Lab Power Supply

Here is a great power supply project. No, it isn’t just some simple case mod with binding posts. A lot of thought was put into this, plus a lot of disclaimers. I wouldn’t be too scared though, Andy Batts has got a lot of information covering most everything you need to know: Dell’s weird wiring, expected current, using a sandbar load, and not poking around inside while the thing is plugged in. I’m going to do this to a couple power supplys because it is sure to make future projects a lot easier.

[thanks momotarosan]


  1. machiavel says:

    Old school, I saw it on many other websites but without the labels on it, btw they are awesome ;)
    keep up the good work!!

  2. Jeremy p says:

    it’s not really a lab power supply until he installs a built in meter that’s always -5 volts.

  3. xenodious says:

    “…and not poking around inside while the thing is plugged in.”

    Luckily, I am still alive to attest to this.

  4. dephyler says:

    discharging capacitors don’t feel so chippery either.

    I always preferred to just stick wires into the molex connectors, but this is definately an improvement. I like the idea of hackaday posting enough hacks for a nicely hacked hacker lab.

  5. dexim says:

    This is great. I have some old AT power supplies just sitting around. This would be a great use for them. Of course the mod will be a little differant with an AT power supply, but it gets me in the right direction.

  6. david says:

    Add an LM317

    a resistor and a variable resistor and you can make a variable power supply*.

    *make sure you watch the power rating of the resistors, and heat sink the LM317 if you use any significant current.

  7. nfn_nln says:

    I’m already using an old PS for powering up stuff :) but this project is alot cleaner. Very nice.

    This has inspired me to use a variable VRM and an old DMM to make a tunable PS. If anyone has done this please post a URL!

  8. BoomBoX says:


    Altough the voltages are low, the power these supplies can deliver is enormous. A good 350 watt supply can output 5V with 10’s of amps.
    So what? You think…

    Imagine you are working on a breadboarded circuit containing a lot of logic chips. One 74LS00 has been miswired VCC to ground, and ground to VCC.
    When you reverse logic chips they become low ohmic resistors with a voltage drop (2 diode drops).
    Result, exploded chip, damaged breadboard, melted wires.
    This was a old AT 400W powersupply out of a server, it had a rating of 5V 30A. It didnt even shut off like it should do as it was just a heavy load to the powersupply.

    Fuse the connections with polyfuses set at 1amp. To prevent accident of this nature. They are cheap, and going to save you some parts someday.

  9. dpixel8 says:

    call me stupid…but what would one want to do this for? I dont understand the purpose.

  10. Jesse curtis says:

    #8 first off you can use it to save money. These can retial for $50+ and have the same functionality. But you would USE it to power any gizmos and gadgets you are working on, I use one for powering radios.

    This is not a new story, I saw it in QST, an amateur radio magazine. It was called the ‘st louis switcher’ for whatever reason.

    here is a thread that has links to a lot of articles including the one from QST. An excellent mod.

  11. Jesse says:

    _here_ is a thread….. ;)

  12. Paul says:

    Ive done this to several psu’s ive found lying on the side of the road. They work great, I use one to run my Dynamite Peak Charger(you rc people out there know what im talkin about) when I am not at the races. Ive seen tutorials like this before, but this one is much more in depth.

    Thanx HAD keep en comin 8)

  13. Mark says:

    What a great hack! I really like this idea because it provides a convenient ground connection for my anti static strap. Coincidently, I built something similar just a few weeks ago and I have a few suggestions from my experience:
    –This a great use for an old AT power supply instead of trashing it. The pinouts are a bit different but it’s easy to figure out with a voltmeter
    –The old AT power supplies typically have built in power switches which are convenient
    –FUSE EACH SUPPLY BUS – Fried electronics smell horrible, I know from experience.
    –Desolder the power supply connector from a dead floppy drive. The pins will fit into your breadboard nicely.

  14. GSX says:

    My old one, not as neat as this one though…..

  15. Jesse says:

    …is that a bottle of soco i see in the background?

    Computers and boose….the cause of and solution to all of lifes problems.

  16. Kyle says:

    I’ve used one of these for almost two years. I made it out of an old gateway pentium pro ps. The best thing about it is that although it puts out 20 amps at 5v, it shuts off instantly if there’s a short. For the instant shutoff alone it’s invaluable.

  17. elg0nz says:

    Here is my design for a “linear” powersource i made for a class:

    It uses an +5V Regulator (7805), an -12V Regulator (7912) and a variable regulator (LM350, LM117 on the schem).
    The big capacitors 33000uF should be 3300mF.

  18. Snyper says:

    do u know how i can change my dreamcast into a computer or something. And if you do can you show me. thanks

  19. Phillip Milks says:

    Please comment on the use of an external fan – is the internal one insufficient ? It normally serves as the dummy load, anyway.

  20. stevecrozz says:

    this is for use in a lab enviornment? it says the voltage is about 5? im not sure what kind of ‘lab’ this is for, but when i buy lab grade power supplies usually the first spec i’m interested in is stability, and +,- .5v is not very good to say the least.

  21. david says:

    Not a lab “grade” power supply but rather a power supply for tinkering and projects; think hobby lab. Besides lab power supplies easily cost >$100. This is just a simple hack to get some low level dc supplies; which could easily be extended to build a stable, accurate supply by adding a linear regulator. There are plenty of uses for a cheap PS like this.
    As to the fan it seems like it the power supply did not include an internal fan in its design.

  22. andy s says:

    save money on the switch and use the one from the old case the PSU came from.

  23. bfzhou says:

    I’m trying to build an external SCSI case using an existing tower case. But without connected to tha mainboard of a PC, the power never turns on. I’m desperately looking for a tip to force the power supply to turn on. I just want it to supply the 12V to the many scsi drives.
    Is there a way to do this?

  24. MiKe says:

    I just finished building one of my own using a gateway 200 watt power supply. This tutorial guided me through pretty easily, but I did stumble at one point. It may sound stupid, but make sure that the posts you use DO NOT make electrical contact with the enclosure. I am sure glad that I had fuses on the lines. Now I just need to figure out how to make this thing look a little better. The posts are screwed into a piece of cardboard just sitting on the table.

  25. arash paydar says:

    I have an old AT PSU, am I right in presuming that I can just use the power switch mounted on the case as and not use the load resistor?

  26. cute2like says:

    Dear Arash Paydar
    Are you from Shiraz? If so please reply back to me. Thanks

  27. Lavell says:

    I’ve seen reference to this project before, but I do very few 5v projects. It would be great to get more output at 12v from one of these. I notice the average 250w PS usually supplies about 60w at +12v. Does anyone know of a way to sacrifice some of the other outputs to get greater 12v output.

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