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7 volt 3 pin fans

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Old 06-21-03, 11:00 AM Thread Starter   #1
Tical
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7 volt 3 pin fans


I have 2 120mm fans that are 3 pin & I want to quiet them down. Can I hook them up to 3-to-4 pin adapters & the do a 7 volt mod on the adapter? Will that work? I don't want to have to buy new fans & don't know if there is any other way to 7 volt a 3 pin fan. Any help fellas?
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Old 06-21-03, 11:05 AM   #2
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Hmm...im not sure but I imagine that you would just be able to switch the necesary pins in the 3pin header to go onto the corresponding one that would go in a 4pin setup.

To get the pins out of the 3pin molex get a small standard screwdriver...or whichever is the flat one and turn the connecer so that u see 3 gold/brass looking things. Press those 3 things down with a bit of force, and then u just slide them out. IIRC, to put them back in you won't have to move that tab up, it will squeeze itself in i think.'

This is just what I think, I personally have never done this..(w/a 3pin)
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Old 06-21-03, 11:19 AM Thread Starter   #3
Tical
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I am trying it by switching the pins in the 4 pin molex connector just like you would if your fan were 4 pin, & I just left the 3 pin connector alone. I'm not sure if it's working though as I am not sure how I'd even check it. Just sound I guess.
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Old 06-21-03, 11:59 AM   #4
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Here is what I have done:
Take the 3 pin connector of the fan and pop the 12V and GND wires out. Leave the signal wire in the connector then plug the connector to your MB (this will allow you to monitor the speed of the fan). Then take the GND and 12V wires and wire them to the 5V and 12V wires of a spare molex connector. YOu have now essentially done the 7V mod AND you can monitor the fan speeds.
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Old 06-21-03, 12:00 PM   #5
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sidewinder sells a3-4pin adapter, but you'd still have to mod that and doing it yourself is just more fun

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Old 06-21-03, 12:05 PM Thread Starter   #6
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I have the adapters, that's no prob, I just wasn't sure if it would even work or not.
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Old 06-21-03, 12:33 PM   #7
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Quote:
Originally posted by Tical
I have the adapters, that's no prob, I just wasn't sure if it would even work or not.
It will work.

12v lead on the fan goes to the 12v molex connector, Ground wire on the fan goes to the 5v lead on the molex (red). That will give you a potential difference of 7v on the fan. It's just a question of securing it into the connector correctly.

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Old 06-21-03, 01:17 PM Thread Starter   #8
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THX Cjwinnit.
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Old 06-21-03, 01:37 PM   #9
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Personally, I would still wire the signal from the fan to a mobo header. But maybe I just enjoy monitoring my fan speeds more than other people
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Old 06-21-03, 01:39 PM   #10
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Quote:
Originally posted by Lord_MiL
Personally, I would still wire the signal from the fan to a mobo header. But maybe I just enjoy monitoring my fan speeds more than other people
Don't do this if you 7v mod it, you will kill the headers and possibly damage the board.

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Old 06-21-03, 02:06 PM   #11
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How would connecting the signal pin to the mobo header and then 7V modding the fan from a molex kill the mobo headers??

It wouldn't be any different than wiring your fan up to a rheostat and still monitoring the speed on the mobo, and I've never seen a problem with that. In fact some companies make pre-built devices expresslyfor this purpose.

Do you know something that I don't?
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Old 06-21-03, 02:25 PM   #12
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Well, in a normal fan the signal wire oscillates a voltage of 0v and 12v. Every half revolution the fan gives out a pulse 12v signal.The chip measures this and works out the RPM. If you 7v mod the fan then the wire oscillates between 12v and 5v. In other words, there is always a potantial difference on the chip, so it permanently draws current, which buggers it up.

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Old 06-21-03, 02:40 PM   #13
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Hmmm....your reply makes perfect sense.
I guess I just assumed that the fan had some sort of switch that went on and off with each revolution rather than switching between the 12V and GND lines from the PS, which in this case would be 12V and 5V. Since all my mods have been rheostats, I assume this would explain why they still worked as it would be switching between GND and whatever voltage the 12V has been dropped to by the rheo.

Hmm...interesting. Well I guess I won't give that advice anymore! Thanks
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