Convert PC PSU into bench power supply

[Andryu]

Hello, I want to convert my old PSU into a nice bench power supply.

I found this video on youtube https://www.youtube.com/watch?v=eEs8nVUB72k, which I found really insightful so I decided to build a similar one.

My goal is to have:

1 banana plug for the 3.3Volts (5 orage cables available)
1 banana plug for the 5Volts (8 red cables available)
1 banana plug for  the 12Volts (7 yellow cables available)
1 banana plug for variable output split from the 12Volts (using a buck-boost converter)
1 banana plug for GND
1 usb type C for fast charging
1 LCD amp/volt meter for the variable plug
Potentiometer knobs for the variable plug for Volts and Amps

My PSU specs can be seen in the attached image.

---

After asking a lot chat GPT and contemplating how much I want to spend and how much power I should get. I decided do something I read on a comment and that is to  use 2 cheap back-boost converters in parallel in order to get more of the PSU's potential at a price that makes sense.

My issue  is that my electronics knowledge is at a hobby level and thus I am unable to discern the BS from the truth of chat GTP.
If someone with proper knowledge can please check my plan and parts bellow and let me know if there is any BS, I would appreciate it a lot.

PLAN:

• Take 5  out of the 7 yellow wires from my PSU and connect them into a THICK wire. (PSU 12V is rated at 310W MAX)
• Do the same with black wires.
• Split the thick wires to the input of 2 identical back-boost converters (100W MAX each)
• Add a schottky diode (20SQ045 20A 45V) on each positive output of the converters
• Connect the outputs of the converters to 2 banana plugs, 1 for GND and 1 for (+)
• Use 2 stereo potentiometers to replace the volt and amp pots on the converters (200kΩ each)
• Add a Digital Car Voltmeter Ammeter (50A 100V) + a shunt. (No idea how I'll connect it,  I'll see if it has a manual when I buy it otherwise search for one on the internet)
• Connect 2 yellow wires + 2 black wires to a USB C decoy board for charging
• Connect the rest of the black wires to a banana plug, connect the red wires to another banana plug, connect the orange wires to another banana plug.
• Contemplating whether I should split the 12V  thick cable to 3rd cable which will directly connect to a banana plug for direct 12v and not  the variable one. IDK if this splitting is too much.

PARTS:

• Buck-Boost converter -> link
  5-30V to 1.25-30V 8A 100W
  
• Schottky Diode -> link
  20SQ045 20A 45V
  
• Stereo Pots -> link
  200K Ohm
  
• Type-C decoy board -> link
  Random one I found
  
• Banana plugs -> link
  Rated 30V-60V/Max 19A
  
• Digital meter -> link
  100V 50A
  
• Shunt -> link
  50A 75mV 0.5Class
  

Any help, tips, opinion will be deeply appreciated.

PS: Let me know if you need more details from me.

[bostonman]

This may not be safe.

A bench power supply has current limiting. With this unit you're not protecting yourself and the circuits from excessive current.

[nctnico]

Don't do it. There are good budget options from Korad to have a decent (linear) bench PSU. If you need lots of power, then the adjustable switching PSUs from Gophert or Rek are a good choice. You might want to replace the binding posts on any of my suggestions though.

[nonius_]

A bench power supply has current limiting. With this unit you're not protecting yourself and the circuits from excessive current.

Hm. I've converted about a dozen AT PC-PSU's to variable voltage (2.5-28Vdc), variable current (0-10A) power supplies. Wasn't that hard. All supplies were based on the TL494 (=KA7900). The trick to add (adjustable) current-limiting to the circuit was to add a short bit of sensing wire in the transformer's ground return, and use one of the unusued comparators in the TL494. Worked a treat. If you want to know more about this method, search 'Oztules PC PSU conversion', you'll probably end up on the old forum fieldlines.com

But reading the original question of OP, I suspect this kind of modification is a bit beyond his skill-level at the moment.

I've used those modificied PC PSU's for many projects: lab power supplies, capacitor-discharge spotwelder (to recharge the 1.56F capacitor bank), in a CNC-controller, etc. Some were converted to a 15-50V dc and 50-350Vdc supplies.

I must admit that, on occasion, some conversions weren't entirely succesful, with bits of exploding semiconductor flying all over the place....  Anyway, it is possible to modify these PSU's to adjustable voltage and adjustable current-limiting. Would I do it again these days? Probably not....

[SteveThackery]

You can buy adapters specifically for this purpose. Some of them are fused and have an on-off switch. I've used them - they work perfectly. I'll see if I can find a link.

EDIT: here we go:

https://m.banggood.com/ATX-Power-Computer-Supply-Adapter-Board-Module-24-Pin-5A-USB-Interface-for-Computer-Desktop-Electrical-Accesories-p-1983774.html

[madires]

Did ChatGPT also tell you that an ATX PSU's ground is connected to earth/PE? And why that could be possibly a bad idea for a bench PSU?

[Andryu]

This may not be safe.

A bench power supply has current limiting. With this unit you're not protecting yourself and the circuits from excessive current.

You can buy adapters specifically for this purpose. Some of them are fused and have an on-off switch. I've used them - they work perfectly. I'll see if I can find a link.

OK, it seems to be a good idea to fuse each rail of the PSU. Chat GPT suggested 25A car fuse for the 12V  rail, 20A car fuse for the 5V rail and 30A car fuse for the 3.3V rail. Will this be okay or do you guys recommend something different?

Don't do it. There are good budget options from Korad to have a decent (linear) bench PSU. If you need lots of power, then the adjustable switching PSUs from Gophert or Rek are a good choice. You might want to replace the binding posts on any of my suggestions though.

I am mostly doing this for learning and to feel good since I always wanted to convert a PC PSU. Realisticly I probably don't need a bench PSU. My use cases are somewhat limited as I mention further bellow. Also thank you for the recommendations I will keep them in mind for the future 

A bench power supply has current limiting. With this unit you're not protecting yourself and the circuits from excessive current.

Hm. I've converted about a dozen AT PC-PSU's to variable voltage (2.5-28Vdc), variable current (0-10A) power supplies. Wasn't that hard. All supplies were based on the TL494 (=KA7900). The trick to add (adjustable) current-limiting to the circuit was to add a short bit of sensing wire in the transformer's ground return, and use one of the unusued comparators in the TL494. Worked a treat. If you want to know more about this method, search 'Oztules PC PSU conversion', you'll probably end up on the old forum fieldlines.com

But reading the original question of OP, I suspect this kind of modification is a bit beyond his skill-level at the moment.

I've used those modificied PC PSU's for many projects: lab power supplies, capacitor-discharge spotwelder (to recharge the 1.56F capacitor bank), in a CNC-controller, etc. Some were converted to a 15-50V dc and 50-350Vdc supplies.

I must admit that, on occasion, some conversions weren't entirely succesful, with bits of exploding semiconductor flying all over the place....  Anyway, it is possible to modify these PSU's to adjustable voltage and adjustable current-limiting. Would I do it again these days? Probably not....

Did ChatGPT also tell you that an ATX PSU's ground is connected to earth/PE? And why that could be possibly a bad idea for a bench PSU?

You guys gave me a headache xD. I think messing with the PSU circuitry is way above my skill level and probably overkill for this project hence the use of cheap back-boost converter. Also isolating the GND is too expensive or hard for me and probably overkill as well for this project. IK chat gpt is bad which is why I posted here but it's convenient AF for noobs.

I plan to use this PSU only on household devices (cheap battery devices) like toys, cheap DC RC motors, laser pointers, cheap flash lights  etc.
Thanks to you guys I've added some rules for using it:
1. don't use it with more than 1 device at a time
2. don't use it with expensive devices
3. use the USB TYPE C to charge only smartphones and tablets
4. be careful not to ground a device connected to the PSU. I should place it on non-conductive surfaces and touch it only if I am 100% not grounded.

I also plan to power breadboards with simple circuits and maybe more complex ones in the future, is this use case ok or should I use batteries instead? 

---

I understand that it will have a high risk of frying a device, that it is not meant for a PC PSU, but is there also a high risk of frying the PSU itself even with the added car fuses? Is there anything else I can easily or cheaply do for added safety or even rules to follow?


As I understand my plan should work but with a big asterisk on safety, correct?

---

Thank very much for your knowledge guys and enlightening my noob *ss 

PS Sorry if I misunderstood anything as my elctronics knowledge and understanding is very poor

[bostonman]

If you're new to electronics and want to experiment, don't tinker with such lethal power.

[Smokey]

...

...

what enclosure/rack is that? 

[BadeBhaiya]

I say go for it. Its a fun educational project and you get usable equipment out of it. ATX power supplies are cheap and relatively safe. Just make sure its earthed properly and you're good to go.

I too have wanted to build something similar but for the time being, I just use 18650 cells to make whatever voltage I need

[UnijunctionTransistor]

My recommendation?
Put more than a single banana plug for the ground connection.

If you plan to draw several amps from one of the high current outputs, an Anderson powerpole connector would be useful.

[bostonman]

I'm still uncertain why the support to work with such lethal currents for someone new to electronics.

The voltage is low, but you have lethal high current potentials along with a mix of positive and negative voltages.

Too many wires which may cause confusion. Next minute something is wired wrong or something is touched by accident, and the person will get a bad shock.

[madires]

4. be careful not to ground a device connected to the PSU. I should place it on non-conductive surfaces and touch it only if I am 100% not grounded.

Nope, it just means that any DUT's ground is connected to earth/PE via the ATX PSU. It doesn't make the DUT dangerous.

(DUT: Device Under Test)

[bostonman]

My point was simply: the more wires, the more potential to connect something wrong.

It's just my advice that if the OP is starting in electronics, start with simple stuff until the basics are learned; then move up to larger stuff.

[Andryu]

I'm still uncertain why the support to work with such lethal currents for someone new to electronics.

The voltage is low, but you have lethal high current potentials along with a mix of positive and negative voltages.

Too many wires which may cause confusion. Next minute something is wired wrong or something is touched by accident, and the person will get a bad shock.

I am not new to electronics. I can test and replace every component on a PSU safely without issues, thankfully my 2 brain cells can do that. My issue is that my knowledge in electronics theory and physics is so basic that's not even worth mentioning but not non existent. I have enough confidence to safely do this project and that's also the reason I don't want to mess with the ATX PSU circuit itself but only with the output of it. Also I didn't straight out jump on the project, I watched youtube videos, googled around and asked for advice on discord and on this forum which fortunately got me plenty valuable  knowledge to make this project better and safer.

[blackdog]

Hi Smokey, 

The case is olmost for shure from the brand Schroff from Germany.

https://www.nvent.com/nl-nl/schroff/products/desktop-cases

Kind regards,
Bram

[bostonman]

Also I didn't straight out jump on the project, I watched youtube videos, googled around and asked for advice on discord and on this forum which fortunately got me plenty valuable  knowledge to make this project better and safer.

My opinion was an opinion based on being safe.

You can learn electronics, especially power supplies, much easier and safer. You're basically trying to learn about electricity by climbing up a telephone pole to check how it's wired.

[Andryu]

Also I didn't straight out jump on the project, I watched youtube videos, googled around and asked for advice on discord and on this forum which fortunately got me plenty valuable  knowledge to make this project better and safer.

My opinion was an opinion based on being safe.

You can learn electronics, especially power supplies, much easier and safer. You're basically trying to learn about electricity by climbing up a telephone pole to check how it's wired.

I heard you the first time and thanked you for it. At this point it's becoming annoying, please move on and let me climb my telephone pole  in peace.

[bostonman]

I heard you the first time and thanked you for it. At this point it's becoming annoying, please move on and let me climb my telephone pole  in peace.

Seeing as how you only have four posts, I assume you're unfamiliar with this forum implying you're new here.

People on here take extensive personal time to answer questions for complete strangers. It's something I appreciate, and, unfortunately, find myself more often than not unable to answer a question due to not knowing the answer; or it's already been answered. If anything, I want to contribute more to this forum because of al the generous contributors on here (and I'll give a shout out to Lemon64 too).

Your comment was uncalled for. I took the time to place emphasis on the safety aspect of your project and you respond with an ignorant reply. You seemed adamant to take on a task that I, along with a few others (nctnico was one of them), suggested not to do.

Maybe as you use this forum a bit longer, you too will have respect for the time others take to provide answers and realize you got sarcastic with a person who took the time to show concern for your safety.

I've read threads where people want to float their scope and numerous users on here repeat over and over the safety issues. I was following suit by placing emphasis on the safety aspect of it and making sure I was in no way part of contributing to the possibility of you injuring yourself.

watched youtube videos, googled around and asked for advice on discord and on this forum which fortunately got me plenty valuable  knowledge to make this project better and safer.

By all means, climb the telephone pole and touch the wires because you watched YouTube videos and know how to be safe. If you can, please post an image of the Engineering degree you earned from YouTube University because I'm sure it's worth more than those (including myself) who earned Engineering degrees from accredited colleges/universities; or have extensive experience (which I've found in my years to sometimes be more valuable than a degree).

[SteveThackery]

Did ChatGPT also tell you that an ATX PSU's ground is connected to earth/PE? And why that could be possibly a bad idea for a bench PSU?

ChatGPT? Don't know what you are on about. I went to Banggood, because I've bought the linked item before. Good point about the earth connection, though - thanks for pointing it out.

[Doctorandus_P]

Oh my, this guy is crossing the wires (07:40) He clearly has not seen Ghostbusters

Also, you can buy littleconverter PCB's on Ali / Eaby / China direct with an AT power supply connector, fuses and screw (or other) terminals. There are different models available.

[madires]

Did ChatGPT also tell you that an ATX PSU's ground is connected to earth/PE? And why that could be possibly a bad idea for a bench PSU?

ChatGPT? Don't know what you are on about. I went to Banggood, because I've bought the linked item before. Good point about the earth connection, though - thanks for pointing it out.

Sorry, my comment was meant for the OP. But I'm glad I could help.

[SteveThackery]

Also, you can buy littleconverter PCB's on Ali / Eaby / China direct with an AT power supply connector, fuses and screw (or other) terminals. There are different models available.

Try reading the thread. I linked to one way back in post 4.  And there's a picture!

[marco58]

Dear OP,
I don't want to be rude, but I cannot avoid some considerations.

As some others members already said, perhaps you do not have necessary skills, now.
Please trust more our help (and not GPT or youtube) and study some basic theory. 

If you need asking GPT about fuse choice, when you do have nominal values of your PSU, I must think you do not know (or are too lazy to think yourself) how current and power relates.
Your PSU value mention voltage, current and total power (I suggest take these values with a grain of salt: these are intended for PC load and are referered to instantaneuos peak load, I presume. If not plain "advertisment data") so you have all needed information.

I hope you know how fuse are generally specified. Nominal current is the current that can be sustained indefinetily without burning. Burning current is much higher and can be also twice the nominal and intervention time is also somewhat long.
Fuses are ok to protect wiring cables, but electronic stuff is another story.

I don't know if car fuses are different, but use GPT  to find a real datasheet and check current and time intervention.

You think to use 2 buck-boost converter in parallel, I suppose with schottky diodes and stereo pot.
I think this is not a good idea.
Stereo pot tracking between sections is poor and a so voltage outputs do not match well (and also resistance / voltage ratio may differ from unit to unit due to other components tolerances).
Also schottky diodes have tolerances.
So a little voltage difference may cause one only converter to supply all requested current until it overloads and I don't how a 5 euros converter  may react to misuse.

Generally speaking power supplies can be paralled only if stated by constructor and with the specified info.

Hope this help
ciao
marco

[MariuszD]

I'm still uncertain why the support to work with such lethal currents for someone new to electronics.

The voltage is low, but you have lethal high current potentials along with a mix of positive and negative voltages.

Too many wires which may cause confusion. Next minute something is wired wrong or something is touched by accident, and the person will get a bad shock.

Looks like you don't know what is the difference between potentials and currents. There is no such thing as "lethal high current potentials"  There is no chance of being electrocuted by 24V. 
By scaring with a non-existent threat, you divert attention from important issues.

A power supply with high current and low voltage (3.3V 30A) can melt a long thin wire (eg AWG 24) if a short circuit occurs.

The power supply has internal protection. The fuses at the output are meant to protect the wires and connectors (eg USB), not the power supply. The thin wire will melt before the protection in the power supply activates.

I also plan to power breadboards with simple circuits and maybe more complex ones in the future, is this use case ok or should I use batteries instead?

A linear power supply with adjustable voltage and current limiting is the best for this purpose. If your circuit has errors but you connect it to a power supply with the limit set correctly, the power supply will protect your circuit.