AT/ATX power supplies

[Jaguarjoe]

I am building a power supply for my shop. 0-24vdc/2a, +/-15vdc/1a, +5vdc/2a, +3.3vdc/2a. The 24v and 15v outputs will be fed from isolated voltage converters to keep them independent.

Rather than spend a ton on an expensive boat anchor transformer I would like to use an AT/ATX power supply to feed the voltage isolaters with 12v, and use the 5 and 3.3 outputs direct but thru current limiters.

I can get new supplies for $11, used ones for $5, and maybe even a free one from my buddies geek son. Are there any sucker traps with this plan? Any suggestions?

 

[MikeMl]

Switching noise if you plan to run analog or audio circuits, or are a ShortWave Listener or a Ham Radio enthusiast.

I hate switchers. Any place I can put an iron transformer in place a piece of radio-spectrum-polluting Chinese crap switcher, I will do it...

 

[dougy83]

Are there any sucker traps with this plan? Any suggestions?

You may need to put a permanent load (>=5W) on the 5V ATX output to stop the psu from shutting down.

 

[Jaguarjoe]

One 1 ohm resistor on the 5v output will satisfy all the other outputs too?

 

[dougy83]

One 1 ohm resistor on the 5v output will satisfy all the other outputs too?

I think the outputs track due to the transformer configuration, so yes, it's fine for the other outputs. 1 ohm is too small (it'll dissipate 25W!).

Last time I looked, a 4.7 ohm was used, but checking now, it seems 10 ohm is fine:

ATX to Lab Bench Power Supply Conversion :: mbeckler.org
How to Convert a Computer ATX Power Supply to a Lab Power Supply - wikiHow
Converting a PC Power Supply

 

[Jaguarjoe]

Thabks for the links, Dougy. They're good.

This is twice in 2 days I had a brain fart. When I said a 1 ohm load, I meant to say a 1 amp load or 4.7 ohms like you said. Yesterday in another post I said to put 3 5volt/30amp supplies in series to get 15volts and 90amps. I can magically turn 450 watts into 1350. I'd be rich!

 

[3v0]

I managed to make my old ATX supply happy by connecting the 12V fan on top of the supply to the 5V rail.

 

[dougy83]

I managed to make my old ATX supply happy...

Well.. you must still have it..