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A Maker's Guide to ATX Power Supplies by Lynxsys on November 29, 2012

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A Maker's Guide to ATX Power Supplies by Lynxsys on November 29, 2012 Food Living Outside Play Technology Workshop A Maker's Guide to ATX Power Supplies by LynxSys on November 29, 2012 Table of Contents A Maker's Guide to ATX Power Supplies . 1 Intro: A Maker's Guide to ATX Power Supplies . 2 Step 1: Background Information & Suggestions . 2 Step 2: Wire Colors & Functions in the PSU . 3 Step 3: The ATX Connector . 4 Step 4: Other Connectors . 5 Step 5: Tips, Suggestions, & Anomalies . 7 Step 6: Sources & Further Reading . 8 Related Instructables . 8 Advertisements . 9 http://www.instructables.com/id/A-Makers-Guide-to-ATX-Power-Supplies/ Author:LynxSys I'll tinker with anything, but I'm often to be found repairing, improving, and restoring things. I'm always looking to develop new skills (anyone near Boston want to teach me welding?), but am currently best at woodwork, general construction, wiring, fiberglass, and general fixing stuff. Intro: A Maker's Guide to ATX Power Supplies There are tons of Instructables on how to make a lab bench power supply out of a discarded ATX (computer) power supply unit (PSU). This is not one of them. My observation is that most makers, hackers, and mad scientists don't follow instructions very well. We like to improve on what already exists and fit the product to our needs. My objective here is to give you all the information that you might need in order to hack an ATX PSU to meet your needs. This isn't so much an Instructable as it is an Informable. This is meant as a reference guide and so I've tried to avoid extensive explanations. If you want a greater depth of information, see Step 6. Table of Contents "Introduction" ~ <-- You are here. "Step 1" ~ Some background information and suggestions for projects "Step 2" ~ A list of standard wire-colors and functions in an ATX PSU "Step 3" ~ A chart of wire-associations on ATX connectors "Step 4" ~ A chart of wire-associations on other connectors (molex, floppy, PCI-e power, etc.) "Step 5" ~ Tips, tricks, warnings, anomalies, and conspiracy theories "Step 6" ~ Sources & further reading Requisite Disclaimer: Electricity is scary (where fear is equal to voltage x amperage / [stupidity + EtOH]). If you're not afraid of electricity, then there's a good chance that you don't understand it and should do more research before messing with it. Everything in this Instructable is correct to the best of my knowledge, but please use your own good judgement. I am not a licensed electrician, professor of physics, PhD engineer, or any other remotely-credible title. You should clearly not trust anything that I have written. By using this information, you are agreeing that I am not responsible for any of your actions or their results, even if I totally am. Image Notes 1. Negative voltage terminals. Kind of a strange concept, but necessary to... umm... impress your friends. 2. Don't forget to check the label for max outputs. PSUs that are old enough to have -5V rails will probably be 150-350 watts. 3. This enclosure is open because I wanted to know what smelled like burning. (Answer: the fuse.) Step 1: Background Information & Suggestions So, you want to hack an ATX PSU, but you don't really know where to start? There are basically two common hacks. Either, A. Open the PSU; cut the connectors off the wires; drill holes in the existing housing; insert binding posts, switches, etc.; and attach the wires appropriately (See the photos for my version of this method). OR B. Build a box with the requisite binding posts, switches, LEDs, etc.; wire them to ATX and Molex connectors; and plug your creation in to an unmodified PSU. Method B is more work, but allows you to easily swap out the PSU when you burn it out doing something dumb. (Did you see that pretty power supply box in the photo? it's now a paperweight. With binding posts.) It also gives you more room to add functionality. And you get to build a box! Birdseye maple and dovetails, anyone? One piece of vocabulary before we continue: A "rail" generally refers to a PSU's output of a particular voltage. In the context of ATX PSUs though, "rail" refers to each output that has a separate group of current-regulating circuits. This nuance is why it makes sense to talk about having multiple +12V rails in some PSUs. http://www.instructables.com/id/A-Makers-Guide-to-ATX-Power-Supplies/ Image Notes 1. Obvious visual indicators are good for your health. 