How to Make a 0 - 240 VAC and 0-350 VDC Power Supply

I made a variable high voltage AC DC power supply with as any bells and whistles I could put in easily and ended up with quite nice specifications.

For AC outputs; Isolated 0-120 VAC, Non-isolated 0-240 VAC.

For DC outputs; 0-200 VDC, 0-350 VDC. With options to connect or disconnect from Earth for true isolation, and to switch the poisition of LIVE. In the US the live pin is opposite from that of many international AC sockets.

And the new low-cost digital meters really make it easy to monitor AC voltages, power, amperes, power factor and energy usage. Plus of course a separate nice digital meter to read the DC voltage. The DC voltage meter only comes on when DC is selected.

And all of this in a nice compact 6 inch cube painted in an ugly grey battleship color!

WARNING: This device has lethal voltages. Only attempt this build if you are comfortable working with mains AC.

I had most of the main parts from teardowns of a microcentrifuge (origin of the isolation transformer), electrophoresis power supply (2.5A 0-140V variable transformer) and switches and sockets. Had to purchase the AC Power meter and then modify it to read from 0 VAC rather than the original spec of about 80 VAC making this meter incredibly more useful (see my previous instructable on this mod) and DC meters that read to a maximum of 500 VDC. If I had to buy the parts, the cheap variacs with similar specs cost about $45 on amazon/ebay/aliexpress. The isolation transfomer is a bit harder to find but some of the step-up/step-down 120/240 VAC converters seem to use isolated windings.

I etched and cut the front panel from 5mm plywood that I had pre-painted gray, with a K40 laser cutter.

I had to repair the variable transformer with a solder splint for a broken wire.

To help figure out the wiring, I stuffed most of the parts onto the front panel and then attached the isolation transformer and the IEC AC input with an integrated fuse into a back panel. The panels are 6 inches square.

Once I had the parts laid out I drew up a wiring diagram. Looks a bit complex but essentially divided into three sections.

1. The variable 0-120VAC section. This starts of with a wire from the neutral terminal being connected to the neutral terminal on the neon power switch and to one end of the variable transformer. The other end of the variable transformer was connected to the switched (center) live terminal on the power switch and the third terminal on the power switch was connected to the IEC AC sockets live terminal.
2. The second section is the 120 VAC to 240 V conversion. This section centered around a 2 pole 3 way switch that I already had (actually a 2 pole 2 way would have worked better). For 120V selection, this 0-120-240V switch connects the wiper of the variable transformer to one end of the top coil of the isolation transfomer with the other end of the top coil being connected to the neutral terminal of the power switch (or the IEC socket). Also in the 120 V position, the second coil is fed into the input of the AC power meter. In the 240 V position, the two coils of the isolation transformer are connected in series.
3. The third section is the AC to DC converter centered around the AC-DC switch. The converter uses a bridge rectifier I made from four diodes with a 10uFd capacitor and a 450k bleed resistor made up of a series of 1/2W 90k resistors (shown in two of the images).
4. The fourth section is the two digital meters (the converted AC Power meter and the 0-500V DC Voltmeter) and their separate 5 VDC power supplies that I made from USB two 5V power supplies.

This switches the LIVE wire to either the left of the AC plug socket when looked at from the front which is the US standard or to the right which is compliant with most International standards. Just in case.

Zooming into the AC / DC switch, I show the circuit and the wiring diagram guide to make sure that I do not mess up. The DC Voltmeter was switched on and off depending on the AC / DC switch position.

The diagram shows all the wiring completed and the final product. And it works!