Quick Question About Small Case Fan Wiring

Discussion in 'The Projects Forum' started by Falafel Flop, May 15, 2015.

  1. Falafel Flop

    Thread Starter New Member

    May 12, 2015
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    Hey everyone, just about to start the build of my charging station, but I had one last question in regards to the fans.

    They're little 60mm 12v dc case fans which I plan on soldering directly to the power supply (it won't get too hot to begin with, but these are an extra precaution anyways) as I've seen countless do with a similar build; unfortunately the wires are just barely too short.

    [​IMG]

    When looking at the wires, I see there are three coming from the fan (obviously line, neutral and ground), but with the adaptor that makes the wires reach there are only two.

    [​IMG]

    Would it be safe for the fan and power supply if I snipped it after the adaptor and wired it without what I'm assuming is the ground?

    [​IMG]

    Thanks in advance! This really is a great and helpful community here

    Regards
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    What is the voltage rating of the fan and can you identify the power pin polarity ?
     
  3. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,539
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    Are you sure these ae AC fans? Could be DC fan with a tach output or fan speed control input. Also, if you really don't need cooling, consider only 1 fan. Less noise, less heat, etc.

    ak
     
  4. Reloadron

    Active Member

    Jan 15, 2015
    963
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    12 VDC case fans likely do not have a Line, Neutral and Ground. The third wire is likely a Tach Out (Tachometer Out) signal which you likely won't be using. Just a matter of getting the fan polarity correct. That would be my guess anyway. :)

    Ron
     
  5. Falafel Flop

    Thread Starter New Member

    May 12, 2015
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    It's this fan. Definitely DC and VERY quiet so I'm not concerned about noise

    [​IMG]

    The wires are both solid black, no white stripe...
     
  6. Reloadron

    Active Member

    Jan 15, 2015
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    Yeah, the adapter only picks 12 VDC off the molex connectors. The third wire is the tach signal and not used.

    Ron
     
  7. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Fan is 12VDC
    You need to find out the positive and negative pins of the fan
     
  8. Falafel Flop

    Thread Starter New Member

    May 12, 2015
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    How do I find that? The wires are not marked in any way that differentiates them and neither are either end of the adaptor. That aside, the molex connector is labeled 1,2,3 and 4 on each pin but that's it.
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,548
    2,373
    Modern small DC fans are actually BLDC with a fail sensor.
    The sensor output can be ignored where just DC supply is available and no failure circuit is present.
    In some cases the paper cover can be pried back and disclose the terminations and if you are lucky you can identify the + &- DC.
    Max.
     
  10. Falafel Flop

    Thread Starter New Member

    May 12, 2015
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    Bummer, just pried it up and one side was solid plastic and the other didn't allow a view of the terminations. Could I simply touch the wires to the outputs to find out since its such low current or would that be a bad idea even on this small scale?
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,548
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    If it is any help, the sensor is generally an outside conductor on the connector, so by trying the centre and an outside in turn should be OK.
    Max.
     
  12. Reloadron

    Active Member

    Jan 15, 2015
    963
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    The two center pins on the 4 pin molex are Ground. One outside pin is 12 V and the other is 5 V. Your fan adapter only goes to a Ground and 12 V pin. Look at the adapter and note which of the two black wires goes to the outside pin of the molex. Should be Pin 1 of the 4 pin molex. Pin 1 is 12 V, pins 2&3 are Ground and pin 4 is 5 Volts. On the small connector for the fan, pin 1 should be Ground, pin 2 is 12 Volts and Pin 3 would be the unused RPM Tach Signal.

    Ron
     
  13. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    May be you can trace the polarity looking at the Molex connector ( if the molex wires are according to standard )
    Or use the DMM to check the voltage and confirm molex connection
     
  14. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,986
    745
    before you hack the plug off, the two black wires will go to the ground and 12v terminals on the four pin molex, so you can work out the pos and neg, chances are it will run backwards or not at all if wired reversed.
     
  15. Falafel Flop

    Thread Starter New Member

    May 12, 2015
    8
    0
    Thank you all SO MUCH! Going off the molex that way gets the polarity all figured out all the way back to the fan. You guys are great!
     
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