# Capacitive Discharge Welder



## Packhorse (Dec 29, 2008)

Ever wonder how they weld those little tabs on to batteries to make battery packs? No? Oh. Well I did.

There are 2 ways.
Spend $5k and buy a commercial unit or spend $200 and DIY!!

The process is fairly simple. The power supply (on the left) chargers up the capacitor (top). Since the capacitor can represent a very large electrical load I have put a resistor in line with the power supply. This means it takes a few seconds to charge. The resistor is actually a 20watt halogen light (Bottom left).
Next to the light is a simple volt meter (bottom centre).
Once the capacitor is fully charged you place the electrodes (seen externally on the end of the thick cables) on to a nickel tab resting on the battery and depress the foot operated switch which triggers the silicon controlled rectifier SRC ( Bottom right). This then dumps the full charge of the capacitor onto the tab and welds it to the battery very quickly with minimal build up of heat.


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## darkzero (Dec 29, 2008)

Packhorse said:


> Ever wonder how they weld those little tabs on to batteries to make battery packs? No? Oh. Well I did.


 
Yup I have & always wondered how I could do it at home. Great job & thank you for posting! Would you be able to provide more details & specifics on how to build one? Thanks. :twothumbs


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## cnjl3 (Dec 30, 2008)

check this link:
http://www.ledhacks.com/power/battery_tab_welder.htm


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## Packhorse (Dec 30, 2008)

Thanks.

Yep thats the link I would have supplied too.


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## darkzero (Dec 30, 2008)

Thanks fellas! :twothumbs


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## Der Wichtel (Dec 30, 2008)

Instead of the resistor you can use a larger inductor plus a diode to prevent voltage peaks when the voltage is turned of.
Then you will have a higher efficiency :twothumbs


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## Fallingwater (Dec 30, 2008)

How much did your welder cost you?


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## Packhorse (Dec 30, 2008)

It was about $200 NZD. Although I used 2 SCR's that I got off Ebay. The shipping cost more than the SCR's. I alreadfy had the case, cable and power supply.

I went through 3 capacitors before I found one that actually worked. The first 2 were 3 and 4 farad and new. The one that worked was 1.2 farad and second hand. Go figure?!

DW. How large of an inductor?


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## Fallingwater (Dec 30, 2008)

From what I hear, most large caps' capacities are drastically overrated in an attempt to sell to people for whom more is better...


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## LuxLuthor (Dec 30, 2008)

It's interesting to see the innards of my Sunstone CD welder, and the parts they used as compared to this homemade model. Luckily I got one of the last two single phase before they upgraded lowest end model to an astronomical price. It continues to work perfectly, and is nice to be able to adjust to lower energy for Lithium cell welds.


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## Daravon (Dec 30, 2008)

Where did you get the cap?


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## Packhorse (Dec 31, 2008)

LuxLuthor said:


> It's interesting to see the innards of my Sunstone CD welder,


Got pics?


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## Der Wichtel (Dec 31, 2008)

Packhorse said:


> DW. How large of an inductor?



Had a closer look about the inductor solution but it won't work.
You will get oscillations


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