The Ultimate ATX Power Supply Mod With USB Charging Ports

I know there is already a bunch of these on here, but I didn't see any quite like this so I thought I would post it, so here it is.

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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.

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WARNING

This 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

Parts

• 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

Tools

• Wire Strippers
• Wire Cutters
• Crimpers
• Utility Knife
• Pliers
• Hot Glue Gun
• Soldering Iron & Solder
• Drill & Drill Bits
• Screw Driver
• Volt Meter

Step 2: Mount Binding Posts

I Mounted 7 Pairs of binding posts on the front panel.
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

The pair of USB ports are soldered on a small piece of strip board.
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

Wire Colors For The ATX Power Supply

Color	Signal
Black	Ground
Yellow	+12v
Red	+5v
Orange	+3.3v
Blue	-12v
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

The old connectors need to be removed and replaced with some butt splices. Because the wires are thin and it will put out a lot of current we need to bunch up several wires so it will handle the current. I left the 4 pin molex connectors on so i could use them to test old computer drives.
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

Tighten down the connections, add labels, and double check the wiring. Flip the switch and if everything is done right it should come on.
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.

The power supply label in the zip archive was made in adobe fireworks and can be edited.

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.

Comments

[amclaussen]

Hi there! I have seen several power supply mods, some using power resistors, but what has given me the very best results, is to use plain old automotive bulbs! Look for the best match of filament current. The common brake light 12V automotive bulb, when operated at 5 volts, will have a very loooong life!, and it produces enough light to be seen from far away ( which is a better pilot light!), and best of all: the bulb only requires some distance from the glass envelope to the nearest surface to keep temperatures reasonable... which is definitely NOT the case with a power resistor! Try it, I'm sure you won't return to using power resistors again! Amclaussen.

P.D.: and the cost is lower, as the socket and bulb only cost pennies, which is in accordance with the Instructables spirit.- Best Luck.

[abductd51]

You mite need a time machine to read this but Norman Labs used 1157 in their speaker systems as resistors. They were hifi out of Norman Oklahoma. Best speakers I have ever heard.

[rocketman221]

I had considered using lightbulbs for the load, I just didn't have any that would pull enough current from the rails.

I did end up replacing the original power resistors with a custom made one. It is a tin can with a coil of nichrome wire and is packed full of sand. The outside stays cool enough to touch.

[amclaussen]

Mine is a very common 1157 brake/rear light bulb, that pulls enough current from the 5V rail as to keep the supply happily running at 12V. I use it to feed an intelligent battery charger designed to recharge NiMH, LiPo and lead-acid batteries used in model airplane flying. At the required 7 Ampere demand when topping up my car battery, the small supply can barely maintain 11.8 V, which keeps the charger working, but I'm looking for a beefier supply, as other two smallish ones (about 180 watts) have failed after some use when recharging large (auto) lead-acid batteries. Have you found a particular brand or brands of Power supplies that are more reliable than the run-of-the-mill ones used by PC manufacturers?

[rocketman221]

I would try a 400+ watt atx12v power supply, they are designed to supply most of their power from the 12v rail. Get a good brand name one like a Corsair or Antec. Some of the cheaper ones will die if ran at their full rated power very long.

There are some really good 12v power supplies available, but they are much more expensive.

[amclaussen]

Thanx for the suggestions! I've traced the failure to two causes: one failed because of plain bad quality electrolytic capacitors, the other from a failing coil.

Evidently, there is a lot of GOOD engineering, but directed to produce a very well defined (limited) lifespan... designed to endure the year or so of warranty and then fail! Another possibility someone told me, was to search for a 12V power supply designed for LED lighting applications, but I haven't located any here (I live in Mexico City, and materials and devices are in short supply!

[rocketman221]

I have seen lots of those LED lighting power supplies on ebay, some up to 60 amps.
I don't have any of them, so I'm not sure about the quality. They are probably built similar to cheap atx power supplies though.

[Mark Boulton]

Hi, great instructable, could you show me how to determine the minimum load or loads on a coolbox basic 500gr? Photo attached
Thanks

[Jimbo724]

Any problem or concern with the binding posts being rated for only 10A or 15A? That's all that seem readily available.

[ArijitKumar]

Can you please explain how the automatic power cut-off during accidental short-circuit is working here?

[rocketman221]

ATX power supplies have a protection circuit that will trip if too much current is drawn. It is reset by turning the supply off and back on again.

They will typically use a current shunt and comparator to detect over current and a latch to keep the power supply shut down until the supply is reset. It can be built into the controller chip or separate depending on the power supply.

[michael_nonan]

Question: Can I combine the yellow and orange wire to get an output voltage of 15V?

[rocketman221]

No, You would get 8.7 volts and many power supplies will trip out if you try that.
You can use the -12v and the 3.3v rails to get 15.3v, but the -12v is typically rated for less than 1 amp.

[michael_nonan]

thanks for the reply. I'm trying to use my atx power supply to charge a sealed lead-acid battery which came from a UPS. After 7 hours of charging i only get 10.8V from the battery. Any ideas?

[rocketman221]

Is the battery drawing any current when you charge it?
It may have a bad cell if it doesn't draw much current.

[jdias7]

Hi there. Im building a bartop arcade based on rPI3. I bought a 500W PSU (this one: http://www.tacens-anima.com/fuentes-de-alimentacio...) to feed the raspberry pi 3 VIA MicroUSB port and an 2.5" USB HardDrive.

Connected to the rpi is the xiaomi controllers encoder, and the USB Drive. My first attempt one month ago was to solder 2 usb ports to the MOLEX connectors from 5V rail but rpi3 keeps showing low current sign (low AMPS) and its boot is too slow. So, im asking you guys (as im a noob on this stuff) to help me. What do i need to do? Ive already stripped the PSU cable connectors but i dont know which kind of high power resistors should i use to keep a stable current AMPS both on rpi3 and on the USB drive.

Thanks in advance :)

[rocketman221]

The power supply should provide plenty of power for the raspberry pi (it could run 10 of them). The 5V rail might be running at a lower voltage if you don't have enough load on the 12V rail though.

Did you measure the voltage on the 5V rail while the raspberry pi is connected?
It should be between 4.75 and 5.25 volts. If it's good, the USB cable might not use heavy enough wire.

[jdias7]

Yes, with the rPI connect im getting about 5.15v. The problem is the current... Im only having a maximum of 530mA. I've installed a POWER_OK led to the grey + GND wires and it keeps on as soon as i power the PSU on. The problem is that im not having enough AMPS to keep both rpi and HD working properly... by the way, tried dummy loads on all rails

[rocketman221]

You need a better USB cable. Try to find one that is as short as possible and that has heavy gauge power wires. You can try measuring the 5V pin on the raspberry pi. I believe the low voltage warning shows up if it's below 4.65 volts.

Since your power supply doesn't list the minimum loads, you will have to experiment to see what works well. The 5V and 12V rail loads are most important since they can't be controlled individually. If one rail doesn't have enough load, the voltage on the other will drop. A minimum load of 1 to 2 amps is pretty typical though.

[jdias7]

my PSU dont have any info about min load required on each rail... is there a way to find out those values?