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pc power supply

Pontiacg5

Pontiacg5

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Not what you might think!

I have an actual PC power supply, Google tells me the format is actually called PC. It has a 12 pin mobo connector and it actually has a power switch! Supposidly its good for 20 amps on the 5v rail and 8 amps on the 12v rail. There is a -5 and -12v rail, both good for 300mA too. Supposedly the first pin is "voltage good" so I don't know weather to ground this pin or tie it to one of the 12 or 5 lines. I also don't know if this is a switchmode supply or not so I'm trying to figure out if I should use some sort of load or not. I'm tempted to just plug it in and turn the switch on but I don't want to kill it, its practically an antique! Another supply this old will be hard to come by, and it looks pretty promising so far.

Does anyone know how to get a supply like this running as a benchtop supply? Googling PC benchtop power supply only gets me atx info...
 





BShanahan14rulz

BShanahan14rulz

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Eh, it's only 8A on the 12V rail, you can find ATXs that do better.

A picture of the label? any markings?

With most ATX you just have to connect the power on pin to ground. Some people say you get more stable operation if you put a load on the 5V rail. I don't have an o-scope, I wouldn't know :yabbmad:
 
magonegro

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Well, I have several ATX power supplies modded for my needs, that 5v/12v lines are quite practical. To start it out simply shortcircuit the GREEN and any black wire in the mobo connector. thanks to this I have supressed a lot of those little power supplies that come with almost any electronic equipment, and it finish getting dust on your desk, or in a bag.

edit: BTW these are SAFE, inexpensive and easy to find, so very convenient.
 
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goninanbl00d

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Yes it is switchmode.

It's the AT form factor, which preceeded ATX. The power supply should be visually identical to an ATX supply.

The plugs look like this, no?

img11355.gif


I have run them without a load for short durations of time, but it's not recommended. Some supplies are fine, others will burn out quickly.
 
Pontiacg5

Pontiacg5

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Alright cool, that is what I needed to know. In that picture there the first pin on the left (orange) is the power good wire. Do I ground that or strap it to a certain voltage to turn the supply on?

I'll just hook up a large fan or something to give it a load for testing...
 
goninanbl00d

goninanbl00d

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To turn this one you use the big fat switch.

There should be one coming out of the power supply. It's the 4-pin black wire that's at mains potential.

Also, you want a load on both 12v and 5v rails. An old hard drive does fine. Also, check the voltages beforehand. They can vary quite a bit.
 
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Pontiacg5

Pontiacg5

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goninanbl00d said:
To turn this one you use the big fat switch.

There should be one coming out of the power supply. It's the 4-pin black wire that's at mains potential.

Also, you want a load on both 12v and 5v rails. An old hard drive does fine. Also, check the voltages beforehand. They can vary quite a bit.
Click to expand...

Ah alright, that is what I was hoping for. So the power good signal is unnecessary?
Thanks!
 
Fivos

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I connected my 1w 445nm diode with a ps psu at 400w (connected green with black wire and have yellow as positive and black wire as negative and with an lm317 voltage regulator with an 1ohm resistor) and when I turned the potentometer my diode stop working. Also when I touch the wires or even the psu I get electroschoked. Do you know whats the problem???
 
Prototype

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Fivos said:
I connected my 1w 445nm diode with a ps psu at 400w (connected green with black wire and have yellow as positive and black wire as negative and with an lm317 voltage regulator with an 1ohm resistor) and when I turned the potentometer my diode stop working. Also when I touch the wires or even the psu I get electroschoked. Do you know whats the problem???
Click to expand...

That's not really relevant...and you killed your 445nm diode.
 
Fivos

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but do you know what was the problem. Why the diode was killed. Shouldn't it work properly like styropyro's 1w laser with psu???
 
Bionic-Badger

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If it's zapping you when you touch the power supply, you've probably shorted something to the case. Check the pin outputs for the PSU and make sure you're connecting things up right.
 
Fivos

Fivos

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I already did. Even when I touch a single wire. I can guess the voltage is low...
 
T

Things

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If it's shocking you, either your skin is moist (Sweat?) or your PSU isn't grounded properly.

Was the LM317 and diode heatsinked? Was it a TO-220 LM317? A 445nm diode requires a lot of power for high output, and the TO-220 LM317 is only rated for 1.5A. It gets extremely hot running at even close to that, so you need good heatsinking. Same applies for the diode.

Or, you've wired something up wrong.
 
Fivos

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my diode was heatsinked but not my lm317. I don't know about the voltage regulator, but i don't think it would be the problem the diode died. maybe if the two pins of the transistor with the 1ohm resistor touched each other( no resistance).. Would this kill my diode??
(sorry for my bad englih)...
 
Benm

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The problem is with the input mains filter. That consists of a pair of inductors, but also 2 capacitors that run beween both power line and ground, which is (usually) also connected to the chassis and 0 volt output.

In europe this effect is more pronounced since we have 230 volts mains, and the chassis floats at 115 volts if the pc is connected to a non-grounded outlet. When you are standing with bear feet or moist socks on a concrete floor, you get a healthy jolt when grabbing the pc case. The impedance of the capacitors is quite high, so there is not enough current to be really dangerous.

I can imagine you could fly a laser diode when this chassis voltage somehow ends up as reverse voltage - that would easy destroy one even at low current.
 
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