Discussion in 'The Projects Forum' started by MikeL, Nov 19, 2008.

  1. MikeL

    Thread Starter New Member

    Aug 12, 2008
    Here's the back story, I've been working on chain Maille projects for a few years now, everything from micromaille to armor.
    Recently, I decided to build a welding aparatus in order to close my links permanently. I havent begun building yet, or even collecting supplies as I am still in the 'design' phase.
    I've heard of people building spot welders out of cannibalized microwave transformers as well as capacitor discharge welders.
    I havent decided which type I am wanting do. i've found decent plans for building both, though I question which would work better.
    Here is the link to the capacitor discharge welder i found.
    I planned on tweaking the design a little bit, as some of the parts have not been easy to find.
    the better looking plans for the transformer based one I found through www.instructables.com

    I guess my overal purpose in posting this, is I need some advice. I'm not quite sure on all the pros and cons of using one vs the other. (I am especially rusty on my capacitor theory) I plan on using it for several different gauges of wire and for wires of different composition. I was also thinking of using different size electrodes based on the wire gauge I am welding. I know I will need to be able to vary the amoung of current being output through the electrodes, though if i go with the capacitor discharge welder, would I also be able to vary the duration of the discharge.

    I appologize if my thoughts aren't entirely coherant. I am open to any and all suggestions/comments, etc.

    Thanks in advance.

  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    I have built both the Poor Man's Battery Tab welder and a microwave transformer based (MOT) welder. I designed a zero crossing trigger and timer on the microwave device so I could control the number of cycles.

    Both worked. For battery tabs, the capacitor discharge gave a smaller heat-affected zone. Welds were through and quite strong. With small bore (0.188 to 0.25), thin-wall SS tubing, the capacitor gave a very nice tack weld that held up to brazing. The MOT was just too much heat for my liking.

    For my capacitor discharge welder, I used #4 cable for the added flexibility compared to heavier cable, 1/4" copper electrodes, and compression fittings. My best results were obtained with 16 to 22 V and 432,000 uF. I tried a variety of audio capacitors (up to 3 F), but the limitation on voltage is a problem for the thicker SS tubing. They do work, however, for battery tabs. Remember that Joules goes up as the square of the voltage. I will try to find a table I made comparing semi-quantitatively weld strength with voltage and capacitor size for thin steel sheet and post it tomorrow.