Spot Welder

[Mike Amick]

I have a pile of 16850 batteries and want to make some battery packs. Getting ready to order
a Sunkco battery welder, This one.

I have an arc welder and didn't know if there was a way to use the voltage from that to make a spot
welder ? I can actually handle the electronic end as far as pulse control and such but I am not familiar
with what makes my welder works.

I watched a vid of a guy that just used a big car battery and a timing circuit to pulse a starter relay.
Seemed to work ok.

I've seen the vid of guys taking the microwave transformers and tearing them apart. I have never been
able to get one of those apart, I tried.

[MattiJ]

Arc welders don’t have the needed current for spot welding so it’s not going to work.

[lakeside53]

And car batteries have a LOT of current capability, so take care.

[Mike Amick]

Arc welders don’t have the needed current for spot welding so it’s not going to work.

Nor my mig ?

[mixdenny]

The one you linked to goes up to 800 amps and only does .2mm material.

[J Tiers]

The current depends on material and thickness. Steel is fairly easy, it takes only around 1500 amps to weld ,040 or maybe 0,060 steel, because it is high resistance and heats up well.

I had to weld a bunch of 0.020 aluminum at work, and had only a 120V HF spot welder to do it with. By finding the right outlet at the shop, and using a timer to control weld time, I got it done pretty consistently. I had to do a coupon every 30 welds or so, to check the weld with a peel test, bit got it done. It took just the right conditions, and an estimated 2500 amps to weld that low resistance aluminum.

I di not know what the material is for the battery tabs, but if it really is mickel plated steel, that should be reasonably easy. but not with a regular welder, unless you do regular welding and not spot welding. Spot welding will likely take about 800 amps in a short pulse. You can actually figure it out by calculating the energy required, and determining the resistivity of the material, working back to find the current-time product required.

Those welders seem to mostly charge up a capacitor bank, and then discharge it, probably through a transformer, to develop high current. Similar system to a magnet charger, or a regular spot welder, except that the input to the spot welder is a pulse and not a continuous AC as with the HF piece. High voltage, heavy SCR, and a transformer with a one turn secondary of heavy strip, that would be the approach.

Might be cheaper to find a different method, unless you will need the thing again. If you have a big soldering iron, and a quick touch, you can do that effectively. That's how I have done them.

If you have the "Batteries and bulbs" chain near you, they rebuild packs and have all the stuff. Usually not that expensive

[Mcgyver]

I've seen the vid of guys taking the microwave transformers and tearing them apart. I have never been
able to get one of those apart, I tried.

I've done this a few times to get the voltage needed - you can do this either by drilling and hacking out the copper winding you want to replace.....or grind out the weld and and it just comes apart.

Also, consider the ballast from an industrial light fixture. They're free or small dollars used (the igniter goes and they're tossed) and are larger. Like the MWT, the advantage is the two windings are separate vs on top of each other so they're easily rewound.

This is for a resistance solderer I'm making

[Noitoen]

A regular spot welder will ruin the batteries. Usually a tab welder is made of a capacitive discharge unit. I'm building one at the moment with some capacitors I got for free. It has 12 10000uF 200v capacitors connected in parallel that I charge from anywhere between 0-65 VDC. The weld is controlled by a 2500A thyristor that discharges the capacitors through 2 thin copper electrodes spaced 4mm apart. The power is regulated by the charge voltage of the capacitors. Even this will ruin the battery if the electrodes are't firmly in contact with the tab being welded as the short circuit arc will melt the tab and battery. In my case I use a little pneumatic cylinder to obtain a constant pressure on the electrodes.

[CCWKen]

Have any of you experts actually made one? I have and the M-wave X-former works great. I made a new battery pack for my .01 gram scale about two months ago. I've had X-former from a microwave for years but life kept getting in the way. My Tab Welder is pretty simple and crude but worked fine for my use. I'll try to get a couple of pictures if it warms up a little. It's 30*F right now and WAY TOO COLD for me.

The one in the OP's link won't be in stock until April 1st so keep that in mind.

[J Tiers]

I do not see why the microwave transformer would not work..... it's just a spot welder, it is the timing that controls whether you kill the battery or make a weld. Same for welding thin sheet, the weld time determines if you get a weld, or if you melt the nugget to the point that it is not connected to the rest of the sheet.

