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Basics of different fan types and PWM vs voltage reduction/controller

post #1 of 4
Thread Starter 
There is a 3-pin molex which can be controlled by lowering voltage (via a fan controller) but could not be controlled by the motherboard since it doesn't support pulse width modulation (PWM), correct?

A 4-pin molex can receive PWM from the motherboard, do fan controllers ever support PWM or is it always better to send lower voltage instead of PWM if you have that option?
To me it seems like the best option would be 4-pin molex and then software can monitor temperature and increase/decrease fan speed appropriately, yet it seems like the higher end rigs prefer using a fan controller? Why should someone with an air cooled rig ever want a fan controller instead of PWM, just $$ cost savings since PWM fans may be more difficult to find or expensive?

One thing I've found is that lower RPM's on the PWM Slipstream fan get better nosie to airflow results than lowering voltage on a standard slipstream fans.
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post #2 of 4
PWM is slightly more expensive to implement as it requires you to sync a PWM signal to the 12 V output going to the fan itself which requires some extra electronics. PWM also is slightly more power efficient though and can run a little cooler.

PWM fans can still be control using varying voltage but it is not recommended as the electronics on the PWM fans like a constant 12 V. 3-pin fans on the other hand would always be at 100% since the PWM control provides a constant 12 V to the fan at all times. To control a 3-pin fan, you need to reduce the voltage from 12 V to whatever you want, typically with a rheostat or potentiometer.

So let's say you want 8 V, you apply 12 V to a the potentiometer and tap off if at about 65% to give you 8 V output. That means that you have wasted heat and energy on the other 35% of that resistor.



To answer your question regarding the use of fan controllers though. The headers on the motherboard are typically limited to only 1 A at 12 V which is about 12 W. This is good for more case fans, but when you get into having more fans then headers, using 3-pin and 4-pin splitters can be dangerous coming off the motherboard.

Here's a small list of pro's to having a fan controller:
  • Most motherboards don't have support for additional temperature sensors
  • Higher output per channel to allow for more fans and/or bigger fans
  • Physical control for quicker adjustment
  • RPM, Voltage, Temperature readout in one place that doesn't take up screen real estate
  • Some just look amazing on the front of your case
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post #3 of 4
Thread Starter 
Thanks for the reply, very good to know PWM not suggested for simple voltage lowering.

I'm looking at the Maximus IV or V Gene in an air-cooled build I'm working on, and it has 5x PWM fans as far as I can tell, but then I've found references to people being able to use bios/software to reduce fan speed using 3-pin fans !?? source

Do newer/expensive motherboards have voltage controls built in, making the concept of a PWM fan obsolete? I'm not going to want more than 5 fans (2 for motherboard, 3 for case is plenty for my build) and am having a hard time getting this fan part figured out.
Quote:
* Most motherboards don't have support for additional temperature sensors
I'd be okay with 1 temp sensor for the CPU that controls CPU fans and then all 3 of the case fans being in sync with eachother based on a single temp sensor (maybe northbridge).
Quote:
* Higher output per channel to allow for more fans and/or bigger fans
5 fans is enough for me, probably going to be 1200 rpm quiet fans anyway
Quote:
* Physical control for quicker adjustment
That part almost seems like a negative to me, I'd kind of prefer full automation by temperature, although that would be useful when trying to test/move/test/move fan location configurations.
Quote:
* RPM, Voltage, Temperature readout in one place that doesn't take up screen real estate
That's a huge thing and seems like enough of a reason alone. Maybe I can get an expensive keyboard that has it on a little LCD screen or find a cheap 5.25" bay screen.
Edited by avaya - 3/7/12 at 12:27pm
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post #4 of 4
Some motherboards support using 3-pin fan control on a 4-pin header. My Asus M4A89GTD Pro/USB3 did for example, in the BIOS I would change the fan type to DC fan and it would control by adjusting voltage. My ASRock Fatal1ty 990FX on the other hand doesn't have that option so a 3-pin fan plugged in to a 4-pin header will always be at 100%.

As for the physical control, I apologize for not being a little more clear, many fan controllers that have temperature sensors also offer automatic control.

The reason I prefer manual fan control though is that after about a week of use, I have memorized my fan controllers 5 sliders and where they should be for gaming, everyday use, and sleeping. Setting this up in software could be done, but being able to just reach over and slide or twist the fan controller to a certain spot is beautiful.

I find I can pick up the change in speed of a fan and it's rather annoying to me so I like to be able to set a fan at a certain RPM for a certain load.
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CHILZ - Lan Rig
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CANARY - Main Rig
(16 items)
 
CADILLAC - HTPC
(14 items)
 
CPUMotherboardGraphicsRAM
Intel i5-4570s Asus H97M-Plus AMD R9 280 G.Skill RipjawsX 16 GB (2x8) 
Hard DriveHard DriveHard DriveCooling
250 GB Samsung 840 240 GB Kingston 3 TB USB 3.0 Drive Custom Loop 
OSMonitorKeyboardPower
Windows 10 Preview BenQ GL2450 Filco MajesTouch2 Ninja PC P&C Silencer Mk III 600 W 
CaseMouseMouse PadAudio
Fractal Design Core 1000 Mionix Castor Monoprice XXL JL Amps + Custom Morel Bookshelf speakers 
Other
Scythe Kama-Panel 3 
CPUMotherboardGraphicsRAM
FX-8150 @ 4.6 GHz Fatal1ty 990FX Pro 9800 GTX+ 512 MB G.Skill Ripjaws X 1866 CL9 
Hard DriveHard DriveCoolingOS
120 GB OCZ Vertex 3 1 TB WD Black 5x 120mm + MCP350 + EK Supreme HF + MicroRes Windows 8 Consumer Preview 
MonitorKeyboardPowerCase
2x Dell U2212HM Logitech G110 Cooler Master 850W Silent Pro Cooler Master 690 II Adv. 
MouseMouse PadAudio
Razer Death Adder 3.5G Staples Gel Cushion Asus Xonar DG + Senn. PC333D 
CPUMotherboardGraphicsRAM
Q6600 Acer X1800 ATI 5670 2 GB Kingston 
Hard DriveOptical DriveOSMonitor
2 TB WD Green Asus BD-R Windows 7 Home Premium Sony 50" LCD 
KeyboardPowerCaseMouse
Acer Media 220 W SFF Acer X1800 Acer Optical 
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