Introduction: Super Recycled Benchtop Power Supply

About: Studying to electrical engineer

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.

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