Introduction: Super Recycled Benchtop Power Supply

Working with electronics you are bound to need different voltage sources for your projects. So having a good and reliable benchtop power supply is way, way, waaay easier and more convenient than having to combine batteries in different ways or trying to find a power adaptor that can deliver just that right amount of voltage.

Now, obviously you can easily get one of those pro made power supplies by trading a sh*t load of money for it. But in my opinion that is both less fun, easier, more safe and less recyclingy...(that should be a word) and also it costs more... and will make a less interesting instructable... unless you tend to review them...

Anyhow this is not going to be a full super detailed instructable on how to mod a PSU to a benchtop PS since there is a ton of those all around but rather give some tips and inspiration and show how I did mine.

Step 1: Get a PSU

So first step is to get yourself a working Power Supply Unit (PSU) from an old (or new If you want) computer and start tinkering with it. Mine came from an old computer found in the dumpster... one mans trash...

Some tips here, Older PSUs have, part from the 3.3V, 5V, 12V also -5V and -12V which can be useful to get 24V, 17V, 10V and 8.3V. Although the -5V and -12V usually are quite limited in the amount of current they can deliver.

Wires color code:
Red +5V
Black GND 0V
White -5V
Yellow +12V
Blue -12V
Orange +3.3V
Grey Power on
Green On/Off
Purple Standby

A bit of warning though. PSUs have large caps that can hold quite a
charge. These are enough to cause some serious damage or pain if touched so BE CAREFUL!

Step 2: Preparing the PSU

Now that we know to be careful we can start by making sure it's unplugged before we open it up.

Even though the PSU might not be connected to the mains it could still hold enough charge to give you a nasty unwanted kiss so make sure not to touch anything.

First thing I did was to cut down all the wires to a more suitable length. Then I connected the green wire to ground for the PSU to be able to start at all. I then connected the wires to the white terminal block also known as sugar cubes here. The reason for this is that I wanted to be able to easily switch out the PSU in case it failed me in the future.

I also added a 10W power resistor to the 5V rail to add some load for the PSU because apparently some PSUs need that.

Step 3: Adding Variable Voltage

Using a voltage regulator like LM317 some caps and resistors you can decrease the voltage and since I had a voltage regulator just lying around waiting to be useful I decided to end its boredom and build myself a small circuit for voltage control.

The LM317 can output 1,5A which can be a bit limiting depending on what you plan to drive but there are other voltage regulators out there that are capable of delivering a higher output current

Just remember to add a proper heatsink since this sucker is gonna get hot when limiting the voltage.

I soldered all the parts to an experiment board according to the schematics shown above.

Step 4: The Case

For the case I used some aluminium that I cut to shape and some plastic from a broken led light/speaker thingy also found in the dumpster.... the things people throw away :-D

The steps for this goes:
Find the material, do some measurement, try and cut it straight, fold where needed and use some force to compensate for previous sloppy measurements and cutting

.

Step 5: Putting It All Together

since the case is aluminium you want to make sure none of the cables touches the case or you will short out your PSU.

Squeeze everything in there and screw on the case with some old scavenged computer screws.

I also turned the fan to blow in cold air rather than suck air out since the airflow might not be as good as in a PC.

Handy add-ons: I added a 12V connector for a fan I use as a solder fume extractor and I also added a usb port and connected it directly to the 5V rail for usb driven devices. Don't know if it's recommended to charge cellphone on a power source that can easily deliver over 20A but no more slow charging :-)

Step 6: Test It!

After everything is done, spark it up and see what happens.

If it works then congrats, if not then something went wrong (...duh!)

My goal with this project was to recycle as many parts as possible to see how far one can go without having to buy stuff. The only thing I bought was the voltage meter and the amp meter for a total of 6 bucks from ebay, rest of the stuff was either borrowed permanently from other broken devices found in the dumpster or I already had them at home.

Comments

author
GabrielK10 (author)2015-09-14

author
piyasak.saraphan (author)2015-09-12

thanks <3

author
mjackson42 (author)2015-09-06

Thanks for this instructable. Love it, great job. Love the bit about bending til it fits. Suits me down to the ground. Ace.

author
juaspo (author)mjackson422015-09-08

You're welcome! and yea that's kind of how I work most of the times :-D

author
fartnuckles (author)2015-09-07

I built a PSU similar to this a few years ago now. You can make this a continuous variable power supply all the way from about 3V to 27V or so volts simply and very cheaply by using a DC-DC buck step up/down convertor. You can get these on Ebay from China for around $9.00 Aussie dollars (or about $7.00 Yankie bucks I guess). These buck convertors can usually output up to about 6 Amps and most will accept an input down to 4.5V. So simply hook it up to the 5 rail (or 12V is less current is OK) of the PC power supply, wind the output on the convertor up to 35V and then use the standard LM317 style circuit on the output to create a variable supply. I have had one of these running flawlessly for years now. Oh, just remember that you will need to heat sink that LM317 regulator VERY VERY well as is will be dissipating a lot of heat if you have 35V on the regulator input have the variable output set to a low voltage (say 3V). You may also need to use a bypass transistor to handle the current requirements of your load. There are plenty of tutorials and circuits for the LM317 on the net.

author
juaspo (author)fartnuckles2015-09-08

yea I've thought about that and might do something like that in the future. This project was mainly to re-use as much stuff as possible

author
jeff96 made it! (author)2015-09-07

Thanks for the instructable! I built mine on a Sunday, so I could only use what was around the house or at the auto parts store. I couldn't find an appropriate resistor so I used a 12 volt automotive signal bulb on the 5 volt rail which seems to work well.

I should have put the fuse block inside the junction box, but I didn't have enough space. In hindsight, I would have tied the ground wires and 5 volt wires together outside of the junction box, and run single thicker gauge wires into the box to give me more space. Also, my alligator clips aren't insulated, and could short out.

IMG_20150907_131504.jpg
author
juaspo (author)jeff962015-09-08

Nice!, I'm glad I could help
Re-usuing old stuff is the best :-D

author
JoeI2 (author)2015-09-07

I want to do this as a power supply for my amateur radio that really needs 23amps 12 v Could you put in a parts list?

author
juaspo (author)JoeI22015-09-08

If you are going to connect it to a unit that requires that much power you might be better of just adding the psu directly. But as I said, I only bought the meters (V, Amp) most things were scavanged from other electronics like;
-the usb was from a 12V usb car adaptor
-the knob and potentiometer and switch was a volume knob and on/off button from a music box
-the banana plugs came from an experiment board at my university
-the leds, from computers
-caps can be found in almost any kind of electronics
and I had a voltage regulater lying around, don't really remember where I got that

author
jwhitten (author)2015-09-07

Nice build!

author
juaspo (author)jwhitten2015-09-08

thanks :-)

author
nwonharp (author)2015-09-07

I like it ! It is always a good thing to recycle/re-purpose things that are considered junk , scrap or trash . I am known to be a " dumster-diver "! You can build some very useful things , and not spend much money at all . I have seen a lot of home-brew power supply projects , the design depends on your your individual needs , and how you intend to use it . The possibilities are endless ! BTW, I have used the LM78xx series of regulator chips with good results , about a dollar apiece .

Cheers , take care and have a good day !....73

author
shrirami (author)2015-09-06

good dc to dc converter chip using lm 2596

author
mopsiok (author)2015-09-06

That's a nice one! Thanks!

author
VicP1 (author)2015-09-06

What is R1 connected to on the lower end?

What other reg can we use other than LM317?

author
juaspo (author)VicP12015-09-06

and as for the voltage regulator you need to pay attention to its output current limit. I used 317 since I had one laying around. This will limit me to draw max current of 1,5A. But you could use a 117 or 338 which have different maximum current output which is what will determine the amount of power you can draw from your supply.

author
juaspo (author)VicP12015-09-06

I've added some comment in the picture to make it a bit more clear but it's connected to the negative terminal of the output (or GND). The reason I don't want to call it GND is that it all connects to the input of the AMP-meter so it's not really GND. But if you skip the AMP-meter it's GND.

author
PeterRP (author)2015-09-06

I got an old ATX psu laying around, now I know what to do work it. Nice hacks!

author
jmacielsud (author)2015-08-31

Thanks for your good idea and information.

author
juaspo (author)jmacielsud2015-09-03

you're welcome hope you got inspired :-)

author
AllanB9 (author)2015-08-24

Often PC powersupplies will not work unless a load is applied to one of it's outputs. Some people use a 100 ohm resistor on the 5V. So if your supply doesn't start (all the outputs are zero volts) even though it is turned on, you may need to do this fix.

author
magkopian (author)AllanB92015-09-02

100Ω is not enough, most PSUs require a minimum load of around 5W in order to be stable. The load needs to be on the rail that has the biggest current capacity, so you need either a 5Ω resistor on 5V or an 22Ω resistor on 12V depending on the PSU. Note though that I'm not saying it's not going to work with a smaller load, what I'm saying is that it's not going to be stable, in other words you will have too much ripple.

author
juaspo (author)magkopian2015-09-03

ah my mistake I actually have a 10Ω resistor and not 100Ω but yea I
tried mine before adding the resistor and it worked but the general
saying was that it was better to have one than to not

author
SeanT7 (author)2015-08-26

What Does The N$5 Symbol at the end of the variable circuit diagram mean? and whats it supposed to connect to?

author
juaspo (author)SeanT72015-08-28

that is the cathode for your application so you connect the minus pole to whatever you wish to power up. The N$5 Symbol is just the default name of that net so it doesnt really mean anything

author
russ_hensel (author)2015-08-24

Welcome to the club: Just a note to let you know I have added this instructable to the collection: Encyclopedia of ATX to Bench Power Supply Conversion

>> https://www.instructables.com/id/Encyclopedia-of-A...

Take a look at about 70 different approaches to this project. This topic is one of the more popular of all instructables.

author
mianrelie (author)2015-08-24

Can you tell us how work regulator amp? Thanks!!

author
electrowiz89 (author)2015-08-24

The large knob is for current controll. I think

author
juaspo (author)electrowiz892015-08-24

actually it's for switching between 12V and 24V for the voltage regulator so that I can use it on lower voltages whitout overheating my voltage regulator

author
dmhoke (author)2015-08-23

just curious, what is the large knob for???

author
juaspo (author)dmhoke2015-08-24

It is actually a 3-pole switch to switch between different voltages for the voltage regulator circuit. Since the efficiency goes down quite a bit if the voltage in and output differs too much I've added a switch to switch between 12V and 24V so that I can use it on lower voltages without having to worry about the voltage regulator getting too hot. But I rarely use that function so I decided to skip that part in the instructable.

author
smandal13 (author)2015-08-23

good job

author
juaspo (author)smandal132015-08-24

Thanks!

author
ThomasVDD (author)2015-08-24

Nice build. Charging your phone with it is no pronlem at all. It will take the current it needs, not the full 20A.

author
juaspo (author)ThomasVDD2015-08-24

Yeah I kind of thought so :-)

About This Instructable

60,692views

787favorites

License:

Bio: Studying to electrical engineer
More by juaspo:Illuminated WhiteboardMake yourself a treasure ChestTie hanger
Add instructable to: