Welder

Simulations of the welder's output before and after the conversion to DC.

In high school, I built a very simple welder out of two microwave oven transformers. It's output was simply high-current AC, which led to difficulty in maintaining and starting an arc when welding. This is caused by the brief periods of low voltage between the peaks of the voltage oscillation. I designed and built a simple full-wave rectification circuit with smoothing capacitors to eliminate the fluctuations in voltage in the AC output that made welding difficult. A full and more technically detailed summary of the project can be found here.

Left: sections of aluminum heatsink. Right: parts for the rectifier before assembly.

Because of the high currents running though the diodes, heatsinks were necessary. In the interest of simplicity, I cut pieces of heatsink to double as the current buses between diodes.

Left: detail of heatsinking compound between the diode and the heatsink. Right: assembling the bridge rectifier.

Left: the assembled bridge rectifier. Right: testing the rectifier. The waveform on the screen is the equivalent of the absolute value of a sine function.

I tested the rectifier by passing the output of a simple 12 volt transformer across the AC terminals and observed the voltage across the DC terminals while they were under the load of a small test resistor (essential for obtaining a useful measurement of a bridge rectifier). As can be seen above, the circuit fully rectified the AC input and produced fluctuating DC output.

Left: the modified microwave oven transformers. Right: a cooling fan.

The rectifier wired for attachment to the capacitor bank and transformers.

The 0.3 Farad capacitor bank to smooth the DC output.

The installed capacitor bank.

Measuring the output voltage across a light bulb.

Because it would be dangerous and cumbersome to attempt to measure the welder's output voltage with an oscilloscope during welding, I elected to measure the voltage across a light bulb instead. I was able to safely measure both the AC and DC components of the welder's output.