Author Topic: My ATX power supply  (Read 20404 times)

travis77

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My ATX power supply
« on: August 24, 2009, 09:02:40 PM »
Here's a quick little explanation of my ATX power supply.

For starters, I based my hack off of one i found on instructables. http://www.instructables.com/id/ATX--%3E-Lab-Bench-Power-Supply-Conversion/ I found this one to be the best one on there. The best piece of information was the following diagram he drew up:



You dont have to do the fancy LED's. If you choose not to, just clip the wires and tape the ends so that they dont make contact with anything. What I did was the following:
    1. Trim all the wires down to a manageable size. Group the same colors: Black, red, yellow and any other colors
    2. Made a switch that connects the green power on wire to any black (ground) wire. This tells the power supply to turn on.
    3. Added an 8 ohm, 10 watt resistor between any black wire and any red wire. Got that at Radio Shack for 2 or 3 dollars.
    4. Bundle the same colored wires together and crimp on connectors to the ends. These then are connected to the binding posts you see on top of the supply. These "binding posts" are just small machine bolts I had laying around. The fist nut is tightened down firmly where the second nut is loose or finger tight. The second nut on top of the first is used to secure wires to the binding posts. I think Im over explaining..

SEE instructable or picture above for correct wire colors/voltages. Follow the more detailed instructions on that instructable above. Its pretty well written. And make sure the power supply is unplugged when the case is open and your hands are in there!

If you are using a dell power supply, the special wire colors will/may be different. Look on the circuit board and there should be white lettering explaining the wire such as PGS, Standby, remote etc. My power supply was dell, the equivalent of the green (remote) wire is colored grey. When in doubt, use the multimeter and check the voltage. Will save headaches having to go back and re-wire things.. Oh ya you might have negative 12 volts and negative 5 volt lines. These only work for small loads. Dont try to run +12 and -12 to get 24 volts to run a CNC setup. It will blow the power supply for sure.

Now for the fancy top I made. I drilled 4 holes in the top of the power supply. Ran 4 bolts up to a piece of MDF wood. I made a printout on Photoshop (you could use MS paint or MS word) with all the different voltage rails the power supply outputs. I sandwiched that paper printout between the wood and a piece of plexiglas. I then marked where I wanted the binding posts to poke through the printout I made. Drilled those holes, took the top off and connected all the corresponding wire connectors underneath. Then put the top back on, and its finished. When I say top I mean the wood, design, plexiglas sandwich. Here are some pictures. If they are too large, please let me know, I'll resize them down.










« Last Edit: September 11, 2009, 05:22:04 PM by travis77 »


BackyardWorkshop

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Re: My ATX power supply
« Reply #1 on: August 25, 2009, 04:22:35 AM »
Awesome - thanks for posting this - I think one of my next projects will be a few small CNCs - and I'd like to use stuff I already have (have a bunch of smaller motors) so I think this will be perfect as I already have a bunch of old PCs too :)

now to find free controller board plans... ;)
Check out my CNC projects (and more) at http://www.backyardworkshop.com


Davetech

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Re: My ATX power supply
« Reply #2 on: August 25, 2009, 05:50:33 AM »
Nice power supply... nice presentation.  Thanks!

Jon

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Re: My ATX power supply
« Reply #3 on: August 28, 2009, 06:54:32 PM »
I like the idea of using common nuts and bolts to make wire connections, and a platform to hold it all steady.  I guess if anyone needs an adjustable supply, they can use a LM317 voltage regulator IC chip in a type of circuit/box that can utilize these voltage connections or can be used anyplace they can find a DC voltage.

[Update, I meant the LM317 and not the LM741....so I see why the post was made below, however, my further post gave some good links to the LM317, I seemed to still get it wrong in the text, which I did eventually change.

LM317 - Voltage Regulator
LM741 - Audio/Operational Amplifier

Thanks for not removing the post,  I did realise this later on and changed them to the right ones.  So, if anyone sees a mistake or an incorrect reference feel free to let others know, or to clarify what they meant in order to change things quicker.

]

« Last Edit: December 05, 2009, 06:15:27 PM by Jon »

xqp

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Re: My ATX power supply
« Reply #4 on: November 14, 2009, 08:57:50 AM »
[...]if anyone needs an adjustable supply, they can use a LM741 voltage regulator IC chip[...]

An LM741 is not a voltage regulator; it's an op-amp, and a pretty ancient one at that. It could be used in the control loop of a variable power supply but it would need a power stage because its output current is limited to a few tens of milliamps.

I know people have used PC power supplies as the basis for a variable supply and I can see several problems:

PC PSU's high current rails are low voltage and vice versa.

Steppers have low voltage ratings but it's the current that matters and they're generally over driven (using chopper circuits) to get this current as high as possible as quickly as possible.

An addon circuit will need some sort of protection, and this have to be clever and/or pretty chunky if connected to the PC PSU's high current rail. Your 10A overcurrent problem is a trivial load for a 40-60A rail, so your protection must cope.

Switch mode power supplies need some sort of load to work. This is probably taken care of internally in modern supplies, but older PSUs would refuse to start up unless there was some sort of load on one or all of the rails.

[covering my arse mode: ON]
Take the following as advice rather gospel. I am/was an electronics engineer but I do not have experience of designing switch mode PSUs. I know how they work though and the insides are not a safe place if you don't know what you're doing...
[covering my arse mode: OFF]

On a safety note, switch mode supplies work by rectifying their input (in this case, mains voltages) and chopping it up at high frequency to make smaller voltages. Unlike a traditional bench supply which isolates the mains on the input side, so that the most of the internal circuitry is floating until earthed, I'm pretty certain that (for efficiency/space reasons) a switch mode PSU has its isolation on the *output* side, meaning that most of the innards are *live*.

This is OK as long as the PSUs are used *as intended* because their designers know what they're doing, but if you modify one then whatever you put inside had better be *secure* because if it falls off it's got a pretty good chance of finding something live, bridging that isolation and killing you...

That "on/off" switch looks nice, but it's *not* an isolation switch even though it looks like one, so the innards are still live when it's "off". It would be safer (and look a lot less like a mains switch) mounted on the top with the connectors.
Martin


Jon

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Re: My ATX power supply
« Reply #5 on: November 18, 2009, 08:09:44 PM »
I think the LM317 is capable of 1.5 amp continuous when it has a heatsink.  I think there are some versions of the LM317 that have 5 or 10 amp rating, but I've never had one.  The basic chip is cheap, averaging about one dollar from a large distributer, or check on ebay for a handful at a discount.   I do have two or three homemade power supplies using that chip (it is loaded inside with "op amps"/transistors).  Some use a 120 to 25V transformer, and one uses no transformer but uses a 9V internal battery or any input voltage at the external voltage input terminals.  This is an easy/few parts  project for many electronic types of testing/building, though if you look on the internet I see there are many more advanced circuits using that chip/IC with all kind of protection diodes and stuff.  I thnk the LM317 has some thermal protection and a high/short circuit shut off internally.  It also has some "ripple" control, after all it is a voltage regulater to output a fixed voltage, but a capacitor at the input can also provide some nice smoothing of that too.  The LM317 is a variable regulater meaning the output voltage can be regulated from about 1 volt or so to about (I think) 36 or 40 volts.  A problem with fixed voltage regulators is that sometimes you may need a bit of adjustment without wasting any power, and it would be hard if a bit more voltage is needed.   For the LM317, the adjustment is made using a variable resistor, however, if you want a fixed voltage, all you need then is to calculate or through experiment using a variable resistor, and use a fixed resitor to have that fixed voltage.  Note, basically as long as the input voltage is larger, and even fluctuates higher than the output voltage, the regulator will maintain that set/fixed/constant ouput voltage for your devices and projects.  This is good for perhaps you have a windgenerator setup where the output voltage is constantly changing due to variable windspeeds and you need a fixed voltage to charge the batteries.

I guess alot of people might get this confused with the LM741 chip, I'm sure I have at some point, including this posting.  That chip is mainly used for low power audio amplification today.  There are some low power/surface mount or DIP (dual inline package IC) versions of the LM317 that are  basically low power supplies, maby thats what you seen.

Here is some links for the LM317:  http://images.google.com/images?hl=en&source=hp&q=lm317t&um=1&ie=UTF-8&ei=adMFS5n4NMf8nAeaxYi4Cw&sa=X&oi=image_result_group&ct=title&resnum=4&ved=0CCkQsAQwAw

Basics:  http://www.reuk.co.uk/LM317T-Voltage-Regulator-Chip.htm

Make a solar battery recharger with the LM317:  
http://www.reuk.co.uk/Basic-4-AA-Solar-Battery-Charger-Plans.htm    OR:
http://www.reuk.co.uk/Solar-Battery-Charger-With-LM317T.htm


For 5 Amps supply: try the LM338T: http://www.reuk.co.uk/buy-LM338T.htm


Keep in mind that a computer power supply can be used for your variable voltage power supply.  When you see a freshly tossed out computer, it's a good chance the power supply in it is still in good shape.  Check with a voltage meter to see the voltages ouput from it: usually 12V and 5V dc.  Sometimes you need to enable the supply to work by connecting one of it's wires to ground or one of the power lines usually, so look on the internet for the schematics/operation of that supply.

Since the LM317 uses up/drops about 2 or 3 volts from the voltage source, it is not suitable for greater than 9V or 10V dc supply applications when using a 12Vdc auto battery.  One similar chip is this that has about only a 0.5 (half a volt loss):  http://www.reuk.co.uk/LM2941-1A-Low-Dropout-Adjustable-Regulator.htm
« Last Edit: December 05, 2009, 01:24:55 AM by Jon »

Jon

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Re: My ATX power supply
« Reply #6 on: December 05, 2009, 06:18:14 PM »
I had more or less a typo in some of my posts above, so I see why the follow posts by others. such as XQP, was made.  I had the LM317 in mind totally, but my hands typed LM741, clearly though, the links above were correct to the right chip.  I wasn't just tossing chip numbers and ideas, I have actually made some voltage regulators using the LM317 Adjustable Voltage Regulator.  It's requires very few parts and the hardest part is probably finding a box to put it in, unless it will be mounted internally on a specific projects board.


LM317  =   Adjustable Voltage Regulator

LM741  -  Audio/Operational Amplifier


If a certain post interests you, always recheck it since I guess most people will update their posts for many various reasons. I have updated, usually lengthened them, several posts here rather than make a new post, wasting space and repeating some of what was said before.
« Last Edit: December 05, 2009, 06:42:33 PM by Jon »

Jon

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Re: My ATX power supply
« Reply #7 on: December 24, 2009, 01:19:29 PM »
Once you have a spare computer power supply, or something similar, you might want to make it an adjustable/variable power supply.  Here is a basic vid of the LM317 voltage regulator IC chip in some homemade power suplies.  This chip or something similar can be put into your projects too, such as for green energy voltage regulation or anything.

Some Homemade Power Supply Ideas and Green Energy Use
« Last Edit: December 25, 2009, 01:11:14 PM by Jon »