Big transformer for light-duty welder?

I've seen quite a few web articles on making home-made welders using microwave over transformers (MOTs). I happen to have a somewhat larger
transformer, from an old Biomation logic analyzer from the 1970's. (Huge linear power supply, with several hundred thousand uF of electrolytic caps!) The transformer itself weighs 23 pounds, which I think is heavier than most MOTs. I'm pretty sure I can get the secondaries off the core, and can add some heavy-gauge windings for a welding winding. I have ready access to all sorts of electronic parts, such as diodes, switches, heat sinks, fans, etc., and I know how to safely hook them up. (I'm an EE, just getting my feet wet in metalwork, lathe, mill, casting, welding.)
I'd like to rig this thing up for simple, light-weight welding. I've seen a few spot welder designs that are quite straight-forward. As well, I could try a small arc welder.
For those of you who have built your own equipment, what would you do if you had one of these transformers?
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walter snipped-for-privacy@hotmail.com wrote:

Sell it to a chump like you used to be and look on craigslist for a welder like you want. For a small buzzbox I recommend Miller Thunderbolt AC/DC, the older ones where the leads detached. I've seen these go locally for as cheap as $160 recently (Seattle). It is not worth your time to fiddle around and make up a tiny AC welder, the parts will cost you more than buying one. You could be welding by dinnertime.
GWE
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Welding requires either constant current (SMAW or stick) or constant current (Mig) Either one requires some gymnastics as far as windings and core are conderned. The constant current is often done by using a saturated core and either wiring taps or adjustable core shunts.
If you want to take a EE approach to welding, consider an inverter power supply that is lightweight and can be built to spec. http://www.irf.com/technical-info/appnotes/an-1045b.pdf http://www.irf.com/technical-info /
walter snipped-for-privacy@hotmail.com wrote:

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RoyJ wrote:

So for CC you follow it with a big scrap transformer primary in series with the output (i.e. inductor) or for CC you follow it with a bank of giant electrolytic capacitors. Like I said, by the time the OP's done, he'll have spent more $$ than he would have buying a perfectly good welder. This world is full of idiots buying stuff they don't need, and then dumping them cheap a few years later. Just find one of those with a welder.
GWE
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AC welders do not have inductors in the output, or at least none of the ones I have had open had any inductors.
The easiest welder to build would be a spot welder. With a large transformer like yours, the output of the secondary is likely to be close to two volts per turn. Check what it actually is. Also check the Miller web site for the specs of their spot welder. Consider buying some spot welder tips as they are a copper alloy of some sort. I don't think you will have any problem with winding the transformer. The work will be in making the tongs of a spot welder.
Dan
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at least none of the ones I have had open had any inductors. (clip) ^^^^^^^^^^^^^^^^ They accomplish the same thing by winding the transformer so it has a lot of leakage flux.
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The copper rods you want are made from Alloy 182. MSC sells this i n 1/8" to 3/4 in 6 sizes. 3' and 6'. Alloy 182 is Chromium Copper Rod Offers relatively high electrical conductivity combined with good strength and hardness plus offering some resistance to softening at elevated temperatures. "Principal use is resistance welding, electrodes, welding tips and holders."
When I had one in the 70's - a hand spot type - the rods were electrical copper and got very soft after several points. I think 182 must have been developed after that time.
Resistance welding uses alloy 1751 Beryllium Copper rods. 45% conductivity.
mscdirect.com page 1764 in the search
Martin
Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH, NRA Life NRA Second Amendment Task Force Charter Founder
snipped-for-privacy@krl.org wrote:

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IIRC, pounds of metal divided by 10 multiplied by 1kw - 2.3kw you have ? was it a 25 amp current draw? Hope you have the physical space for the windings you need.
Martin
Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH, NRA Life NRA Second Amendment Task Force Charter Founder
walter snipped-for-privacy@hotmail.com wrote:

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