Miskatonic Institute of Technology

Miskatonic Institute of Technology
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1.1.10

PC power supply modification. ATX PSU hack with regulated variable voltage and LCD voltmeter.

I needed a PSU (Power Supply Unit) for my electronics projects, so I modified an old ATX PSU (computers' power supply unit). It outputs a total of 400W and has a regulated variable voltage output of 1.25V to ~21.75V (DC).
Click here to see the full slideshow
I used a LM317 voltage regulator, some switches and the original PCB of the PSU. The project turned out to be extremely easy to build, minimum soldering, finished it in 1 day!

The original PSU was  a Τ & P MEIJI, Model: MEIJI 400-ATX (400W) and it now outputs:
  •  +3.3V, 28A
  • +5V, 40A
  • +12V, 18A
  • -5V, 0.3A
  • -12V, 0.8A
  • Vvariable: 1.25V - 10.75V or stand-alone 1.25V - 21.75V
Ελληνική δημοσίευση: http://www.hlektronika.gr/forum/showthread.php?p=337521#post337521

Read more for more photos and schematics...

Click on thumbnails to see larger photos:









The schematic i used: (right click/"View image" to see full size)


The LCD voltmeter operates on 5V, so i had to use a 2nd LM317 to get 5V from the 12V line. The small veroboard was the only thing that needed to be soldered, and it holds the 2 LM317s.


The box used was this one.

22 comments:

  1. Anonymous15/2/10 16:42

    a standard PSU already has 5V lines, so why the need for the second LM317?

    ReplyDelete
  2. Because if i power the LCD screen from the same 12V line that i power the variable voltage. WHEN the variable voltage output is switched ON, the LCD is switched ON too.
    If i had used one of the other 5V-lines, i would have had the LCD screen ALWAYS ON, even when i did not use the variable voltage output.

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  3. Anonymous16/2/10 12:09

    But couldn't you install a simple switch on that 5V line, just before the LCD? It could be a double switch so it would switch both the variable voltage output and the 5V LCD on at the same time.

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  4. Its true, i could have! But i wanted to use the red LED switch i had used on the other top corner, so i used a LM317! :)

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  5. Anonymous17/2/10 04:36

    OK, just making sure :) I really like this project, KISS in the making ;)

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  6. Total cost of 39€ (with 18€ for the 2 red LED push-switches). If you have the PSU, you can do it for as low as 20 Euros..

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  7. Anonymous6/2/11 06:23

    where did you get that case its custom right

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  8. Nope, the case is not custom. It was a generic case which I modified to fit my needs. The generic case was from this family: http://www.teko.it/it/prodotti/famiglia/AL/serie/15 . I is made of aluminum and cast iron. The aluminum was very easy to drill and cast iron gives great structural strength..

    ReplyDelete
  9. To be perfectly honest, i used this box: http://www.normabox.gr/website/product_info.php?cust_id=&template_id=&lang=gr&cPath=8&products_id=36. A greek copy of the Italian one..

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  10. Anonymous6/2/11 19:35

    Thanks but i live in the U.S. have any idea where to get a similar box in the U.S.

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  11. Anonymous6/2/11 19:55

    i was thinking about using BNC instead of banana jacks and binding posts what do you think of that

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  12. It's much better to use BNC than to use banana jacks in terms of noise. But you have to think that you are using a switching power supply, which means that you will always have some ripple... It's up to you to decide. Personally, I went with bananas :)

    As for the BOX, just go to your local electronics project shop and find something in which your project can fit in. Mine was 200mm X 160mm X 100mm.. Measure your PSU's PCB first..

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  13. Anonymous7/2/11 01:52

    thanks i'll do that what are the two switches on the top right is one for the voltmeters power and the other for the variable power main just guessing

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  14. Anonymous7/2/11 02:53

    what is your variable voltage max amps output because i think this would work its 3 amps max http://www.dimensionengineering.com/DE-SWADJ3.htm
    there is also a smaller 1 amp version what do you recomend

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  15. Anonymous7/2/11 06:04

    what is your voltmeters scale .1 or .2
    thanks

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  16. Voltmeter scale: 0.1V

    Max Vvariable current: 1.5A (due to LM317)

    What do you need the step-down converter for? You want to use it instead of a LM317? If so, yes, it's more powerful and you may consider it.

    The switches: top left is POWER, top center is FAN ON/OFF and top right is VARIABLE VOLTAGE ON/OFF.

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  17. Anonymous7/2/11 21:21

    ok so what is the fourth switch for then and a step down convertor would work for me since 12 vdc is the highest that i would need for stuff it also would be less wiring

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  18. i also want to know what the fourth switch is or is it an indicator light

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  19. There is an indicator light and a switch. The switch switches the variable voltage from 1.25V to 10.75V to the stand-alone 1.25V - 21.75V. This is because the LM317 is connected to the GND and 12V line (giving maximum 10.75V) and the -12V and 12V line (giving an maximum of 21.75V BUT THE GND IS THE -12V NOW, which means you have to connect every ground of your circuit to the GND of the VARIABLE SUPPLY or -12V!! That is why it is stand-alone..). The yellow LED light turns on when the "stand-alone" function is activated to warn you.

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  20. Anonymous28/9/12 22:35

    To have available the -5V pin connector means that you had an old atx psu, cause the latest ones doesn't have it. Keep up.

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  21. I hardly understand ... the process, if you pleas send me the full schmatic for this ..
    Olso the volt cntroler the yellow wheel .. why i have to make other outputs if i setup the voltage regulator ?my inglish is bad i know . Its not my native language

    ReplyDelete
  22. I hardly understand ... the process, if you pleas send me the full schmatic for this ..
    Olso the volt cntroler the yellow wheel .. why i have to make other outputs if i setup the voltage regulator ?my inglish is bad i know . Its not my native language

    ReplyDelete