3pin cpu fan question

[isma]

Hello everyone,

I'm a bit confused about 3pin aftermarket cpu fan.

Does the fan rotate at a constant speed when plugged into a 4pin fan header ?
Or those the fan speed goes up as cpu temperature goes up ?

It is my understanding that a 4pin cpu fan does variate it's speed according to cpu temp.

Thanks for your response and Happy Holidays.

 

[[BRO]Alaskan]

It depends. Some MBs can set the fan speed in the BIOS as a % of max. Some MB's settings in the BIOS for Off< Set Temp..... Medium speed...... Full speed>set temp. I am sure there are others that can completly vary the speed based on a set temp.

 

[isma]

Not sure though if the mobo I want to buy as those options.

I want to get an Intel DG965OT mATX and put it into a Thermaltake Lanbox.
But there is not a huge choice of 4pin cpu fan that fits in the lanbox.
And I don't want to manually adjust the cpu fan speed with a fan contoller, I want it to be controlled by the bios.

Thanks for your help [BRO]Alaskan.

 

[bldegle2]

the three pin MB connector prolly has a temp control int he bios, and the fan speed will be adjusted by bios temps reading.

HOWEVER, there are some fans that actually have there own thermister built in, so when you plug it in via a four pin molex to a a three pin mini fan connector, it will monitor the temps and adjust the fan speed accordingly....

confused now?

baldy

 

[Party2go9820]

the three pin MB connector prolly has a temp control int he bios, and the fan speed will be adjusted by bios temps reading.

HOWEVER, there are some fans that actually have there own thermister built in, so when you plug it in via a four pin molex to a a three pin mini fan connector, it will monitor the temps and adjust the fan speed accordingly....

confused now?

baldy

Just to add a bit more - if you take a normal three pin fan and connect it to a 4 pin molex connector the fan will run at maximum speed and not be monitored or controlled by anything. The MB/Bios can't adjust the voltages to a fan if it is connected via 4 pin molex.

Another option that you might see is a fan with a 4 pin power connecter but a three pin mb tail. This allows the MB/Bios to read the RPM's for monitoring purposes but it can not adjust the speed based on temp. It basicly allows you to monitor for a dead fan (RPM==0)

 

[isma]

I was talking about a 4pin fan header just like those on Intel mobo's, not a 4pin molex.
Sorry for not being precise.

 

[[BRO]Alaskan]

the three pin MB connector prolly has a temp control int he bios, and the fan speed will be adjusted by bios temps reading.

HOWEVER, there are some fans that actually have there own thermister built in, so when you plug it in via a four pin molex to a a three pin mini fan connector, it will monitor the temps and adjust the fan speed accordingly....

confused now?

baldy

The fans (most stock coolers) that have the thermisters built in control the fan speed based on the case temps not the cpu temps. so if you have good case ventilation the fan will run at it slowest speed. If you want more fan speed you can remove the fan and short the thermister (the fan is going to spin really fast and really loud). I did this on my AMD 4 heatpipe cooler with the 70mm fan and had to run the fan speed at 60% in the BIOS to keep the noise down but now I have 100% control (it will override the BIOS) of the fan speed via Speed Fan and if I don't start Speed Fan it runs at a quiet 60%.