Essential Benchtop Lab SMPS From a Computer SMPS

You may be about to close your tab or browser to see yet another instructable or how-to guide on converting your Computer SMPS into a Benchtop Lab SMPS. But hold on, you might want to have a look or you would be sorry to miss it.

I was finding myself to search for pure DC power to test and run various circuits I make. I was used to pull power from this board or that but all I need was a rigid supply sitting on my bench. Actual Lab supplies are costly enough to empty your wallet. This instructable uses a cheap computer SMPS (costs about 10$ or less) and a few components. Along with that you, couple of minutes and you have a reliable DC source on your desk always ready to provide power !

To be frank, this idea didn't come out of my genuis mind but is inspired from Sparkfun's Benchtop Power Board Kit.
http://www.sparkfun.com/products/9774

If you are lazy enough to read this instructable or noob enough to make a PCB or to solder; you can go ahead and buy above product. You can have your benchtop power source in no time with it. Also Sparkfun has availed layout files, you may go for making that board if you'd like to.

But if you are geeky enough, read on !

So what I have basically done is, I've made a PCB where we solder wires coming out from SMPS board and added terminal mounts. For extra protection, I have added fuses since short circuit is common on a geek's electronic workplace.
I know computer SMPS is equipped with short circuit shut off feature but it doesn't kill to have more fuses for protection.
Better to be safe than sorry.

I have also got a big illuminated mains button on the back side. For convenience small slider button on the front side switches this benchtop SMPS on or off.

Please refer to the images since I am tired now to type a lot.

Caution : Computer SMPS works on AC mains. Care for your own safety and follow all the safety measures such as unplugging it before opening. I hope you are smart enough.

Step 1: Tools and Components

Oops, I forgot to click a photo of all the materials required. But not to worry, its just simple list and you will observing all the components actually mounted on the PCB.

So here is what we need:

Tools
1. Screwdrivers, if you couldn't remove screw with your nails.
2. A laser printer, photo paper, FeCl3 for etching.
3. Drill Machine and soldering equipments.
4. Hacksaw, um and others

Components:
1. A Computer SMPS (New or Old, any working unit would do. Make sure it has all the standard voltages). - 5$ for used or 10$ for new.
2. A single sided blank PCB (Preferably Glass Epoxy FR4 grade). - 2$ or less
3. Fuse Holders and glass fuses (5A rating) - 2$ or less
4. Nut-bolts - 1$ ?
5. An LED, Resistor (470 Ohm), Mains Switch. - Couple of cents

I know that computer SMPS can source a lot of current, but 5A is a fair current limit for a benchtop supply.
If you need more just add a fuse of more rating. Make sure you are not drawing current beyond SMPS's capabilities.

Step 2: The PCB

I have designed this PCB in my favorite tool KiCAD. An open source free PCB design suite.

Find attached PDF Layout / Artwork. If you want to learn KiCAD, that would be an another instructable.

You can just print the PDF I have attached with 1:1 scale on a photo paper (80+ gsm) using a laser printer.
And then use it to transfer using Toner Transfer method and make your PCB.
Etch it, drill it and mount all the components.

Refer several instructables or resources if you want to learn how to toner transfer, etch and drill a PCB.

Power Supply Header Board.pdf
Download

Step 3: Hacking the Computer SMPS

In this step I have-

1. Opened SMPS
2. Removed AC Main Out socket
3. De-soldered extra wires.

Step 4: Soldering and Testing

Now get your solder gun and solder everything.

You do not need to solder Banana Terminal mounts. They simply are tightened with screws and they get connected due to big pad I have kept.

After soldering do a test run and see if you get proper voltages.

Since this one is a home made PCB, to avoid corrosion of the tracks I simply apply clear varnish coat.
Dry the coat with a hair dryer or hot air gun.

Step 5: Mount the Header Board

Remember that whole metal or aluminum case of the SMPS is Ground/GND/Earth or whatever you call it.

So make sure that no +5 or +12 or +3.3V or -12V pin touches it.
That's why I have used long nuts to keep proper spacing.
Its totally fine if these nuts are tightened with screws on GND pad of the PCB.