elec:welder

Battery tab welder

Some years ago I needed to weld metal solder-tags onto some nickel-cadmium batteries. A nearby surplus supplier had some 120,000uF computer-grade capacitors in stock for an absurdly cheap price, so I ordered five of them. An SCR was procured from Farnell, and the welder was born…

I ended up using an L200CV linear regulator to regulate the capacitor voltage, and a 7805 to generate the gate drive for the SCR.

I built this thing about ten years ago, so all information here is provided on an as-is basis!

  • 5x 120,000uF capacitors
    • I used these because they were available cheaply from a surplus supplier. A bank of similar screw-mount “computer grade” capacitors should work.
    • It's possible that a 1-Farad “car audio” capacitor might work, but this will have a lower voltage rating (and thus lower weld power). Aim for 25V or higher.
  • Copper sheet, K&S #259 (0.025in thick, 4in x 10in sheet)
    • Used to make the busbars.
  • IRF 50RIA20 thyristor (SCR)
    • Weld power switching
  • High-current cable and crimp connectors
    • “Car audio” cable should be sufficient. Aim for pure copper, 8AWG or so.
  • Welding electrodes
    • You may have to make these yourself. This can be done with a piece of 5mm copper rod – use a file to shape the tips.
  • Nickel sheet or strip
    • This is now commonly available on eBay
    • If you're in the US, you can buy 0.003in thick nickel shim stock from McMaster-Carr under part number 9707K33.
  • Last modified: 2018/12/11 08:52
  • by philpem