Introduction: Mini Regulated Power Supply Unit [UPDATED]

About: I'm an Italian freelance structural engineer, graphic designer and photographer, now I'm teaching physics in Waldorf high-schools. I always investigate electronics, robotics and science in general, I'm a passi…

I've always been attracted by compact instruments, and I love to buy electronics kits and build small and pretty devices.
Years ago I bought a regulated power supply unit (PSU), which has the interesting feature to vary current intensity other than voltage.
Voltage (Volt) is the "pressure" of the electric current, and intensity (Ampere) is the "flow rate" of the current. You have a big power (Watt) when you have a high flow which push hard ;-)

Step 1: Dismantling and Adapting

As first thing I tested my device, and I started to imagine the best way to build something around it. As you can see I connected it to the battery pack I lately refurbished with ten 18650 cells. Since that Li-Ion power bank is quite powerful now, I wished to take the best advantage from it. I also thought to incorporate the device inside the battery pack, but space was not enough. This way the regulated PSU can be powered by any battery or wall plug power supply.
Separate the top and bottom boards unscrewing the four screws, which act as connectors too.

Step 2: Think Bigger

If you need to regulate voltage and current often, those small pots are not convenient, and although they're quite precise, they need a lot of turns to travel from low to high. So I decided to substitute them with a couple of bigger pots. I had to choose between many types and shapes, and I opted for two classic pots.

Step 3: Soldering External Controls

The value of the new pots is the same, 10Kohm, the central pin must be soldered in central position also for new pots, and to find the right position of the other two pins you can make a try, but if you look on the side of the original pots you can see a diagram and the pin corresponding to clockwise rotation. I also added a 2.1mm DC power socket connected with wires at plus and minus DC-IN pads, but then I inserted a general switch on the positive wire. As outputs I used two (red and black) banana plug panel sockets.

Step 4: Design and 3d Printing

I think design is the funniest part, as you're totally free to chose any detail, from dimensions to knobs position, from color to grid shape. After decided which components to use, I spent one hour or two drawing, taking measures with caliper, calculating the minimal space required inside the case.

I would't deepen the process to draw in 3D with Rhinoceros since I already explained some basics in other tutorials. You can also use OpenSCAD, which lets you to develop a parametric 3D model. Obtained a good 3D model, which I attach here for you, I exported it as .stl and I loaded it in Cura from where I saved the G-code to upload into my little 3D printer. The result was perfect at the first try, but I added some improvements in the final version of the file.

Step 5: First Test

After having waited something like 5 hours the end of the print, I couldn't wait to try the case. So I plugged in position all the parts, and fortunately I didn't find obstacles.

Step 6: Some Weight

When you pick up a tool, a gadget, an object in general, the weight transmit a sense of toughness and quality. This is the reason why I decided to use a thick iron plate as bottom. I drilled four little holes for the screws, I removed the rust, and left two big hole there were before. I attached a thick tape on the inside face, to avoid short circuits.

Step 7: The Cooling

I red that this device hardly keeps 5A (maximum load) especially for long time, without heating too much and turning off. So I added in the design a little motor and a very little fan, working always whenever the PSU is turned ON. The motor work at only 3V, consumes a few mA, and makes some noise. If I had owned a small enough brushless motor, I would had used it, because of the reduced noise and the longer life.

The little fan is 3D printed, I made a minor mistake in design and I couldn't use all the space, but I didn't want to make the case again only for that. I attach .stl file of the fan.

Step 8:

To power the motor I used a voltage regulator, which only keeps 100 mA load, but it's perfect for this purpose. Then I also added a 40ohm resistor to reduce speed and noise.

You can see the black small 3.3V regulator and the resistor soldered on the output terminal, the positive comes from after the main switch, negative from wherever you wish, the resistor is soldered on the red wire going to motor. The space is not much, and I had certain difficulty to solder everything in place. In the final version of the 3D model I moved the regulated psu a pair of mm on the left, to let more space to the motor.

I secured the motor with a thick copper wire and two screws, a simple but effective method.

Step 9: Some Labels

I wrote some useful information on bot top and front faces. I also wrote on the bottom info about Load and socket polarity. These info are non totally exact, they should be "DC IN 6-35 V", 30V is the maximum output. I know, the style is also ugly, but you can make a stencil or simply use a better calligraphy.

Step 10: Display Filter

Red LED displays like this are barely visible at sunlight, and they often are covered by a dark red transparent plate. I tried different solutions, and I chose a orange-yellow plexiglass. The display is now still barely visible with a strong light, only a little better than before, but the effect of the light scattering on the border is IMHO astonishing.

I cut the small plate with a simple iron saw, then I sanded its perimeter on a sandpaper, time by time with a finer grand, and I polished all four sides with a brass polisher product.

Step 11: Enjoy the Little PSU

That's done! The mini-regulated-power-supply is ready! I really had fun during this few days project, I hope you will try to make your own. Le me know if you have some suggestions, improvements, reviews, ideas.

Step 12: [UPDATE] Proper Fan

I bought a few mini fans, 3 cm (link) and 4 cm side (link). Smaller ones are powered with 5V, and 4cm sides ones need 12V, you can use a voltage regulator, L7805 or L7812, to power them. They are really quiet compared to my first solution.

Step 13: [UPDATE] New Design

To contain the new bigger fan I modified my design, unfortunately I had to increase the PSU height too. I decided to insert a big hole to show the fan, I know it's easy to interfere with rotation, anyway it's not dangerous and I think it's nice. I also changed the switch with a model easy to find, so that you can use the 3D model without too many changes, you can download it here.

Step 14: Hidden Side

Inside you can see the LM7812 voltage regulator and all the connections. Then I added the heavy metal plate as bottom side, with four rubber feet.

Step 15: Here It Is

Here is the new model, I hope you enjoy it.