What is a power_fan socket on my MOBO?

[Mephisticles]

I have an Asrock MOBO. There are many chassis or case fan sockets and a couple CPU sockets to provide juice to the fans. But there is one socket called a "power_fan" and I have NO earthly idea what it does. Can you all help me with this please? Thanks!

For reference here is my build:

http://pcpartpicker.com/user/Mephisticles/saved/vGtNnQ

 

[kanewolf]

There might be power supplies that provide a cable that would allow control-of or monitoring-of the fan built into the power supply.

You can probably ignore this if you don't need it.

 

[Rookie_MIB]

If I'm not mistaken, it's probably for the fan inside the power supply. Some PSU's have a separate fan header so the system can monitor the speed of the fan. Because it's controlled by the PSU itself, it is helpful to know the speed it's running at.

My Antek ISK unit has it.

 

[bignastyid]

It'a just another spot to plug in a fan. Some power supplies have a fan connection so you can control it's fan speed. Asrock simply set aside a fan port for that purpose, but you done have to use it just for that, you can plug a chassis fan into it.

 

[Paperdoc]

The mobo port called PWR_FAN has a special purpose. It is designed only to be used with power supply units (PSU) that have emerging from them a 3-wire set that looks just like those on a 3-pin fan, and ends in a 3-pin fan connector. IF your PSU has one of these, you plug this into the PWR_FAN port. All it does is feed the speed signal generated by the fan inside the PSU to your mobo to be monitored. This port does not actually provide power to the PSU's cooling fan, nor does it attempt to control that fan. IF the PSU fan is speed-controlled, that control is done internally by the PSU itself.

So, ideally, if you do NOT have such leads coming out of your PSU, you plug into the mobo PWR_FAN port NOTHING. However, many mobo makers have actually supplied the standard +12 VDC on port Pin #2, and Ground on Pin #1. So, if you plug into this port a standard 3-pin OR 4-pin fan, that fan will run at full speed at all times. Note that the port does NO speed control. If you do this, your fan monitoring software will tell you that the speed of the PSU fan is nnnn rpm, but of course that won't actually be the speed of the PSU fan.

Since any fan plugged into this port always runs at full speed, that is the same as connecting that fan (via adapter cable, perhaps) to a fixed +12 VDC and Ground connection directly from the PSU via a 4-pin Molex connector of the type used more commonly for IDE devices.

 

[Mephisticles]

Why would the power supply fan need power? And there isn't a separate fan header as far as I know. Read nothing about that, nor is there a cord.

 

[hwc1954]

On the MBs I've looked at, the PWR_header is simply a fixed +12V 3-pin fan header in contrast to the CHASSIS_fan headers that have variable voltage speed adjustment.

You could use the PWR header for a fan that you want to run at 100% speed all the time, pretty much like hooking it up to a molex except that you'll probably be able to see the fan speed in SpeedFan or BIOS.

 

[Mephisticles]

The mobo port called PWR_FAN has a special purpose. It is designed only to be used with power supply units (PSU) that have emerging from them a 3-wire set that looks just like those on a 3-pin fan, and ends in a 3-pin fan connector. IF your PSU has one of these, you plug this into the PWR_FAN port. All it does is feed the speed signal generated by the fan inside the PSU to your mobo to be monitored. This port does not actually provide power to the PSU's cooling fan, nor does it attempt to control that fan. IF the PSU fan is speed-controlled, that control is done internally by the PSU itself.

So, ideally, if you do NOT have such leads coming out of your PSU, you plug into the mobo PWR_FAN port NOTHING. However, many mobo makers have actually supplied the standard +12 VDC on port Pin #2, and Ground on Pin #1. So, if you plug into this port a standard 3-pin OR 4-pin fan, that fan will run at full speed at all times. Note that the port does NO speed control. If you do this, your fan monitoring software will tell you that the speed of the PSU fan is nnnn rpm, but of course that won't actually be the speed of the PSU fan.

Since any fan plugged into this port always runs at full speed, that is the same as connecting that fan (via adapter cable, perhaps) to a fixed +12 VDC and Ground connection directly from the PSU via a 4-pin Molex connector of the type used more commonly for IDE devices.

Thanks! That answered my question perfectly. I have a fan plugged into it and it works so I was confused. Guess I'll have to leave one fan at full speed. Decisions, decisions...

 

[Paperdoc]

Glad that helped. Now, you have raised another item. You had a fan plugged in there, and it runs full speed, which you did not want, I gather. So let's see how to work that out.

First we need info:

1. How many fans do you have? For CPU cooling I see you have a Corsair liquid cooing system that REALLY should be plugged into the CPU_FAN mobo port. Other fans are probably for case ventilation. How many of these do you have? Your list suggests two. Do you have more?
2. What types of fan are these? The lists suggests they are both 3-pin fans. Is that correct? Are any others different?
3. What fan ports does your mobo have? The manual for the mobo you posted says it has one 4-pin SYS_FAN port plus two 3-pin SYS_FAN ports. Is that correct?

In general it is best to connect 3-pin fans to 3-pin mobo ports and allow the mobo to control those case fans automatically. If you connect a 3-pin fan to either a PWR_FAN port or to any 4-pin port, it will always run at full speed.

If you have more fans than ports, you can use fan splitter adapters to connect two similar fans to one port. But I recommend no more than 2 fans per single port, because of limits on start-up current.