Diy bench power supply

[Archie_Altz]

I saw that you can make a Variable bench power supply with an old PSU and a breakout board.

I want to ask if there are any safety precautions except  adding a few fuses to the breakout board and the classic stuff.

Here is a link for the guide (ill get a breakout board with inbuilt fuses and potentiometer)
https://shorturl.at/jGRY1
Edit 1: I dont plan to buy the crappiest psu i find so i am searching for something cheap but with a couple of features such as a back switch and maybe overvoltage protection i will see what i can find

so in case you dont understand i want to use this breakout board :https://shorturl.at/cnvQ3

(note i am 14 and doing this since i want a career in EE , for details ask in dms)

[mariushm]

It's not a variable power supply, it outputs only 12v , 5v and 3.3v  (well also -12v but in very low amount, not worth exposing it to outside world).

 

Depending on power supply, it's not well regulated... voltage on 5v and 3.3v may change a bit depending on how much power is taken from 12v.

 

You can use these voltages as unregulated inputs to adjustable dc-dc converters (buck / step-down regulators, or boost / step-up regulators) or linear regulators that actually give you the voltage you desire.

 

[Applefreak]

18 minutes ago, Archie_Altz said:

I saw that you can make a Variable bench power supply with an old PSU and a breakout board.

I want to ask if there are any safety precautions except  adding a few fuses to the breakout board and the classic stuff.

Here is a link for the guide (ill get a breakout board with inbuilt fuses and potentiometer)
https://shorturl.at/jGRY1

Depends on what you want to use it for. As for safety, use in a dedicated space, on dedicated high amp breaker, have an emergency shut off button installed, get a fire extinguisher for electrical fires etc. the list goes on and on. It really depends on what you want to use it for. If powering 12v equipment is your goal here, I suggest using a 12V automotive battery, sealed or AGM with a breaker grounded to an outlet for safety. I would not buy those boards from aliexpress again. 

[manikyath]

it's not any more dangerous than the things you plan to be doing with it. you're essentially just replacing the connectors of a power supply with something more generic.

 

having that said.. if you're wanting an actual variable output voltage supply, look into ruideng (or riden, or RDtech)

 

https://rdtech.aliexpress.com/store/923042

 

1 minute ago, Applefreak said:

. If powering 12v equipment is your goal here, I suggest using a 12V automotive battery,

but a 12 volt lead acid isnt 12 volts, and is HILAREOUSLY much more dangerous than an ATX power supply assuming you dont actually take apart the power supply.

 

as for the rest of your advice.. yes.. but largely irrelevant to the specific question of re-using an old ATX power supply. any time you're messing with electronics you need to be prepared for something failing spectacularly.

[Huntsman]

Back in the days where I was a student, building a DIY PSU is a must to work on the range of projects I would get involved in. Nowadays, I would recommend students buying a USB-C PD based PSU for convenience. The standard voltages provided matches what the projects would be using anyway.

 

But to answer your question, nothing much in terms of safety to watch out for unless you plan to remove the PCB from the metal case to put it in your own housing. The capacitors inside are rather nasty if you touch it the wrong way.

[FlyingPotato_is_taken]

Ask at https://www.mikrocontroller.net/ if somebody has an old lab PSU. Most are German plebs, some are from Austria or Swiss.

 

On 9/13/2023 at 5:48 PM, manikyath said:

look into ruideng (or riden, or RDtech)

Can't say much good about these modules. Kept blowing them up or they broke within months (without abuse).

[manikyath]

4 minutes ago, FlyingPotato_is_taken said:

Can't say much good about these modules. Kept blowing them up or they broke within months (without abuse).

mine's been doing great for years, and i dont necessarily take good care of it.

[Heats with Nvidia]

On 9/30/2023 at 4:32 AM, Caroline said:

I still work with the same design only with higher quality components, it's more than enough if all you need is 3 amps (317T w/ small heatsink or use the PSU's heatsink).

The maximum current rating of the LM317 is 1.5A. The version of the LM317 that is capable of 3A of output current, is the LM350. Also please be aware that both chips need a little bit of a load (just a couple of mA) to actually regulate the output voltage and the LM350 has an a little bit lower maximum voltage differential between input and output than the LM317.

[fulminemizzega]

On 9/13/2023 at 5:22 PM, Archie_Altz said:

I saw that you can make a Variable bench power supply with an old PSU and a breakout board.

I want to ask if there are any safety precautions except  adding a few fuses to the breakout board and the classic stuff.

That is not variable, as others already said here. Buy a kit of fuses similar to the ones already on the breakout board, shorts may happen and fuses will blow. Having spares helps, just choose reasonable values based on the max current that the PSU can output on each rail (+12, +5, +3.3, -12). If you need the output to actually be variable (that is, you need to output for some reason 9V or 6V or anything that is between 12V and 0V) a potentiometer will not do anything for you, you need something called a "regulator", linear regulators are simple and produce a clean enough output. Imagine measuring the output voltage value over 10 seconds: a perfect noise-free voltage supply doesn't exist, but on such a supply when you measured voltage, you would see exactly the set value for any period. A noisy supply's measured value would fluctuate continuously around the set point. If you could hear it, it would sound "noisy" - the perfect one would be "whisper quiet".
Be a bit careful - PC PSUs can provide a lot of power and you can easily blow things up if you make mistakes (and they do happen). In a short circuit, these can generate significant heat. This is another good reason to use linear regulators like the LM317 - their max current output is low compared to the PSU. If you make a mistake, the LM317 will limit current and/or go into thermal overload rather than destroying the rest of your circuit or breadboard.
Checkout the LM317 wikipedia page, do not bother with anything related to DC-DC converters or switching regulators. Read an LM317 datasheet, for example this one from Texas Instruments https://www.ti.com/lit/ds/symlink/lm317.pdf , there will be many things that make no sense to you but the paragraphs 3, 8 and 9 will give you a few ideas of what this component does.
Checkout the eevblog forum and youtube channel, you will find a lot of discussions and explanations (and bickering) about linear voltage regulation.

The best advice would be to just grab a book, The Art of Electronics by Horowitz and Hill, especially chapter 9... but once you have the book, you can just read and learn there what you need and you will be satisfied by it.