PC power supply question (not in case)

[Ginsu Victim]

I'm going to use a second PC power supply I have lying around to power lights and other misc items.

I don't have it in a PC case, so what's the best (or simplest) way to handle the ground?

[lanman31337]

Jumper the green and black, use the molex connectors for your 5 volt and 12 volt. 


Red Black Black Yellow

+5  ground | ground +12

[Ginsu Victim]

I'm not talking about the ground on the molex connectors. I'm talking about the ground that you attach to the case.

BTW, it's an older psu. The kind you turn on and the switch stays closed.

[lanman31337]

Is it an AT power supply?  I've never seen a separate ground from a power supply to a case.  They'll work fine outside of a computer case.

[boogieman]

As far as I know they don't need grounded.  I just epoxied mine to a wooden shelf.

[Ginsu Victim]

This has four wires that run to the power switch, plus a ground wire that was attached to the case. I figure it's there for a reason, so I wanted to be sure I don't f--- anything up by not grounding it to something.

[boogieman]

I suppose you could run the wire to a ground block terminal, or a metal plate with a screw, then run all the button grounds and such run to the same block.

I am not an expert, but shouldn't the power supply be grounded through your outlet in the wall?  The wire coming off the power supply may be used to ground other things, like buttons, etc.?

In other words, maybe the wire that went to the computer case was meant to ground other things, like disc drives or hard drives and such.

[Ginsu Victim]

It has nothing to do with buttons.

I'll just run it to one of the metal plates that's holding my monitor shelf up. Hopefully that'll do.

[SavannahLion]

In other words, maybe the wire that went to the computer case was meant to ground other things, like disc drives or hard drives and such.

IIRC, an AT power supply runs high voltage through the switch. The ground wire was probably put there to prevent an inadvertant short from a careless technician from killing someone. I can't ever recall a manufacturer from cheating on costs so much as to depend on the case of the PC itself to supply a reliable ground return... but I could be wrong on that regards.

[MonMotha]

The little green wire up by the switch is just to make sure that all the metal faces of the switch (which switches AC) are safely grounded.  In most PC cases, that would be a redundant (but still welcome!) feature, as the supply's enclosure is ground, and the enclosure is mounted in the metal box.  However, some PC cases have plastic fronts with no connection to the rest of the case, so it's not always a redundant thing as in this case it serves to ground any front metal that may be present but unconnected to the rest of the enclosure.

FYI, in PCs, ground is ground is ground is ground.  That is, earth ground (green wire in the AC plug) is frame/chassis ground is power ground.  They're all tied together inside the power supply.  However, it's still a very good idea (and it is always done) to run dedicated ground/return wires for all your power.  This avoids currents on the chassis which cause EMI and ground bounce.  In many cases, the metal case is required to meet FCC Part 15B which is yet another reason it is "ground"ed.

This commonalty of grounds is not always present in other situations.  There are some disadvantages to doing it that can lead to things like "hum" on your audio due to multiple ground return paths.  A/V equipment specifically avoids doing this common frame/earth/power ground thing for reasons such as this.  The setup in arcade cabinets varies.

As for what to do with the little green pigtail, I just take a screw and screw it directly to the metal face on the switch when the switch is "loose" or mounted to something nonconductive.  This gets it out of the way and fulfills its safety purpose.

[Ginsu Victim]

As for what to do with the little green pigtail, I just take a screw and screw it directly to the metal face on the switch when the switch is "loose" or mounted to something nonconductive.  This gets it out of the way and fulfills its safety purpose.

Funny, that was my first instinct, but I wanted to be sure. Thanks!