Dead UPS to DIY Spot welder

While i was looking for some spot welder ideas, i saw a project with some transformers of industrial UPS (Uninterrupted Power Supply). Then the old dead UPS lying around my room clicked to my mind and the transformer was huge as i hoped!

The rectification of the UPS was originally done by the diodes built into MOSFET’s used to drive the transformer from battery. To test the rig I used some 1mm copper wire and short circuited it, the result was quite good while the wire got very hot.

Playing more around the transformer showed that it had a center tap for the low voltage winding and a 40A fuse going to the battery. With some trouble, the centre tap got divided to separate coils and I connected them in parallel to increase the maximum current output (nearly doubling the initial amount). From the initial heated 1mm house wiring cable, I switched to multi stranded heaveier guage wire which got less heated and can melt the metal through it’s two connectors pretty easy.

My final conclusion was that using a dead UPS transformer is much easier than modifying a microwave as the risks are less, the coil needs minimal modifications and a nice casing!

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