Connect Molex AND 3-pin fan?

I am building my new PC-- Asus P5B-Plus motherboard, Thermalright Ultra-120 Extreme heatsink, and a yate loon fan to cool this heatsink. It's been years since I last built a rig so I have a question on connecting the heatsink fan.

My mobo has a 4-pin header, but my yate loon fan has the 4-pin molex power and a 3-pin connector. Should I connect JUST the 3-pin fan connect to the 4-pin mobo header? Or, should I ALSO connect the fan molex connector to power it as well?

Thanks for any helpful feedback.

I'd plug the 3pin into the motherboard ONLY. That way you can control RPMs via software (Speedfan) or the BIOS.

One or the other, not both.

-bZj

One or the other, not both. I'd recommend the 3-pin.
Plugging in both has a high likelihood of damaging your board; the 3-pin is variable speed, meaning most likely variable voltage. If your motherboard tries to drop the fan to, say 6V instead of 12V, the Molex will keep pumping 12V across the same leads. Your board will then have 6V pushing the wrong way through the fan header.

mavalpha said:

One or the other, not both. I'd recommend the 3-pin.
Plugging in both has a high likelihood of damaging your board; the 3-pin is variable speed, meaning most likely variable voltage. If your motherboard tries to drop the fan to, say 6V instead of 12V, the Molex will keep pumping 12V across the same leads. Your board will then have 6V pushing the wrong way through the fan header.

Click to expand...

$hit. That's what I just did, and got some nice smoke coming from my mobo. Now, it appears my mobo is dead-- the green light at the bottom right of the board lights up, but nothing else powers up. Should I assume this mobo is now fried?

mavalpha said:

One or the other, not both. I'd recommend the 3-pin.
Plugging in both has a high likelihood of damaging your board; the 3-pin is variable speed, meaning most likely variable voltage. If your motherboard tries to drop the fan to, say 6V instead of 12V, the Molex will keep pumping 12V across the same leads. Your board will then have 6V pushing the wrong way through the fan header.

Click to expand...

Assuming this mobo is fried and I need to get another, exactly which three of the four pins should I connect. Should it be the far right 3 or the far left 3? I also have an aerocool FP-01 fan controller/memory card reader which can be used to control the fan. Should I plug the heatsink fan into this loop so that I can control the heatsink fan from the fan controller?

BTW- this is all inside an Antec P182 case, which has three case fans already connect to L-M-H fan switches, so it looks like the only fan I can control from the Aerocool fan controller would be the heatsink fan (the Yate Loon with the 3-pin connector).

Thanks for any further input. I'd like to not fry another mobo...

If your motherboard has the "new" 4-pin header, the stub will only let you put it in one of the two positions. It is keyed to prevent you from installing it on the wrong one.

mavalpha said:

If your motherboard has the "new" 4-pin header, the stub will only let you put it in one of the two positions. It is keyed to prevent you from installing it on the wrong one.

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It's a new Asus P5B-Plus mobo, so yes it appears it has this stub from what I recall (I've packed away the case and fan, so can't see it right now.)

Thanks.

Two hours of waiting vs. impatience and a dead mobo.

Shameful what the Internet has done to ppl's attention spans....

-bZj

Down8 said:

Two hours of waiting vs. impatience and a dead mobo.

Shameful what the Internet has done to ppl's attention spans....

-bZj

Click to expand...

No. Actually this happened last night but I didn't describe it accurately. I came into HardForum to confirm what I should have done, vs what I already did. But, I would agree that my patience to get my new rig up and running was short at midnight last night when I discovered my fateful error... not enough time to spend building.

I should have followed the sage carpenter advice: measure twice-- cut once.