Home made spot welder Power supply

[metal manny]

Hi everyone

I'm the mysterious 'Buddy in another country' that David's been helping find my way through all this electro-babble.

David initially sparked my interest in building a spot welder with a remark he posted on building his own using a microwave transformer. I already had such a transformer, but simply couldn't believe that such a small common transformer could generate sufficient amperage to fuse metal. In fact, many sites on the net claim tremendous amperages (400A upwards!) from similar mods???

Anyway after picking his brains and researching a little on the net, I have successfully modified 2 similar transformers to individually provide enough heat to melt a 2mm welding rod - and so far, the adaptation has proved quite straightforward.

When cutting out the secondary windings - that's the coil with the fine wire, be sure to not damage the primary as it'll be toast. I wound the secondary coils with 5 turns in each transformer, producing 4,5V and 4,25V in respectively.

transformer.jpg
Microwave transformer with secondary winding cut off on one side

transformer stripped.jpg
Transformer with secondary completely removed.

2 transformers.jpg
2 transformers with crude test secondary wiring. Here I will finally have 2 wire leads per transformer compactly wound 5 turns each to double the existing gauge of wire.


1) The design: Basically modify 2 transformers and wire them in parallel to provide the current - (They must be wired in phase to work). These will be switched on and off via a common domestic (alarm-type) variable timer sourced from a security shop. A potentiometer will vary the time of the weld to keep things constant.

To make the unit light 'n easy to operate, I intend using a locking 'C' vise-grip clamp with copper tips in place of the standard jaws. Heavy duty 4-gauge short length cables between tips and transformers to supply the 'juice'

12V timer.jpg
Variable timer, ex the local security shop

2) Cooling: Reputable commercially produced hand-held units only have a 50% duty cycle. Initially, I intended building an aluminium oil bath box for the two transformers to help increase the duty cycle by dissipating heat, as they do heat up quickly when working. In retrospect though, I'm a bit concerned that the oil may attack the varnish insulation on the primary coils over time, but will investigate this further as it could make the home-built welder gain a respectable duty cycle.

That's as far as I've got to date and I'm having fun. Whether this project will provide enough grunt to weld sheet metal in a car restoration, or even do more than 3 welds without having to cool down for half an hour (or ever weld at all!) I can't say, but I'm giving it my best shot to make this a tool I and the rest of us could put to good use.

It'll be a while before I update you on my progress as I've other work to do, but try this yourself and let us know what you discover...

[Dawai]

Manny, looks like 4 going together now. Mine was started in 2005. That is some time for a "project" to lay idle huh? Around in the corners here is two dozen more stalled things.

ONE microwave transformer is equal to the HF spot welder. (and as compact) I added to the first post here telling "what kind" of transformer to look for to convert.

TONGS.. well.. I am using my hf spot welder clamp and head, but "use enco dot com" has copper bar. I can't find replacement tips for the hf welding tongs, so I foresee having to machine some from bar, they are metric meaning I'll have to modify or buy a metric die.

[metal manny]

Originally Posted by Dawai

TONGS.. well.. I am using my hf spot welder clamp and head, but "use enco dot com" has copper bar. I can't find replacement tips for the hf welding tongs, so I foresee having to machine some from bar, they are metric meaning I'll have to modify or buy a metric die.

David, that's quite a handy spot welder head you have there. I'm sure you could easily tap a non-metric thread into the bars to suit a die you already have.

[Dawai]

Mast mounted, adapter for the HF welder made, bolts on where transformer used to,(2.62 inch square pattern) Slides up onto a piece of 5/8" rebar tig welded to a piece of 1 1/4 tube which slides down over the "1" neck jig" from the harley frame jig. At least I will know where it is now when I want it for that again? I think I used a plumb bob and piece of water pipe last time to straighten a frame.

It all can slide up to mid chest, or go down to knee level. My favorite position is going to be there where I can sit in a chair and tack weld electrical boxes. Loosen the two pinch bolts on the tongs and is "free" to hand use on a car at the end of 6' of cable. You can also swivel it over the box to reduce footprint on floor. Foot pedal is dangling, needs a magnet or a flat strip & hook to store it.

I made some crimp-wire terminals from copper tube, flattened one end, used the punch to knock a 5/16ths hole, they crimp tight on the cable.

Powder coated "Miller BLUE" and cooling. I need to finish transformer box, have metal cut out. I am thinking a swing-out tray over the electrical panel too to keep small things in. Or a toolbox. In hindsight the electrical panel should have been vertical on side, a tray on top.
Needs a lifting hook now. over 100lbs.

[Stretch]

How much has been spent on this project so far?

[Dawai]

A few dollars perhaps, a dead HF spot welder, My time, stuff I demo'ed here and there. (junk) About four tablespoons of blue powder, some welding cable.
Cash out? I am hunting some copper bar to machine some new tips. So far use-enco.com has the bar, cheaper than most on ebay. Not placed a order yet so I have no money out.

I played with the heat-shrink function today. THE screwdriver got hot. that is what I was most interested in trying. I have no clue what that rig costs here. This is Three tools in one, a dent puller, heat shrinker, spot welder.

There has been a dozen people wanting to haul them transformers off for copper scrap since 2003-Now. There was one guy when I redid the bridgeport that showed up twice a week, it was worrying him real bad that there was scrap copper sitting here and not buying him beer. Eventually he quit coming around.

Mike suggested I add a few more coils, tie on one end, some diodes and have a output suitable to boost start a car. That is what these transformers were, so that'd be a step backwards.

8:15 pm edit, adding pictures of working unit. PC went sour on handles on unit, possibly corroded aluminum?? COILS on transformer were overheating, So I paralleled them.Those are them copper tube wire crimp connectors I made bolting the windings together.
2 second welds on 22 ga stainless, I had filed the points on the tongs. Lil tiny kernels blue in middle. GOOD enough for me. I'll have to replace the leads going out to the welder. THEY heat up awful hot.. RUNNING 30 amps on 220vac now with all them windings added. It's got the 60hz humm I've heard for years. THE cables going up to the welder "twitch" with power on.

Thursday 5/31/2012 edit, Unit performs fine, but.. SHORTEN leads as much as possible from windings to welding. THE cable gets so hot it will burn a blister. Cooling, the tips start melting after three or four welds. My math says that is 1650 amps going through machine. THERE is no welding cable sold capable of that much. SO? Looks like it needs flat bar, a cooling pump and radiator. *Filling the transformer.. you get better current transfer the more full the core is.. why? perhaps the magnetics are distributed along the core and you have to spread out to get it? I may have been taught why once, but forgot all that. Plan is now to build a "rack to get transformer up to height of welding, place a cooling pump/tank under it. PLUS I am going to add a copper bar in on one winding side to "select" as many windings as I desire.. delete or select by copper bars-strips. I'll use it as is for the next week and possibly make more notes. I have a stack of stainless toolboxes to do for projects around here.