Homemade Spot Welder

Step 2 The transformer (new secondary)

I lucked out and found a 4 foot piece of grounding wire. It looks like a dozen 10 gauge wires bundled in one insulated coating. The only markings were three triangles. I understand from other sources that 4 gauge is recommended. I can't tell if I followed this exactly or not, but based on how hard it was to wind this monster in there I would hate to think of winding something thicker. It's surprising how stiff a thick wire like this is.

I bent the wire into a long tall U shape and fed the free ends into the transformer core. I then bent and curled and gently maneuvered the free ends back through the opposite sides. I ran out of room in the core before I ran out of length. I could get one more turn out of it if need be.

Transformer theory is a little beyond my ability to write about. There are many sources on the net if you are interested in this subject. The idea here is to have 3 or 4 windings on the new secondary. This will produce somewhere between 3 to 6 volts. I measured 2.5 when I plugged it in for a quick test. The lower the volts, the higher the amps. This is the main reason that such a thick piece of wire is used.

Comments

[harlyquin]

I'm sure I'm restating general knowledge here; if you can get wire for the secondary new, it will make winding much easier. Copper work hardens and becomes ridged and brittle if any deformation occurs. If you find 10 g wire difficult to wind, it will only get harder if you try to redo it!

[maxpush99]

It would help if you try to have the 2 windings in resonance. after you remove the secondaru windings you should weight it you use the same amount of copper by weight in your new winding,\ Just calculate lenght by thickness or weight the new windings good luck

[student.mckinney]

Yeah, and the primary can have anywhre from 200 to 3000 turns, depending on your transformer. That means that  if you have 4 turns on the secondary, and the transformer primary has 2200 turns, you've got yourself a 110v 60Hz to .2v 33kA transformer. So that's 550 times greater amperage on the secondary than the primary. Wear some rubber gloves.

[xBrainstormerx]

Uhm i got a transformer and I took out the secondary wires already but what if I only got a 12 awg that is 2ft and 6" is that okay or is that too little?

[jds1969]

Not even close. You will likely melt a wire that thin. It is always advisable to follow the recipe, especially when electricity is involved. Look for something thicker.

[espin66]

excellent experiment felicity

[eric m]

Am i right in saying that you should just try to fit as many winds as you can and not worry about how many.

More winds = more power?

[jds1969]

In this case: more winds = more volts and less amps. It's the amps that are doing all the heating through resistance in the piece to be welded. I would suggest one, two or three winds on the secondary and no more.

[eric m]

ok

[BobbDobbs]

I also want to say that once you have a core ready to go, you can wrap some temporary small guage wire, like 10 turns, just to check what voltage it produces. Adjust the turns (add or remove some) to get around 2 volts. Now you know how many turns you need for the BIG gauge wire (which is a lot harder to wrap, so you want to do it only once.)

[BobbDobbs]

One important "transformer theory" fact is that the power capacity of a transformer is limited by the core cross-sectional area. The bigger the core, the more power you can get to the secondary. This means you want a big enough core, but not too big. If it is too big, a short on the secondary (which we get a lot in spot welding) will allow a huge current on the primary and pop your circuit breaker. Aside from cost, transformer cores are never bigger than they need to be in order to prevent excessive primary draw in the case of a secondary circuit short.