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Quick question on connecting two PWM fans to the same motherboard header.

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post #1 of 13

5/31/12 at 4:08am

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tpi2007
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Hi guys!

This is more of a reliever than anything else. I have already done what I propose to in the title with the appropriate 4 pin Y cable, but there is something intriguing: sometimes the monitoring software I use reports min and max rpms that are below and above the rated specs for the fans.

They are Noiseblockers XLP (120mm), PWM, that go from 1000 to 2000 rpm, and they scale well when under load, but the software reports 500 rpm as the min and 2500 rpm as the max. Surely this is the motherboard sensor getting mixed up because there are two of them connected to the same header, right ?

If I connect them to separate headers this doesn't happen. The reason I don't want them connected to separate headers is because the chassis header has a different PWM algorithm that keeps slightly ramping the fan up and down at the slightest system load; besides, having them both connected to the CPU optional fan header makes them ramp up according to the CPU load, which helps make equal push / pull from the heatsink, that also has a Noiseblocker, this time an M12-P, but with the same 1000rpm - 2000rpm, so they end up working as a team like this (and I don't get that pesky ramping up and down from the fan connected to the chassis header each time I open a webpage).

Thanks in advance!

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post #2 of 13

5/31/12 at 4:46am

mm67
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Only one fan should have it's rpm signal wire connected to motherboard header, otherwise rpm monitoring doesn't work properly.

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post #3 of 13

5/31/12 at 4:51am

mablo
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Hmm so that's why one of the headers on the splitter i got, had only 3 pins instead of 4 like the other does. That explained it.

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post #4 of 13

5/31/12 at 4:59am

windfire
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Not all PWM Y-cables are created equal. Some are just not well thought out.

For example, both fan connectors of the OKGear one has all four pins. This will confuse the mobo as PWM signals come from both fans. This is not good.
http://www.newegg.com/Product/Product.aspx?Item=N82E16812123298

Gelid one has done it right. One fan connector has 4 pins while the other has 3 pins. This is good.
http://www.newegg.com/Product/Product.aspx?Item=N82E16812718001

post #5 of 13

5/31/12 at 9:02am

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tpi2007
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Quote:

Originally Posted by mm67

Only one fan should have it's rpm signal wire connected to motherboard header, otherwise rpm monitoring doesn't work properly.

Quote:

Originally Posted by windfire

Not all PWM Y-cables are created equal. Some are just not well thought out.
For example, both fan connectors of the OKGear one has all four pins. This will confuse the mobo as PWM signals come from both fans. This is not good.
http://www.newegg.com/Product/Product.aspx?Item=N82E16812123298

Gelid one has done it right. One fan connector has 4 pins while the other has 3 pins. This is good.
http://www.newegg.com/Product/Product.aspx?Item=N82E16812718001

Thanks! Rep+

Man, I've got the first kind of Y cable. I think I read somewhere that the new PWM fans were able to work with this kind of cable.

Now that I think of it, I've got regular three pin Y connectors that do the same thing, where only one fan sends the rpm information to the motherboard. So, in this case I have to cut the rpm wire (windfire, I think you mean rpm signals and not PWM signals in your post, right ?). The PWM wire stays intact, so both fans receive the same PWM signal to work at the same speed, based on one of the fan's rpm.
Edited by tpi2007 - 5/31/12 at 9:17am

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post #6 of 13

5/31/12 at 9:18am

doyll
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Quote:

Originally Posted by tpi2007

The PWM wire stays intact, so both fans receive the same PWM signal to work at the same speed, based on one of the fan's rpm.

Not my post but yes, PWM goes to all fans but only one fan supplies RPM signal to motherboard.
Akasa and Gelid both make PWM splitters that use a molex connector for 12v power. I'm using them running 7 fans from mobo cpu PWM socket.

post #7 of 13

5/31/12 at 6:03pm

windfire
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Quote:

Originally Posted by tpi2007

(windfire, I think you mean rpm signals and not PWM signals in your post, right ?). The PWM wire stays intact, so both fans receive the same PWM signal to work at the same speed, based on one of the fan's rpm.

Yes, I did mean the rpm (fan speed) signal and not the pwm signal. In my haste, I typed that wrong. The description in my pics are right.

Instead of buying a new cable, just carefully remove that rpm pin from one of the fan connector and it will be fine.

post #8 of 13

5/31/12 at 7:47pm

GeneO
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Best bet is to get one of these. It is a splitter but takes its power from a Molex connector (so won't overload your MB fan header), the rpm signal from the motherboard is sent to all fans, and only reports the rpm from the fan to the motherboard for one of the connectors.

http://www.newegg.com/Product/Product.aspx?Item=N82E16812119248

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post #9 of 13

11/17/12 at 10:24am

BulletProofGeek
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Sorry for digging up this thread, but does anybody know where i can get a 3-pin version of these things?
Much obliged.

post #10 of 13

11/17/12 at 10:55am

doyll
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Quote:

Originally Posted by BulletProofGeek

Sorry for digging up this thread, but does anybody know where i can get a 3-pin version of these things?
Much obliged.

What exactly do you want?

There is no such thing as a 3 pin fan PWM splitter because the 4th pin is the PWM control.

There are 3 pin fan splitters

There are molex socket to 3 pin fan splitters.

There is no such thing as a motherboard controlled 3 pin splitter with molex power socket.

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