>-----Original Message----- >From: Philip Pemberton [mailto:piclist-bounces@mit.edu]=20 >Sent: 14 April 2005 09:35 >To: piclist@mit.edu >Subject: Re: [EE] Spot welder for battery terminals > >I'm building a welder at the moment. Currently, my biggest=20 >problem is getting hold of some nickel for the battery tabs=20 >(Ni200 or Ni201 alloy, 0.003" thick). McMaster-Carr sell it,=20 >but that's no good to me - I'm a few thousand miles away from=20 >their nearest store.. Anyone feel like ordering a roll of it=20 >and splitting it with me? McMaster-Carr's order code for the=20 >stuff is 9707K33. > >Tracking down some 5mm solid copper rod for the electrodes is=20 >alsos a bit tricky.. no-one seems to sell anything above 2.5mm=20 >around here. > >I'm using an International Rectifier 50RIA20 SCR to switch the=20 >power over, and an SGS L200CV regulator to allow the capacitor=20 >voltage to be controlled. My capacitor bank consists of five=20 >Cornell-Dubilier computer-grade 120uF 25V capacitors, giving a=20 >total of 600uF, or 0.6F (the tolerance is -20/+75% though). > >Also, FYI the device you're talking about is called a=20 >"capacitive discharge resistance welder". IIRC spot welders=20 >are completely different devices... The idea is that you send=20 >a high current pulse through the metals that are going to be=20 >welded. The resistance of these metals needs to be higher than=20 >that of the electrodes - hence why copper is used. When the=20 >current pulse is fed into the battery tab (or whatever) the=20 >heat buildup concentrates at two points - the two points where=20 >the electrodes were located. The intense heat melts the metals=20 >together. > That is essentialy what a spot welder does, though usualy using a low vol= tage/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 eno= ugh current for spot/resistance welding. Controlling the current is tric= kier, multiple taps on the primary would probably be the way to go, and n= o expensive SCR's are required, just a relay to switch the mains into the= primary. >Like I said - the only place I've found Ni200 nickel around=20 >here was a scientific supplier, who wanted =A359 for a 15cm=20 >square piece of Ni200 foil. Given that McMaster-Carr sell 6"=20 >by 50" rolls for $62, I'm a little hesitant to pay =A359 for=20 >such a small amount. I'm having a simmilar problem, I was hoping that I would be able to buy i= t in a roll of the appropriate width so I could just cut lengths off, rat= her than having to cut lengths out of a big sheet. I'll let you know if = I find anything suitable. Regards Mike =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D This e-mail is intended for the person it is addressed to only. The information contained in it may be confidential and/or protected by law. If you are not the intended recipient of this message, you must not make any use of this information, or copy or show it to any person. Please contact us immediately to tell us that you have received this e-mail, and return the original to us. Any use, forwarding, printing or copying of this message is strictly prohibited. No part of this message can be considered a request for goods or services. =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist