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DELL PC Fan question

Posted: Sat Apr 14, 2007 10:13 am
by nickvd
I'm re-purposing a dell fan (4.75 inches in diameter about 1.5 inches thick) for an exhaust fan in a small painting booth I'm constructing. The fan has 4 wires wired to it, red, black, white, blue.

Red and black are of course + and - as I have successfully hooked it up to a power supply. My problems is its noise... It's VERY loud and moves far too much air. The other problem is the size can't be more perfect unless I had someone custom built me one.

My standard response would be to hook up a rheostat to the fan, but then I got to thinking... There is no way dell would let the fan run at it's full speed all the time, they would be able to hear it from their corporate hq. So this leads me to the other two wires, blue and white.

I've done quite a bit of searching on this, and found the datasheet for the fan in question (Delta AFC1212DE), but it only tells me about the running specs, not the wiring specs. My question should be obvious by now... What are the other wires used for, I'm almost certain one is for speed reporting as on most other 3-wire fans, but that 4th wire is new to me...

If anyone has an idea I would really appreciate it.


Alternatively... If using a standard rheostat won't hurt the fan or the PSU (re-appropriated 100w atx) won't hurt it, that would be the best way to do it...

Posted: Sat Apr 14, 2007 1:52 pm
by Kieran Huggins
just to be clear, are you powering the fan at it's correct voltage? It seems to me that Dell fans are typically notoriously quiet...

Posted: Sat Apr 14, 2007 2:29 pm
by nickvd
Yeah, it's rated for 12v@1.6a

I rigged up a molex connector, using A yellow/black pair which should be +12v Right?


Image

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It's a massive suckah (quite literally, well over 100CFM) ;)

Posted: Thu Apr 26, 2007 12:32 pm
by tomk
The fourth wire is used to control the speed of the fan.

The four wires are:
1. 12V Power
2. Ground
3. Tach output
4. PWM-drive input

It's probably running full speed because you are not providing the PWM input.

BTW, here's a spec that explains the use of the wires:
http://www.analog.com/library/analogdia ... _speed.pdf

Posted: Thu Apr 26, 2007 1:00 pm
by nickvd
Why thank you for registering in order to help me, I really appreciate it!

I am at work right now, so I cant read that PDF file, would you be able to, ever so briefly and simply explain what items i would need to use it's own speed controller? Right now I am (was) planning on adding a simple rheostat to it. I would much rather use the fan's own mechanism for that though as it should drastically increase the life-span...

Posted: Mon Apr 30, 2007 2:51 pm
by tomk
Basically, you will need a device/circuit to generate a Pulse Width Modulated signal. I just swapped out the exact fan in one of our systems. Since electronics is also a hobby of mine, your post inspired me to start thinking about how I would create a circuit to control the speed of the fan. I have an idea I want to try. I can get back to you in a couple of days with the results.

Posted: Mon Apr 30, 2007 4:39 pm
by nickvd
That would be fabulous... I have electrical experience (plugs, sockets, switches, etc..), but not much electronic experience...


I can build circuits if I have a parts list and a schematic for it, but the designing is beyond me :)

Just Registered

Posted: Fri May 04, 2007 11:02 pm
by ncspecv81
Hey - i saw your post and like you I was dying to know what wire done what as i have a few of these afc1212de fans.


anyways figured ide register and share with you guys


red - power
black - ground
blue - pwm wire
white - rpm sensor wire