Have you ever wanted to see what's inside a computer power supply?
Well here's your chance.

P.S. this is my first Instructable so I hope it's good enough

Caution: Don't do this at home unless you know about the risk of shocking yourself even after turning it off! If you want to take that risk, Always discharge those 1 or 2 large mains filtering capacitors by jumpering the green wire in the 20 or 24 pin ATX plug to a black wire in the same plug while the PSU is unplugged. You should hear a click. Remove the jumper and disassemble.

You might want some rubber gloves to keep your hands from getting electrified

Don't forget to rate if you like it and comment, I accept constructive criticism

Step 1: A look inside the power supply

This particular power supply has a un-switched output meaning the output always has voltage. the rectifier down the bottom of the psu uses 4 diodes to change AC to DC. On the primary side of the board, we see the X-Y caps dominate the space. They serve as the mains filters. Lower down, just to the right of the torroid, are some yellow rectangles. These are caps designed to help the power supply handle surges and inrush current. To the right of the fuse is another inductor (the white thing) used for more mains filtering. It may actually be an isolation transformer. In the middle, we see the heatsinks. attached to them are the mosfets, used to raise the frequency of the AC. This allows the transformers to be smaller, and results in less ripple to be filtered out. On the upper right is the voltage regulating parts. On the heatsinks are more Vregs. On the upper right is the secondary side, with its filter capacitors and inductor.


