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Power fan with PSU, but monitor and control speed with MOBO?

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December 16, 2012 3:42:34 AM

I went through 4ryan6's 2012 fan roundup and decided to buy a couple of Cooljag 120 and 140mm fans. Of course, having something to compensate for, eh hum, <cough>, excuse me, I saw that Cooljag offered a higher CFM 140mm than 4ryan6 reviewed and had to get a couple of those. BTW, I bought them directly from Cooljag as I live 15mi away and they charged an arm and a leg $18 compared to FrozenCPU's prices.

I want to mount one of the 140mm Cooljag F121425BU in a Antec One Hundred case with an Asus P8Z77-V Deluxe. This fan can draw up to 1.1 amps, which is a bit much for a MOBO header. Asus only lists the current rating of the CPU_FAN header, which is one amp, and not any of the other five headers. Asus' tech support doesn't know the difference between electric current (measured in amps or joules) and electric potential difference (measured in volts), so the only answer I've gotten so far is "12v." :pt1cable: 

My idea is to power the fan directly off the PSU, but use the MOBO header to obtain and control fan speed. Anyone done this, and if so what were your experiences and what should I look out for?

Thanx for your input on this.

Cheers

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December 17, 2012 12:45:38 AM

I'm not one to argue with Asus's specs, but I wouldn't have any problem running a fan that is rated at 1.1A off a motherboard sys fan header. Besides, if the fan has a 3-pin header connector, it is safely designed for that purpose. I feel you are worrying over nothing. Again, just my opinion. A 12V DC motor at 1.1A is only 13.2W, and then only at full speed.

But to do what you want to do, you would need to splice the (+) and (-) from a PSU's Molex connector (or use an adapter) to the fan's header connector so you could plug it into the motherboard while using the PSU to supplement power in parallel with the header. That would allow the fan's RPM feedback wire to provide input to the board.
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December 17, 2012 5:11:58 AM

clutchc said:
I'm not one to argue with Asus's specs, but I wouldn't have any problem running a fan that is rated at 1.1A off a motherboard sys fan header. Besides, if the fan has a 3-pin header connector, it is safely designed for that purpose. I feel you are worrying over nothing. Again, just my opinion. A 12V DC motor at 1.1A is only 13.2W, and then only at full speed.

But to do what you want to do, you would need to splice the (+) and (-) from a PSU's Molex connector (or use an adapter) to the fan's header connector so you could plug it into the motherboard while using the PSU to supplement power in parallel with the header. That would allow the fan's RPM feedback wire to provide input to the board.



If I knew that all of the fan headers were rated for 1A I too wouldn't be concerned as one would hope ASUS, being a top-shelf brand, wouldn't skimp on quality and rate their products with sufficient padding to allow for real-life variances, within which I believe 10% should fall.

As for the how of what I was planning on doing, I was planning on pulling the positive and negative leads from the PWM connector and connect them to a standard Molex connector and plug it into the PSU. Thus the PSU would power the fan, and yet the motherboard would still be able to sense the RPM and send control signals to the fan's PWM.

As luck would have it, I'm not the first genius :pt1cable:  to have this idea. It turns out Gelid has a product designed to do just what I'm talking about, except theirs is made to control four fans, and not just a single as I was wanting to do. It is called, funny enough, "PWM 1-to-4 Splitter," and is under their Silent product line.

http://www.gelidsolutions.com/products/index.php?lid=2&cid=11&id=63&tab=3

But all-in-all, you are right, I was probably being overly cautious. Plus I was exhausted, and shouldn't be posting when I'm dizzy with sleep deprivation.
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December 17, 2012 5:12:06 AM

Best answer selected by PheckPhul.
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