Adjustable Power Supply

About: I like to make stuff. All kinds of stuff! ZepLabs HandCrafted Nikos Zepidis tonginos@gmail.com

Ladies n' gents,

welcome back in the shop! It's Zep here and today we are making us a power supply unit!

Ok, here's how it goes...

If you are into working with electronics, you can skip this intro. I could not convince you any further! But if you are not, and you are into woodworking instead, or metalworking, or working of any kind (!), if you are a technical fella, or even if you own a battery or two, chances are someday you are gonna need a power supply!

In my case, I need one of them quite more often! So I decided it was time I put one together to have here around the shop...Well to be accurate, it is intended to live in my father's electronics shop, but it's not that far from where I get my stuff done!

So let's get to it....

Step 1: The Brains..

At this point, you may be a bit frightened, that I'd start throwing capacitors, resistors, fancy coils and ferrite beads your way! Then there is diodes, of course, integrated circuits, custom circuit boards with the according CAD software, surface mounted devices, Nicola Tesla and Michael Farraday...

Well, don't get me wrong, I consider those stuff to be extraordinarily awesome, but I'm not here to assign you homework. Today folks, we are keeping it simple!

For the brains of the machine, we are gonna use a ready-made Step Down Programmable Power Supply module that I got online. And to be fair, with all the different functions and specs of this little thing, and given the price it retails at, there is no good enough reason to get yourself involved with all the electronic fundamentals I mentioned above. Other than the thirst for knowledge and the love of making I mean. Financially speaking! Ok, I'm right at the redline of starting talking philosophically again, so I cut to the case! Here is the little thingy.

By the way, the link provided above is an affiliate, so if you decide to buy through there, I may also make a buck. I'm just saying!

So this little thing is pretty darn awesome! In reality, it is more of a sophisticated step-down board, a DC-DC converter, than a power supply by itself. You throw a voltage as an input, and through the built-in menu, you program the output voltage and current limit. It has two decimals for setting voltage and three of them for setting current. It has also a Watt-o-meter in the main display, so you can know your exact load without even multiplying. I tell you, this thing can make you lazy! Also, it offers a menu, through which you can programme up to 10 different memory profiles. I got myself the 50 V / 5A version, but you could use whichever your needs require...

Off we go!

Step 2: The Muscle

The muscle here is this big n' bulky toroid transformer you can see in the photos above!

We need a way to get the power coming out of my wall's socket down to a more appropriate input voltage for the P.S. Module. I live in the 220s area of the world, and as I already said above, the little thingy expects from me any amount up to 50 Volts DC! So there are a few different solutions to this problem...

First one of them includes all the electronic theory I mentioned above, right before you got your headache. So let's pass on this one!

Second one: You get a switching power supply to do the job.

Third: You salvage a big-ass toroid transformer from a formerly-expensive medical machine, and you are up n' running in no time!

Ok, I'm getting serious...

This thing really depends on the version of the P.S. module you are gonna choose. If it is up to 25 V let's say, the easier thing to do here is to also buy a 24V switching power supply for really cheap and be golden. You just have to make sure that it also has an Amp rating capable to accompany your little module's current capacity. But when you start going higher than that 25 V, I find that the odds lean more and more towards the transformer choice. Again, financially speaking...

I'm not saying that you couldn't use a transformer for lower voltages, or even a switching or two for higher ones. I just put it the way I think of it. Plus that, I happened to have quite a collection of transformers laying around, so that's what I went with! The one I 'm using has one primary and two secondary windings, putting out 24V / 12.5 Amps max each.

And of course, using just a transformer you convert AC to a lower (or even a higher) voltage also AC. So those 24 we talked about, they are AC! But we 'll get to that shortly...

Step 3: The Heart..

The Heart of this machine is, of course, the part that involves the make! It is what makes it unique, what makes it pop out from the rest power supplies out there. It is the part that requires heart to make, and also the one to give you most of the joy! It is just the case!

If you know me, you 'll also know that I love working with wood. If not, now you know also!

So wood it's gonna be. I grabbed a piece of 15mm thick okoume plywood (marine) that I had laying around for a while now, and I quite liked the grain pattern ion it. With this, I made the side parts of the machine, left and right. I cut it to size using the table saw, an then using my bandsaw (which I also made myself. You can find an instructable on that here) I trimmed the corners. After that, using the lathe as a disk sander, I sanded them smooth.

Now it's time to customize them a bit further. Add a personal touch! I mounted the first piece on the CNC machine (also self-made. Instructable on that here!) and after a little graphic designing in Inkscape, I used a 1502 engraving bit to carve up there a logo (pictures above!). Then I repeated the process on the opposing piece, and when both of them were done, I painted them using some black spray paint and after a moment or two I gave them to dry, I sanded my ply boards back to a wooden surface. This way I had blackened my engravings, and made them really pop out!

Took a moment to figure where everything is gonna live inside that box we are making, and after having set my mind, I drilled some ventilation holes on one of them sidepieces, and a 40 mm wide whole on the other, where we are later gonna mount a cooling fan.

After that, I resawed a piece of spruce into a 25x25 mm board (just enough to match the 25 mm radius I made in me sidepieces' corners), and after cutting in length four identical pieces out of that, I used them to joint the already made sideboards on the corners. Once again, when the glue was dry, I used a little hand plane to break the corners on the spruce sticks, until they match the profile of the side pieces (25 mm radius). It's way easier than it sounds!

For the bottom part of this machine, the base, I used 20 mm thick poplar plywood, which after I cut in size, I glued in place in the space formed between the, already assembled now, frame. I then drilled to the bottom and through the side pieces using an 8 mm drill bit and glued some dowel to stiffen the structure. The transformer I'm using here is quite heavy!

For the front, upper, and back faces of the power supply, I used 8 mm thick poplar plywood. After cutting it to size, I mounted it in place using some spruce block on the inside as stop blocks on which I glued the faces (except the upper one, which is mounted with screws, to be removable. Prior to that of course, decided where everything is gonna live, on the face of the machine, and made the according mounting holes using some drill bits and the jigsaw...

On the front face I am mounting the P.S. Module, of course, two banana plugs on which I'll take my output, a female USB socket and a switch to control the power to that socket. On the back, you are gonna need just a whole, through which you 'll get the power feed in your new power supply!

I used some walnut stain to darken a bit the front/back/top covers, and a waterbased poly varnish to finish it.

And that's pretty much all there is to it! Now let's do some wiring...

Step 4: The Nervous System!

Yep, you are gonna need a nervous system for that! Wiring diagram embedded above!

Ok, the main idea here is this one...

Having two secondary windings putting out 24 AC each, I was intending on rectifying only half the wave on both of them, throw them now-DC signals in line, and get just about 50 Volts DC which is also the maximum input voltage on my module. Now that's right in the sweet spot, right???

Wrong...

I suppose my math was a bit off, and even though half rectifying the waves, I was getting an output greater than those 25 I was shooting for! So I decided to make things right. After adding a full bridge rectifier and some capacitors I ended up with a DC signal around 36 Volts, which I used to power my module with. I am not using it to its full potential, as you cannot step-up the voltage with that thingy, but at least it's now rock stable!

I used a DC-DC converter to get those 36 down to 12 V DC which I used to power a little CPU fan salvaged from an old computer. As a general switch I am using the one I already had on my transformer's connector, but if you don't have one, you can always place one on the line entering your box.

The USB socket I placed there mainly for cell-phone repairs, on cases where you want to check to power consumption. It is connected in parallel with the banana plugs, which pretty much means that you have to set your module's voltage output to 5V manually before you use the USB socket. The switch placed there is for the rest of the times, where you are running your power supply in a voltage greater than those 5 Volts. The idea is that you use the switch to disconnect the USB socket from the circuit, and avoid any drama in case someone tries to hook in there his cellphone while you are putting out 35 Volts! But since we are all human and we all make mistakes, I also used an LM7805 voltage regulator in that line and just before the switch, which pretty much means that you can indeed charge your phone while putting out 30 Volts! It' ll just mess your readings on your other load there!

Of course, If you are using a ready-made power supply to power your module with, you are not gonna need any bridges and diodes and rectifiers and stuff. As long as it's putting out DC I mean!

Step 5: The Epilogue

In this world we all live into, you can buy a ready-made and state-of-the-art power supply for $$$$. Or you can compromise and get you one that is not that close to a piece of art one for $$.

Long story short! I' am not implying I made the best power supply of the planet, but for the amount of money and work that went into this, this little thing is a pleasant surprise. A very pleasant I dare to say!

And you know. I just love to make stuff!

If you made it to this point, thanks for reading this whole thing! And if you want a P.S.?

Go for it! I highly recommend it.

So see you all next time, probably with another make!

And if you enjoyed this one, feel free to follow me here on Instructables, or my yt channel . We have quite a lot of stuff to make yet!

Have a nice one!

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