Variable Power Supply/Battery Charger

I wanted to create a variable DC power supply that was compact and had a reasonable degree of accuracy. For this I used a DC to DC buck converter and a small digital voltmeter/ammeter. This came about because I had been charging my sealed lead-acid batteries with a buck converter stuck to a piece of wood. It was sloppy and cumbersome. It also required a screw driver to adjust the voltage and a multimeter to read it. This compact design would make it more portable, less prone to damage, and less dangerous.

Project Log

The voltmeter/ammeter is a cheap Chinese product, and, surprise, it had very little documentation. I've seen other similar models with wire diagrams on the Internet, but I couldn't find documentation for this exact one. Through trial and error, I found the purpose for each wire and I ended up wiring it according to the following diagram. Note: in this diagram, the relationship between the pins of the potentiometer and the through-holes under the trimmer capacitor (after it is removed) is accurate in the given orientation.

Here you can see the circuit laid out. The LED is the load in this case.

The rest is pretty self-explanatory. I tried to fit everything into the smallest space possible. I find that solid core wire is good for keeping things tidy and making good use of space because it tends to stay in whatever shape you bend it. You can stuff it into a corner and it stays there, whereas stranded wire is springy and wants to expand. Hot glue is also quite magical when you want to keep wires organized, but before you glue something down, be sure you are ready to make it semi-permanent. Turns out you can solder something that is completely encased in hot glue. Just plunge the soldering iron into the blob, and when the hot glue is molten and the copper contact is hot, dip your solder in there and do the deed. The hot glue doesn't seem to impede the solder's ability to adhere, and the soldering iron cleans up just fine.

I am very happy with the end result. Finally having a variable power supply with a 0.1V accuracy is very convenient. I could have bought one, but this was much cheaper and more fun.