This instructable will show how I built my benchtop power supply from the power supply unit in an old computer. This is a very good project to do for a number of reasons:
- This thing is very useful for anyone who works with electronics. It supplies nice, clean DC power in a number of voltages with overload and short circuit protection built right in!
- It is a very easy project. Most of the work is already done for you inside the computer. It's just a matter connecting a few wires and you're done.
- It's very cheap. I got the old computer for free and the rest of the parts were under $10. A commercially built benchtop power supply like this could run you more than $150!
- It's somewhat environmentally friendly since your recycling old parts to make something new.
I should mention that this is not an original idea of mine. I learned everything I know about this project from other Instructables about power supplies (there are dozens). My project is unique only because of the enclosure I built for it. The guts are the same as any other one.
My particular unit is capable of suppling +12, +5, +3.3 VDC and -12, -5 VDC. These 5 rails along with the Ground rail can be mixed and matched to provide many different voltages eg. the voltage between the +12 and -12 rails is 24 volts). There is also a handy on/off switch in the front with lights that indicate how the unit is operating.
Since I don't have any electronics projects on the go yet, I am only able to demonstrate a simple relay circuit. Here you can see the relay powering different combinations of indicator lights based on the state of the pushbutton.
Step 1: Gather Your Tools and Get Yourself an Old Computer
The things you'll need for this project vary greatly depending on your own design but you'll definatly need:
- A multimeter
- A pair of wire cutters / strippers
- A screwdriver with a Phillips head and flat head
- An electric drill with a set of drill bits
Other Materials / Tools I used that you might want to consider:
- A sheet of 1/4'' craftboard
- Carpener's glue
- Clamps of various sizes
- Table saw
- Carpener's square
- Measuring Tape
- An on/off toggle switch
- Red 5mm LED
- Yellow 5mm LED
- 330 Ohm resistors
- Solder iron and solder
Connectors and Rails:
- Machine screws
- Hex nuts
- Ring terminals
- Zip ties
The washers, hex nuts and ring terminals should be sized appropriately to fit the machine screws. The ring terminals should be able to accept 16 to 14 guage wire (this allows several wires from the power supply to fit in at once).
Finally, you're going to need a computer. I put a wanted ad for old computers in the local online classifieds. A week later I had 3. Or perhaps you already have one lying around. A lot of schools will throw away a bunch of computers once in a while too. People should be happy to give them away since it costs them money to dispose of them. Either way, when you get your hands on one you'll be ready for the next step.