PWM vs voltage-regulated non-PWM fans

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PWM vs voltage-regulated non-PWM fans

Postposted on Thu May 03, 2012 2:40 am

This post is based on various suggestions in the forums to use PWM CPU and case fans.

Some of the enthusiast motherboards have voltage-regulated fan controls for non-PWM fans (includes the Asus P8Z77-V with its Fax Xpert 2 software). In that case, is it still recommended to replace stock fans with PWM ones for a more silent and efficient operation.

If there are any articles / forum posts already covering this, please let me know. Could not find any, in my limited search around these forums.

Context - Am considering replacing the Antec Tri Cool 120 mm fan that came along with my Antec Sonata III case.
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Re: PWM vs voltage-regulated non-PWM fans

Postposted on Thu May 03, 2012 3:39 am

I actually find PWM fan control to be noisier than voltage based fan control. It depends on the frequency of the PWM signal being sent and the motor of the fan, but it can range from barely noticeable to downright loud. In contrast, voltage control exhibits no buzzing at any voltage. The sole advantage to PWM in my opinion is being able to sustain lower RPM. This is not an issue for me thanks to careful fan selection. My Scythe Kama Flow 2s spin as low as 300-400 RPM and silent in practical terms.
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Re: PWM vs voltage-regulated non-PWM fans

Postposted on Thu May 03, 2012 6:01 am

PWM fans are generally great, but kidsafe has a very good point. A lot of people can hear a slight "ticking" sound that's associated with PWM fans (I'm guessing its the control signal measuring RPMs?). However, I think generally, PWM fans run a bit quieter than a lot of the other fans out there, and they can "auto adjust" to suit the current need of the case environment so that they're spinning even slower when appropriate.

Great.

That being said, there's a lot of 3-pin / Case fans out there that are just as good (if not better) for quietness. SPCR is a big fan of the Nexus Real Silent 120mm for instance, and so am I :) Pair a a nice quiet 3 pin fan up with some sort of voltage regulation (as you noted) and you've also got a pretty good deal going.

Either way you go, if you're interested in building a quiet rig, I'd almost always replace the stock fans as a rule of thumb:

- Fans that come with stock heat sinks (AMD/Intel) always should be replaced, along with the heat sink
- Fans that ship as part of a 3rd party heat sink can usually be replaced to some benefit
- Fans that come stock with cases generally can be replaced with something better

In your case of the tricool, I'd definitely consider getting a quieter case fan. They're not terrible, but you can do a lot better on the quiet front.
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Re: PWM vs voltage-regulated non-PWM fans

Postposted on Thu May 03, 2012 6:41 am

In general there's probably little or no difference between PWM and non-PWM connected to a "voltage controlled" header. Most likely the "voltage controlled" headers are actually pulse-width modulating the power voltage to the 3-pin fan, so it's just a question of whether the PWM circuitry is on the motherboard or internal to the fan itself.

Properly designed fan PWM circuits should not make audible noise, as the PWM switching frequency is supposed to be above the range of human hearing.
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Re: PWM vs voltage-regulated non-PWM fans

Postposted on Thu May 03, 2012 6:55 am

I have actually made motor controllers, and I couldn't tell you the difference between PWM and other means of voltage control .. I have always used PWM for voltage control. I guess you could use a POT for voltage control, maybe a fixed Voltage regulating transistor, or a pot controlled voltage regulating transistor. I'm not sure how there could be a sound difference, but I never looked into it when I was building controllers, it didn't make any difference for what I was doing.
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Re: PWM vs voltage-regulated non-PWM fans

Postposted on Thu May 03, 2012 11:04 am

I just go with whatever my motherboard headers support. The cheaper boards may have PWM for CPU fan and the rest are 3-pin (not even voltage regulated necessarily). I am not a fan of extra extensions/adapters that add to the amount of cabling inside the case (I recently had an instance where the extension allowed me a routing advantage so I made that an exception).
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Re: PWM vs voltage-regulated non-PWM fans

Postposted on Thu May 03, 2012 11:47 am

Very useful information. Thanks all for your input. Am reading other forums too (like these threads from SPCR).

Based on the information, it seems resistor-based voltage control for 3-pin fans could generate heat, while 4-pin PWM fans could generate clicking sounds based on the PWM signal frequency.

Flying Fox wrote:I just go with whatever my motherboard headers support.

Yes, so PWM is what am going with. The P8Z77-V has 3 chassis and 2 CPU 4-pin fan headers. Thank you.
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