2. You can see my 10 Ohm 10 Watt "sandbar" resistor, wired between a 5V (red) wire and ground (black). Note that it is tied to an aluminum heatsink on the left that happened to be there (although the positioning against the big bad capacitors Image Notes to the right may be less than ideal). 1. Negative voltage terminals are clearly labeled. Mistakes in this department 3. I got your 5V riiiiiight here. can cook a PSU (or whatever you're powering) in short order. 4. There's no such thing as too many ground wires. 2. A reminder to pay attention to your max outputs, not just per rail, but overall. 5. 12V 6. 3.3V 7. -12V 8. -5V (This PSU is old enough to have a -5V rail). 9. Kind of a mess of wires, and probably not so excellent in the ventilation department. Step 2: Wire Colors & Functions in the PSU Upon opening a PSU, you will find that it is a jubilee of wires in the worst way possible. Thankfully, the colors are (typically) standardized as shown in the chart. Your PSU may not have all of the wires on the chart, depending on the age and output of your unit. See the notes. Whatever nefarious plans you have for these wires, realize that each pin in an ATX connector is rated to a max of 6 amps. It might be a prudent assumption that other portions of the circuit are similarly rated. So, if you plan to use all 20+ amps that the +5V rail can throw, you should probably connect as many of the red wires as practical to whatever you're powering. That might mean sticking a bundle of wires on your binding post (if you're using option A from Step 1), or it might mean taking connections from the ATX connector and a few molex connectors (if you're using option B). Either way, the more wires, the better. You should also know that a PSU requires a minimum load in order to provide consistent voltage. Most people suggest taking one of the +5V (red) wires and wiring it to ground (black) through a 5 or 10 ohm, 10 watt resistor. For some PSUs, the fan is just enough load to get them to power up without the resistor, or they may have a resistor built in. Given that not having a large enough load will detract from a unit's reliability in unpredictable ways, I would strongly suggest using an additional resistor (or use it to power a tiny USB hot-plate to keep your coffee within spilling-distance of your sensitive electronics. That's fine too). If you want to waste the minimum amount of power or if your unit behaves erratically, you can usually look up your PSU's minimum loads for each rail on its spec sheet. From there, you can probably figure out which rails need resistors, and how big those resistors need to be. Image Notes 1. And sometimes, just to mess with you, this second yellow has no black stripe. 2. You found Waldo! (10 points to whomever gets that obscure Maxis game reference.) http://www.instructables.com/id/A-Makers-Guide-to-ATX-Power-Supplies/ Step 3: The ATX Connector The two common ATX connectors are 20 and 24 pins. There are also 20 pin connectors with adjunct 4 pin connectors that can be mated together to function as a 24 pin connector. 24 pins is the newer standard. Chances are that if you have a PSU with a 24 pin connector you will not have a -5V rail. You can also buy adapters to use a PSU with 20 pins on a 24 pin motherboard connector or vice-versa. These adapters are also a good source of a pre-wired connector if you don't want to scavenge one off of a motherboard and then spend an eternity soldering wires to each pin. (Mmmmm, de-soldering and re-soldering 20+ connections. Have you gotten your California-recommended dose of lead today?) If you are planning on connecting to your PSU through the connectors (i.e. "method B"), you will need to use more than just the ATX connector to safely use the PSU's full power. As mentioned in "step 2", a conservative estimate would be to use at least one supply wire per 6 amps carried (based on wire-gauge-to-amperage tables, as well as the max rated amperage of a molex motherboard connector). Image Credit: Please note that the supplied graphical chart is not my work. It is reproduced here for informational purposes only from http://www.smpspowersupply.com/connectors-pinouts.html This site is also linked to in References & Further Reading (step 6). Image Notes 1. The end of a 20-plus-4 pin ATX connector. Image Notes 2. Notice that there is no white (-5V) contact. 1. A 20 pin (older style) ATX connector. Image Notes Image Notes 1. The underside of a 20 pin ATX connector.
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