AT power supply to bench power supply

[Dust]

I have found all the stuff is for ATX, and want to use the little AT power supply I got from school. ANy suggestions on where to look for instructions. It has a switch, but there is no "white" wire which supposedly all AT power supplies have.

[McTimson]

Instructions for what, to turn it on? Or for what wires provide certain voltages?

For pinouts, just google 'AT power supply pinout', and you'll get a lot of results, here's one that looks good.

I'm pretty sure every AT PSU I've owned had its' own power switch, whereas ATX PSU's require you to jump 2 wires if you're not connecting them to the motherboard. What brand PSU is it?

[Dust]

The write-up I saw for AT supplies said tat I needed to cross a blue wire and a white wire, and I don't have a white one, so I am trying to figure out how to get it to turn on without a MB hooked up to it.

[rmay635703]

Originally Posted by Dust

The write-up I saw for AT supplies said tat I needed to cross a blue wire and a white wire, and I don't have a white one, so I am trying to figure out how to get it to turn on without a MB hooked up to it.

You would just turn the switch on and you would have +/-5v +/-12v and grounds along with a power good wire and some other items rarely used.

You need to remember though, very old AT power supplies require a load resistor of sufficient size to turn on or an old hard drive or something with sufficient power load to bring them up, I have NEVER had an AT PSU that required anything other than a load to turn on, the power good line prevents the PSU from turning on by showing a voltage or a connection to ground, so if it isn't there then the PSU will turn on anyway. (assuming the supply is standard and not damaged)

Good Luck

[NiHaoMike]

13.8 V / 15 A from a PC Power Supply

[Dust]

I have an extra HD and a bigger fan I will try to hook up and see what happens. I am kinda pissed at myself. I ruined a perfectly good PSU by trying to get some of the wires cleaned up. Had it wired up and had been using it, but it was time for me to cause problems for myself, since I had something to use it for that night.

[Dust]

Hooked up the HD and still no love.

[hummingbird]

A certain minimum load on the main feedback output is always required for any SMPS to give a stable output - In most cases the auxiliary voltages are linked with the main output only through their output winding ratios. This situation leads to very poorly regulated auxiliary voltages, when the main feedback voltage is not loaded enough. There are smarter power supplies that try to cross-balance the feedback, but most cheap ones won't to to those lengths.

So, as I suspect, a fat wire-would power resistor (fat only for wimpy electronics guys) would be required on the main voltage to ensure stable outputs regulated enough.

Generally +5V is the main winding and 10 ohm 10W would be good ratings for the power resistor.



You would need the pins 14 and 15 on the ATX connector shorted to bring up the power supply

[rmay635703]

Originally Posted by hummingbird

A certain minimum load on the main feedback output is always required for any SMPS to give a stable output

Generally +5V is the main winding and 10 ohm 10W would be good ratings for the power resistor.



You would need the pins 14 and 15 on the ATX connector shorted to bring up the power supply

He has an AT power supply which gets hard wired on through an old contact switch, your comment on load resistor is accurate though.

I suspect that his paticular AT PSU required a load to operate, he attempted to fire with insufficient load and blew out the primary so now its non functional. (not all AT power supplies will survive being powered on without a decent load)

Can the OP try the PSU on a mobo to see if anything happens? My guess is the PSU gave up the ghost.

Anyway I have used old AT supplies for everything from battery chargers to lab power, it should not be real complex, you just need to take care that you always have sufficient load, also what MODEL and TYPE of AT PSU do you have? Are you positive it was functional before you tried using it?

Take a pic, maybe it is not truly an AT but a proprietary unit from a compaq, packard bell or the like.

Good Luck

P8
Pin Signal
1 Power Good
2 +5V or N.C.
3 +12V
4 -12V
5 Ground
6 Ground

P9
Pin Signal
1 Ground
2 Ground
3 -5V
4 +5V
5 +5V
6 +5V

[hummingbird]

Originally Posted by rmay635703

He has an AT power supply...

Oops! *retreats to the far corner*