Instructables

Use a computer Power Supply for desktop electronic projects

Picture of Use a computer Power Supply for desktop electronic projects
IMG_0649.JPG
IMG_0509.JPG
IMG_0510.JPG
IMG_0511.JPG
Building electronics with Arduinos, motors and other gadgets, I came up against a common problem: powering the circuits with a consistent voltage and adequate current. Like many people, I realized that a computer power supply can be a perfect solution, albeit with some modifications. It provides regulated 3.3V, 5V and 12V power at a current level high enough to satisfy almost any project requirement.

Most of the examples I found online did not fit my requirements, so I decided to modify my own. The requirements I set out were:

- ability to switch 24 pin ATX connector for other projects
- variety of connectors
- fused
- ample power

Bill of Materials
1x 300W power supply with a rear fan - $30 - Newegg
1x Cytron ATX Power supply breakout board - $9 - Robotshop
1x Power distribution block - $2 - Adafruit
5x 2.1mm DC barrel jack connectors - $5 - Various
5x 5mmx20mm fuse holders - $5 - Various
4x M3 brass standoffs
5x 5mmx20mm fuses (assorted of 5A, 3A, 1A) - $10 - Various
5x 5mm screw terminal pairs - $2 - Various

Tools
Assorted drill bits
Step drill with 3/16", 3/8" and 1/2" sizes
Power drill
Assorted screwdrivers
Soldering iron
solder
wire stripper
diagonal cutters

The core component that makes this project easy is the ATX breakout board. It takes a 24 pin ATX power cable and splits the components out to their different voltages, while also providing indicator lights, an ON/OFF switch, and room for screw terminals.

Be sure to properly research the power supply: you'll need to select one with a full 24 pin ATX power cable, rear fan instead of the top and enough connectors for your project. If you decide to copy my barrel jack configuration, you'll be using 1 4 pin Molex and 1 SATA cable.

Please remember that a computer PSU provides a dangerous amount of power and has a warranty sticker on it. Since this is a hacking contest and website, I'm sure this won't deter many people. Just be smart.
 
Remove these adsRemove these ads by Signing Up
Philiprocks10 months ago
Hi, I found this instructable very useful, congratulations. I have a question what's the name of the 3d cad software?
rimar20001 year ago
Useful info.

Do not need to do a short between two pins in a connector?
Some of the other instructables, which do a full conversion, they also seem to want to short PG (Power Good) and the +5V-Stby (the constant +5 used for momentary switch on/off control).. Sometimes, yes, Sometimes, see 2nd reply to wesg... caused a smoke-show. the PG signal is supposed to be a signal back to the switching chip in the supply, from the computer, that either everything is A-O-K, and if not, shut-down A-S-A-P!
wesg (author)  rimar20001 year ago
The ATX breakout board has a switch that does the switching for you. It shorts between the green cable and ground.
Gelfling61 year ago
I've run into a few of the older ATX supplies, which required a load across the +5V (Not stby) to keep them going, does this breakout board add any negligible load for this purpose? Or, is it relying on the supply already having the load resistor built in?
wesg (author)  Gelfling61 year ago
That's a good point, and one I didn't mention. So far in my testing I've found that to be the case; the PSU shut off after a few minutes without anything connected to it. The breakout board doesn't add any load, as far as I can tell, so I think I'm going to try adding a small power resistor to keep the system going.
Gelfling6 wesg1 year ago
One of the converted supplies I have, (a 350W ANTEC), had a 33-Ohm, 5W metal film resistor hard-soldered to the board between the +5V & GND.. Some of the instructables for converted supplies, suggest a 10-ohm, 10W, which honest truth, seems a wee low for resistance.. (unless they want it warm?) when I converted a 200W Dell supply (fan on top), I clamped a 33-Ohm, 5W sandblock to the opening on the side, and sacrificed 1 +5 wire and one GND wire to it. Though, mine, I completely scrapped the ATX connector, also because I've heard some of the Dell supplies, possibly even some of the Compaq supplies before they standardized under HP, have an incorrect wiring scheme (swapping a fan signal with -5V, PG & Pwr-On, etc.. I smoked one supply that way..(Nice loud POP, followed by a wisp out through the fan.))
Gelfling61 year ago
In the first photo (on this step), note the two canisters at the bottom-left, as "The Micro Killers!" which people need to be wary of.. these are the capacitors which hold the converted AC to DC before it is fed into the switching circuitry. Specifically, these range from 200-400uF, but with a 200-250V working voltage. equate these to a miniature version of a defibrillator paramedics & doctors use to stop/restart the heart, with the exact same potential! Most supplies have a bleeder resistor (I see one, to the left, above the "ZD" print, not sure if that one to the upper-right of the right one is.. looks too small.) across both, which should bleed-down the high voltage within about a minute or so.. but, if those resistors are corrupted (seeing these as metal film type resistors, they can still burn through like fuse), those capacitors can knock you on your keester, or worse!