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Converting Old Computer ATX Power Supply into 12V, 9V, 5V, 3.3V Workshop Supply

mateusz2015_5102 8328 11
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  • #1 16773403
    mateusz2015_5102
    Pupil
    Posts: 542
    Help: 1
    Rate: 81
    Hello. I got an old computer power supply from a friend. It does not yet have an on / off switch. I would like to convert it into a workshop and at the beginning I thought to check the electronic components, especially electrolytic capacitors with a universal meter for PLN 20. I brushed the top cover a little with a brush and cleaned its center. Where should I start when building a workshop power supply? He wants 12V, 9V, 5V and 3.3V. Please help.
    Thank you.
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  • Helpful post
    #2 16773429
    Pedros050
    Level 43  
    Posts: 17906
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    Hello. For example, see here. Link
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  • #3 16773574
    mateusz2015_5102
    Pupil
    Posts: 542
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    PITERRR wrote:
    Hello. For example, see here. Link

    The link you provided does not work.
  • #4 16773583
    JacekCz
    Level 42  
    Posts: 8670
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    You can turn on.

    It is feasible or not possible to obtain other voltages according to the used inverter chips.
    The chip that is known on the Internet (I will not give the symbol right away) is usually not used anymore, and in my real power supplies there is a chip about which (almost) nothing exists.

    On the other hand, they are not mentioned in older protection materials, e.g. on mine I did not manage to get the popular voltage of 13.6V (or get close to it)
  • Helpful post
    #5 16773594
    Pedros050
    Level 43  
    Posts: 17906
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    Rate: 3901
    @ mateusz2015_5102 How about this. Link
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  • #6 16774128
    mateusz2015_5102
    Pupil
    Posts: 542
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    Rate: 81
    PITERRR wrote:
    @ mateusz2015_5102 How about this. Link

    I read this article early on majsterkowo.pl but thanks for the link.
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    #7 16774547
    monti18
    Level 9  
    Posts: 75
    Help: 3
    Rate: 5
    My experience shows that you should start with checking all power supply lines to see if they give the correct voltage. To do this, short-circuit a jumper and use the green wire to ground. If all the voltages are correct and there are no visible signs of damage (e.g. spilled capacitors), go to work. How did I do it:
    1) Checking the condition of the power supply.
    2) Take it out of the housing.
    3) Preparation of appropriate banana sockets in my case 3.3 5 and 12 V and two outputs for ground. It is also worth installing a USB connector.
    4) Installing LED indicating power and on-of switch. The housing is ready.
    5) Preparation of wires. I connected 3 wires to each voltage and soldered an appropriate equalizer. In order for everything to look aesthetically, the individual lines are protected along the entire length with a heat shrink tubing.
    6) One red one for the LED indicating the operation of the power supply. The previously mentioned green and black for the ON-OF switch.
    7) Lubricating the fan. It is also a good idea to mount a speed controller that significantly mutes the work of the power supply.
    8) connecting the appropriate lines to the banana sockets.
    9) There are many theories about loading the 5V line. I did not do it and I never ran out of electricity. But if you choose to do so, remember to thoroughly cool the resistors.
    10) Reassembling the casing and re-testing whether everything works as intended.
    11) Constructing the necessary connection cables for various types of systems.

    Final conclusions. The operation is not difficult, but requires a little patience.
    ATTENTION!!!! We do not work at a voltage of 60V alternating current under normal conditions it can kill.
    Build, have fun, remember about safety.
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  • #8 16774864
    mateusz2015_5102
    Pupil
    Posts: 542
    Help: 1
    Rate: 81
    monti18 wrote:
    My experience shows that you should start with checking all power supply lines to see if they give the correct voltage. To do this, short-circuit a jumper and use the green wire to ground. If all the voltages are correct and there are no visible signs of damage (e.g. spilled capacitors), go to work. How did I do it:
    1) Checking the condition of the power supply.
    2) Take it out of the housing.
    3) Preparation of appropriate banana sockets in my case 3.3 5 and 12 V and two outputs for ground. It is also worth installing a USB connector.
    4) Installing LED indicating power and on-of switch. The housing is ready.
    5) Preparation of wires. I connected 3 wires to each voltage and soldered an appropriate equalizer. In order for everything to look aesthetically, the individual lines are protected along the entire length with a heat shrink tubing.
    6) One red one for the LED indicating the operation of the power supply. The previously mentioned green and black for the ON-OF switch.
    7) Lubricating the fan. It is also a good idea to mount a speed controller that significantly mutes the work of the power supply.
    8) connecting the appropriate lines to the banana sockets.
    9) There are many theories about loading the 5V line. I did not do it and I never ran out of electricity. But if you choose to do so, remember to thoroughly cool the resistors.
    10) Reassembling the casing and re-testing whether everything works as intended.
    11) Constructing the necessary connection cables for various types of systems.

