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Thread: new PC fan has a 3rd wire what's it for?

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    swords's Avatar
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    new PC fan has a 3rd wire what's it for?

    I bought a 217 CFM PC fan for my new vivarium setup but when it came it has 3 wires instead of two. What is the 3rd wire for? Can I run the fan just using the red and black hooked to a 12V wall wart as usual or does the yellow wire (or is it blue) have to go somewhere? I've wired up a few two wire fans before but never messed with a 3 wire one.

    I got an awesome lot of 10x two wire/12V 3" 32 CFM fans for $1.39 each off evilbay for use as tank to tank airflow and lamp heat extraction on the new vivariums I'm planning, but this was to be my main workhorse input fan for the whole rack. I'd hate to think it's essentially "useless".

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    Jag's Avatar
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    maybe a ground wire or maybe the fan can be used as a 3 way fan... hhmm connect the black and red and see if the other wire has any power.
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    Jesse

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    ground wires are usually green, not blue or yellow.

    lemme guess, you are color blind between the blues and yellows?

    here in canada it goes like this:
    2 wire: red hot, black neutral/return.
    3 wire: red hot, black return, white neutral.
    i think green(or bare) is standard for ground(earth) no matter the country.

    here's the link for us standards
    http://www.allaboutcircuits.com/vol_5/chpt_2/2.html

    what you could have is a three-phase fan, where the black and red are line 1 and line 2, and the blue would be line 3, in this case, you'd need a transformer to convert 120v to three-phase.. wherever you bought your 12v converter, will probably have what you are looking for...

    hope this helps

    edit: a little about three phase electricity http://en.wikipedia.org/wiki/Three-phase_electric_power
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    http://terraforums.com/forums/showthread.php?t=114907

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    Hello, I must be going... Not a Number's Avatar
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    The third wire is for the tachometer to measure the RPM. If you put power through it you'll fry the circuits and kill the fan.
    Grand Hotel... always the same. People come, people go. Nothing ever happens.

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    blokeman's Avatar
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    Well I'm glad you chimed in, I knew I 'could' be right, but had a feeling I was a little off...

    Sorry for the misinformation swords :S
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    http://terraforums.com/forums/showthread.php?t=114907

    “Experience: that most brutal of teachers. But you learn, my God do you learn.” C.S. Lewis

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    swords's Avatar
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    Thanks, NAN so what are my options? Put it back on ebay? lol

    No Bloke, I'm not colorblind. I've just boxed it up while starting my renovations and don't remember what color it was.

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    Not really I am Bob's Avatar
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    You could just use the other two wires and not use the one that is the different color. I think that NAN is saying if you use that wire, it will fry the circuit. if you use the regular colors the fan should work fine.
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    Hello, I must be going... Not a Number's Avatar
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    Yep, that's what I meant. Don't answer technical question at 2 in the morning
    Grand Hotel... always the same. People come, people go. Nothing ever happens.

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