Pressure used for spot welding, different thicknesses and weld times

Just got myself a new welder (similar to this one: https://www.banggood.com/pt/650A-Mi...America&&akmClientCountry=SE&cur_warehouse=CN) since I never got enough peak current from by old 12 V SLA + this guy (https://www.ebay.com/itm/DIY-Portab...ry-Various-Welding-Power-Supply-/264906371037).

The welds seem more dependent on how much pressure I apply rather than time in milliseconds of the weld. When I think about it, it's the (peak) power developed in the interface between the battery and nickel strip which does the job, not the current. If I press hard enough, resistance drops and although the current is slightly higher (I=U/Rtot, U is fixed and ESR of the battery and cables make up a not insignificant amount of Rtot), power and thus heat in the weld is less. Vice versa, if I press really softly, I melt the nickel strip.

At your run-off-the-mill 4.1 V welder, how much time in milliseconds and how much force do you apply for:
0.1 mm nickel?
0.15 mm nickel?
0.2 mm nickel?

I need a starting point to practice around.

An SLA would need to be a larger size to deliver enough current.
That banggood unit looks too small to be a serious unit, it seems to have only one cell inside? Hope I'm wrong?
I would think a spot welder needs a pack of minimum 6 or so cells.
You need the pressure to get good contact between the probes + nickel strip + the battery terminal.
The current has to mainly flow in a U shape down through nickel strip, across battery metal up through nickel strip.
This needs pressure as you found.

To get the right time, you just have to practice with your gear, your nickel strips & some old cells

Ignore the SLA, that's just some background.

It's a single cell, 4.1 V.

How hard do you press and with what time setting for which nickel strip thickness?

As far as pressure, you always want to apply firm pressure. Hard enough to make good contact, but not quite enough to bend your probes. So it is pretty firm pressure.
If you get sparks, this is because there isn't enough material making contact. Pressing firmly can help minimize this issue.

winny said:

It's a single cell, 4.1 V.

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This is probably not going to last. Spot welders require a LOT of amps to run. The wires get hot pretty quickly because of this.
You'll need something that can handle repeated 20+ amps w/o loosing voltage during the process.

I have the red color one (ebay link) and I use to weld 0.2mm pure nickel strip with 12-13 points (milliseconds actually) settings.
To weld nickel plated iron steel 0.1mm - 2-3 milliseconds is enough.
Yes, I modified it (added 1000mF capacitor behind diode on 5V power rail, to keep MOSFETs/drivers in safety voltage range) and added 10mm2 copper "busbars" for traces to/from MOSFETs on PCB.
I made a really strong 3S14P (26650 high-drain) Li-Ion battery (~30Ah in total) with total IR (proper AC 1kHz measuring by YR1035+) on external 12v connector - as low as 3.9mOhms.
Yes, I use all cables between battery/welder/one-hand-weld-probe not longer than 1.5 meters long in total, 25mm2 to connect all that.

I recommend you check this youtube channel, if you are still using the red welder https://www.youtube.com/c/Luca_Techy

Yes, pressure does mater when you have a weak battery !
But if battery is strong, you cold press as strong as you want and it will weld. Actually with strong battery it's more safe to press strong enough to avoid a risk to have an explosion of strip under weld, when conductivity is weak which leads to too fast temp growing on a strip itself.
On the other hand - too strong press makes a risk to make a hole in strip AND cell as well during welding, which is very critical on negative cell side.

Just make a ton of tests to find what works for you.

winny said:

I need a starting point to practice around.

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Oleksii said:

Just make a ton of tests to find what works for you.

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@winny
One thing that you don't want to leave to chance is your spot welding. Besides proper cell testing (IR and mAh)!
I have nothing against "cheep" spot welders if you want to save a buck or two, but with most inexpensive devices you have to play with them and modify as @Oleksii has done for them to give you a consistent result. I am an avid DIYer and initially was contemplating building my own spot welder. I came to the conclusion that someone else has done the heavy lifting and perfected the ultimate spot welder.
I am of course speaking of the kWeld. Is it expensive? Yes! Does it produce consistent predictable results? Yes!
The last thing I want to do after putting a pack together and getting ready to spot weld is inconsistent results. Nevermind blowing through a cell and having to start all over.
The kWeld when set up right will measure the resistance between the 2 probes, adjust the ms and amperage needed for a proper weld according to the Joules you dial in.
My kWeld has a minimum of 17,920 successful spot welds under its belt and I have no doubt it would do that again 100 times more. Give it the proper power supply and it will just work every time.
From the kWeld web site.

