Description
A home-built spot welder capable of joining materials up to 2.5 mm thick.
It uses a 1000-watt transformer whose secondary winding has been removed and replaced with two turns of heavy-gauge cable (electric cable for stick welders). To double the power, two of these windings were wound in parallel. The hand lever operates the microswitch, which in turn starts the timer. At the same time, the hand lever loads the pressure spring so as to obtain uniform weld spots. With the timer and the power selector you can set times and currents suited to every type of sheet metal to be welded between 0.05 and 2.5 mm thick. The power selector uses the various taps of the primary winding: 160 - 220 - 300 volts.
Tips
It is best to use transformers of no less than 500 watts which, once the secondary winding has been removed, leave enough room on the core to wind a heavy-gauge cable. After winding 2 - 3 turns, power the transformer primary at 220 volts and check the voltage of the newly wound secondary, which must be between 1 and 2 volts; if it is lower, add one turn at a time and check, otherwise remove one. If there is enough room on the core, make a second winding to be connected in parallel with the first, to double the output power (amps). If the primary winding has several inputs (110-160-220-280-380 volts) they can be kept, but you will need a power selector with a suitable number of positions. The copper electrode tips must be insulated from the support.