In message <23075D38FE1C8144847DFAECA3565F2704E54DF4@pai-smx-01.europe.bk= hm.net> "Michael Rigby-Jones" wrote: > I'm after a spot welder suitable for welding tabs onto NiCd/NiMh cells > for making custom battery packs in low quantities (i.e. not enough to > get the cell manufacturers to do it). Cost is a major factor and I'm > happy to DIY something if needs be. I have found a hobby spot welder a= t > http://www.hobbyspotwelders.com/HS300A2.php which just uses a bank of > capacitors and a solid state relay, but the price seems very steep for > something that was clearly knocked up from a Radio Shack hobby box. I'm building a welder at the moment. Currently, my biggest problem is get= ting hold of some nickel for the battery tabs (Ni200 or Ni201 alloy, 0.003" thick). McMaster-Carr sell it, but that's no good to me - I'm a few thous= and miles away from their nearest store.. Anyone feel like ordering a roll of= it and splitting it with me? McMaster-Carr's order code for the stuff is 9707K33. Tracking down some 5mm solid copper rod for the electrodes is alsos a bit tricky.. no-one seems to sell anything above 2.5mm around here. I'm using an International Rectifier 50RIA20 SCR to switch the power over= , and an SGS L200CV regulator to allow the capacitor voltage to be controll= ed. My capacitor bank consists of five Cornell-Dubilier computer-grade 120uF = 25V capacitors, giving a total of 600uF, or 0.6F (the tolerance is -20/+75% though). Also, FYI the device you're talking about is called a "capacitive dischar= ge resistance welder". IIRC spot welders are completely different devices... The idea is that you send a high current pulse through the metals that ar= e going to be welded. The resistance of these metals needs to be higher tha= n that of the electrodes - hence why copper is used. When the current pulse= is fed into the battery tab (or whatever) the heat buildup concentrates at t= wo points - the two points where the electrodes were located. The intense he= at melts the metals together. Like I said - the only place I've found Ni200 nickel around here was a scientific supplier, who wanted =A359 for a 15cm square piece of Ni200 fo= il. Given that McMaster-Carr sell 6" by 50" rolls for $62, I'm a little hesit= ant to pay =A359 for such a small amount. Later. --=20 Phil. | Acorn Risc PC600 Mk3, SA202, 64MB, 6= GB, philpem@philpem.me.uk | ViewFinder, 10BaseT Ethernet, 2-slic= e, http://www.philpem.me.uk/ | 48xCD, ARCINv6c IDE, SCSI ... Mental Floss prevents Moral Decay. --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist