ATX Bench Power Supply - Convert a Computer Power Supply

@derek

How did you design this power supply?

Which software did you use? Looks good. 😀 

@robotbuilder

Just never heard it referrer to as a SMPS.   Seems like I just remember calling them switching power supplies.

@sumanta

So yes the ATX power supply is a switching power supply.  It is in a particular form with the proper connectors for a PC motherboard.  The purpose of the video was  to demonstrate how you could modify an existing ATX power supply into a bench power supply, which will of course still be a switching power supply.

You can of course buy many switching supplies with either 24, 12, 5, or other voltages.  This is just a example of a project repurposing something you may just have laying around.

Posted by: @codecage

So yes the ATX power supply is a switching power supply.

@codecage

Thanks for the reply. 😀 

@sumanta

I actually used OnShape: https://www.onshape.com/en/

@derek

Thanks for the reply 😀 

A couple of questions and one minor issue (but still worth reporting) -

So Questions First -

1. I have always wondered why these wires from this ATX power supply are paired? I mean, there are two wires into each pin and I never could find out why. Okay, I have assembled a lot of PCs (desktops?) but never questioned this - as I always believed that if you know to ride a bicycle, all you need to know is to ride. But with age, I realize that it is good to know some repairs as well.

2. The Video shows 3 wire sets being used for each pin out. So again, why is that? I mean, if they (the manufacturers) ship with 2 wires going together, why do we need to change that and opt for 3 wire sets instead.

3. Which wire ends were trimmed off from the inside the Power Supply - there was a mention on the video, but I could not figure out which ones. (this is just a minor problem because I understand the wires that are cut are eventually removed and so the other needed Sets should remain).

The minor issue -

The link to the PDF at the moment, does not work. Not sure what that PDF has/had on it, but it might be good with some sketches (non related to Arduino Codes but as in Images/Diagrams).

Parts List is not detailed out (reasons explained on one of the replies here from Bill on earlier pages), but still if someone would help me know what those terms for components are, I might look out at alternatives if I cannot find them locally.

Posted by: @sid

A couple of questions and one minor issue (but still worth reporting) -

So Questions First -

1. I have always wondered why these wires from this ATX power supply are paired? I mean, there are two wires into each pin and I never could find out why. Okay, I have assembled a lot of PCs (desktops?) but never questioned this - as I always believed that if you know to ride a bicycle, all you need to know is to ride. But with age, I realize that it is good to know some repairs as well.

2. The Video shows 3 wire sets being used for each pin out. So again, why is that? I mean, if they (the manufacturers) ship with 2 wires going together, why do we need to change that and opt for 3 wire sets instead.

There are basically two things going on with paired connections.

1) The ATX specification requires sense lines on some of the supply lines. If you see a thick and thin wire attached to the same pin, the thin wire is almost certainly the sense line. Sometimes it's easier for the manufacturer to just use the same guage of wire for both. If you measure resistance across the two and you get something that is not essentially 0, you're looking at a sense wire.

2) The other reason for using multiple wires is simply current/safety. Common ATX power supplies are capable of generating absurd levels of current for what most of us do on the benchtop. If you have a wire-fraying issue and lose one of your wires, with a second wire you're less likely to have a small space heater/firestarter appearing suddenly in your computer case.

I suspect Bill combined wires out of a combination of safety considerations and "why not"? As long as they're all on the same power rail (feedback circuit), there's no issue joining them.

3. Which wire ends were trimmed off from the inside the Power Supply - there was a mention on the video, but I could not figure out which ones. (this is just a minor problem because I understand the wires that are cut are eventually removed and so the other needed Sets should remain).

I would recommend a slightly different approach.

Buy and chop up one of these, and just zip-tie the PSU cables neatly. I would particularly recommend this approach if you're having any difficulties with mapping which wires do what. I very much regret not taking this approach when I built mine. ( https://forum.dronebotworkshop.com/show-tell/an-atx-based-power-supply/)

Parts List is not detailed out (reasons explained on one of the replies here from Bill on earlier pages), but still if someone would help me know what those terms for components are, I might look out at alternatives if I cannot find them locally.

I live in an "electronics supply store desert" and therefore get all my parts online... I forget that some people are lucky enough that getting things locally is an option. 🙂

Regardless, which parts are you referring to specifically?

@dronebot-workshop I’m soooo confused. I thought that the fues was for the current drawn by the item ( esp32cam for instance). 
5v or 3.3v at max 800ma. Isn’t the fues put in place incase there is a higher current demand for some reason??? Please link me to an article or video that explains this. I don’t expect you to explain in detail, thanks

ps , I’m asking because I’m in the process of building one. 

@electronic-zookeeper 

With regards to the ESP32 are you thinking of the "eFuse (Electronic Fuses) are microscopic one-time programmable fuses that can be "burned" (i.e., programmed) to store data into the ESP32"?

An old thread on the subject.

https://forum.dronebotworkshop.com/electronic-components/when-to-use-fuses-in-circuit/

Fuses as I understand them is to break the circuit if the current is too high for the device being powered and thus burn out before the device catches on fire. In houses the modern fuses click off the power if there is a short (pulls extra current) and are probably much faster than the old glass incased fuses thus preventing electrocution as well as protecting the device and can then be reset.

@electronic-zookeeper What post are you reacting to?

In conventional electrical circuits a fuse is sized to prevent the insulation from catching fire.

In electronics circuits there are often several other reasons like protecting expensive sensitive parts from unforeseen spikes. This is more art and experience but now that all the information in the world is on the internet, it's simply a question of asking the right question.

What in particular is it you are wanting to know?

Hi Ron, sorry it’s not clear. what I’m asking is .

- what fuses do I need to put inline on my atx bench top power supply, 

- my understanding of fuses was they are to provide a lower current demand than the circuit so the fuse burns and not the circuit. 

- do I need to change fuses on my power supply to accomodate different devices? 

im aware that I’m asking questions that I don’t fully understand, which is why I’m asking the questions. 

@electronic-zookeeper Look at the power supply spec. For instance it will say at 5V it can supply 3A. That means you should use maybe a 5A fuse. It's a little bigger because the event that will cause it to be needed will be a spike. For normal use they are allowed to draw 3A and the next size is probably 5A, if you can find a 4A go ahead, but I wouldn't sweat it.

are you using a fuse to protect the atx power supply or the microcontroller your powering???

@electronic-zookeeper Ok, I am confused. Who are you replying to? You know that Icon on the bottom right of a post that says REPLY and inserts the handle (@zander for instance) at the beginning of your post. Also, are not you the one who started this topic?

As to your question. Since current is drawn or pulled from the source, or even more correctly is allowed to flow then it protects the supply against a short circuit most commonly but in reality any current above the ATX design point.

I think you are over thinking it. For a set of 5V posts, add a fuse to the + post (just behind it actually) of either 500ma (USB2.0), 900ma(USB3.0) BUT if you are powering more than MCUs and/or MPUs then use a fuse that accounts for the extra draw. If you will be powering a Pi5 then allow 5A but it would be much better to use an official Pi5 wall wart for Pi5 power supplies.

What commercial bench supplies do is they have controllable voltage as well as current  but the ATX DBWS project does not have that feature. IIRC, the newer Linear supply that Bill designed does have a typical CV and CC function.

IF you are still confused, 3A is a good ball park or even as high as 5A PER set of 5V or 3.3V or even 12V posts. I use 5A in the 5V, 3A in the 3.3V and 10A in the 12V but I have 2 of each so there is a total of 6 fuse holders on the back of my supply.

Remember it's motors that need the most power, all your Micro Controllers or Micro Computers and almost all sensors only use a few 10's of ma up to a maximum of a small number of 100's of ma.

Sorry Ron, I’m new to forums I’ll reread the how to