Did anyone of you made experiences with ? lets say? 3 Volts or 20 Volts ?
And :
Did anyone make a 6pence-SW with High-Power-Cap instead of car battery?

greets and thanks for your experiences.

Notger

[pguk]

This battery will blow your welder instantly. Try with 30 Ah instead of 180 and see if it fits you.

I'm sure Okashira was using some kind of lithium battery as current source for the JP welder. Perhaps this is how he came to implement flyback diodes, which we have onboard here.

I have never tried with lithium yet so I can't speak from experience. Maybe take baby steps in building your battery, try with a single pouch cell first and go from there?

[pguk]

Hi notger,

I did play around with car audio capacitors at early prototype stage. I had 2 Proel caps in parallel, a 2F and a 0.5F. Results were poor. They charged to 15v and then leaked. I never got a good weld. Texaspyro has some info in here somewhere. He found that most brands had a much smaller capacitor inside that enormous shell. He found only 3 brands worth their salt. Jeremy Harris built something with a bank of decent industry standard electrolytics, but this will be pricey compared with using a car battery or two.

[notger]

And dit you try two car batts in series->24Volts ? or would the Fets actually be capable handling that Voltage ?
cause i'd like to weld 0,25mm Hilumin too, and that might work better with higher Voltage?

notger

[pguk]

The MOSFETs are rated 24v but I wouldn't go anywhere near there. There is a voltage spike at every turn off event. Also, the TVS diodes I supply are dialled in for 12v lead acid.
What is Hilumin??