Easy Benchtop Power Supply

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Introduction: Easy Benchtop Power Supply

About: I am currently working as a computer and network tech, where I fix and build networks and computers. I love learning and figuring out how things work. I've also done work in construction, elecrical work, plu...

This is a very simple way to make a pretty decent, but cheap benchtop power supply out of mostly old PC parts.
I work for a pretty small computer company, and we end up scrapping a lot of old PCs with tons of still working parts. Getting 'old' power supplies and hard drives is free, as they are typically considered trash. So, finding myself in need of a power supply, I figured this would be a fun weekend project and would put those old parts to good use.

Step 1: Gather the Parts

Things you'll need:
· Working ATX PC power supply
· Large laptop power brick or project box about the same size
· 6 banana jacks
· Switch
· Green LED
· 100 ohm resistor
· Strong double-sided tape
· Velcro with sticky back
· Heat shrink tubing or electrical tape
· Hotglue gun (w/ a glue stick)
· Soldering iron (w/ solder)
· Drill
· Set of drill bits
· Saw or dremel
· Razor knife
· Phillips and regular screwdrivers
· Wire snips
· Wire strippers

Step 2: Breaking Open the Brick

If you decide to go with a project box, this step can be skipped.

Start with clamping down the laptop brick and cutting the cords off.
Next, cut along the seam all the way around.
Then pry the two halves apart and pull the insides out.
Finally, drill a hole where the wires for the power supply will feed through.

I live in an apartment with neighbours, so power tools like my Dremel are out of the question. I went at it with hand saw and a miter block.

Step 3: Prepping the Power Supply

Unscrew and open up the PC power supply.
Snip off all of the plugs.
Separate the wires you'll need plus a couple of spairs from the ones you don't need.
I needed five ground (black), one 12V (yellow), one 3.3V (orange), three 5V (red), the Power Supply On (green), and one extra of each.
Trim back the extra wires. Trim as many as you can level with the pcb. The others you'll have to leave some length to tape or heat shrink.
Close up the box and screw it back together.

Step 4: Start Piecing Things Together

Now, make sure things fit and all of your holes line up. If there are extra tabs hanging off the power supply, like mine has, drill a hole to match in the brick to help hold it in place.

Stick your double-sided tape on the power brick half with the hole for the wires.

Thread all of the wires through the hole in the brick and press it firmly to the power supply. (Glue or screws could work here, too!)

If you had any useable tabs and did drill a hole, put a screw through it to hold it on.

Step 5: Making the Faceplate

Use a pencil or marker to mark the holes for the banana jacks. I had two sets of four, which made things pretty easy to line up. Also be sure to leave room on one side or the other for the switch, wires and any extra parts you want to add later.

Drill all of the holes for the jacks and fit them in place. You could glue or screw them in place if they're like mine. I actually melted the pegs on the back of the jacks to the holes in the brick.

Step 6: Wiring Things Up

Solder the green wire from the power supply to one lead on the switch and one of the black wires to the other lead.

Next, solder the resistor to the lead on the flat side (negative) of the LED.

Solder one end of a scrap black wire to the other lead of the resistor, and the other end of the wire to the lead on the switch connected to the black wire of the power supply you solder previously.

Now solder one of the red wires from the power supply to the lead on the round side (positive) of the LED.

Finally solder in the rest of your red, black, orange, and yellow wires from the power supply to the back of the banana jacks.

Plug in the power supply and test all of your connections. When you flip the switch, the LED should come on and all of the jacks should have power/ground.

Hot glue all of the connections and tape or heat shrink all the wires.

Step 7: Closing the Box

Now, cut a few pieces of the Velcro tape in half length ways and stick them on either side of the brick, so they follow the seam.

Holding the two halves of the brick tightly together, take strips of the Velcro the same length as the last few and stick them over the cut ones to hold everything together.

You could glue or screw the two halves together, but I'd rather always make things that I can take apart pretty easily.

Step 8: Enjoy Your New Power Supply

So now that you have a fairly stable and efficient power supply, you can use it to test circuits or power projects. Depending on the size power supply you use, you could power quite a few projects at once.

It would also be kool to add extra features like an ammeter or a couple potentiometers.

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    45 Discussions

    Hi everyone i'am new to instructable I'm looking to build a power supply out of a computer power supply i need 12v 4amp but the power supply says 12v 12amp for a amplifier please help me thank you

    This is a nice piece of work and overcomes a problem I had with my own variant on it. I used a free standing project box, and the weight of the cable bundle tends to move it around. Attaching the project box to the power supply looks like a nice simple solution to this. (My version is at http://moosteria.blogspot.com/2015/04/atx-power-supply.html.)

    I had the impression (and please correct me if I am wrong) that you are supposed to add a minimum load to each voltage output according to the power supply's specs so it won't burn out. Not being able to find those specs on an old power supply of mine has kept me from doing one of theses myself

    7 replies

    Some (mostly older) computer power supplies need a minimum load on just the +5 volt supply. And it is not to keep it from burning out... They are designed to not tun on unless there is a load attached. Typical value used is 10Ω 10W.

    Mine doesn't specify any. On this https://www.instructables.com/id/Convert-an-ATX-Power-Supply-Into-a-Regular-DC-Powe/ the load is on the 12v line. On this one https://www.instructables.com/id/The-Ultimate-ATX-Power-Supply-Mod-With-USB-Chargin/ it has on every line. I wish I knew what was the deal with mine

    I read, on another site, that the load resistor should be used on the voltage rail that has the highest amperage. As stated here by another, use 10Ω 10W.

    10Ω 10W will provide a 0.5A 2.5W load on a 5V line. If you were to put the same resistor on the 12V line, it will draw 1.2A which translates to 14.4W, which exceeds the resistors power rating. It will get very hot and will likely burn out. Do not put a 10Ω 10W resistor across a 12V supply!

    Oops! You are absolutely correct! Don't know where my brain was... must be the "medication". ;-)

    Try the 10Ω 10W resistor on the 5V line first. If that doesn't work, I'd try a 25Ω 10W resistor on the 12V line (this will draw 0.48A and dissipate 5.76W)

    Can this be achieved using a laptop charger? I have an old one and would be nice if I could up cycle it into a bench top power supply.

    2 replies

    Yes. But a laptop charger will rarely go beyond 5 Amps. If that's all you need, that's fine. Voltage will be in the high teens so like kd1uc said, you can make it adjustable. Good luck!

    The charger brick is a decent power supply but it has only one voltage output and probably has tons of ripple. A nice electrolytic cap will smooth things out but will remain charged if you forget to put in a bleed resistor. You can also put in a regulator circuit that sets the voltage where you want it. It can also be made to be adjustable.

    Try it, the worst thing is you might learn how not to make a PS from a brick.

    I'm pretty sure 4mm, but you can get smaller or bigger depending on your need. just remember to match your plugs and jacks!

    Love how everything is recycled from old bits...Even the plastic enclosure!

    By the way, that 3rd hand device is brilliant! I might steal that idea. ;-)

    1 reply

    thanks! that 3rd hand was made from an old car antenna magnetic base, portable camera tripod, alligator clips and some random bits from my junk drawer.

    Nice idea, I may just have to make one. I have plenty of old PCs hanging around.When marking the holes for the binding posts mark the 3/4 of an inch apart. This will allow you to use the standard prefabricated dual banana jacks if you so desire.