UPDATED: 05/20/2009
See the stuff in purple at the bottom:

POP QUIZ:

What do you get when you combine  Tab welder 1,  Tab Welder II with the Higher V Welder  and add one simple sixty-five cent electronic component?

You get the world' cheapest and easiest Dual Pulse capacitive discharge welder capable of welding copper sheet to steel or other somewhat resistive metals!!!!!

The natural inductance of a CD welding pulse WILL activate a reed switch to trigger the gate of the SCR in two parallel Capacitor/ SCR banks.

What I did, was to put the 1.5F capacitor from the first project in parallel with the '5F' audio cap and 14V 14A power supply from the second project;

Then wired the higher voltage CD welder setup in parallel with that.

All you have to do to get this  Frankenstein Monster  to work as a dual pulse welder is to attach  a cheap little glass encapsulated reed switch to the negative welding cable somewhere between the lower voltage capacitor bank and the electrode.

Then, use the regular foot switch to activate the SCR to the  first capacitor bank:
And a fraction of a second later the second capacitor bank should fire.  (You might have to play with the orientation of the reed switch a bit to align the contacts with the magnetic field created by the first pulse.)

I'd estimate that I had about a quarter-second delay between pulses. (I imagine this would vary quite a bit between different reed switches... The stiffness of the electrodes inside the switch and the inductance of the pulse along the cable would be the determining factors, I guess.) While the Pro dual pulse CD welders delay may be in the high nanoseconds to mid milliseconds range, this somewhat slower 'mechanical' delay would seem to have potential for ease of implementation and low cost for those of us who aren't competent enough to design and build more complicated electronic delay circuits.

With the dual pulse, You can achieve results nearly as good as with a $5000 or more professional dual pulse CD welder!!!

Here is my usual crummy drawing of the basic circuit:

Here are a few examples of the variety of materials you can weld with this thing:

All the welds above are what I'd call 'serviceable' ; some aren't quite as good as I would like, but should hold up under normal use.
On the ones that look like copper on 'non'-copper metals; That is residue from the electrodes that 'burned off' the tips.
It is just too hot for 'pure' copper electrodes... I think with Cr-Cu or Zr-Cu or maybe Tungsten electrodes, things will work a lot better.  SEE THE UPDATE ON THIS ON THE ELECTRODES PAGE.

If you are planning to weld batteries using copper tabbing material with a homebuilt welder, it would be wise to use .005 to .008 inch thick strip. I had no luck at all welding .024 thick copper to anything; The .016 inch thick stuff produces marginal strength welds at 30V with the 'pure' copper electrodes (although at 40V with better electrodes it would probably work, OK, I'm guessing.) and the .004 copper is pretty flimsy, although it will weld nicely to steel at 22V, rather than 30V.

Watch the pressure on the tips of your electrodes!! The higher the voltage, the more pressure you need. 15 to 20 pounds on each electrode seems to be about right for around 30V.
I darn near burned a hole all the way through the copper coin above when I got a little careless and only had a couple of pounds pressure on the electrode.

Oh, yeah....  It will work on batteries too: ;-)

The above is a 4P2S sub assembly of 5AH 32650 Lithium Ion batteries I'm using to build my current ELECTRIC BICYCLE battery packs.

Here are a couple of photos of my current setup.  It isn't elegant, it isn't pretty and it is pretty darn bulky.
But it works.
And I only have about $350 invested in it,  not five thou$and:

It would be better if I 'hard wired' the second capacitor bank instead of using the alligator clips, but since I use the lab power supply on other things, I wanted to be able to just unclip it quickly.

The three parallel SCRs on the second cap bank are probably overkill...  But I had a single one fail (for possibly unrelated reasons) during my early experiments, so I decided to err on the side of being sure they would handle the power.  And the huge SCR on the first bank would probably handle 10000 watt second pulses, so it is definitely overkill.  But I got a good deal on them all, so why not ??  ;-)

The really neat thing about this basic idea is that it is flexible and scalable.

You don't really have to use a higher voltage bank of 'real' Capacitors and a separate high voltage power supply;

That simple little reed switch will let you do dual pulse welding with, for instance:

Two decent 5F audio capacitors hooked up in the same way, but powered by one single 12V power supply... or even a car battery.....  I'm not sure if you will be able to weld copper or silver with it, but just about any other metal should weld OK.

Or two banks of 'real' capacitors charged by one single heavy duty power supply.

Either way would be much neater and more compact:  I just did it the way I did because that is what I already had available....  If I had been building from scratch I would have tried to be more elegant.

OH, And one more thing:  My usual legal weasel words:

You will, of course, insulate all of the exposed metal, (except for the very tips of the electrodes),  with electrical tape, heat shrink, self vulcanizing rubber tape or something safe, and submit it to Underwriters Laboratories for safety approval before you plug it in and try to use it, won't you?

If you short it out, anywhere other than the electrode tips on semi-resistant material (steel, nickel etc.) you will get a big spark, and possibly a major meltdown, fire, death and destruction.

Just because I don't show something or write about it or am completely ignorant about it myself, doesn't mean it should be ignored.

Lithium batteries especially are inherently hazardous.  Understand the chemical and electrical characteristics of them before you even touch one, much less try to weld one, charge one or use one in any device not specifically designed for the specific battery.  They can blow up, burn, stink, release poisonous gasses, fluids,  particulates and solids.  If you swallow one, it will probably kill you in several unpleasant ways.  Do not stick them in any other bodily orifice.

Nickel Metal Hydride, Nickel Cadmium,  Alkaline, Silver Oxide, Carbon Zinc, Zinc Air, and Lead Acid batteries are only slightly less dangerous in general.  Don't abuse them either.

It is very likely that I forgot something important;  So unless you absolutely know what you are doing around electricity, electrical components, hot and sharp tools, ask an expert licensed electrician and/or electrical engineer.  Make sure that all your wiring is up to code, and get it inspected by your local code and zoning authorities.  If disaster befalls you from following the previous and following instructions, don't call a lawyer and try to sue me.  I spent the last of my money on parts for this thing and on batteries.  I'm broke, and there will be nothing for you or your lawyer.

Finally got my nickel sheet from Admiral Steel. They were out of stock on the .01 thickness, and didn't see fit to let me know about it until I asked after a couple of weeks of waiting with no delivery and no notice. So, I told them to send the .005 instead. About a week later, I finally got it. (I still want to try the .01 thickness, but that will have to wait.)

It is significantly lower cost; welds just as well as the strip from Sunstone, and with the paper cutter as I mentioned up above a few posts, you can easily and neatly cut any width of strip you need. Other than the delay I'm very pleased with using the stuff from Admiral.
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And after welding several hundred tabs of both nickel and copper, I've decided to stick with using nickel, despite its somewhat lesser electrical efficiency. Getting good, strong, durable welds on copper is problematic with my setup. You guys experimenting with FETS and other things to give you more control over your pulses might eventually get it perfected, but I'm just not happy with the consistency . 

For one thing, the extra energy that I have to use to weld copper to the batteries I'm working with is just more than I feel safe using... If electrode tip pressure is just slightly too light, the weld is either just a weak thin halo... if it is significantly too light, I have literally blasted holes in the battery 'can'. 

So, I've disconnected all of the stuff of my dual pulse setup and am using 14.6V single pulse through my '5F' and '1.5F' audio caps in parallel. With that, nickel strips and regular copper electrodes, I get strong, consistent welds with no worries about blowing holes through battery cans.

If I ever need to do spot welding on stuff that is heavier than batteries, I'll hook the dual pulse stuff back up, plug in the molybdenum or elkonite electrodes and use it: My test welds on mechanical components, including exotic materials are quite satisfactory.

Other than that, Have fun.

Please don't try to contact me for more information.  Everything I know about this is covered on these pages.  For more ideas and information go to: http://endless-sphere.com/forums/viewtopic.php?f=2&t=2633&hilit=welder  The guys over there have expanded on my design and tried different approaches.  Maybe you can find out what you want to know over there.

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