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Turning on a 300w computer power supply.

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Dacr0n

Member
Hi...

I am trying make some use of this power supply I have.

Unfortunately is doesn't have an on/off switch and is triggered by "TTL signal"

Which I know nothing about...

I found the wire that the signal needs to be fed to.

Here is the data sheet for the supply..

Is it going to be a pain in the butt to get this thing going or can I just feed some voltage to the on/off wire?

Thanks in advance.
 
It's been a while but i think you need to connect power good to gnd or 3v3 rail (one way will not work but can't damage the psu) and then on / off connection needs to be momentarily connected to 3v3 to start the psu. You will know its going by the fan coming on. To turn the psu off either hold down on / off switch for over 5 seconds or disconnect at the mains side.
 

Sceadwian

Banned
Jules it's not a momentary switch it's a green wire (pin 14) on the motherboard connector that needs to be tied to ground to turn the supply on. If you don't want to modify the power supply and just want to turn it on without a PC attached just use a jumper to short the green wire to ground.
 
What I meant was the power good wire needs to be grounded or connected to 3v3 / 5v to get the psu to stay on, and the power on wire is touched to ground (not 3v3 as I said before) but the green wire is not permanently connected to ground to keep the psu on.
 

Dacr0n

Member
Okay....

Wow.... I am amazed at how you knew the green wire was the signal wire without me even saying... maybe its the norm...

I guess I will give that a try... So just momentarily touch the green(on/off signal wire) to ground? and how does it turn off? Do I touch the ground again?
 

Sceadwian

Banned
The power supply will turn 'on' as long as that green wire (the one one the ATX motherboard connector) is shorted. I would hold it on for at least 2-5 seconds, the power supply fan itself will take that long to spin up so that you even realize that it's on.
As long as it's an ATX compliant power supply, the colours are standardized.
 

Dacr0n

Member
I tried grounding out the green wire and the fan spins momentarily then stops if I leave the wire connected... then if I disconnect it and reconnect it again the fan starts up again for about 2 seconds..

The same goes for the power output... I get a 5 volt reading momentarily when I connect the green wire and then it slowly goes down until it reaches zero.

BUT if I keep tapping the green wire to ground the fan stays on and the voltage stays relatively stable...

Not sure how to proceed from here.

______________________________________


Okay... i watched a video on wiki and apparently since I didn't have a load on the supply it doesn't stay on.... I will try with a load and see if I can get the sucker to stay on.... Thanks for all the help everyone.
 
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Sceadwian

Banned
I've never had issues with starting up ATX's under no load, but I've only done it to 2, they may have been loaded internally. If you read through the pages that do 'conversions' for ATX to bench top supplies one of the things they do is put a couple power resistors to draw a half amp to an amp of current at all times and mount them to the case. Generates a negligble amount of heat but keeps the power supply stable under no load. In case you ever need it to there is a standby 5volt line that will always produce power. It's the purple wire. It could be used to control a micro controller or other circuitry to handle switching or control of power supply loads. According to the doc you supplied your standby line is good for up to 3 amps (this is not bad) If you notice the doc also has minimum current specs. You should only have to load the 5 volt line to get he power supply to turn on though. The doc says 1amp for the 5V line, but I'm gonna go with blueroom and say it's probably closer to a half amp. Just toss a few case fans on one of the molex connectors and that'll take care of it.
 
The power supply will turn 'on' as long as that green wire (the one one the ATX motherboard connector) is shorted. I would hold it on for at least 2-5 seconds, the power supply fan itself will take that long to spin up so that you even realize that it's on.
As long as it's an ATX compliant power supply, the colours are standardized.
I don't think that's true, the green wire is mometarily connected then left open to keep the psu on. To turn the psu off, hold green wire to ground for more that 5 seconds or disconnect at mains side.

I connect a 20R or something resistor to load the 5v, but only if the psu moans about a minimum load. The reason it wants a load is to maintain regulation, the cut-out is caused by the feedback circuit sensing out of regulation condition.
 
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Sceadwian

Banned
Jules you are incorrect, I've personally turned 3 seperate ATX power supplies on using a SPST switch or jumper, and have used one as a bench supply for over a year. If you have used a supply that turns on and off in this manner it is not an ATX supply.
 
The PSU I'm thinking of is 20pin (2x10) connector.

Just for clarity - A standard ATX psu is the new(ish) type that has 'remote' on / off button not a switch on the mains side of the psu. The button on the front of the case is a non latching type (momentary). when the psu is on if you hold the power button down for more than 5 seconds it switches off. The power good wire has to be connected to 3v3 or 5v for the psu to stay on.
 

Sceadwian

Banned
The button on the case is momentary, but it's not connected to the power supply, it's connected to the motherboard, which is receiving a standby 5 volt line to power the electronics which actually control the power supply turn on line. The motherboard of a modern PC is never actually off, unless disconnected from the wall, sometimes there's a bypass switch on the back of the power supply but not always. The momentary on, and push and hold to turn off is the standard method motherboards use to control the switch that goes to that green line, and is not part of the ATX standard. Look it up.

As I said, I'm not guessing here, I've done this, on more than one power supply.
 
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Sceadwian

Banned
No problem, should try moding an ATX to use as a bench supply some time, they're great. I did mine in a couple hours, and most of that was drilling holes in the casing for the banana jacks. The wiring itself is pretty simple, and you can use any latching switch for the power button. If you wanna get snazzy you can do capactive touch switches run from the 5V standby line. But this isn't usually a good idea for a power supply, don't want to 'brush' it off =)
 

Dacr0n

Member
well... the supply is being a bit of a *****....

It is very reluctant to stay on unless there is a pretty good load on the thing...

And i don't know what type of computer power supply this is, but the green wire always has to be grounded to keep it on and unless there is a good load on it it shuts off in 2 seconds. It will not even stay on with a computer fan as the load. I had to hook up a 12 volt automotive light to it to get it to stay on.

Is there a simpler way to do this? I've tried putting load on the lower voltage lines like the 5 and 3 volt and that doesn't seem to keep it on. Only the 12 volt.
 

Sceadwian

Banned
How much of a load are you putting on the lines? You should only have to load the 5 volt line though use resistors to draw the minimum current from the 5 12 and 3.3 volt lines as well if that doesn't work. Sounds like an overly protective power supply, but ATX's can be pretty dramatically different in design internally while still meeting standard ATX specifications.
 
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Dacr0n

Member
So if I wired a couple resistors from the 5 volt line to ground, that could possibly keep it on? What would be a good resistance?
 

mneary

New Member
I would use a 12V automotive bulb such as SAE1156 single filament stop light on the 5V line. It won't glow real bright, and won't get unbearably hot.
 
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