I ordered a XY-SK120 buck-boost converter with digital controller with LCD screen from Aliexpress. With it I can dial up any desired voltage and use current limiting to forestall damage when first powering up projects. It has many other features. From the specs it's quite an impressive piece of electronics for its small size. Input can be 6-36 VDC and output 0-36 VDC at up to 6 A and it handles up to 120W.

I chose the cased version. It's more than just the bare converter board with banana sockets in an enclosure. At the back is a cooling fan and a power input panel that takes various sources, including terminal block, barrel socket, some kind of Molex socket, and even USB-3 PD input. A cursory inspection shows that diodes isolate the inputs from each other. These extras account for the higher price.

The fly in the ointment is poor documentation. It would be nice to know how to operate the UI without trial and error. Not even a slip of paper in the box. But a bit of hunting found an instruction manual online. From the modification date, less than 3 months ago, the firmware is still being improved, and in the future it might be possible to update it using the serial interface.

Normally one would use a SMPS or an old laptop power brick for the input. I decided to put to use an old school power supply board possibly from an LA30 Decwriter that the board for #Flashing LEDs from old printer electronics came from. In the board pictured below, only one set of bridge rectifiers and one large capacitor are in use. There are actually two independent power supplies on the board. The low voltage one supplies digital logic via a 5 V regulator, one of the large TO-3 cases. I won't be using that half. The high voltage one supplies the electromechanics. The capacitor is a whopping 10000 µF rated for 50 V so lots of margin. Nominal voltage level was probably around 30 V. A 24 VAC appliance transformer that I was given feeds the board.

For the enclosure I used an old Ryobi timer saved from e-waste. It seems to have been an appendage to unknown industrial equipment. The inside was gutted to fit the PS PCB.

That such a small controller can provide 6 A is a testament to how much the power density of electronics has increased over the years. (But some reviews mention that the cooling fan may be inadequate at high power levels.) The current is more than the old bulky linear power supply can supply. The fuse on the rectifier board is rated at 2.5 A. The transformer is rated at 1.5 A. (Although at lower output voltage, more current can be supplied, as the converter is switching mode.) Anyway this is enough for my needs for the near future.

Oops, I forgot to order 4 mm banana plug cables. Next round then. Can't buy everything in the shops all at once. 😉

Well that takes another tuit off my round tuit list.