"Michael Rigby-Jones" > That is essentialy what a spot welder does, though usualy using a low > voltage/high current transformer rather than a capacititive discharge > method. I have used a spot welder for car body repairs and it's a pretty > crude (though effective) device, but is far too large for spot welding > battery tabs. Either technique is "resistance welding" as they both rely > on the resistance between pieces of metal to create the heat for welding. > My plan was to recycle one of the large (500-1000VA) transformers I have > under my bench at home. By stripping off the secondary and winding a few > turns of very heavy cable around the primary I should be able to get > enough current for spot/resistance welding. Controlling the current is > trickier, multiple taps on the primary would probably be the way to go, > and no expensive SCR's are required, just a relay to switch the mains > into the primary. How much current does a gun-style soldering iron put through its element? If you took the tip off, that might provide enough current to do battery tabs. It would be pretty convenient, too. Just take a spare tip, split it in two and sharpen the ends to appropriate points about 1 cm apart. Then you can hold it in one hand, use it to press the tab against the battery and pull the trigger for a few seconds. I suspect that the battery manufacturers do it with lasers, for minimum heating outside the weld. There's a company that advertises in NASA Tech Briefs all the time with examples like this. -- Dave Tweed -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist