Introduction: YAPS 750 Power Supply

About: I am a contract software developer, mainly web based these days. My hobbies are fixing stuff that wasn't broken until I got my hands on it, electronics, Arduino and Modern Jive Dancing.

I have a small, cheap power supply which gives me variable voltage etc.
I rarely work with voltages above 12 volt so it has served me well for a few years.
My main issue with it is its limitation to have multiple things connected at once.
I have created a small board that takes a 12v supply and breaks that out into 3.3v, 5v and 12v, but even that is limited to one output per voltage range.

About three months ago my desktop PC decided that it had ‘had enough’ and died.
It was the motherboard, so I bought a ‘bare bones’ machine so that I could re-use all my drives, graphics card etc.
This new box came with its own power supply, so now I had a perfectly good 750 watt supply from the old box.
I have seen many Instructables in the past where people have utilised their old ATX supply into a bench supply, so I thought that I would also give it a go.

I thought about it for a while and came up with a list of requirements:

1. Power requirements:

1. 3.3 volt
2. 5 volt
3. 12 volt
4. Variable voltage (really for common use of 9 volt but who knows what else)
5. QI (maybe)

2. Other

1. USB for communicating with a computer

3. Outputs

1. Banana plugs
2. BNC (just in case)
3. Binding posts
4. 5.5 x 2.1 Jack
5. USB for charging etc
6. 12v car cigar lighter (maybe)

With my requirements thought out I sat down with my favourite drawing package which is Affinity Designer. It is my favourite because it is affordable.
I started with an A4 size but very quickly ran out of real estate so increased it to A3. Yes I know that is going to be a huge power supply, but my goal was to have everything that I needed all in one place, and hopefully give me many years use.

I wanted to be able to see what current was being drawn at any one time so I needed gauges for each of my output voltages.

I wanted a number of areas to be switchable.

I thought about the possible increase of internal temperature and therefore would need an extra fan of some description, and an indicator to say that the fan was running.
The power supply already had its own fan but another one will not hurt.

Before long, most of my A3 layout was full and looking quite good.

So that was it. Done thinking and done designing (for now)

Parts List:

Power supply unit:

1 X 750 watt ATX Power Supply (It has its own power switch and kettle socket)

Power On:

Red button (large)
Green LED (to show that power supply is connected to mains)
Red LED (to show that the power supply is on)
2 X LED sockets

Internal Temp:

Red LED (to show that the fan is running (or not))
1 X LED socket
Temperature gauge


1 X White button
1 X White LED
1 X LED socket
1 X QI power set (more about this later)

USB Comms:

2 X Green buttons
2 X Green LEDs
2 X LED sockets
4 X double USB sockets


2 X Yellow buttons
1 X Yellow LED
1 X LED socket
1 X Volt/Amp meter
2 X Black banana sockets
2 X Yellow banana sockets
1 X Black binding post
1 X Red binding post
2 X BNC sockets
2 X 2.1mm jack sockets with dust covers


2 X Red buttons
1 X Red LED
1 X LED socket
1 X Volt/Amp meter
2 X Black banana sockets
2 X Red banana sockets
1 X Black binding post
1 X Red binding post
2 X BNC sockets
2 X 2.1mm jack sockets with dust covers


3 X Green buttons
2 X Green LEDs
2 X LED sockets
1 X Volt/Amp meter
2 X Black banana sockets
2 X Green banana sockets
1 X Black binding post
1 X Red binding post
2 X BNC sockets
2 X 2.1mm jack sockets with dust covers
1 X Cigar lighter

Variable voltage:

2 X Blue buttons
1 X Blue LED
1 X LED socket
1 X Volt/Amp meter
2 X Black banana sockets
2 X Blue banana sockets
1 X Black binding post
1 X Red binding post
2 X BNC sockets
2 X 2.1mm jack sockets with dust covers
2 X Multi turn potentiometers and knobs

USB 5v only:

4 X Black buttons
4 X Different LEDs
4 X LED sockets
16 X USB sockets

That’s a big list, but like I said before, I am expecting this to last for many years, so the effort should be worthwhile in the long run.

