Using a Computer Power Supply for 5V?

[BWay]

I am putting together a CNC router and am using a server computer case for my control enclosure (Servo drives, Breakout board, & DC power supplies). Originally I was hoping to use the computer case power supply to run the cooling fans and a 5V for my breakout board. What is the easiest way to accomplish this? Will the power supply run ok without being connected to a motherboard? The power suppy is a ATX style.

Thanks!

[idtkid]

Yep, power supply will run fine. A simple voltage meter reading of the red and black wire pairs should provide you with more than enough 5V connections for fans and a B.O.B.

Just something to think about, a spare/old cellphone charger that outputs 5V may prove to be a smaller, quicker, simpler solution?

[LeeWay]

Isn't there something you have to jumper or modify to use a PC PS as a stand alone source?

[jalessi]

BWay,

Grounding the green wire (pin 14) will turn the power supply on.

Hope this helps,

Jeff...

[Eurisko]

+5V is always available at pin 9 ( +5VSB, purple wire ) when AC is applied.
This line is a standby line for general motherboard functions.

This output is limited to about 2 amps of current. Would be good for a microcontroller circuit or a BOB, but I wouldn't use it to run the fans.

[BWay]

Originally Posted by idtkid Just something to think about, a spare/old cellphone charger that outputs 5V may prove to be a smaller, quicker, simpler solution?

I had thought about this but since the power supply came mounted in the case with wires ready to use it just seems too easy. (Famous last words!)

I tried turning the power supply on by shorting pin 14 to the ground. This seems to turn the power supply on for a second but then it shuts off. Any thoughts?

[CalG]

Eurisco

The chart displayed in the post above indicates only 10ma available from Pin 9 5V. You indicate 2 Amps! Big difference. Have you more info on using this to supply a BOB?

Regards

Cal

[BWay]

Originally Posted by CalG Eurisco The chart displayed in the post above indicates only 10ma available from Pin 9 5V. You indicate 2 Amps! Big difference. Have you more info on using this to supply a BOB? Regards Cal

Looking at my power supply the +5VSB output will supply .8A.

[Al_The_Man]

The simplest access to 5v is off one of the 4 pin P.S. connectors, if is is a server supply the wattage capacity should nice and high.
Al.

[jpardue]

There is a great Wiki article on exactly how to convert an ATX power supply. This is the power supply used in millions of computers, often free for the taking from junked machines.

I have built several of these for various projects. Of note, the Wiki design yields a Power ON indicator and switch and jacks for all the available Voltages. It uses a 10 Ohm, 10 Watt load resistor to keep the supply running. On several of mine I used a 12 Volt bulb in an automotive fixture as a load resistor, preserving all the 5 Volt Amperage for my project.

The common PC built since year 2000 will have a perhaps a 350 Watt power supply, which will deliver some impressive numbers:

+ 3.3 Volts at 20 Amps
+ 5 Volts at 25 Amps
+ 5 Volts Standby at 2 Amps
- 5 Volts at 0.5 Amps
+12 Volts at 12 Amps
-12 Volts at 0.6 Amps

A 1,000 Watt server power supply sports big 12 Volt Amps, but note the 5 Volt Amps available isn't much more than the smaller supply:

+ 3.3 Volts at 30 Amps
+ 5 Volts at 30 Amps
+ 5 Volts Standby at 2 Amps
+12 Volts at 20 Amps (80 total Amps, 4 separate 20 Amp circuits)
-12 Volts at 0.3 Amps

The 5 Volts Standby is there to power a motherboard's circuits to sense the power ON switch and wakeup functions. This 2 Amps is there as long as the supply is getting AC power.

Every PC power supply I have worked with has a 110/220 Volt input selector switch, so they can be powered from either AC line Voltage.

Link to the article:

http://www.wikihow.com/Convert-a-Com...b-Power-Supply

Hope that helps,

Jon P.

[Eurisko]

Originally Posted by CalG Eurisco The chart displayed in the post above indicates only 10ma available from Pin 9 5V. You indicate 2 Amps! Big difference. Have you more info on using this to supply a BOB? Regards Cal

Cal, the ATX specifications recommend that the +5VSB line provide 2 amps of current. The 10 mA mentioned in the chart has to be a typo. That's barely enough current to light an LED.

The only sure way to know how much current can be drawn is to check the specifications label on the power supply.

My ChiefMax 450W supply does indeed supply 2 amps at the +5VSB line.

[Eurisko]

Originally Posted by BWay ... I tried turning the power supply on by shorting pin 14 to the ground. This seems to turn the power supply on for a second but then it shuts off. Any thoughts?

Make sure that you're grounding the right wire (green, pin 14) and you have a tight connection. If the connection is good you either have a bad power supply or you're shorting the wrong wire to ground.