I'll put this over here, with the rest of the fire.
November 11, 2012 4:10 PM   Subscribe

I replaced a PSU and have received the original, cheap so-called 500W power supply. It has a dead fan. Works great except for the fan; cleaning didn't revive it. I don't own a desktop computer. Makers, hackers, what fun can I have with this PSU? What should I read to bring me up to speed?

What can I do with a fanless PSU? I have almost no working knowledge of electronics and I'm afraid to open up the PSU itself (out of fear of shocking myself mainly due to said uninformed state) -- but I could overcome this with sound instructions and safety precautions. And, I like projects and learning things.

I'm handy with some power tools, and I will have access to saws, wire cutters, vices, other helpful things of the household grade. I will also have access to a working dot matrix printer, an inkless inkjet printer, PS/2 and USB mice and keyboards, an HDD that is laughably tiny in capacity, and other, non-computer things including electronic learning toys for kids. Can I (eventually) build a toy robot safe for a child? Or something that is just functionally awesome? (Even something basic would be novel to me.) I don't remember if I have access to a soldering iron but I probably could. I'm happy to get inexpensive bits and connectors for this, though I don't know enough to establish a budget.

I'm a PC/Android/novice Linux person with rudimentary programming background, if that helps.

Instructions or links to projects would be extremely helpful. I'm inclined to follow steps until I feel comfortable enough to start my own projects. I have found articles like this but I don't know what the next logical steps would be. Consider me enthusiastic but clueless. Recommendations for reading material to get some grounding in this would be much appreciated, too.

Dear hivemind, please help me go on an adventure with my little PSU!
posted by mayurasana to Technology (8 answers total) 3 users marked this as a favorite
PSUs have capacitors (especially so-called "X caps") that can carry a charge for a long time after being unplugged, and in some cases have even killed folks hacking away inside of one. Conventional wisdom says to leave them alone.
posted by ellF at 4:24 PM on November 11, 2012 [2 favorites]

As someone who would have loved to have you around as a kid - Unfortunately, not really.

For learning about robotics, Lego has a ton of really great gear with a programmable controller (Google "NXT") that you can buy a pretty solid base kit for under $300.

As for the hardware you mention - Only the PSU will kill you (printers can have some pretty big caps in them as well, but not usually actual killers). HDDs have a ton of cool shiny things inside, really neat to see how they work, but aside from getting a pair of strong magnets out of them, not much you can scavenge.

If you really want to take things with large capacitors apart, though, I can suggest a "safe" way to do it (note that the following will not suffice for CRTs, which have their own special rules-of-not-dying). First, let them sit unplugged for at least a week, most hardware has an internal slow drain specifically to avoid killing people who ignore the "danger, do not open, you might die" stickers. Second, work with one hand tied behind your back (literally, if you can't resist using two hands). Third, once you carefully remove the PCB from the PSU, set it down on a steel wool pad repeatedly (dab it it, more or less). If you get sparks or fire, come back in another week.

Finally, you'll only really get two useful things out of a PSU - heat-sinks and the fan (and if you collect copper scraps, you can get a few messy ounces out of the transformers) - And you mentioned the fan has already died.

Oh, and wear safety glasses. HDDs and printers contain a lot of small sharp bits attached to springs under tension, which when you remove a seemingly innocuous part will suddenly find themselves able to pounce toward your eyeballs.
posted by pla at 4:51 PM on November 11, 2012

Id replace the fan or install a new one and make a benchtop 12v power supply. They're handy for a lot of things.
posted by sanka at 4:53 PM on November 11, 2012 [1 favorite]

Sanka's got it. The fan in your PSU is almost guaranteed to be a standard size; it even likely plugs into the board with a connector. That fan is like $5, tops $10. Replace it and you have a halfway decent bench power supply that can pump out good amounts of decently regulated 12vdc, 5.5vdc and maybe 3.3vdc.

You may want to check out the power supply repair section at the Silicon Sam technology resource.
posted by werkzeuger at 5:18 PM on November 11, 2012

I bought one of these to turn an unused computer power supply into a desktop power supply. It's so much easier and safer than opening up the case and installing plugs into the power supply case itself. By the time you include the cost of the parts you'd have to buy if you were doing it yourself anyway, it only costs literally a few dollars.

I'm not even sure you'd need to replace the fan if you are using it for table top electronics. I'm pretty sure my fan starts up when I first turn it on, then turns off straight away and never comes back on. I'm typically only using it for up to ~150mA @ 5V though, so if you wanted to do anything that required more power (i.e. anything that moves), the fan might be required.
posted by trialex at 5:53 PM on November 11, 2012 [1 favorite]

rather than take apart the power supply, why not replace the fan and re-use it for another system? a good quality 500W power supply is fine these days for any desktop PC that's not going to be running a super high powered video card. it is almost certainly a standard size of 80x80x25mm or 120x120x25mm fan which you can replace in five minutes.
posted by thewalrus at 9:54 PM on November 11, 2012

Output voltages on these power supplies are usually 12V and 5V, regulated. Caps across these aren't going to see more than 12V and 5V, neither of which is going to kill you unless you take extraordinary preparation to make them kill you. I think the risk is overstated, generally.

The unregulated internal voltages in these units are higher, but if the supply is a linear supply (i.e., not a switcher) there is a premium in getting the unregulated voltages fairly close to the regulated output voltages, and these caps would not be charged too high relative to the 12 and 5 volt outputs, maybe 16 and 8 V or thereabouts.

In switchers, the unregulated voltages would be higher, and it's hard to generalize, but again, I wouldn't expect to see extremely high input (unregulated) voltages AND high capacitance. These are cost sensitive units and among the most costly components are high voltage, high capacitance capacitors. Hence, I suspect they aim at lower voltages.

The danger is in transcardiac shock. The most common way to get one of those is hand to hand. Pla's suggestion (above) is conventional wisdom for safely probing energized (or unknown) circuits. The biggest danger, in my experience is the reaction to a shock.

There's enough power in these things to do a lot of stuff, but in truth, I find 'wall warts' to be much more useful. With a range of output voltages and currents, they are good power sources for a lot of projects, encapsulate the dangerous parts, and are usually well labeled as to voltage, current and type. I hardly ever throw one of them away, but at the same time, never keep a desktop power supply. I find them too big, loud, ugly, and with unusable connectors. Were I you, I'd take the thing to a computer recycler and trade for some wall warts. The best are the ones from Thinkpads. 16-18V and several amps, they have disconnectable power cords and large enough wire on the outputs for amateurs to manipulate. You can adjust the output voltages using simple linear regulators as needed, and these are also available in adjustable form (LM317's, for instance.)

As a learning experience, using one to teach yourself how switching power supplies work, for instance, they are good. Not good enough to keep, IMO. Unless you are a power supply designer (? probably not? ) this would rate low on a scale that included anything else. Linears are approachable by the non-cognescenti, but switchers? It's unlikely you'll find yourself in need of that info unless you already are.
posted by FauxScot at 3:17 AM on November 12, 2012

Response by poster: Thanks for the great answers everyone! There is a lot of info here, and though it is difficult to pick one best answer, I appreciate the detail -- I have a lot to learn. I'll keep the PSU as a back-up in case another one fully craps out for the PC desktop users I know. It will be handy while they wait to get a new PSU in shop or via post. I'll also look into a benchtop power supply and related projects.
posted by mayurasana at 11:10 AM on November 18, 2012

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