A Question...

[WingZero30]

Hi guys I need a bit of help in clarifying a matter with regards to fans and pwm.

My fan set up is as follows:

The two Akasa vipers (1900RPM rated) and 140mm CoolerMaster (CM) fan (1200RPM rated) are connected via akasa pwm splitter cable to 4pin 12V cpu_fan header.
http://www.overclockers.co.uk/showproduct.php?prodid=CB-031-AK

The rear 120mm CM fan (1200RPM) is connected to 3pin 12V sys_fan1 header.

The front 200mm CM fan (700RPM rated) is connected to 4pin 5V sys_fan2 header.

The top 200mmCM fan (700RPM rated) is connected to 3pin 12V pwr_fan header.

I have been using HWmonitor to monitor fan speeds by running IBT. The thing is HWmonitor only displays one value for the 3 fans connected in pwm config which I believe is for the vipers as they run faster than 140mm fan even at idle.

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Fan0 (Akasavipers + 140mm fan)
Idle speed: 828-830RPM
Load speed: 1675-1704RPM

Fan1 (Front 200mm fan)
Idle speed: 339RPM
Load speed: 392RPM

Fan2 (Top 200mm fan
Idle speed: 738RPM
Load speed: 738-740RPM

Fan3 (Rear 120mm fan)
Idle speed: 1222RPM
Load speed: 1227RPM

As you can see Fan0 shows load speed of around 1700RPM where as 140mm fan can only go upto 1200 +/-5% RPM. At idle it shows speed of around 830RPM whereas 140mm fan could only go upto 600RPM which I tested when I connected it to 5V header separately.

So my question is as following:

1)Does 5V header always runs your fan at half it's rated speed more or less as it seems to be the case with my front 200mm fan and 140mm fan? So when I connected 140mm fan to 5V header, it spun at around 600RPM. When I connected it to 12V header it spun at around 1200RPM.

2) Does akasa pwm splitter cable allows fans to run at their max speed independantly? So if both vipers were running at around 1700RPM, will the 140mm fan be running at around 1200RPM even though it doesn't show up in HW monitor?

I would really appreciate the help.

Many thanks

 

[WingZero30]

1) I think it will be a bit less than half. Fans are generally designed to run with 12V so running them with 5V will give you roughly 41.6% of their top rated speed (assuming speed scales liniarly with voltage)

2) I am pretty sure that the Akasa splitter will allow all fans to run at top rated speed. I am not sure but my reasoning is:

The fan's power comes direct from the molex on your PSU so max power will be available to the fan.

The fan's speeds are controlled using PWM which slows a fan by turning the power on and off rapidly rather than reducing the voltage. This should mean that if the PWM header is specifying 100% speed then the power will be fully on and each fan will receive 12V so they will all run at their maximum speed.

Not totally sure though. I would be interested if anyone else has the info because I use the PWM splitter as well. Great bit of kit.

Thanks for the reply.

This is what I was thinking aswell.

Does 4pin header always correlate with PWM function even if the header is 5v provided that mobo supports such function?
As you can see that during load my front 200mm fan speed also increased but whereas those which were connected to 3pin always ran at full speed with very little variation

 

[WingZero30]

that must be super cool. what does your cpu run at

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Although the type of thermal paste you use will also affect core temps.