Basic 3pin/4pin case fan questions

[DugnDog]

Apparently these are such obvious questions that no one needs to ask anymore. Quess I'll have to display my ignorance. Hope someone can clarify this for me.

1. Why would you want to power a case fan through the motherboard? Why would you NOT want to?

2. In the forums, I see warnings on wattage limits for motherboard fan connectors but can't find any spec on what is acceptable. Does anyone have a reference or knowledge on this?

System: Antec KS282 case(PP303x PS), K7TPro2A MoBo, Tbird 1GHZ, Tai-sol CEK733092 cooler (tentative)

Note: First homebuilt in several years, purpose is work & fun. Plan to experiment with moderate overclocking once up and stable. I'm planning to add 1 80mm exhaust fan to the back of the case.

 

[clumsum]

1) You can monitor fan speed through mb if using fan header on mb.........

2) Wattage limits on mb fan headers,..............if exceeded could damage mb header circuits, you would not want to connect larger case fans to mb headers unless you are sure the header can handle the load......................and maby the total wattage of all headers being used, combined...........?

I think some mb's or future mb's will be able to control fan speeds (noise) by monitoring system temps and automatically adjusting fan speed to compensate............?

I personally did not want to take a chance on connecting my 120mm front case fan to my KT7-R fan header, I read on the KT7 FAQ page that each mb header will handle up to 5 Watts........but, better safe than sorry.......!
(There was also a note stating that not all model Abit mb's are rated this high.)

I would also guess that not all (possibly NO other) mb mfg's have rated fan headers this high?
So...............be sure to double check w/mfg before taking a chance on a large fan.........

 

[cavingjan]

clumsum hit the nail right on the head. Now take it one step further. There are some fans you definitely want to monitor and those that frankly you really couldn't care about. Your hsf is one to definitely monitor and when the little alarm goes off, I'd be shutting down quickly. But if you have 4 case fans, could you care in the immediate time that one fails? Not really. You'll notice the higher temp and track it down. More than likely you've already heard the grinding, clicking, or whining of its bearings dying the slow death. The less things pulling power from the motherbaord, the more forgiving that motherbaord will be in the stability department.

 

[DugnDog]

So, hook the hsf to the motherboard (that's critical!). But keep it simple on the case fans and just hook them up to directly to the power supply.

Reduces the stress on the mobo and I'll probably hear any case fan problems long before they actually die anyway.

clumsum & cavingjan, thanks for the input. Very helpful.

FYI, I'm actually building two of these and the one for my son will have a 1.1GHz Athlon. The Antec power supplies are only rated for 1GHz but the case seems to have good ventilation so I'm hoping I'll be OK with just the one extra case fan exhausting out the back.