What is the difference in 3-pin vs. 2-pin fan headers?

[Epsil0n00]

So, I am about to buy a fan to put on an Alpha PAL 8045, but I don't quite understand the difference between the different connection styles that some fans come with. There's 2-pin and 3-pin... what other types are there? If someone could explain the differences and which types plug into what, I would be very grateful! Thanks in advance! Also, where do temp. controled fans factor into the scheme of things? THX.

Epsil0n

 

[Colt45]

2,3,4 pin
2= +12,grnd.
3= +12,grnd, rpm sensor
4= normal molex plug..

 

[NTB]

The only difference between a two and three pin connector is that the third pin (assuming that your mother board has a three-pin connection as well) allows you to monitor the fan's rotation speed. Another connection that you might see is the two/three pin header going to something that looks like the connectors on your computer's power supply. This is for high-speed/high-output fans that draw more power than the little three pin connector on your mainboard is capable of providing. These power supply connections, as far as I know, will NOT let you monitor the fan's RPMs.

Nate

(edit) gotta learn to type faster (/edit)

 

[cleverhandle]

<< These power supply connections, as far as I know, will NOT let you monitor the fan's RPMs. >>



Actually, there are some nifty splitters available that let you run the power through a molex connector, but also split into a three-pin plug to let your mobo monitor the RPM's as well.

 

[Epsil0n00]

So, let me know if I am correct in saying that the Abit KR7A-Raid has 3-pin fan headers.
The picture of the KR7A can be seen HERE

If I am looking for the right connectors, it looks like there are 4 fan headers on this board. They're red with 3 little pins, right?
2 next to the main power header, 1 above the AGP slot and one down by the floppy IDE header. Is that correct?

Let me know what you think... all this new stuff is so confusing for me!
Thanks!

Epsil0n

 

[flyerI]

You are correct. I would not run any fans except the northbridge fan (as shown in the picture) and the cpu fan off of the mobo. It is not only a problem of too much current drawn through the small three pin connector but also the amount of current drawn through the mobo. I would connect all other fans to the psu. There are harnesses that will let you convert from three pin to four pin molex and still plug in the rpms sense wire to the mobo (I think someone already said that).