    Final conclusions. The operation is not difficult, but requires a little patience.
    ATTENTION!!!! We do not work at a voltage of 60V alternating current under normal conditions it can kill.
    Build, have fun, remember about safety.

    And how to make the power supply give 9V?
  • #9 16775067
    monti18
    Level 9  
    Posts: 75
    Help: 3
    Rate: 5
    Hmm, you can make an output adjustable on the LM 350. It's not that hard. As in the diagram. Or also a constant 9V output on this chip. Converting Old Computer ATX Power Supply into 12V, 9V, 5V, 3.3V Workshop Supply
  • #10 16775224
    Anonymous
    Anonymous  
  • #11 16787554
    zbychmg
    Level 31  
    Posts: 1169
    Help: 182
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    If the power supply works and you checked the capacitors
    at the 200V input, probably 470-680uF, the capacity should not be less than 30%,
    power supplies work even with a loss of 80%
    At the output 1000-3300uF 12V 2200-4700uF 5V and similarly at 3.3V
    here likewise not less than 30%
    Check what the power supply control IC is, you can find its applications and read how it works, or find a diagram on this basis, and then the conversion is much easier.

    here you have a dozen example power supply diagrams

    http://danyk.cz/s_atx_en.html

    You can soie adjust the output voltage and get 9V by lowering 12V
    or increasing the voltage of 5V. One should remember about the control circuit of output voltages,
    which turns off the power supply when the output voltages differ from the nominal by more than 10-20%

    Therefore, sometimes with a significant load of one voltage, the voltage increases on the others and the power supply is turned off. Therefore, it is loaded with a 5V resistor so that it can be loaded with a higher current of 12V
  • #12 16795352
    mateusz2015_5102
    Pupil
    Posts: 542
    Help: 1
    Rate: 81
    I found a nice 20 minute video about this power supply. Even without a load, it works. https://youtu.be/f6FhRkhgLcM

Topic summary

✨ The discussion revolves around converting an old ATX computer power supply into a versatile workshop power supply capable of outputting 12V, 9V, 5V, and 3.3V. Initial steps include checking the power supply's condition and verifying output voltages using a jumper to ground the green wire. Users suggest installing banana sockets for different voltages, a USB connector, an LED indicator, and an on/off switch. For achieving 9V output, options include using an LM350 voltage regulator for adjustable output or modifying existing outputs. Safety concerns are raised regarding high voltage areas within the power supply, and users recommend checking capacitor values and the power supply control IC for successful modifications.
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FAQ

TL;DR: Convert an ATX PSU by shorting PS_ON (green) to ground, verifying rails, then adding banana jacks; note many units shut down if outputs drift ~10–20%. “Adjust the output voltage and get 9V.” [Elektroda, zbychmg, post #16787554]

Why it matters: This FAQ helps beginners turn spare PC supplies into safe, low-cost 12V/9V/5V/3.3V bench power.

Quick Facts

How do I safely power on an ATX supply on the bench?

Bridge the green PS_ON wire to any black ground wire to start the unit. Verify 3.3 V, 5 V, and 12 V with a meter before modifications. Build outputs only after this baseline test. Use proper insulation and strain relief on leads. [Elektroda, monti18, post #16774547]

Do I need a dummy load on the 5 V rail?

Many builders skip it and the supply still works for light-to-moderate use. If you add a load resistor, heat-sink it well to avoid overheating. Measure temperatures under sustained load. Keep wiring short to reduce voltage drop. [Elektroda, monti18, post #16774547]

How can I get a stable 9 V output from an ATX PSU?

Use an LM350 adjustable regulator module. Feed it from 12 V, set the trimmer for 9.0 V, and add adequate heat sinking. You can also configure it for a fixed 9 V output with the proper resistor network. [Elektroda, monti18, post #16775067]

Is it possible to adjust ATX rails to reach 9 V directly?

You can tweak the feedback network so the controller raises or lowers a rail. That can yield 9 V by slightly lowering 12 V or raising 5 V, but protection may trip. “You can adjust the output voltage and get 9V.” [Elektroda, zbychmg, post #16787554]

What’s the quick 3-step process to build the front panel?

  1. Drill and mount banana jacks for 3.3 V, 5 V, 12 V, plus two grounds.
  2. Add a power LED and main on–off switch.
  3. Route three wires per rail to each jack, sleeve with heat-shrink, and reassemble. [Elektroda, monti18, post #16774547]

How do I check electrolytic capacitors before using the PSU?

Inspect visually for bulging or leaks, then measure capacitance/ESR if possible. Input caps are around 470–680 µF; outputs often 1000–4700 µF. Replace parts whose measured capacity has fallen below ~30% of rated value. [Elektroda, zbychmg, post #16787554]

What safety hazards should I know about inside ATX supplies?

Primary sections exceed 230 V and can be lethal. Do not touch the primary while powered. Discharge capacitors before work. As one expert warns, “there are places with life-threatening voltage higher than 230V.” [Elektroda, 65469, post #16775224]

Why does my PSU shut off when I load only one rail heavily?

Supervisory circuits monitor rail accuracy. If one rail sags or rises, others can drift; a deviation of ~10–20% triggers shutdown. Add a modest 5 V load or balance loads to keep rails within limits. [Elektroda, zbychmg, post #16787554]

Can I add a USB 5 V port to the front panel?

Yes. Bring a 5 V line to a panel USB-A socket and include an inline fuse for protection. Label polarity. Verify 5.0 V under load with a meter before plugging devices. Keep wiring short and tidy. [Elektroda, monti18, post #16774547]

How can I make the fan quieter?

Lubricate the fan and, if desired, add a speed controller on the fan’s supply. Confirm airflow and temperatures after slowing the fan to prevent thermal issues during high loads. [Elektroda, monti18, post #16774547]

Why can’t I reach 13.6 V on my ATX unit?

Controller ICs vary. Some modern designs limit adjustment range or use undocumented chips. You may fail to reach 13.6 V without deep control-loop changes, which risks tripping protections. [Elektroda, JacekCz, post #16773583]

What is LM350?

LM350 is a 3 A adjustable linear regulator. It sets output via a resistor divider and needs heat sinking for higher drops. Use it to derive 9 V or an adjustable output from 12 V. [Elektroda, monti18, post #16775067]

Can I convert an ATX PSU to a 0–30 V adjustable bench supply?

It’s possible but risky for beginners due to lethal primary voltages and design differences between units. Prototypes may not match your PSU, requiring custom changes and troubleshooting. Prioritize safety and experience first. [Elektroda, 65469, post #16775224]

What is PS_ON and how do I use it?

PS_ON is the green wire that enables the ATX supply when pulled to ground. Tie it to any black ground wire through a switch for convenient on/off control. [Elektroda, monti18, post #16774547]

My ATX works with no load—should I still add one?

Some supplies run fine unloaded, as confirmed by users. Still, test stability under your typical loads and consider a small 5 V load if you see regulation or ripple issues. [Elektroda, mateusz2015_5102, post #16795352]

Any beginner-friendly starting checklist?

1) Verify rails by shorting PS_ON to ground and measuring outputs. 2) Inspect/measure capacitors; replace weak ones. 3) Add jacks, LED, switch; retest under load and watch temperatures. [Elektroda, monti18, post #16774547]
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