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ATX Power Supply Help! Answered

i have this power supply. is it an atx supply? because i want to turn it into a bench top power supply but i can only use an atx. it has a 20 pin connector. i heard that if its not an atx, it wont work for some of the ibles on here. thanks.


Hi, I put 330ohm resistor and LED between green and black wire and put switch between gray and black wire to be able to switch the power supply from it's front side. I didn't put the LED between gray and black since it's current is too low for the LED. Is it ok or green and black should by directly shorted (without any additional resistance)? I don't have exactly +12, -12, +5, -5 but something like +11,1, -10,9, +5.11, -4.2 Is this ok or there is probably something wrong with my power supply / connection? Thanks guys.

I Forgot to mention that I put 10ohm 20W resistor between red and black wire as well.

That's not an answer to my question...

you need to connect them for the entire time you want the supply on in the computer there is a circuit that switches it on of orr on demand. when the comp is on the circuit holds the green connected to black all the time. the circuit reacts to many things like the button / software asking to shut down the computer / wake on LAN (turn on by request from network) etc. those signals are all momentary

. So /PS_ON and /PSON are not the same thing? I thought it was a typo.

Then how come the power button on a PC is momentary?

because its only supposed to be momentary. add a momentary switch if you want a switch.

. hmmmm The chart at http://pinouts.ru/Power/atxpower_pinout.shtml says:
14  /PS_ON  Green  Power Supply On (active low). Short this pin to GND to switch power supply ON, disconnect from GND to switch OFF.
but then there is a note at the bottom that says:
/PSON activated by pressing and releasing the power button while the power supply is in standby mode. Activating /PSON connects the power supply
. I'm confused

its 2.5 W load. you calculate it like this

A = V / ohm

W = V * A

the max load for each V is written on the power supply. they like to oversize so take 80 % of that as the max (down to 50 % for low quality power supplies)

should be fine... 10ohm should remain pretty cool; but if possible attach it to the aluminum casing for heat dissipation, anyway.

. I = E / R. E=12, R=10. I = 1.2A
. P = I * E = 14.4W. Ruht-roh!

if connected to 5 V and not 12 v

W (amount of heat) = A * V

A = V / R

its better to use the few watts of required load and not waste it on a resistor

something like a device you otherwise connect with a power brick is perfect - just make sure it draws at least few watts at all times

(btw power supply is more efficient than some really hot power bricks)

or use the supply at night and connect the lights in your room (LEDs or CFL on 12 V inverter) on the supply too

you need ~ 3 - 5 W load (more is ok too)

if you give a resistor above ~5 - 7 W its gonna be hot to an extent where the fan is not enough to cool it and it may heat up the entire power supply

if you give a resistor above 1/2 its designed W its gonna be very hot (possibly > 1000 C when close to its max). its ok for the resistor but not for things around it

i'd tie the resistor to the air intake net and reverse the fan so that air exits through there and blows the heat away

if you use small 5 V loads like USB charging or few LEDs just connect them to 5VSB and you dont need the resistor or the green wire connected to black (save power and dont have the noise of the fan)

That would be ok

You need about 2 - 5 W load

A = V / R

5 V / 10 ohm = 0.5 A

W = V * A

5 V * 0.5 A = 2.5 W load

The resistor is designed for 10 W that is 4 times more. It will not heat much on 2.5 W

I think if it works as is now then its ok

Most power supplies dont have that wire If your have 2 wires connected together to any of the pins in the 20 pin head leave them connected together if you take the head off This wire is a means of self control for the power supply. In most supplies it is all inside and not going all the way to the mainboard and back

Switch on Connect a simple switch to green and black without any resistor Dummy load (optional) Connect a 7 W 47-200 ohm resistor to yellow and black and connect it mechanically to the box so that air blows on it too For large enough loads there is no need in this resistor as the actual load is enough For LEDs etc you may not need the resistor as most PSUs give accurate enough voltages for LEDs (+- 1 volt is ok for leds if there is resistor). However not loading the PSU enough may shorten its life so load it if its not for temporary use LED Connect the LED to the volt you want with an appropriate resistor Orange 3.3 V Red 5 V Yellow 12 V White -5 V (not exists in all PSUs) Blue -12 V The device to be powered is connected to the color wire (+) and the black wire (-) The - states that when connecting something to this wire and to the black wire the color is the - and the black is the + Allways look at the currents written on the PSU and dont load it above 80 % of each of them or of the sum max load (or 100 % for short time) The 5VSB (violet wire) gives 5 V always including when the switch on the green wire is off. This is great way to give 5 V to small loads without turning on the entire PSU (and save some power) Warning - some PSUs have no short circuit protection on the 5VSB wire and may burn if you short it. Add a fuse on this wire to protect the PSU If in the 20 pin connector you see 2 wires coming to one of the pins (most often 2 orange wires or orange and brown) leave them connected - this may be required for the PSU to work AT power supply Most old (before 1995) computers have AT power supplies and are ok too for most what you may need They dont have green wire. Just connect the power switch wire as shown there (usually blue to white and brown to black) and it should work

okay. 1) this is an atx 2) to start it, MOMENTARILY connect the green to a black 3)for an led, you need to attach it to a five volt rail (red wire) 4) the resistor also goes between a red wire and a black one.

JUST TO CLARIFY SOMETHING: you need a high power resistor in between 5volt and ground, for the power supply needs a load to work. I'm fairly sure you don't need a resistor for the on/off swith. You can use a normal resistor for the LED (something around 200 ohms?)

its around 5v... depends on the supply... a multimeter would give you an exact answer

2 things... the resistor needs to be pretty beefy.. the one that "guyfrom7up" recommends is a good idea. a half-watt resistor (the most common kind) will likely blow.
2 for an led, either wire it to a 5v and a ground with a resistor in series (i use the calculator here) or do the same in series with your switch.

. That's part of what gschoppe's resistor does.

> resistor in between the green and the black . Not required for an 20-pin ATX PSU. /PSON (green wire) goes to ground (black) to turn on PSU. . If you had followed my link, you would know that.

I've built one and this is what I did:

buy this resistor from radioshack:

attach one end to 5 volts (red) and the other to ground (black).

If you are doing this inside the psu then you should glue it with thermal glue to one of the giant heatsinks.

My powersupply was a dell.

also, you need to identify the wire that has to be pulled low (ground) for the psu to turn on

that is an ATX...

take one of the 12v connectors, and run it through a LARGE resistor to a ground wire... (the 12v rail requires a load on it to stabilize the voltage on both the 12v and 5v connections in many PSU's) cut the 20 pin connector off, and connect a switch between the green wire and any black wire... that will allow you to get power without a motherboard involved...

this thread shows my final build in one of the comments... I used almost the exact same model (also a Gateway mini-ATX PSU)

. I'm no expert on PSUs, but since no one else has answered and you seem to be in a hurry:
. If you just need the 5 and 12 VDC, any computer PSU should work.
. This should tell you what you need to know. IIRC, the 20-pin connector is the same on all PSUs, but check the link (my memory ain't what it used to be).