# DC Power Supply Mystery



## TomS (Mar 12, 2014)

I scavenged a DC power supply from an old computer to power a 12V DC gear motor.  For reference the power supply is a LiteOn model #PS-5301-08HA.  The sticker on the power supply says it puts out 12V DC at a maximum of 20 amps in addition to 3V and 5V DC circuits.  I powered it up and probed all of the wires with a volt meter and found several 3 and 5 volts circuits but no 12V outputs.  I'm electrically challenged so I don't know if it's me or the power supply.  Any and all help is appreciated.

Thanks,

Tom S


----------



## arlo (Mar 13, 2014)

There are multiple articles on-line about converting computer power supplies to stand alone power supplies.   Your power supply looks to be for an ATX form factor computer.  Here's one article on converting ATX supplies to "laboratory" (read "bench top") power supplies.

http://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supply

In step #8, it is noted:
_*The color code for the wires is: Red = +5V, Black = Ground (0V), White =  -5V, Yellow = +12V, Blue = -12V, Orange = +3.3V, Purple = +5V. *_
So you should find 12 volts on the yellow wires. A key point here is, are you sure the power supply is turned on?  Does the power supply fan turn on?

Step #8 also says:
_*Green = PS_ON# (turn DC on by shorting to ground).*_

To turn an ATX computer on, the green wire needs to be shorted to ground.  Very complete instructions are athttp://www.dvhardware.net/modules.php?name=Sections&sop=viewarticle&artid=5

The green wire should be connected to pin 16 on the motherboard connector but you might have to look at a figure like this one to know which is pin 16.  http://marcomiltenburg.com/2011/09/18/how-to-test-an-atx-power-supply/


----------



## Pmedic828 (Mar 13, 2014)

I agree with the statements above - to get the supply to turn on you have to short the green control wire to ground.  You might want to use a resistor from 12 volts to ground as some power supplies require a load to regulate the voltage.  If too little of a load is connected, the PS becomes unstable.
You can also tie all of the same color wires together to increase amperage.  All red =5.5V, Yellow - 12V, etc.  Gather all black wires together as a ground.  (you might notice if you play around with the PS that as you increase the load, the voltage tends to regulate.  If you don't place enough load, the voltage might be 10% less than you would expect to measure.  Hopes this helps --- White lead might not be available as only older supplies had this negative voltage available.


----------



## TomS (Mar 13, 2014)

Thanks to both of you for your input.  The fan doesn't turn on when the power supply is powered up so it sounds like if I follow your suggestions it should work.

Tom S


----------



## SEK_22Hornet (Mar 13, 2014)

If you have the need to turn the supply on and off, install a switch between the green wire and ground. Any low current switch will work.


----------



## TomS (Mar 13, 2014)

SEK_22Hornet said:


> If you have the need to turn the supply on and off, install a switch between the green wire and ground. Any low current switch will work.



That's my plan.  I'm also going to install a DPDT switch so I can reverse motor direction.

Thanks for your comment.  It's appreciated.

Tom S


----------