Step 1: Preparing the Front Panel

I could really have done with a laser cutter for the front panel, but as I don’t have one, I have to resort to drills and files.
I printed my drawings out and it looked good.
The front panel is A3 white acrylic; but as my choice of labelling for the front was A4, I had drawing for left and right, and hopefully they would meet up in the middle.
I then modified the print to show drill hole centres, and drill holes for the corners of all the rectangular holes that were needed.
A total of 98 holes required and 25 of them are rectangular.
The round holes were not too bad to drill, but acrylic does not really like to be drilled without chipping, even done gently.
The rectangles were worse as they needed a lot of filing and not all came out as accurate as I would have liked.
The USB sockets give no room for error, so when the hole is slightly out, it shows.
But, this is for my use only and will rarely be seen close up by others. It is a tool for my workshop after all.
Making the holes was long and slow and boring and even more boring.

Once the panel was ready, I had this brilliant idea to print the layout onto self-adhesive acetate sheet. In theory, it is a great idea, but not the stuff I bought.
To stick self-adhesive sheets, it is best to make the surface of what you are applying it to, wet.
The reason for this is to stop the sheet just sticking to the first thing it comes in contact with, and give you plenty of time to position it correctly, and also allow you to squeeze out any tiny air bubbles.
I have done this sort of thing many times in the past and used weak washing up liquid with great success.
Not with this stuff though. It does not seem to be just the back that is sticky, although it was just the back that had protective covering. As soon as any moisture touched the front it turned the surface into a gel like substance and made the surface look like you had just poured acetone on it. Basically it looked a mess. So I ripped it off.

I tested it with water, oil and soapy solution, all with the same result.
I had some more sheets of this acetate and decided to try again but this time place it directly onto the surface, knowing full well that air bubbles would be everywhere.
It is now on. Yes there are small bubbles and there they will stay. It is not too bad, but it would have been nice to be able to do this bit properly.

Step 2: Wiring It Up

Once the front panel was drilled and the acetate was attached, I was now ready for adding the board components. It took a while, and I found that my 3mm acrylic was a little too thick for some of the components. 2mm would have been better, but maybe a bit delicate for workshop use, especially the stress of pushing ‘things’ into sockets.
Because over time there is most likely going to be a certain amount of vibration, and some of the nuts barely fitted (because of the 3mm acrylic) I decided to put a dab of hot glue on all of the nuts to stop them turning, just in case.

Next comes the wiring up. Although relatively straight forward for the most part, there is an awful lot of it. Trying to keep the wiring relatively tidy obviously makes it more awkward in tight spaces.
You will see in one of the images that the front panel is fitted and glued into a wooden box covered with a leather look covering. Well, it looked an absolute mess from the front, and even I was not prepared to have that in front of me on the bench.

Plan B for this was to make a plywood box and give it a coat of paint.

Step 3: All the Extra Bits

I know that I have a perfectly good and working power supply in my hands, but what if it decided that enough was enough and packed up. If I stripped all of the cables back and wired it directly into the front panel, like most seem to do, that would mean that if it died then I would have a fairly major job on my hands to get it up and running again. I decided to leave the loom intact and create a breakout board for the main motherboard plug. That way, a replacement would only take 15minutes.

For the temperature detection, I used an Arduino Pro Mini, a DHT11 temperature sensor and a relay for the fan.
It may seem a bit of overkill, but to be honest, I am not a fan of the Pro Minis that I have, and this was a way of using one up.
I added a trimmer so that I could adjust at what temperature the second fan would be turned on. A bit of trial and error in the Serial Monitor, but worth it.

I wanted to have some kind of variable voltage and variable current and I found a small buck/boost converter. Probably not man enough for heavy work, but I don’t do heavy work. What I really wanted is something that would do 6, 9 and 13.8 volts; and most of that would be for basic testing purposes only.
I removed two multi turn trimmer pots and wired in two bigger one of the same value onto the front panel.

When it came to the USB communication, I needed a complete Powered USB setup, ie. All four wires, but the power coming directly from the power supply. The data lines eventually route out to a computer, and having it powered just made sense.
I created a little breakout board for this as well with two different types of female sockets because I wasn’t certain what spare cables that I had kicking around at the time, and I wanted to use proper cables from that point to the outside world.

In the same area, there was an ever increasing need for ground wires, so I added a little board to help me out.

The USB sockets on the right of the front panel are 5v only so they were quite simple to wire up. Probably too many for what I need, but, who knows.

Rummaging through my toy box, I found a load of fuse holders, so I thought that it would be a good idea to add one for each section of the power supply, just in case.

During the wiring up of the front panel and long before I had a power supply in place, I needed to test each part of the wiring as I went along. I created a small makeshift adaptor that I could just feed 12 volts from my old power supply, and get 3.3, 5 and 12 from it. Nothing special really but I am surprised at how much it has been used, during and since (as my son has now liberated it along with my old power supply).
I had to add another board below it to stop it shorting out while on my bench with all sorts of bit of wire, tools etc.

Step 4: The QI Adapter

The QI adapter was originally housed on the top of the original box. Well, that box has now gone, so I have to think of a new plan.

However, I now have to wait for another one to arrive, although I am not so sure that it is a good idea after all.

I had the QI charger all wired up and tested with my little makeshift supply, and it worked surprisingly well.
But, when I connected the supply wiring to the big motherboard socket, I inadvertently wired it into a 12 volt socket. As we all know, if one tries to push 12 volts into something that is designed for 5 volts, something has to give. Well in this case, I turned one of the QI charger chips into a fry. It is surprising how much smoke can fit into a tiny package. I suppose that’s why it is called magic smoke.

Like I said above, I am not sure that it is a good idea to add a QI charger anyway. I have heard of a couple of cases where a component on the receiver has gotten very hot and melted a phone case; and they are only about 45% efficient anyway. Plus they fill the socket on your phone, which is also frustrating when you want to connect it to something else and there is not enough give on the plug to unplug it, so you have to dismantle your phone just to unplug it and plug a lead in.

For now I have just left a USB mini lead out of the back of the power supply. Maybe I could make some kind of QI ornament to sit on the top of the box. Something that I don’t mind getting hot.

Step 5: The Back Panel and a Few Extras

According to my original parts list, I should be just about finished as soon as I fit the power supply into the box.

I have already mentioned the fuses that were added as an afterthought.
Well, I had a couple more afterthoughts.

I have all sorts of bits and pieces in my toy box that I have collected over the years and never used.
I have a number of speaker connectors left over from my DJ days (probably the worst DJ in the World, but that is another story).
I used some of those connectors to give me 5 and 12 volts on the rear of the box. May be useful one day.

As I never dismantled the ATX supply, the loom was still intact, so I decided to extend a molex supply to the outside World.

I put an Arduino UNO inside the box as well. Currently it gives a bit of a light show in the dark, but I’m sure that will be changed sometime in the near future. What to, I’m not certain, but the Arduino is all wired up to be programmed directly from a computer and it has its own 5 and 12 volt supply right next to it.

When I put the back onto the box and tried to connect everything up, I found it awkward making sure that plugs didn't come unplugged, so I added detachable chains to make life just that little easier.

Lastly, but probably one of the most important additions, is a banana plug/binding post that is wired to mains Earth so that I can plug my ESD wrist strap directly.

Step 6: All Done

I hope that this has been an interesting read. It was definitely interesting to build.

This Instructable is not about how to do everything step by step because I know that would be a waste of time for this sort of thing.
I like to think that I have explained the more interesting aspects of it though and maybe it will inspire others to do ‘their own thing’ with an old but fully functional ATX power supply.

Epilog Challenge 9

Participated in the
Epilog Challenge 9