I have opened many power supplys, well 2, but i have never gotten shocked, i don't know why thought, lol
<p>That's because the big capacitors were discharged...</p>
i know, its called being lucky thats what...
I've got about 10-20 old ATX's lying around in a cupboard somewhere
With great number of power supplies, comes great possibilities. (with apologies to Stan Lee, LOL!)
Haha, or just being good.
either way hes should be thankful.
it's only 250 watts, (whats that purple thing?? ooooo.) *sizzzzle.
Doesn't matter what wattage.. It's the storage capacity &amp; voltage potential of the filter caps. Granted, they're only 200-400uF, but the working voltage (anywhere from 200 to 400WV. That WV is short for Working Volts!) Now, they may not be charged to the full working voltage, but they still kick you with only 110V. Now, usually, it's not the outer case of the caps, they're usually insulated, but sometimes the regulators on the first heatsink carry some of the potential in DC voltage. (the one closest to the filter caps) Hence the warning on some supplies, that the heatsink may cause shock. 2nd rule of thumb.. If you don't touch it with a volt meter first, Don't touch it with your bare fingers! (and those big high voltage test wands is a bit overkill.)
Your luck, may have to do with two 100K (brown-black-yellow) resistors across the contacts of the two mains filter capacitors. (and not touching anything while the supply is plugged in.) These are intended to bleed off the charge once you remove the AC (either unplug or if your supply has one, a 'Master&quot; on/off switch near the power input).. Usually, it's still a good rule of thumb (and keeping your thumbs &amp; other fingers) of letting the supply sit for a minute totally disconnected.
If you opened them after they've sat for a few minutes (one minute is more than enough.) that means a set of resistors, across the pins of the filter caps, are doing their job, and bleeding down the charge. That doesn't mean they can't fail. I've seen a few supplies, with 100K 1/2-watt resistors soldered to the board across both 200uF/240WV caps. they pretty much act as a slow-rate short. But.... I've seen this a few times.. I converted two supplies.. One, has 2 switches.. the one coming from the mains lines, and the one for the Pwr-On wire to GND. IF I turned off the Pwr-On switch, but left the mains switch on, the caps would still be charged. (because they're still powering the standby +5V Logic control voltage. (which gets toggled when we press the power button on a PC, or something makes the PC wake-up.) But, If I THEN turn off the mains switch, within 4 seconds, I flip the Pwr-On switch back on, there will still be trace voltage enough to power whatever is connected. (cooling fan, project, ect.) which proves, it takes time for that mains voltage to bleed off those filter caps.
remember to rate if u like
I haven't either and i have opened and closed about 30-40 (a couple multiple times)
<p>Thanks for explaining how to enable the power supply on the bench</p>
<p>Just a note to let you know I have added this instructable to the collection: <br>Encyclopedia of ATX to Bench Power Supply Conversion <br>&gt;&gt; <a href="http://www.instructables.com/id/Encyclopedia-of-ATX-to-Bench-Power-Supply-Conversi/" rel="nofollow">http://www.instructables.com/id/Encyclopedia-of-ATX-to-Bench-Power-Supply-Conversi/</a><br>Take a look at about 70 different approaches to this project.<br> </p>
so, theoretically, if i desolder the rectifier, add some heavy wire, block up the ac-in with a heavy binding post, it should be just a dc-dc supply. what makes me wonder, is if anything uses the ac as some kind of timer or clock signal, i'd hate to completely ruin a supply cause i don't destroy it in the exact right way.<br><br>i may have an instructable in this... i have the rest of the system figured, the 4 truck batteries will be a killer, just getting them home on the bus.
Yep. If you bypassed the rectifier, you'd have just a DC-DC converter. Probably better to buy one, though, as (depending on where you are), you'll need something akin to 170VDC, or somewhat around 300VDC. (that's what the AC would've put into the PSU after it was rectified.).<br><br>*does some math* If you had a PSU wanting 170VDC, you'd need a bit over 14 12V batteries. I could imagine how fun that would be to take home on the bus.<br><br>Good luck!
i don't think so, doesn't make sense, the transformers, to lower the voltage, likely aren't after the rectifiers, cause transformers are usually piss poor at lowering the voltage to something the motherboard can use. if the fets burned open, it'd be a full 125v to the board, or the person holding the wires, so it's not likely the transformers are chokes. which means, there's gotta be transformers before the rectifiers to lower the voltage, making it more manageable with regular logic chips n stuff. the rectifier chip also looks like a low voltage device(same old fashioned crappy ones that rat shack has sold for 30 years).<br><br>so, there has to be rectified dc at some low voltage, otherwise the switching section would only be on a few percent of the time. i figure it's likely to be at most 15vrms into the rectifier.<br><br>course, if it really is designed to switch rectified line voltage, that'd be nutty...
Yeah, but this type of power supply is a switch mode power supply, which means the mains is first rectified, then switched at a high frequency to drive the transformers, which steps the voltage down to something the motherboard can use. (higher frequency reduces the size of the transformer, and makes it more efficient, generally)<br><br>There is rectified DC before and after the transformers.<br><br>'Tis designed to switch line voltages, if I can find a power supply, I'll grab the part numbers on the switching devices, they'll more than likely be rated for 400V or so.
oh yeah, that makes more sense, though, if the switching increases the frequency... dc could be inverted to ac high voltage, or, the second rectifier stage could be bypassed, and feed dc into it there...
Yep, the MOSFET used in this power supply is rated for 800V at 7A continuous..<br><br>It's part number is 2SK2765, if you want to check it out.
i found out that on a AT power supply with a switch you should never mix the prongs around on the switch because i did and it flipped the breaker to the house when i turned it on
That means that AC outlet is wired correctly! B)<br />
Which is usually a good thing, lol.<br />
Oh, Yeah. That would have happened because you would have had the prongs from the powerpoint connected to either side of the switch and pressing the switch would have short-circuited the whole circuit....
Here's a tip!!! If you have a PSU that does not work anymore, why not take the circuit board out and de-solder the componants to use for other projects. Also you can use the left over case as a project box (yes its metal but a metal cutting bit for a dremel will be useful to cut holes in it for plugs and such.
<p>DUDE thats exactly what i did with mine i used the box to make a thermoelectric heater/cooler&nbsp;with a peltier unit&nbsp;i think ill post a slide show of what it looks like, unfortunately i forgot about making an ible for it :(</p>
And I use the other parts for a lot of other things too...
Yeah, You can do that, I mostly use the capacitors, I've got a 1000uF bank from only computer PSU caps....
i shocked myself on one of thoe things once :(
Ouch, I've been lucky enough to have ones that are discharged...
Good Job Thermoelectric. I like the way you go indepth with the explaining about what to do with it. I've looked at your other instructables and have also liked the way you've done them. I would like to see a new instructable soon.
nice instructable...This question is nothing related to this instructable,but any1 over here knows if its possible to connect a transistor to a transformer to run it with DC electricity?
Yeah, you can, You might want to contact <a rel="nofollow" href="http://www.instructables.com/member/11010010110/">11010010110 here</a> he can help...<br/>
ZOMG i've never seen this ible before!
Nice job. Just a hint though... if you don't know exactly what you're doing you should wear gloves so that you don't get shocked!
I'll add that, thanks
I like your idea of explaining it. You did a fantastic job. P.S. Can people that posts comments for this, can you take a look at my Instructable. Just search for Hypocaust and look for 1 that says "How to Make a Virus that Freezes your Computer.
thanks. i will make the needed changes when i get home
<em>I'm guessing this is an inductor of some sort because it only has 2 leads while a torioid would have 4+</em><br/><br/>This is inaccurate: the term <em>toroid</em> actually comes from geometry and describes the &quot;shape&quot; of the core; i.e. doughnut shaped. Toroidal inductors and transformers are components in electronics, typically consisting of that circular ring-shaped magnetic core of iron powder, ferrite, or other material around which wire is coiled to make an inductor. It has nothing to do with the number of inputs / outputs.<br/>Now, if it has only 2 connections this DOES mean it is not a toroidal transformer, but it IS a toroidal inductor. <br/>
I'll let you be a collaborator as well
I probably will have only enough time to answer some of your questions, when I get a chance, but will probably not have much time for much else, I am sorry. At the moment, I am having difficulties finishing what I started :-)
note: those two capacitors you selected are the X-Y input filtering capacitors. hidden away with the output wires are several 1000 uf capacitors used for output filtering.

About This Instructable




Bio: I am a high school student in Cairns, Queensland. Most of the time I am either at school, sleeping, doing stuff on my computer, making ... More »
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