DIY Fixed & Variable Power Supply

Hello everyone, today I want to share with you guys a project which happened a long time ago (Summer of 2017) and which I was unable to share it back then because of lack of time to write about it. The project which I am referring to is my DIY power supply. I made this power supply because I felt that with the components that I had in hand, I could build a power supply that would be sufficient for most of current PSU needs.

The power supply is made with an old computer ATX power supply and a Boost-Buck converter module from Ebay. This setup allows me to have an output which can go from 1-25v while having some other outputs with fixed voltages such as +12v, -12v, 5v and 3.3v.

I decided to make this power supply mostly because I did not have a proper variable power supply, and because the solution that I had before was extremely ghetto. For my power supply needs, I just used an ATX power supply with some alligator soldered to the 3.3v, 5v, 12v and GND outputs. It also had a cheap Boost-Buck converter connected to the 12v rail of the power supply. Something like this (but with the power supply case over the its PCB of course!) :

So, without further a due, here are the parts that I used for the build:

• Old ATX PSU 200W

• Boost-Buck Converter

• Voltage-Current Meter
• 2x Toggle Switches
• 2x LEDs (Red and Green)
• 2x USB (Type A Female Jack)
• 9x 4mm Female Banana Plugs (5 Red, 4 Black)
• 2x 10kΩ Potentiometers
• 3D Printed Parts
• Many M3 Screws (20mm) and M3 Nuts

The first thing I did was disconnect all the previously made connections to the power supply by cutting all the wires to the power supply. Then, I de-soldered any of the other connections, such as the power switch, and the boost buck module.

Next, I designed and printed all the parts for the outer case of the power supply. I designed all the parts on Onshape and then printed them with my FT Prusa i3. Since the bed of the Prusa i3 was too small to print the top and the bottom parts on, I had to split them in half. The top plates can accommodate the perfectly the 90mm fan which was included with the ATX power supply. It also has some very pretty holes for air intake. The sides have angled holes for air exhaust, which allow the air to be expelled towards to the back of the unit.

These prints were meant to be interlocking with each other, kind of like those laser cut boxes. The sides need to be inserted into the bottom parts and then screwed on, just to be sure that they are square and then the top is placed and screwed. After these parts were printed I did some test fitting to make sure they would fit within each other and they did fit fine.

I then test fitted all the components in the front panel. All the tolerances for those parts seemed to be fine and they (thankfully) slid in properly. I also checked the fit of the ATX power supply PCB and sadly the holes I designed for it did not match, I believe they were mirrored or something along those lines, so I just ended up ditching using screws and hot glued it later on.

Note: I would like to clear things out now. Yes, my front panel looks shitty as hell, I know that. I was trying to have letters with channels where I could drip paint into and then make it look super nice, but that clearly did not work. The reason for that were the imperfections and scaring on the top face of the print. I tried sanding it these down but that did not work either. In the end, I just decided to add hand written “clear” labels over the shitty letters to cover my shame.

After test fitting everything, I decided to move on and solder some little washers that came with the 4mm female banana jacks to the wires of the power supply. They were pretty easy to solder to the wires and the wires made some nice connections with them.

The wires going from the PSU to the banana jacks were not the only ones I had to solder. I had to also fabricate some wires which would link all the grounds of all the connections together. These were just short wires with M4 compatible washers soldered to their ends. I had to resource to this option because every banana jacks bring only one of those attachment washers looking things to solder to, and I needed more for some of the links.

For safety purposes, I decided to also cut all the unused wires to different lengths isolate them from other components by covering them with electrical tape (not shown on the image). This just helps them not short out with any other components or each other.

Next, I decided that it would be wise for me to remove the included potentiometers on the Boost-Buck converter board and solder to it some regular 1 turn 10k potentiometers. To do this, I first carefully de-soldered the small though hole potentiometers with the help of my solder sucker gun and my soldering iron. After that, I soldered some lengthy wires to my 1 turn potentiometers and then soldered those wires to the Boost-Buck converter.

As you might be able to see in the last picture, I also soldered wires to the red LED and then soldered to the Boost-Buck converter’s PCB. There was an LED on the PCB which showed when the board had power, that was the one I removed and replaced with the new LED. Removing that LED was kind of tricky to do because the old LED was an SMD component, but nevertheless it was removed. I wanted this LED to signal when the output was active but that was way too complicated to do with the switches that I had in hand so I decided to just connect it directly to the module.

Next, I soldered the black lead of my panel meter’s current reading connector to the positive output of the Boost-Buck converter. I also soldered to this same pad the voltage reading wire from the panel meter (yellow wire). The red wire of this connector is attached to the positive output banana jack in the front panel of the unit.

Next, I soldered some wires to one of my switches. This switch is the one that will disconnect the output’s ground banana jack from the ground coming from the Boost-Buck converter. Connecting the switch in this way allows me to disconnect anything attached to the variable output of the power supply, while still be able to change the voltage setting safely. In the second picture below, you can see how the white wire of the switch is soldered to the Boost-Buck converter and the blue wire is soldered to a washer looking thing which attaches to the ground  banana jack of the output.

Up next, more switching action! I soldered wires to the main power switch while will turn on and off the ATX PSU. I am not sure about newer ATX power supply, but this one needed to have a green wire grounded in order for it to turn on. Also, this power supply required some load to be placed between any of the rails and ground. In my case, I just added a big chunky 5Ω resistor going from 5V to ground. I got that resistor way back in the day from RadioShack. I also soldered the power indicator LED  from 5v to ground (Look close under the heat shrink and you will find the secrets of the universe).

The last components that needed to be soldered in order to finish all the connections were the USB ports. Their 5V and ground connections were soldered to some wires which contained washers on the other end. As stated before, the ends with the washers were connected to the 5V and Ground back of the banana jacks.

With all connections made, it was time to put all the components on the front panel! Beautiful, isn’t it?

I also inserted the front panel into the bottom panel to make sure that everything would fit properly now that all the wires were in place. It took some convincing but everything fit properly. It does look like a rats nest but as long as nothing is shorting out, I am a happy camper.

I decided that since everything was in place on the front panel, it would be a good time to test out that everything was working fine. Everything worked well except for that very ugly front panel letters!

To keep dust and other particles from entering the power supply, I used a black metallic mesh and placed it onto the closed side of the fan, as well as both of the side plates of the case. The mesh on the sides were glued in place using hot glue.

Afterwards, since the my screw holes for the power supply were not well designed, I had to use hot glue in order to glue the pcb of the PSU to the bottom plates. I made sure that both of the side plates were attached in order for it to have both of the bottom plates be aligned. I also attached the fan to both of the top plates by screwing the fan to these two plates.

Finally, to complete the assembly of the power supply, I attached all the parts together by using M3 screws entering from the top and bottom plates.

To make it not scratch the surfaces it will sit on top of, I added some of these felt-like pads on the bottom surface of the power supply. They can be found easily in dollar stores or other hardware stores for cheap.

And this is what the completed power supply ended up looking like. These pictures were taken before I added the new labels to the front panel of the power supply, as well as some labels on the back plate to remind me of the specifications of the power supply. They have the current rating for every one of the rails (Which depends on the voltage itself) and the voltage and current ratings for the Boost-Buck converter.

To this day, I have not had an issue with this power supply, and it has come in very handy when I needed some odd voltage that I would have no way of obtaining otherwise.

Of course, there are many things that I would like to change on this power supply. I would like to have the output led to turn on when the output switch is turned on. I would  also like to change the potentiometers for the voltage and current to use 10 turn 10kΩ potentiometers to gain far more precision when changing those variable settings.

Although this power supply is not the prettiest, or the one with most features, it does suit all my needs and that’s all that matters to me! I learned a lot from this project, and hopefully in the future I can improve this power supply and add more neat functionality to it.