How to Build Your Own Variable Bench Power Supply Using an ATX Power Supply

Are you looking to build your own high wattage power supply? Are you looking to build it without having to spend money? Bench power supplies can cost you up to 250 dollars. This article will teach you how to build your own variable power supply using an ATX power supply from a computer. This comes in handy for students who are working on little projects at home and need a constant power source for their projects. This power supply will be able to give you a constant +5VDC,+12VDC,-12VDC and 1.2VDC-24VDC variable regulated voltage supply. On an average everything should cost about 50 dollars not including shipping charges. But it is still way cheaper then those 250 dollar supplies.

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 Steps

1. 1
   Unplug the power cord from the back of the computer. Make sure your computer is turned off first!
2. 2
   Cut off the connectors. (Leave a few inches of wire on the connectors so that you can use them later on for other projects).
3. 3
   Open up the power supply unit by removing the screws connecting the top and the bottom of the PSU case.
4. 4
   

   Bundle wires of the same colors together.
   Bundle wires of the same colors together. The color code for the wires is: Red = +5V, Black = Ground (0V), White = -5V (not used), Yellow = +12V, Blue = -12V, Orange = +3.3V (not used except if you have a brown wire in your supply, Purple = +5V Standby (not used), Gray = power is on (output), and Green = Turn DC on (input).
5. 5
   Start by drilling holes using a dremel tool or drill to the size of the banana jack post you are going to use. Also drill a hole for the LED, and also cut out square piece where the LCD will go and also drill room for a potentiometer with knob.
6. 6
   

   wired binding post
   Connect all the pieces together.
   • Connect one of the red wires to the power resistor, connect all the remaining red wires to the red binding posts;
   • Connect one of the black wires to the other end of the 10 ohm power resistor, one black wire to a resistor (330 ohm) attached to the cathode (shorter lead) of the LED and the other end of the LED (anode) connected to the gray wire,all the remaining black wires to the black binding post;
   • Connect the +12VDC wires to the desired post( but leave one wire left alone so that you can use for variable voltage), the -12 VDC to desired post(the excess piece of wire cut and save for variable voltage section).
   • Variable voltage binding should be left alone at this point and nothing should be soldered to it.
   • Note some power supplies might have a brown sensing wire and or a pink wire. If you have a brown wire, solder it to the 3.3v orange wire and cut the rest out since you wont need to use them, and if you have a pink wire, solder it to the red wire.
   • Please also notice the rubber grommets in the picture that are at the binding post. these are to be put on first then put on the nuts because this is to prevent metal nuts from making contact with the metal case so there for no shorting all the other binding posts together.
7. 7
   

   Build the voltage regulator circuit.
   Build the voltage regulator circuit.
   • Using the components gathered, build the following circuit on a circuit board (if you need a datasheet here is the website for the IC lm 317 (http://www.national.com/ds/LM/LM117.pdf)), but solder wires to the potentiometer to make it out of circuit. By that i mean only the wires are to be attached to the pc board rather then the actual pot being soldered. This is because we are attaching the potentiometer to the case so that we can use it as a knob to turn it to adjust the voltage we want.
   • Note that the way you will power up the circuit is using those +12VDC wires and -12 VDC wires.
8. 8
   Attach build circuit board with some kind of liquid adhesive to the case so that it sticks to the side somewhere. Use hot glue to paste it.
9. 9
   Attach potentiometer to drilled hole in case and paste it with the hot glue.
10. 10
    Attach V regulated wire out of the PC board onto the last empty post on your supply case and solder it onto it. This will be your regulated voltage coming out.
    • 

      Attach LCD voltmeter to case and then hook up power to the LCD using +12VDC supply from the bindings and hook up to ground and then hook up the +input to the regulated post and the - output to the ground post.
      Attach LCD voltmeter to case and then hook up power to the LCD using +12VDC supply from the bindings and hook up to ground and then hook up the +input to the regulated post and the - output to the ground post.
11. 11
    Using this LCD will tell you what your regulated voltage out is from that post. This regulator can regulate voltages from 1.2VDC to 24VDC.
12. 12
    Do a check following the checklist in the tips section to make sure everything is connected correctly and everything is cleaned correctly. And please read tips so that you can follow things more clearly.
13. 13
    Once finished power up the power supply using switch in the back of the supply and LED should turn on along with fan and there should be no problems.

Tips

• Make sure all of the wires are soldered together and insulated.
• Make sure you have all metal debris out of circuit. Use a compress air duster to clean everything out if needed.
• Make sure nothing is shorting together. That includes checking the binding post.
• Make sure power resistor is connected to a red wire in one end and a black wire in the other and insulated and taped down to either a heat sink or pasted onto the wall of the case insulated.
• If the power supply was connected to power source, use some discharging capacitors. A way you can check is using a multimeter to see if there is any voltage. if there is use a small motor and attach the - to the - on the cap. and the + to the + on the cap., this will discharge cap. and make circuit safe to work with.
• Use a wrist strap to ground yourself.
• It is a good idea to build the regulator circuit on a breadboard first using a trimmer pot and not the one your going to be using so that you can test and see how the circuit is suppose to work.

Warnings

• Please do not work on this while power is plugged in as it can cause electrical shock or even death with this type of power.
• Remember that if you do power up power supply make sure capacitors are discharged by waiting about 5 minutes.
• Make sure that when drilling the metal case, no metal slivers get anywhere in the circuit as it can cause shorts in the circuit and could cause electrical shorts and the unit can catch fire or explode capacitors and cause harm to you.
• Make sure you insulate and wire everything properly using electrical tape or heat shrink.
• Make sure that when attaching banana jack post to metal casing, that its no metal screws, nuts or washers are touching the outer casing as it could cause shorts.

Things You'll Need

• a Power-Indicator LED (red is always a good choice)
• LM317 Voltage regulator
• 5k potentiometer with knob
• banana jack post
• .1uF ceramic capacitor
• 1uF capacitor
• 330 ohm resistor (1/4W) for power indicator led
• 120 ohm resistor (1/4W)
• 10 ohm power resistor 10 Watt
• LCD voltmeter
• pc board
• ATX power supply
• 5k potentiometer with knob
• banana jack post