Homemade Spot Welder

Step 6 Operation and conclusion

I built this spot welder for two reasons:
1) I always wanted to have a spot welder.
2) I broke the handle off a stainless steel cup measure and I wanted it back on.

I built the jaws so that there was enough room to get it in there without necessarily creating an alternate path for the electricity. It took a little fiddling to get it in there properly but once the cam locks down, the piece stays right where you want it.

I plugged it in and crossed my fingers. Threw the switch and I could hear the transformer hum. Then a small spark and an ever growing red glow between the bolts. The glow starts off red but gets orange the longer you leave it. I count to 10 and turn it off. This seems to create a fairly good bond.

The thickness of the piece changes the time you would require. I tried to join two eighth inch pieces and got nowhere. This is a light duty welder for thin metal. Sheet metal work is about the most you can expect. Heat is not as big of an issue as I thought. Maybe because I used a lot of copper. The bolts and the ends of the jaws are warm after use but not as hot as I would have expected.

For more power I could remove the shunt in between the primary and secondary. I could also add an AC capacitor (~30uF) across the primary connection to adjust the power factor. I'm just not sure why. It works fine for small pieces and I'm satisfied with low power that doesn't shoot sparks everywhere anyways.

Comments

[the.rollie]

those are the only two reasonings i ever needed to build something.... wanted one, and needed one for some miniscule task/problem

[jefftecklenburg]

will this work on car fenders?Or what range of material gauges have you tried

[uberdum05]

It's the opposite in terms of a LED, the higher the temperature, the more current, so it gets hotter and hotter and hotter, until finall it dies.Its called a 'thermal runaway'.

[RCS]

Dear all : You can improve the welder efficiency by change the bolts contact for ones smaller than 1/4 inch

[jds1969]

The same efficiency can be gained by narrowing the tips as much as possible. I sharpened mine by hand on the grinding wheel but I know that industrial spot-welding tips are usually quite sharp (aka. pointy). They are made with alloys of copper (beryllium) that can take the heat without melting. The copper ones need to be sharpened often as they round off after only a few welds.

[Wyle_E]

The magnetic shunt is used to get more power into the capacitive voltage doubler in a microwave oven. When driving a resistive load, it just wastes power. If you need to weld something heavier, there is another Instructable that describes an arc welder made from MOTs with the secondaries, rewound with heavy wire, in series and the primaries in series across 230VAC (for US-market MOTs).

[Laminarin]

First, nice instructable. I would add more warnings on voltage safety. For those not well versed in electrical work, there is a lot of potential danger. On step 5 "heat lowers the resistance in the piece." is incorrect. Increased temperature leads to increased resistance.