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Connecting 3-pin CPU fan to 4-pin motherboard

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July 7, 2010 9:26:38 PM

Hi,

I've got Thermalright Ultra-120 heatsink and Thermalright TR-FDB-2000 Stealth Silent Fan.
My motherboard (EVGA x58) has a 4-pin fan connector and the fan has a 3-pin connector. What will be the right way to connect the fan to the motherboard? Should I get a 3-to-4-pin adapter? Also, what is the benefit of the 4th pin?

Another questions is, if i get the second fan, and make one of them push and the other to pull the air will it make fans to spin slower and be less silent?

Thank you,
Ruben.
July 7, 2010 10:21:28 PM

The 3-pin will plug into the 4-pin fan header the only thing is you wont have pwm control of the fan.
July 7, 2010 10:25:51 PM

What is the pwm control?
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July 7, 2010 10:36:10 PM

It is what the 4th wire would be for to control the fan speed.
July 7, 2010 10:42:46 PM

So the fan will spin with the constant speed? I thought that fan can be controlled with 3 pins by changing the voltage....

What kind of 120mm fan will you suggest which will be PWM controlled? I want the fan speed to be controlled by the system and to go lower when idle and speed up when system is under high load. Also thinking to set push-pull dual fans so they work together under lower RPMs.
July 7, 2010 11:07:27 PM

Your MB might allow you to control the fan on the 4-pin header but mine wont. I moved my HS fans to 3-pin headers that do allow me to control their speeds. I have two high speed fans on my TRUE and have them connected to the fan headers labeled System and Chipset keep them at the 1350rpm area.

Here is what I control them with.

Showing fans at default speeds.


Showing fans at the speed I normally run them at.


How set them.

July 7, 2010 11:34:01 PM

I'm thinking about getting 2 PWM fans and connect them using a parallel Y connector an connect to CPU header so that both of them get the same speed setting. Do you think if it will work?
July 8, 2010 10:10:23 PM

Y Connectors hinder impediance and are not recomended.
July 9, 2010 5:02:51 PM

impediance????

Y connectors simply increase the current draw through the header....which isn't necessarily good for the mobo....in this situation ou can get special connectors that get the power draw from molex from the psu, while combining the pwm wire so you can plug it into the mobo header
July 12, 2010 9:29:59 PM

Guys, I didn't get the idea what it actually means.
Could you please explain it?
July 17, 2010 4:18:27 PM

Too long, don't wanna read:
Impedence is resistance; more wire = greater resistance; more devices = greater resistance.
3-wire fan on a 4-pin interface is fine; match pin1 to pin1.
Having a push-pull fan might not help, because fans work off CFM (air-flow), and the sound you hear comes from the speed of the fan-blade cutting the air (and its design) - which will still be the same even if 2 fans were to work half as hard as 1, because the speed is still the same to provide the CFM.
A larger fan with cowling might be a better option, if you have the space for it.


(more detail)
Impedence is the natural resistance of electricity moving through the wire, though is variable by wire-gage / diameter (or by volume, if in high voltage elec. transmission and distribution bus-work, though that's another story :)  ), length, even chemical properties; Ohm's Law can define it more-better than I can ;) 
Inductance is the opposite, in that the electro-magnetic fields generated by electricity transmission over two or more wires can co-generate a stronger field, and improve the harmonics of the electric sign-wave... Which, is why 'twisted pairs' provide a better signal-strength, especially over longer distances. On a high-voltage 3-phase A/C-system (60hz, with each phase 120-degress apart), you'll often see a 4th wire (neutral, but through inductance will generate a slight amount of current) IE, A B C N; though if a circuit runs many miles, you will see the phase-wires will rotate - that is because phase B running along sides phase A and C will carry higher voltage than the other two, caused by Inductance. SO, by rotating phases periodically, the voltage can actually be transmitted more evenly for 100's of miles IE A C B N and then to C A B N.

As for the fan - To connect a 3-wire to a 4-pin fan connector, just match pin1 to pin1; the connector should have an arrow or a 1 on the back, or, if looking at it from the end, pin1 is the right-side of the U shape. Also, the 4th wire is usually used for an additional sensor (look in the advanced power options of your motherboard) and isn't necessary.

(If I'm TOO far off on my understandings, I welcome correction :)  )
Anonymous
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a b K Overclocking
July 18, 2010 5:19:18 AM

Wow, lots of good responses here! I was just going to echo what has already been said and say simply "Yes, you can use a 3 pin on a 4 pin connector. Generally you line up on the right side (if your looking dead on with the I/O panel facing top left). "
July 19, 2010 7:29:21 PM

ok guys, thanks for useful information!
July 20, 2010 1:10:39 AM

uh_no said:
impediance????

Y connectors simply increase the current draw through the header....which isn't necessarily good for the mobo....in this situation ou can get special connectors that get the power draw from molex from the psu, while combining the pwm wire so you can plug it into the mobo header

Could you explain this a little further?...

I want to slap two 3-pin fans on a Corsair H50 cooler in a push/pull array, but would like the mobo to control their speed via voltage so I want to plug them both into the mobo's one CPU_FAN header

But if a y-splitter is bad for the mobo long-term, how can I get the 3-pin push/pull fans to get their power from the PSU, but have the CPU_FAN header control their speed?
!