Which fan headers should I use for the case/CPU fans?

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Which fan headers should I use for the case/CPU fans?

Postby athlon-power » 2019-1-11 @ 14:34

I have an Intel SE440BX-2 motherboard that I've been using for a little while, and I've always used the system with one case fan, and obviously a CPU fan. I've recently added a front case fan to help and cool the GPU (it isn't really required, but it makes me feel better about it).

Two of the fan headers (FAN1 and FAN2) have CTL/RPM labeled below them, while FAN3 (the closest fan to the CPU socket) is just labeled 'FAN3'- there is no 'CTL/RPM' label beside it, but like the other two, it has a 3 pin header. The front case fan only has positive/negative- there is no third cable because I took it out of a PSU, and so far it's worked fine.

My question is, are the CTL/RPM fan headers PWM-compatible somehow? Or are they just adjustable via software? There is no option in the BIOS that talks about this, last time I was looking through it. And if they are in some form PWM compatible, and FAN3 is not PWM compatible, should I use the CPU fan and the rear case fan in the CTL/RPM headers, and use the non-PWM fan in the FAN3 header?

Is it unhealthy for something like a CPU fan to run at 100% all the time (I'm assuming that FAN3 just has the fan running at 100% the entire time)? I know the PSU fan is okay with running all the time because it can't be controlled, and so runs at 100% while in the PSU all the time, unless the PSU integrates a controller into the PCB that adjusts the voltage of the fan itself.

Here are the labels in question (I didn't take a picture of FAN1, because it's exactly the same as FAN2):

IMG_20190111_092039.jpg
FAN3


IMG_20190111_092133.jpg
FAN2
Custom Builds:
Intel SE440BX-2, Intel Pentium III SL35E, 128MB PC133@100MHz, Creative Labs 3D Blaster CT5823, AOpen AW744L II, Samsung SC-148F, WD Caviar WD400, ca. 1999

Upcoming builds:
Athlon XP 3200+ (Socket 754), 1GB DDR-400, rest unknown, ca. 2003
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Re: Which fan headers should I use for the case/CPU fans?

Postby TheMobRules » 2019-1-11 @ 14:52

I don't think it really matters, however the Quick Reference document that came with my SE440BX-2 motherboard mentions this:

If you are installing a processor with a fan heatsink, connect the processor's fan to the connector labeled "fan 2".


Then there's a picture of a CPU fan next to the "Fan 2" connector and case fans next to "Fan 1" and "Fan 3".
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Re: Which fan headers should I use for the case/CPU fans?

Postby athlon-power » 2019-1-11 @ 15:03

TheMobRules wrote:I don't think it really matters, however the Quick Reference document that came with my SE440BX-2 motherboard mentions this:

If you are installing a processor with a fan heatsink, connect the processor's fan to the connector labeled "fan 2".


Then there's a picture of a CPU fan next to the "Fan 2" connector and case fans next to "Fan 1" and "Fan 3".


Well, that certainly seems to clear things up. I'll probably put it into that orientation, in that case. It's very weird that they mention that, because the FAN3 header is basically right beside the CPU socket, and the FAN2 header is a bit further away. Usually, if they want you to use a specific fan header for the CPU fan, they'll put it fairly close to the socket, and have the other ones further away.
Custom Builds:
Intel SE440BX-2, Intel Pentium III SL35E, 128MB PC133@100MHz, Creative Labs 3D Blaster CT5823, AOpen AW744L II, Samsung SC-148F, WD Caviar WD400, ca. 1999

Upcoming builds:
Athlon XP 3200+ (Socket 754), 1GB DDR-400, rest unknown, ca. 2003
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Re: Which fan headers should I use for the case/CPU fans?

Postby chinny22 » 2019-1-11 @ 15:56

Only thing you'll do by running the fan 100% all the time is to wear it out quicker, but its not like the PC is your daily driver so probably only averages out as on a few hours a week over a year so wouldn't worry about that.
Really it just means if supported, POST would warn you if it detects the fan running slowly/stopped. I'm not even sure P3 fans do speed up/slow down. I think the 3rd wire is just for the monitoring feature. I've definitely used the "wrong" headers because as you say its not always the closest.
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Re: Which fan headers should I use for the case/CPU fans?

Postby athlon-power » 2019-1-11 @ 16:12

chinny22 wrote:Only thing you'll do by running the fan 100% all the time is to wear it out quicker, but its not like the PC is your daily driver so probably only averages out as on a few hours a week over a year so wouldn't worry about that.
Really it just means if supported, POST would warn you if it detects the fan running slowly/stopped. I'm not even sure P3 fans do speed up/slow down. I think the 3rd wire is just for the monitoring feature. I've definitely used the "wrong" headers because as you say its not always the closest.


That makes sense. Like you said, I don't use this machine 24/7, so fan speed isn't really an issue. At some point, I'll get some newer, more resilient ones, but that day is likely far off. SpeedFan can identify the RPM of the CPU fan and rear case fan, but because the front case fan has no monitoring, it can't see the fan and thus says it's running at 6,000 RPM- it says this even when no fan is plugged into that header.
Custom Builds:
Intel SE440BX-2, Intel Pentium III SL35E, 128MB PC133@100MHz, Creative Labs 3D Blaster CT5823, AOpen AW744L II, Samsung SC-148F, WD Caviar WD400, ca. 1999

Upcoming builds:
Athlon XP 3200+ (Socket 754), 1GB DDR-400, rest unknown, ca. 2003
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Re: Which fan headers should I use for the case/CPU fans?

Postby SirNickity » 2019-1-11 @ 22:43

Don't worry about fans running 100%. They're meant to do that. Technically, 3-pin fans aren't really well suited to PWM control. The 3rd pin is connected to a Hall-effect sensor that grounds that pin twice per rotation. It doesn't have any control capabilities at all. The motherboard just uses this to count the RPM.

Some motherboards will change the V+ voltage in an attempt to slow down the fan (fan speed control). This is not 100% reliable, as most of these fans have a fan controller built into the hub electronics. It may not respond to lower voltage (by using current control instead of voltage control to spin the motor), or it may or may not even RUN at a given voltage -- typically >7V is OK, but it may not start correctly at less than, say 9V. It's DEFINITELY not meant to be PWM'd.

PWM control requires a 4-pin connector. Gnd, V+, RPM Sense, PWM. The PWM line is a motherboard-to-fan control line that uses pulses to inform the fan's built in controller how fast it should run the fan.

Now, about matching headers to applications. In short, don't worry about it. Some BIOSes will kind of assume the CPU fan header should always have a fan, and it should always be spinning. In that case, you might have to disable the BIOS alarm on a given fan header. Not a big deal, just weigh whether cable management and convenience outweigh possibly not knowing about a failed CPU fan. (Or, if the closest header can also alarm on fan failure, then you're all set.)
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