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Using a PSU to power external 12v fan(s)

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October 28, 2011 8:24:10 PM

The Situation
I'm putting together a man-cave in the basement for my gaming/office needs. I'd like to incorporate a small intake fan (positive pressure) into a window

I've got a nice Platinum PSU in a new build, and am going to be using a fan controller (matches my case and gets good reviews) to help control the 3 main case fans in my new case.

The Rationale
I'm getting a controller with extra slots because I'd like to use it to control a fat or two outside the desktop, but powered by the PSU. This essentially to take advantage of the super-efficient power my PSU provides, and avoid having to get/wire another small inverter/psu to power these fans. The concern is whether I can use these fans when the computer is off. I know that some PSU's and some MB's provide power to some slots/outlets (typically a few USB ports at least) even when they're "Off."
Quote:
Note: I don't want to use USB fans because they're only 5v and are typically too feeble for this application, and 5v doesn't travel well in long-ish wires.


The Goal
Wire up the power supply/mobo to the controller slots, and to the external fans (I'll have to get some Molex and/or 3-pin fan cable extensions) in such a way that allows for always-on controller and fans.

If that's not possible, wire it so as to at LEAST always be on when the box is on.


Anyone here have experience with this kind of mod?
a b ) Power supply
October 28, 2011 8:55:46 PM

nice idea, just get mains powered fans though, PSUs aren't actually all that efficient. A psu at 80% efficient would be 80% as efficient as a mains powered fan.
October 28, 2011 10:08:20 PM

"Mains" powered fans? I don't want a 120v, 30w fan humming away making a lot of noise and moving hundreds of CFM.

I want a quiet, small, 2-5w fan pushing 20-40 cfm. I have never found ONE 120v fan that wasn't too loud, with the exception of some squirrel cage blowers, but they're too big for the space I'm working with.

Also, if you checked the link to the PSU, this is the most efficient PSU on the market, rating from 90%-94% efficient, even at very low loads. For 5 watts, those losses are negligible.
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a b ) Power supply
October 28, 2011 11:53:24 PM

I don't think you can run 12v rails when the computer is off, or 3.3v or 5v for that matter.

I think all the "off" power for things like sleep mode is through the +5SBv connections which tend not to have high amps and you won't get very much juice out of it. At best one small fan probably.

Just FYI.
a b ) Power supply
October 29, 2011 1:55:05 AM

One problem with using a computer power supply as a 12V power supply.

The 12V supply is NOT regulated but relies on its regulation by ratio of the transformer from the regulated 5V supply. In practice this means that the 12V can drop to less than 9V or more depending on the load. This will cause any fans connected to the 12V rail to run slowly. To get the 12 volts rail to be 12 Volts you will have to provide a load on the 5 volt rail that draws several amps.

Best solution

a c 246 ) Power supply
October 29, 2011 6:41:16 PM
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pjmelect, that is only true of group regulated designs which are on smaller less expensive PSUs, most higher end units and almost all gold and platinum units are independently regulated so each rail is maintained at its nominal voltage naive to the load or voltage of the other rails. Look at the crossloading tests done in the review to see thats its an indy regulated design.
http://www.jonnyguru.com/modules.php?name=NDReviews&op=...


As for the main question, you wont be able to get the 12 V rail to stay hot with the system shut down, only the +5VSB rail is live which supports USB ports. If you hook them into molex ports like normal they will always be on when the system is on.
October 31, 2011 4:47:55 PM

hunter315 said:
pjmelect, that is only true of group regulated designs which are on smaller less expensive PSUs, most higher end units and almost all gold and platinum units are independently regulated so each rail is maintained at its nominal voltage naive to the load or voltage of the other rails. Look at the crossloading tests done in the review to see thats its an indy regulated design.
http://www.jonnyguru.com/modules.php?name=NDReviews&op=...


As for the main question, you wont be able to get the 12 V rail to stay hot with the system shut down, only the +5VSB rail is live which supports USB ports. If you hook them into molex ports like normal they will always be on when the system is on.


Great info from all of you. This Jonnyguru article settles it, though. If I can only expect the 5v rail to run while the system's off, I wouldn't be able to run the 120mm 12v fans I'd like to, so that kinda kills it right there. 5v fans I've seen just don't provide enough pressure to do what I want to do. Also, with a dismal 5v efficiency in the 75% range, I'd be just as well of with the average brick, like netyoda linked to.

Quote:
BTW, I love the coolerguys. I'm building a small 12v exhaust system for my fiancee's cat's litter box, that I'll eventually hook up to a motion detector/timer. Fun project.


I think that the Kingwin Lazer Platinum is really an amazing PSU. Someone should get an award or two for engineering and quality like that. Now, I want them to make a pico-psu to the same standards so I can put it in a custom HTPC built I'm noodling.

Thanks, all!
October 31, 2011 4:48:10 PM

Best answer selected by pdxoutdoors.
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