I am in no way affiliated with kWeld just own the product and couldn't be happier. Besides I have a spot welder for life not just for a few fleeting moments till something else blows up on the less expensive units.
My 3 cents worth.

Wolf

Wolf said:

The kWeld when set up right will measure the resistance between the 2 probes, adjust the ms and amperage needed for a proper weld according to the Joules you dial in.

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The kWeld only adjusts time, not amplitude (voltage and/or current) to get to your preset energy setting. Peak current is only determined by open circuit voltage, ESR of the battery, contact resistance and to a lesser degree, ESL.

I'm sure it's better in every way. Let me re-phrase my question. In your kWeld, what voltage are you running, what energy setting do you use for 0.1 mm pure nickel and how hard do you press? Same question for 0.15 mm.

winny said:

how hard do you press?

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Quite firmly so you get good probe contact + hold the strip & battery together properly

winny said:

what energy setting do you use for 0.1 mm pure nickel .......? Same question for 0.15 mm.

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This is where you have to experiment at your end. We can't tell you what's right for you because your setup is different.
Find some dud cells & try some settings, then inspect eg, try to tear of the nickle strip (it should hold well, not come off easily) , look for "blow through holes" into the cell (too much energy).

winny said:

I'm sure it's better in every way. Let me re-phrase my question. In your kWeld, what voltage are you running, what energy setting do you use for 0.1 mm pure nickel and how hard do you press? Same question for 0.15 mm.

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I use a Turnigy Graphene Panther 6000mAh 3S 75C Battery Pack w/XT90 so that's 11.1V nominal. With a full charge I can weld the pos and neg side of my 80p with 2 welds per connections so that's 320 welds. My settings are 35.9 to 36.0 joules after experimenting for the perfect weld. I use relatively moderate pressure which assures good contact between the strip and the cell. It's a feel thing. I mean you don't want to crush the cell but also not treat it like glass. As far as 0.1mm or0.15mm you just have to experiment on some junk cells. There is no magic number but the kWeld website gives you starting settings to go from for different thicknesses.
Wolf

Wolf said:

I use a Turnigy Graphene Panther 6000mAh 3S 75C Battery Pack w/XT90 so that's 11.1V nominal. With a full charge I can weld the pos and neg side of my 80p with 2 welds per connections so that's 320 welds. My settings are 35.9 to 36.0 joules after experimenting for the perfect weld. I use relatively moderate pressure which assures good contact between the strip and the cell. It's a feel thing. I mean you don't want to crush the cell but also not treat it like glass. As far as 0.1mm or0.15mm you just have to experiment on some junk cells. There is no magic number but the kWeld website gives you starting settings to go from for different thicknesses.
Wolf
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Thanks! After watching more YouTube videos on the matter, point shape and angle seems to play a role too. Do you weld pretty straight or at a 45 degree angle? Rounded tips or more sharp-ish?

winny said:

Thanks! After watching more YouTube videos on the matter, point shape and angle seems to play a role too. Do you weld pretty straight or at a 45 degree angle? Rounded tips or more sharp-ish?

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I generally weld at a 40° to 45° with slightly rounded tips after doing 1000 or so welds I scuff the tips up with a bit of sandpaper but never a very sharp point.
Wolf

I have one of these.
It has auto-detect setting too and 4 different power levels.

I have tested with my Ni stripe (I think it's 0.1mm but can double check) and it took the 3rd power setting to weld properly. I tested on junk 18650.
On the initial level 2 setting it seemed to weld but then I could remove the strip easy enough.

Anyway, this is overall a precision welder, not a power welder. If I want to go serious I can always use the one I made from an microwave oven transformer.