What type of relay is needed to connect AT ps to ATX ps?

[qsw911]

Hi,

I want to connect my AT psu( for fans only)to my ATX psu so that both will power up when I turn on PC. So far I found guides on connecting 2ATX or 2 AT power supplies. Radioshack sold me a relay that had only 4 terminals, but my AT psu already have 4 leads ( blue, white, brown, and black)going to the switch. Can anyone tell me what is the type of relay that I need? So far all I know now is that I need a 12vdc relay to hook up the 4 wires to 12v + ground from the molex of my ATX psu.

I was looking thru the Jameco catalog, and I am overwhelmed by the choices there. Now I am more confused as I do not know how to read the schematics.

Any help will be appreciated.

Thanks

[ck42]

CQ:

You don't really need a realy to do this. Just a SPST switch. Hook-up the ground wire and one of the 120V AC wires of the AT PSU to the ATX 120V input or whatever...

Then the one remaining 120V AC wire for the AT PSU can just be run through the switch.

Of course, with this setup, you'd need to flip the switch to turn the AT supply on.

If you're wanting it to be automagic, then you'll need to do something like run that last 120V AC wire through a relay. The relay could be activated by the ATX 12V or 5V ouputs....so, whenever the ATX PSU turns ON, the 12V or 5V lines become active. This is turn energizes the relay which then gives the AT PSU the second leg of the 120V AC it needs to turn on.

[qsw911]

Thanks for the reply, I would prefer the relay method as I am very sure my wife will forget to switch on the AT psu when she uses my PC :P

So can I assume that the relay must have at least 6 terminals, 2 for the ATX 12v and 4 for the wires from the AT switch? Do I get a 12vdc (coil voltage?) SPST, DPST,DPDT or 4DPT relay? What ratings should the coil resistance, contact volatge, contact current be?

[ck42]

So can I assume that the relay must have at least 6 terminals, 2 for the ATX 12v and 4 for the wires from the AT switch? Do I get a 12vdc (coil voltage?) SPST, DPST,DPDT or 4DPT relay? What ratings should the coil resistance, contact volatge, contact current be?

CQ:

No, the relay does NOT have to have 6 terminals.

If you're wanting the 1 switch to power up both supplies by controlling the 120V AC, you'll need to modify your ATX supply. ATX supplies always have 120V going to them...it's a signal from the m/b that tells them to actually supply power...if that sounded like it didn't make sense.....just trust me.

Best way to do it is to have a SPST relay control 1 leg of the 120V AC power going to the AT PSU. The relay would be energized by either the 5V or 12V power from the ATX PSU.

Rememeber, you DON'T need to switch both sides of the 120V signal...only one of them needs to go through the relay. The other one can just be hardwired. Without the two completing the circuit, it won't work...so when the relay kicks on and passes the second leg of the AC, then it will work.

Hope this makes sense.

[qsw911]

Thanks ck42.

I wired up everything and it works!

[ck42]

Glad to hear you got it going.