Current is primary current x transformer ratio, so you can calibrate it, if you want. All a regular spot welder consists of is a high ratio transformer with a very low resistance secondary. People that fail in making one usually try too many turns of wire that is too small as a secondary, and have resistance issues that keep the current too low. Might work for a battery welder though, most want a regular spot welder for sheet metal, and that takes a good deal more current.

I have not tried making a spot welder, since If I wanted one I would just buy one that works.... they are not uncommon on CL. Ones for battery welding are much less common, don't know I have ever seen one of those on CL.

[Mcgyver]

I do not see why the microwave transformer would not work....

good luck getting enough amps. I think was a few thousands and probably more like 3-4 thousand.

I tried, I could get metal to start to stick together, but not a full weld and concluded the transformer design just wasn't efficient enough/put through enough current. I used a timer, foot switch and SCR's trigger mains into a rewound ballast like above. ultimately it proved a waste of time compared a commercial one....experimentation end when someone took pity and gave me a commercial spot welder

[pinstripe]

If you have a big soldering iron, and a quick touch, you can do that effectively. That's how I have done them.

That's how I do them as well. A hammerhead tip like this allows you to work very quickly. You can also use it to join batteries end-to-end without a tab. I think there is a YT video showing the technique.
https://hobbyking.com/en_us/hammer-h...___store=en_us

[CCWKen]

good luck getting enough amps. I think was a few thousands and probably more like 3-4 thousand.

I tried, I could get metal to start to stick together, but not a full weld and concluded the transformer design just wasn't efficient enough/put through enough current. I used a timer, foot switch and SCR's trigger mains into a rewound ballast like above. ultimately it proved a waste of time compared a commercial one....experimentation end when someone took pity and gave me a commercial spot welder

You have too many loops on your secondary winding. (In previous photo). Mine works great and will burn a hole in the tab and/or battery if left on too long. It's been longer than yesterday but I think I have ONE loop on my secondary. You don't want voltage, you want current. The way to get current from the MW transformer is to use ONE loop on the secondary. I didn't have a timer so I rigged a button to tap. It only takes a split second to weld a tab to a battery.

I'm getting dressed now for the Artic Blast we're having. I'll be back later with pictures. I just used stuff I had around the shop so don't expect a retail quality machine.

[Willy]

I too need to make some 18650 battery packs and have also contemplated the purchase or build of battery tab spot welder.

I have to rationalize the purchase or build of a spot welder vs the amount of use the thing will actually see. I fully realize building battery packs isn't going to be a full time hobby, nor do I want to make a commitment to building a spot welder with all of the timing and current bells and whistles that a pro model would include.

I just want to weld a few tabs onto some 18650 batteries once or three times a year. So what, other than my ability to time consistently, would be the downside with going ultra cheap and using the method below? I already have all of the needed components so zero cost of entry is a big plus.

Oh and Ken, -23°C here this morning and I haven't even thought about long underwear yet.
Although moving has crossed my mind. LOL

[Mcgyver]

You have too many loops on your secondary winding. (In previous photo). Mine works great and will burn a hole in the tab and/or battery if left on too long. It's been longer than yesterday but I think I have ONE loop on my secondary. You don't want voltage, you want current. The way to get current from the MW transformer is to use ONE loop on the secondary. I didn't have a timer so I rigged a button to tap. It only takes a split second to weld a tab to a battery.

I understand all that. Failure for me it was it barely would do 22 gauge steel (or maybe it was a bit lighter, it was ages ago), it would stick but not produce a proper weld. I'm not sure what a battery tab is or how thick it is. I had 240 in and 1.5 volts on the secondary which from what I read is what you want. As I said, the above is for a resistance solderer not a spot welder. I've an extra variac so will put it in front of the transformer for ultimate control on the solderer. A bit of overkill but the hardware is sitting there so why not?

How many amps do you think you'll get with the MOT and at what voltage? I think I was getting about 2300-2500 but it was inadequate. It wouldn't do metal thick enough to say make an enclosure out of, but whats adequate will of course depend on the intended use.

anyway, the main point of my posting was to show how to get the transformers apart and to suggest another source - light ballasts. My trials with heavier gauge stuff have little to do with battery tab welding I suppose, so I'm going a bit OT with it