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Old 10-16-2013, 01:11 AM   #21
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Does turning the pot do anything to the speed? Are you sure you have hooked up the correct terminals on the pot?



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Old 10-16-2013, 04:32 PM   #22
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your potentiometer (pot) should be wired as shown... using one side and center terminal on pot. (The on/off power switch can break either leg)

Components MUST match - both Fan and transformer output (Direct Current)

if AC, start over, get a light switch dimmer...

good luck!





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Old 10-16-2013, 05:30 PM   #23
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Everything is hooked up correctly. I know this because the fan works the exact same through the pot and switch as it does straight to the power supply. I've tried two power supplies now both say output is 12V - 500mA and on was .2A and the other was .3A. The second power supply was actually purchased from an LED site (rapidled.com) that actually sells these to run pc fans as cooling units in light fixtures. I've had it hooked up to 2 smaller fans before that worked great. I think the issue must be the fan. For whatever reason the fan just isn't work. Any more ideas would be greatly appreciated but I just can't figure this out.

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Old 10-16-2013, 05:33 PM   #24
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Quote:
Originally Posted by DaleHair View Post
DC power supply, AC fan
How can I tell if a fan is ac or dc? I'm guessing this is the problem since both power supplies aren't working strong enough and I know the 2nd one ran two other fans I've had.
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Old 10-16-2013, 05:38 PM   #25
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How can I tell if a fan is ac or dc? I'm guessing this is the problem since both power supplies aren't working strong enough and I know the 2nd one ran two other fans I've had.
It is DC.

1. It's a computer case fan, and they are all DC since everything in a PC except for the power supply itself runs on DC. AC fans are common for all types of enclosures and other uses, but never for PC use.

2. It should tell you on the fan itself on the sticker on the back of the motor housing.

3. If it was an AC fan it would not run at all when hooked up to your DC power supply.

Do you have any other fans in a computer you could borrow for a test? Are you anywhere near Edmond OK?
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Old 10-16-2013, 05:44 PM   #26
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Originally Posted by STL_Lucas View Post
How can I tell if a fan is ac or dc? I'm guessing this is the problem since both power supplies aren't working strong enough and I know the 2nd one ran two other fans I've had.
It should have a label on it, stating something like 12VDC. Most computer fans are DC, just because the power supplies include taps at that voltage. But low-voltage AC fans are not unheard of.

Find another fan. They are dirt cheap. You can even get them for around $5 on Amazon.
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Old 10-16-2013, 06:10 PM   #27
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I don't have another fan on hand I can try but I'll pick another one up just to be sure. Also I've read ten times that the middle wire on the fan is useless and not needed. Is leaving this out of the equation part of the problem? Should it be added to either end of the power supply?

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Old 10-16-2013, 06:36 PM   #28
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Also I've read ten times that the middle wire on the fan is useless and not needed. Is leaving this out of the equation part of the problem? Should it be added to either end of the power supply?
On a 3 pin fan you have:

Red = 12V power
Black = Ground
Yellow = Tachometer lead

The Red is the positive power lead, the Black is ground and connected to the negative pole, the yellow is not connected as it is merely for sensing the speed of the motor. sometimes you will have a white wire it serves the same purpose. A 4 pin fan has a different layout and a 4th wire for PWM, but yours is a 3 pin so that doesn't apply.
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Old 10-17-2013, 07:39 PM   #29
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Ok so the way I have mine hooked up I have the Red to the hot wire, the yellow to the negative and the black is not hooked up. Could this be the issue with the fan running slow or should it not run at all like this? I'm going to swap out the yellow and black wire when I get home and try that.

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Old 10-17-2013, 07:42 PM   #30
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Originally Posted by STL_Lucas View Post
Ok so the way I have mine hooked up I have the Red to the hot wire, the yellow to the negative and the black is not hooked up. Could this be the issue with the fan running slow or should it not run at all like this? I'm going to swap out the yellow and black wire when I get home and try that.
Yes. The Red is the positive, the black is the negative, and the yellow is the sense wire, or at least it should be. I've never seen a case fan wired any other way except that sometimes you will see a white sense wire instead of yellow. One option is pealing up the sticker on the back of the motor housing until you can see the wires themselves soldered onto the board and look at the +/- symbols next to the cables. If these symbols are there it proves which wire is which.


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