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Whats a PWM fan?

post #1 of 11
Thread Starter 
Hello guys, i just placed an Order for a Corsair a70.

i've seen in reviews that it only come with Fans that have 3 holes (for 3 pins) and i've read that they are no PWM fans.

My BladeMaster fan has 4 holes and i've read that this makes it a PWM fan.

So my question is would i still be able to control fan speed in the Bios with a non-PWM fan? My bios had 3 settings for the CPU fan. Silent/Optimal/Peformance and i usually keep everything on Optimal as its a Nice balance between Heat and noise so i'm hoping i can do it with this new cooler.
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post #2 of 11
You cant adjust the fan speed in the computer with a 3 pin fan. But you can with a potentiometer.
post #3 of 11
Thread Starter 
Seriously frown.gif

That blows....
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post #4 of 11
Some motherboards can control 3pin fans, in my bios i can choose 50-75-100% so it's rather limited
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post #5 of 11
Pulse-width modulation

Pulse-width modulation (PWM) is a common method of controlling fans. Modern computer motherboard PWM control when used with multi-core CPUs reads data from Digital Temperature Sensors on each core of the CPU.

Unlike the linear methods above that are based on voltage loss, PWM switches the input voltage between (nearly) fully on and fully off. This means there is practically no voltage or power loss and associated heat output. PWM controller can be a relatively small, low-power and cool-running, albeit complex, component that doesn't require heavy duty resistors, diodes or transistors and associated heatsinking.

hope that helps.
    
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post #6 of 11
Thread Starter 
Hmm My Bios Has two options under its Fan Speed setting.

Fan Type [PWM] or [DCFAN]
Profile [Silent/optimal/Performance]

the Profile commands remain whether i select PWM or DC. so i hope i can control these new Fans.
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post #7 of 11
Non PWM fans can be controlled by bios but only in quite big steps,the best way isto use a fan controller though as that way you will have a more varied control over speed/noise.When connecting to a 3pin connection its the blue wire that does'nt need connecting.
post #8 of 11
PWM Fan is a fan that can be automatically controlled by the motherboard at all times (meaning it's capable of constantly changing it's speed according to the stress on the CPU) and it's got 4-pin connector (the blue wire being the PWM control).
for example, while idling the fan will run at, say.. 1200rpm
at minor to moderate stress it would go to around 1400-1600rpm or more
and 100% full load it would max itself out at 2000rpm (these examples are for a 1200-2000rpm fan)

Sometimes you can also control 3-pin fans but it's not as easy and efficient as 4-pin fans.
post #9 of 11
I personally hate the trend towards PWM fans these days. Yes, it's more efficient, and it does let you run cheap fans at lower speeds before they start stalling.

With high quality fans that support running at lower voltages though, you get a much quieter system without PWM.

PWM causes the fans to pulse as the speed gets lower which I find to be very distracting. I would rather run most fans at full speed than lower speeds via PWM. As long as your fans are good quality ones that work well at low voltages, I would recommend running them like that.

I was very disappointed to see ASUS advertise how good their fan control is on the new boards, to find out that it only works with PWM fans. Older motherboards used to let you control the fanspeed by dropping the voltage, it's something that I'd like to see return so I can ditch my fan controller.
post #10 of 11
Quote:
Originally Posted by th3illusiveman;12810573 
Hmm My Bios Has two options under its Fan Speed setting.

Fan Type [PWM] or [DCFAN]
Profile [Silent/optimal/Performance]

the Profile commands remain whether i select PWM or DC. so i hope i can control these new Fans.

If you fan only has 3 connections then it is not a PWM fan. The 4th wire on a fan connection, the blue one, is the one used to send PWM signals to the fan. If you do not have this wire then PWM will not work. Instead use DCFAN, it will probably try to control the fan speed by varying the voltage going to the fan. It will not have as much control over the exact fan speed, but should work ok.

Quote:
Originally Posted by NotAgain;12813165 
PWM causes the fans to pulse as the speed gets lower which I find to be very distracting. I would rather run most fans at full speed than lower speeds via PWM. As long as your fans are good quality ones that work well at low voltages, I would recommend running them like that.


PWM is by far the best way to control the speed of a fan. There is no way that you will be able to tell that the fan is running on PWN from seeing it 'pulse'. The period of the waveform is way to small to be noticed by human senses. It simply supplies full voltage to the fan for a certain percentage of the period, call the duty cycle. But with the period being so small it keeps the fan at a constant speed.

PWM is pretty much the standard for powering DC motors of any kind. Its even used to control the brightness of LEDs by making them pulse, however its so fast that our eyes just see them as being dimmer.
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