ATX power supply for use outside of computer case

If I remember corectly you have to link two pins together before it will turn on. Can't remember which two sorry.

BLACK

+12V -12V

cdrom

the

In article , snipped-for-privacy@cinci.rr.com says... | ello all, | I'm having some trouble turning the above label power supply on. I.E. I'd | like it to run outside of the computer. | I'll be using this power supply to run a CNC engraver. The motors are | three(3) 6vdc unipolar. | I read elsewhere that I have to supply a small load across one of the red | and com leads. | Such as an old cdrom or 25ohm resistor. I really don't want to use the cdrom | drive as it will increase the weight of | my unit and I'm sure one of you guys are quite capable of creating a load | that would be necessary to make this work. | |

I would first suggest you try to get it to work with an old CD ROM drive or old hard disk. I think the way to turn the PSU on, is to momentarily link PS-ON to ground or the common connection in you list.

Once you have got that working, then think about replacing the above temporary load with a more permanent one in the form of resistors. Connect two 10w 25 Ohm resistors, one between +5v and ground, the second between +12v and ground. This should make the PSU hold up. You might consider trying other higher values of resistor, which would waste less current.

3 x 3amp stepper motors does seem rather a lot for a PC power supply, if that is your intention. You might get away with adding 10 Ohm resistors, one in series with each phase wire. This would restrict the surge current a little and might enable it to work without tripping the PSU.

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I'd

red

cdrom

load

In my experiance you don't need to force the 12 volt, only the 5, if you put a load on of about 1 amp or just under on the five volt rail the PSU will come on and stay on. I think they are designed this way because the 12 volt rail is not regulated if the 5 volt is not drawing current.

I'd

red

cdrom

load

resistors

On one of the disc drive power plugs put a resistor between the red wire and the black wire next to it. Make it a 5 ohm to start with to prove that the power supply stays on, don't touch the resistor when it is powered on, it will burn you. Increase the resistor size until the power supply shuts down then come back a little bit to make it stay on. It's best if you have the biggest value resistor you can while maintaining the power supply's ability to function. I guess it will be about 8 ohms that you end up with. Make sure the resistor can handle the power dissipation ie minimum 5 watts. If I were doing this I would probably use a bulb because the hot bit is behind glass and it tells you the supply is on.

Thank you for all the input guys. Now I have to figure out why the fella used current limiters on his motors phase lines.

Thanks again.