Newbie fan question

[Virgule]

Hey,

 

Can someone explain the difference between fans with 3 pins and 4 pins connectors ? Does that have something to do with PWM fans being able to ramp down speed ? Finally, does a fixed speed fan (3 pins I guess) run at max speed all the time ?

 

Thanks for the clarification.

[DavidTheWin]

PWM allows for voltage control (what controls the RPM) through the 4th pin. E.g. running a fan at 12v will make it run at a faster RPM than at 7v or 5v (the common voltages for fan control). A 3 pin header will output 12v to the fan but you can add resistors into the cable (low noise adaptors) that reduce the voltage to reduce the RPM. 

[Enderman]

PWM fans are controlled by length of pulses to turn down the speed. 3 pin fans turn down speed using voltage control. For example, a PWM fan will switch power to 100% for 1ms, then to 0% for the next1ms, then repeat, and that makes the fan go at 50%. A 3 pin fan will just use 6v to run at 50%. Some PWM fans can turn at lower speeds than regular 3 pin fans, but 3 pin fans can also be controlled to not run at 100%. PWM fans are also backwards compatible with 3 pin fan headers, and can be controlled with voltage control too.

[Virgule]

PWM allows for voltage control (what controls the RPM) through the 4th pin. E.g. running a fan at 12v will make it run at a faster RPM than at 7v or 5v (the common voltages for fan control). A 3 pin header will output 12v to the fan but you can add resistors into the cable (low noise adaptors) that reduce the voltage to reduce the RPM. 

So 3 pin fans run at max speed ?

[Trail Mixorz]

yes, 4 pins are generally pwm, which can control the speed through your mobo

[DavidTheWin]

So 3 pin fans run at max speed ?

 

Not quite that simple.

A 3 pin header will output 12v but you can have fans attached to one that don't run at max speed by reducing the voltages using low noise adaptors between the header and the fan. E.g. Say I have SP120 performance edition fans that run at 2500RPM at 12v attached to a 3 pin header. I can get a low noise adaptor that reduces the voltage to 5v, attach that to the header then attach the fan to the adaptor so the fan is only receiving 5v and will run at five twelfths of the RPM (~1050), so the header is outputting the same voltage but the fan isn't running at "max speed".

[Virgule]

PWM allows for voltage control (what controls the RPM) through the 4th pin. E.g. running a fan at 12v will make it run at a faster RPM than at 7v or 5v (the common voltages for fan control). A 3 pin header will output 12v to the fan but you can add resistors into the cable (low noise adaptors) that reduce the voltage to reduce the RPM. 

 

PWM fans are controlled by length of pulses to turn down the speed. 3 pin fans turn down speed using voltage control. For example, a PWM fan will switch power to 100% for 1ms, then to 0% for the next1ms, then repeat, and that makes the fan go at 50%. A 3 pin fan will just use 6v to run at 50%. Some PWM fans can turn at lower speeds than regular 3 pin fans, but 3 pin fans can also be controlled to not run at 100%. PWM fans are also backwards compatible with 3 pin fan headers, and can be controlled with voltage control too.

 

yes, 4 pins are generally pwm, which can control the speed through your mobo

 

Not quite that simple.

A 3 pin header will output 12v but you can have fans attached to one that don't run at max speed by reducing the voltages using low noise adaptors between the header and the fan. E.g. Say I have SP120 performance edition fans that run at 2500RPM at 12v attached to a 3 pin header. I can get a low noise adaptor that reduces the voltage to 5v, attach that to the header then attach the fan to the adaptor so the fan is only receiving 5v and will run at five twelfths of the RPM (~1050), so the header is outputting the same voltage but the fan isn't running at "max speed".

 

 

Thanks everyone.

[DavidTheWin]

PWM fans are controlled by length of pulses to turn down the speed. 3 pin fans turn down speed using voltage control. For example, a PWM fan will switch power to 100% for 1ms, then to 0% for the next1ms, then repeat, and that makes the fan go at 50%. A 3 pin fan will just use 6v to run at 50%. Some PWM fans can turn at lower speeds than regular 3 pin fans, but 3 pin fans can also be controlled to not run at 100%. PWM fans are also backwards compatible with 3 pin fan headers, and can be controlled with voltage control too.

 

Interesting, didn't know quite how PWM worked, makes sense. Also some useful corrections on my explanation of 3 pin headers. Thanks for the info 

[Enderman]

Interesting, didn't know quite how PWM worked, makes sense. Also some useful corrections on my explanation of 3 pin headers. Thanks for the info 

NP

3 pin and 4 pin are basically the same, except 4 pin you can control the speed in 2 different ways