(Continuing from last blog) Regarding the homemade spot welder, the transformer used requires the removal of the secondary coil that  generates high voltage. This coil must be replaced with one that provides low voltage and high current for use in spot welding. Initially,  I thought about cutting the secondary coil itself with a saw or angle grinder without removing the core, but since the coil was wound so tightly,  it couldn’t be easily extracted without first drilling holes to create gaps. Simply hammering it didn’t work. After quite a bit of trouble, I ended  up cutting through the core of both transformers with a hacksaw, which made the removal of the secondary coil much easier.

I planned to purchase a high current cable for the secondary coil on the output side and wind it several times around the space where  the high-voltage coil had been removed. While flexible cables made of thin twisted wires are convenient, they are expensive, especially for thicker  types, and the core wires tend to be relatively thin compared to the overall thickness. To ensure a stable supply of high current, I decided it would  be better to use solid copper wire. I chose a 6.4 mm diameter copper wire, coated for insulation. I found a 2-meter copper wire for about $25 (around 1700 yen) and purchased one. Since the wire was stiff, I softened it by heating it thoroughly  with a gas burner until it became easy to bend. For insulation, I applied two coats of enamel paint and allowed it to dry, then wrapped it with  tape to create a double layer of insulation.

I wanted to wind this copper wire as the secondary coil around the cores of two transformers in series, but winding it directly posed a risk  of damaging the insulation tape. To avoid this, I made a wooden mold the same size as the transformer core, fixed it in place with a vise,  and began winding the wire. Since the wire, being almost like a 6.4 mm copper rod, was difficult to wind smoothly even after softening, I had to  hammer it into shape using a rubber mallet. In the end, I managed to wrap it three times around one transformer and two and a half times  around the other, which was the best I could do. After finishing the coils, I removed them from the mold and fitted each onto the corresponding transformer. However, the sharp edges of  the cores posed a risk of damaging the insulation upon contact. To address this, I used an angle grinder to round off the corners of the cores,  which allowed the coils to fit properly without damaging the insulation.

Now, I need to test if everything works properly. Although I still have to weld the cut transformer cores, I decided to perform a test before that.  Since the cores were still cut, I placed an anvil on top of them as a weight and then connected the power. Of course, I checked  the continuity and insulation with a tester beforehand. Here, unlike Japan’s 100V system, we use 240V, so I had to be extra cautious  to avoid the risk of electric shock. After thoroughly checking everything, I connected the primary coils in parallel and planned to measure  the voltage across the secondary coils in series. With great caution, I flipped the power switch, and the moment I did, there was an incredibly loud “BANG!”