# Build your own CD battery tab welder for $100



## Silviron (Nov 11, 2007)

Hi Gang. Long time no see; I kind of lost interest in flashlights and the like so I haven't had anything worth posting about here at CPF. But I've recently been working on a something that several of you might be interested in building for yourselves.

Lately I've gotten interested in electric powered bikes and scooters, (Mostly I blame Darell for that) and am in the very early stages of building a few different designs. And of course one of the critical components is the battery pack, and I want to be able to build my own without the danger of damaging cells by soldering them.

So, I decided to try my hand again at building a Capacitive Discharge spot welder , And have come up with a design that works fine and is of nearly insignificant cost. Even if you have to buy just about every component, you can build your own functional unit for $100.00 with just a little shopping around.

A lot of you that are into making your own stuff will probably have most of the components needed already.

I'm not going to post all the details of it here, but I have a pretty extensive and ongoing documentation of text and photos (and soon a video or two) over at the ledhacks.com website, to which I will be adding as I refine the design.

Here is just a teaser:










You can read all about it here:
http://www.ledhacks.com/power/battery_tab_welder.htm


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## chimo (Nov 11, 2007)

Thanks for the link!


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## koala (Nov 11, 2007)

50RIA120
[email protected] Continuous
[email protected] Surge :devil:


Your right about those car audio capacitors, out there probably 20% has low enough esr suitable for it's job.
If you can find a good 12V capacitor with low esr, maybe you can wire it in series to increase voltage, and it will double the esr.
Also, you might want to shield the cap with something, cause shorting them may cause unknown effects... I don't think it will 
explode but better becareful.

Still looking for capacitors, maybe I'll post mine, IF i get it working...


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## Fallingwater (Nov 11, 2007)

I made my welder by rewinding the transformer of an old microwave oven.
It works, kinda, but the welds aren't as clean as with an instant CD welder and considerable heat is generated on the surface of the welded materials (the points under the tips get red-hot, even if for a very short time).
It also tends to eat the tips (sharpened copper rods) pretty quickly.

I'll eventually build a proper CD welder, but the MOT one has the advantage of being extremely simple to make and costing almost nothing (if you have a broken oven at hand).


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## Silviron (Nov 11, 2007)

Fallingwater said:


> I made my welder by rewinding the transformer of an old microwave oven......



Yes, I experimented with that too. 

It does work, sort of, but not something I would use for 'serious' battery pack assembly, especially with smaller NiMH or any kind of Lithiums.

5.5-6v secondary with 6 or 8ga wire seems the best for battery work, but still not what I'd call GOOD. I occasionally got decent welds on larger things like D cells, but the one LiIon I tried welding with it .... 
Well. lets just say I wouldn't feel safe with it around me anymore. 

Higher AC voltage just blasts through the battery can... (especially the raised positive tips). 

Anything lower than 5.0V heats the 'guts' of the battery up as badly as soldering to it by the time you get a weld, which may not hold, so that isn't a good solution.

I also tried going DC, running it through a 200A bridge rectifier and adding 1 1/2 more secondary turns to the MOT to make up for the voltage drop through the diodes. That didn't improve operation at all. unfortunately.

I can't recommend it for battery or any kind of electronics work. Does OK with light mechanical spot welding though. 

Since the CD method can be done cheaply enough, that is really the way to go for battery work.... and I have a feeling that when the 5 Farad cap comes in, with a variable voltage PS, I'll be able to do mechanical spot welds in even thicker materials.

However, I am going to try the rewound MOT with carbon electrodes for resistance soldering one of these days.



> It also tends to eat the tips (sharpened copper rods) pretty quickly.


You might try tungsten TIG welding electrodes. Make a handpiece out of copper or maybe brass rod by drilling a hole about the diameter of the electrode, then drilling and tapping an intersecting hole for a set screw. That's what I used on the CD welder I built about 15 years ago; It might work better on AC than it did the way I was using it.
Use only about an inch or less of the tungsten projecting from the handpiece, or you might end up with a 'bulb-less light bulb' if you get a stuck electrode.


