Mini Regulated Power Supply Unit [UPDATED]
Introduction: Mini Regulated Power Supply Unit [UPDATED]
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. 267
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 https://www.mouser.it/_/?keyword=L78L33, 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. 646