ATX supply to Breadboard DC

[ClickKlick]

I am trying to convert an Assassin ATX computer power supply into a regulated DC output for my breadboard. When I turn the supply on, the fan spins for one rotation and the built in fan LED lights, but then they stop. I'm thinking a capacitor is allowing this to happen when the switch is thrown.

I have a purple connected to a 330ohm resistor and then to the anode of an LED, the cathode is connected to a black.

I have a grey connected to a 330ohm resistor and then to the anode of an LED, the cathode is connected to a black.

One of the LEDs is supposed to turn on when the ATX supply is plugged in, the other when it is switched on. When I plug the supply in, neither light up.

I have green connected directly to black.

I have a red connected to a 8 ohm 20W resistor, which then connects to a black. To allow the supply to always see a "load".

I have a blue, yellow, and red connected to separate binding posts.

I have a black connected to a binding post through a 1 amp fuse.

There has got to be some reason the power supply isn't turning on. Any ideas? I only have orange, yellow, red, white and black wires left.

 

[blueroomelectronics]

You need a load on the 5v or 3.3v line. IMO a powerful ATX supply is not really ideal for breadboarding projects as the current they can deliver on the 5V rails can melt a breadboard.

 

[ClickKlick]

Is an 8 ohm 20w resistor on +5 to ground not enough?

Its the only supply I had and it lights up I have a 1 amp fuse for "safety"

 

[Mikebits]

Do you have a brown wire?

 

[ClickKlick]

No browns.

 

[ClickKlick]

Also, I tied a 120k 20W resistor (only high powered value I had) to the 3.3v and ground. Still same thing. Switch it one and the fan spins and lights for a split second then....nothing.

 

[3v0]

I agree with Bill.

A wall wart and a 1 amp 5V regualtor will work for most projects. If you need other voltages add them too.

3v0

 

[Mikebits]

Also, I tied a 120k 20W resistor (only high powered value I had) to the 3.3v and ground. Still same thing. Switch it one and the fan spins and lights for a split second then....nothing.

120k? Is that right? Not much of a load. Might also try loading +12v

 

[ClickKlick]

Most guides only recommend a 10 ohm 10W resistor. So i though 120kohm was overkill.

I'm a bit confused. A 250W power supply provides almost the same amperage, at least the one in my old computer does.

 

[Mikebits]

Well if you do the math I=E/R at 10Ω you have 3.3/10= .33A at 120kΩ
you have 3.3/120,000 = 27.5 uA which is not much of a load. Bigger ohms means less load...

 

[shokjok]

Are you loading only the positive supplies? If you are leaving the negative supplies unloaded, this is a recipe for a failed PSU.

 

[ClickKlick]

Hmmm, quite clear right away, bigger amps means bigger load lol. Got it . I don't know I just spent 30$ on supplies to build the box and install this thing and it's not working. I'd at least like to see it through til the end, even if i can't use it for too much without melting my breadboard

 

[ClickKlick]

So I need to load one of every type of DC output? I only have one -5V white, but this should be loaded at all times? Same with the -12V.

 

[Mikebits]

It is worth a try. The minus supplies don't need much of a load. You could always solder the loads to the back of your binding post. Try loading all the voltages just to see if you can get the thing to work, then remove one load at a time to see which one shuts off the supply. Then you know which ones need to be loaded.

 

[ClickKlick]

I'll try it, that's gonna be a bit spendy, power resistors from radio shack are like 2.50$ a piece LOL

 

[blueroomelectronics]

You can probably buy a 5V 2A switchmode wall wart for $2.50 from a flea market. They're commonly used on network stuff.

 

[Mikebits]

I'll try it, that's gonna be a bit spendy, power resistors from radio shack are like 2.50$ a piece LOL

Use lightbulbs instead, just to test.

 

[Mikebits]

Take a look at this document. I think it states min load requirements.
https://www.electro-tech-online.com/custompdfs/2009/01/ATX12V_PSDG_2_2_public_br2.pdf