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## Fallingwater (Nov 11, 2007)

Uh... I'm almost afraid to ask, but what happened to the LiIon you tried welding to?


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## Silviron (Nov 11, 2007)

Fallingwater said:


> Uh... I'm almost afraid to ask, but what happened to the LiIon you tried welding to?



Nearly burned a hole through the 'can' on the negative end, then when I tried tabbing the positive end, it pretty much burned the whole 'nipple' off, and probably even melted the safety valve shut, or opened it up completely..... I didn't want to look too close to find out for sure. Probably just missed making it 'vent with flame' by about 2 watt-seconds.

While it easily could have been much worse, that wasn't as bad as what DID happen with a AA NiMH: Ruptured the positive end and sprayed electrolyte all over the place. Some of the 'magick smoke' escaped too.

I should have been wearing goggles, but luckily no damage, just a little sting and irritation until I could rinse it off.

That's why I say go with CD if you are going to weld on batteries. A 'D cell' has enough mass to survive the AC, a C cell is marginally OK if you are quick and careful, but nothing smaller is even remotely safe.


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## CNC Dan (Nov 13, 2007)

koala said:


> Your right about those car audio capacitors, out there probably 20% has low enough esr suitable for it's job.
> If you can find a good 12V capacitor with low esr, maybe you can wire it in series to increase voltage, and it will double the esr.



Also look for low inductance caps. Those are mostly used for photoflash apps.

If you can't get low inductance, you can use a bunch of smaller caps. and wire them up in paralell. But you need to have all of the wires from each side of the caps. go to one common point. (one for pos. and one for neg.)
And use extra heavy wire of corse.


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## LuxLuthor (Nov 14, 2007)

I went the expensive route with Sunstone...but got one of their last single phase models before the price more than doubled. Just didn't know enough and wasn't willing to take chances with Li-Ions. This larger pix shows how many welds can be done on the (+) end of Eneloop AA. With ps booster, I can zap as fast as I can position leads. Your detailed webpage is pretty comprehensive, and a great accomplishment.


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## kavvika (Nov 16, 2007)

Very cool site, thanks for the link. I've always wondered how the SC NiMh packs I use in my R/C's were welded together.


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## BatteryCharger (Nov 16, 2007)

Hmmm...couldn't you use a couple car batteries wired in series instead of capacitors?


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## Packhorse (Dec 16, 2008)

Hi guys.

I have tried making a CD welder but with success yet.

I have a 3 (?) fadard car audio cap
2 of these SCR's
Copper electrodes
and a 2 level power supply that charges the capacitor up to 18 volt.

It discharges the cap OK but it just does not weld.

I see some DIY welders use a separate battery to fire the gate on the SCR but I use the power supply that chargers the cap. Could this be the cause?
Could it be the capacitor is too small? I dont believe its 3 farad, but Im hoping its at least 1 and shouldnt that be enough to give some sort of weld if even a poor one?


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## Packhorse (Dec 18, 2008)

Anyone got any idea what the minimum size cap would be that could do a decnt weld @ 16volt +/-??


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## VegasF6 (Dec 20, 2008)

Pardon my complete ignorance on how these work, but if is there anyway to non permanently modify a 110V wire feed welder to apply to this application? Or is it a completely different type of technology?


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## Mr Happy (Dec 20, 2008)

VegasF6 said:


> Pardon my complete ignorance on how these work, but if is there anyway to non permanently modify a 110V wire feed welder to apply to this application? Or is it a completely different type of technology?


I think this is like the things mentioned in posts #4ff above. It's basically a no-go. You will as easily destroy the battery as create the desired weld.


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## Fallingwater (Dec 20, 2008)

VegasF6 said:


> Pardon my complete ignorance on how these work, but if is there anyway to non permanently modify a 110V wire feed welder to apply to this application? Or is it a completely different type of technology?


Nope. Continuous discharge welders are a no-no for battery use, as they generate way too much heat. I have a low-power one made with a microwave oven transformer, and even that can't be used to weld tabs to cells. You need a whole lot of energy all at the same time, so capacitors are the only way to go.


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