This power supply has 3 12v lines, 3 5v lines, 3 3.3v lines, 1 -12v line, & 2 USB ports.
It uses a 480 Watt ATX power supply and puts out enough power to run most projects.
It cost about $35 for everything including the ATX power supply.
This is also a good way to make those ATX power supplys that most people have sitting around gathering dust useful again.
WARNINGThis project involves electricity and sharp tools.
however this power supply only puts out 24v max You should not open the case, when plugged in there is a deadly amount of power inside and the capacitors inside will store a large amount of power for days even when unplugged.
This power supply puts out enough current to start a fire. Make sure to use wire that is heavy enough to handle the current and make sure that there are no shorts.
I AM NOT RESPONSABLE FOR ANYTHING YOU DO WITH THE INFORMATION HERE
I am not responsible if you electrocute yourself or anyone else, if you blow something up, or if you burn your house down so be careful.
Step 1: Parts & Tools
- ATX Power Supply
- Binding Posts With Banana Jacks
- Butt Splices
- Eye Connectors
- Type A USB Jacks
- 12 Way Terminal Block
- Small Piece Of Strip board
- Miniature SPST Toggle Switch
- NC Momentary Pushbutton Switch
- Panel Mount Indicator LED (Mine has a built in resistor for 12v use)
- High Power Resistors
- Heat sinks For Resistors
- Wire For Connecting Everything
- Super Glue
- Electrical Tape
- Zip Ties
- Craft Plywood Or Other Material To Make Case Out Of
- Wire Strippers
- Wire Cutters
- Utility Knife
- Hot Glue Gun
- Soldering Iron & Solder
- Drill & Drill Bits
- Screw Driver
- Volt Meter
Step 2: Mount Binding Posts
The horizontal spacing is 3/4" and the vertical spacing is 1".
I drilled my holes slightly small so that I could screw the posts in tightly.
I added the LED & the switches off to the side of the panel.
Step 3: Add the USB Ports
They are mounted to the top panel. The holes were drilled out then cut to fit with an exacto knife.
The jacks are connected to the 5v standby line so they always have power even when the main power supply is off.
Pin 1 on the USB port is +5v and pin 4 is ground.
Make sure that the USB ports are wired correctly
The voltage on the usb ports must be between 4.75 & 5.25 volts
Step 4: Wire the Panel
|White||-5v (Not used as of ATX 1.3)|
|Purple||+5v Standby (Has power even when power supply is turned off)|
|Green||Power On (Short to ground to turn on the power supply)|
|Gray||Power OK (Not used in this project)|
|Brown||3.3v Sense (Leave connected to 3.3v line)|
I used a 12 way terminal block to make connecting everything easier.
My terminal block was only rated for 25 amps so I used 2 sections for the 3.3 & 5v lines with the front jacks split between them.
I used 12 AWG wire for the 3.3 & 5v lines and 16 AWG wire for the rest of them.
The indicator led is connected to the -12v line. (Note: the led used here has a resistor built in normally a red led would need a 500-700 ohm resistor to use it with 12v)
The toggle switch is SPST and the pushbutton switch is a NC momentary. They are wired in series; one side goes to ground the other to the green power line.
Step 5: Wire Up the Power Supply
ATX power supplys have a minimum load which should be listed on the power supply. Mine requires .3A on the 3.3v line, 1A on the 5v line, and 1A on the 12v line. I used resistors for the 3.3 & 5v lines and a mini fridge for the 12v line.
The formula to calculate the the resistor size is Resistance = Volts / Amps.
I needed 11 Ohms for the 3.3v line and the closest resistor avalable was 10 Ohms which gives .33A and a 5 Ohm resistor was needed for the 5v line.
The formula to calculate the wattage is Watts = Volts * Amps which gives just over 1W for the 3.3v line & 5W for the 5v line.
You should use a resistor that is twice the wattage you need to help keep the temp down. I used 10W resistors for both lines. They are mounted between two large TO-220 heatsinks which was then superglued to the case which keeps the resistors below 110o F.
Step 6: Finish It Up
Check the voltages with a volt meter and if the minimum loads have been met the voltages should be very close to what they are rated at.
If one of the lines is over loaded or shorted the power supply will shut down, pressing the reset button or turning the power off and back on will restart it.
If it overheats it should shut down if that happens turn it off and let it cool down and make sure nothing is overloaded and that the power supply has plenty of ventilation and that its not packed with dust.
Double and triple check the wiring on the USB ports before plugging in an mp3 player or camera and test it with a USB keyboard light if you can.
Make sure that the voltage going to the USB ports is between 4.75 & 5.25v
Step 7: Update 9-22-2009
- I have redesigned the layout on the power supply.
- I moved the binding posts further apart so its easier to connect wires to them.
- And I made a nice labels for the front and top.
In order for the pdf to print at 100% size make sure to set page scaling to none in adobe reader.
The full sized label is 200dpi and should print out to be 7 1/8th inches wide.