Non-PC Use of a Power Supply

[JimK33]

I want to use a computer power supply to power two cooling fans installed in an equipment cabinet. As someone else has noted, an ATX power supply will remain in standby mode until it receives an ON signal from the motherboard.

Does anyone know how to simulate this signal so that the power supply will operate eventhough it is not connected to a motherboard. I know this sounds like overkill for a couple of fans, but the cost of the power supply is actually cheaper than some other alternatives I have looked into.

Thanks,
Jim

[Rick]

Put at least 1amp load on the 5+ volt and it will fool the P/S into normal operation

[JimK33]

Thanks for the response. Two questions.

1) can I put a 5 or 10 ohm resistor from a 5v line to ground to do that?

and

2) According to a drawing I have for the powersupply it shows a green wire as "PS-ON". I've noticed that if I put a jumper from any of the positively powered lines, 3.3, 5 or 12v to this pin the power supply seems to operate. I'm concerned that maybe this should only be a momentary contact rather than permanent, or I'm damaging the supply by doing this.

Any thoughts?

[Rick]

#1 ??? I'm sure about this one.

#2 the mother board tells the P/S to stay on as long as it is working
By connecting the +5 volt you may be able to do both power good and stay on..

You may want to try a line to power good and a moment switch to the PS-On and see what happens

[JimK33]

Just so I understand, you said you are sure a 5 or 10 resistor from +5v to common would work, or do the question marks mean you are not sure about this one?

Second, when you say a line to power good (I assume this is the gray wire labeled as "PW-OK"), should this connect to common or +5v?

[JimK33]

Rick,
I did some hunting around on the internet and found a site called Modtown that had the answer I was looking for. You just need to jumper from the green "PS-On" to common to turn on the power supply. As for the 1 amp load on +5v, I haven't tried that yet, but I found another site that said that the voltage might be unstable with no load on the +5v line.

In case anyone is interested here's a link to Modtown: http://modtown.co.uk/mt/article2.php?id=psumod

Thanks for your help.
Jim

[Rick]

The ?? on number 1 /
I'm not sure the 5 or 10 ohm will work.

If you going to use this for fans.
Why not connect a small heatsink fan to the 5 volt

It could be used as an extra fan for the P/S itself
Blowing air into the P/S for example

[zoe]

I have used the power supply to power the car fridge at home.
Just put at least 1 A load on the + 5V out to achieve the correct voltage at + 12 Vdc OUT.
With no load on 5 Vdc 12 V out = 10,8 Vdc; with 1 A load 12 Vdc out = 11,85 Vdc.

Mandi

[Whyzman]

I think I'm going to have to begin putting things on video for myself so I can check out things I seem to remember doing...:rolleyes:

When I put together my SCSI "storage tower," I purchased a case that came equipped with a power supply designed for connection to a motherboard.

Since my "storage facility" was going to be connected via SCSI cable externally to my computer...it had no need for a motherboard...

However, I did need to power up the 4 SCSI drives I planted in there and run a couple of fans to cool the place down...

The solution was not to use the momentary switch on the front of the "storage" case, rather, just use the rocker switch on the PSU when I wanted to crank 'er up...

To accomplish this, I seem to remember connecting the green wire to any ground...

Without a video to prove I did it to myself...I'm having to rely on my frail memory... :(

It works just fine...If you're seriously interested I will pop the case and check my wiring just to make sure for you...

[JimK33]

To: Zoe
I saw voltage values similar to what you reported when there was no load on the PSU. Actually, the voltages bounced around. The two thermaltake fans I plan to use appeared to be enough to stabilize the voltages. The fans are variable speed. The tech info on them says their current draw varies from 0.2 to 0.7. Two of them would be 0.4 to 1.4, but voltages seems stable even at low speeds when the load would have been around 0.5A. More would probably be better.

TO: Whyzman
I'm still thinking about how I want to turn the PSU on and off. I want to use the fans to cool an A/V receiver and thought I'd plug the PSU into the switched utility outlet. That way the fans would come on when the receiver powered up. The PSU rating is more than double the rated capacity of the outlet, but shouldn't be a problem since I'm only planning on running two fans. Still, I'd hate to blow the receiver if there is a short in one of the PSU lines. I hadn't thought of that before. Also, I'm thinking there maybe some interesting things I can do with the extra power. Maybe some red leds behind the TV to give it that vaccuum tube look.

The PSU will probably be inside or behind the cabinet so I can't use the PSU switch for power on. I suppose I could put a switch in the jumper wire so that the PSU would come out of standby when I closed the switch. Have to think about that some more.

As Scotty said, "The more they overthink the plumbing the easier it is to stop up the drain." Maybe I'm making this too complicated.

Anyway, thanks for all your thoughts. They've been very helpful.
Jim

[drewbob]

I'm assuming you already have an ATX power supply for your purpose, but an older AT power supply might work well. I believe that an AT unit will run independently from a motherboard without having to do anything. Also, they often have a "hard" switch that would simplify switching on and off. I would imagine someone would be happy to let you take one off their hands.