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Questions about PSUs with PWM fans

Last response: in Components
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October 31, 2011 3:29:39 AM

Hi all

I have a question about power supplies with PWM fans. What do I need in order to utilise the PWM function on a power supply case fan?

I understand that PWM case fans have 4 pin connectors which require a 4 pin CASE_FAN slot on the motherboard in order to utilise the PWM-driven fan speed control. Do power supplies with PWM fans also have 4 pin connectors which require a 4 pin PWR_FAN connection on the motherboard in order to utilise the PWM fan speed control?

The reason I ask is all of the socket 1155 motherboards that I have looked at so far either have a 3 pin PWR_FAN connector or do not have a PWR_FAN connector at all.

Cheers
a c 157 ) Power supply
a c 487 V Motherboard
October 31, 2011 11:46:07 PM

You can use a 4 pin fan on a 3 pin socket. You just won't be able to control the speed. But you will be able to read the speed.
... if that's what you're asking.
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November 1, 2011 2:13:55 AM

clutchc said:
You can use a 4 pin fan on a 3 pin socket. You just won't be able to control the speed. But you will be able to read the speed.
Thank you for the reply. I understood that to be true for PWM case fans. Does your answer also apply to PWM fans on power supplies (such as the FSP Aurum Gold 700 (AU-700))? That is, does the motherboard's PWR_FAN socket need to have 4 pins in order to be able to control the speed of the power supply's PWM fan?

If so, this leads me to further confusion, as I have thus far been unable to find a motherboard with a 4 pin PWR_FAN socket.

PS: apologies if I posted my question in the wrong place, as it involves power supplies and motherboards.
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a c 288 ) Power supply
a b V Motherboard
November 1, 2011 10:17:36 PM

The power supply controls its fan internally, you have no control over the fan on most PSUs so you dont need to worry about a PWR_FAN connector, very few PSUs have a fan connector.
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November 2, 2011 1:41:59 AM

hunter315 said:
The power supply controls its fan internally...
Thank you for replying. Do you mean there is real PSU fan speed adjustment based on load/temperature going on, or are we talking about full speed vs off? I always assumed the latter to be the case.

Certainly none of my old PSUs came with a PWM fan. However, I am still interested in finding out what it would take to utilise the PWM fan control feature on those few PSUs that do come with a PWM fan.
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a c 288 ) Power supply
a b V Motherboard
November 2, 2011 11:22:00 PM

Most PSUs use a thermistor to adjust their fan speed based on temperature, some do it based on wattage load which correlates reasonably well with temperature, but almost all PSUs on the market these days have a fairly smooth fan curve, not just full speed or zero speed.
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November 3, 2011 2:22:37 AM

Does that mean that a PWM fan on a power supply is less of a feature and more of a gimmick?

Does anybody have first hand experience with the FSP Aurum Gold 700 (AU-700)? Do you let its 120 mm PWM fan be controlled by the motherboard, or do you leave it up to the PSU itself? What do you think of its noise level?

Tom's Hardware gave this PSU a very favourable review (link), remarking on its high efficiency, competitive pricing and "its quiet fan". I am looking to invest in this PSU, but I am somewhat concerned that some of the other reviewers agree on efficiency and pricing, but note that its fan is loud. Unfortunately none of these reviews explicitly state whether or not they relied on PWM to control the PSU's fan speed, so I am unable to explain the difference in opinions. :??: 
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a c 157 ) Power supply
a c 487 V Motherboard
November 3, 2011 8:32:19 PM

Does the PSU provide a seperate fan power cable designed to be connected to an external +12V source? I didn't see any mention of that in the review or the manufacturer web page. If not, then what Hunter315 is telling you is that the fan speed is all contolled internally to the PSU itself. You have no external control of the fan speed.
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a c 288 ) Power supply
a b V Motherboard
November 3, 2011 9:26:19 PM

There are two ways to control fan speed, PWM or adjusting the voltage to the fan, PWM is a bit more precise and more commonly implemented today, so all the PWM tells you is that its a variable speed fan.


Tom's is not my pick for a PSU review, they are all cold tests and aren't done by people who understand the inner workings of a PSU completely. Jonnyguru and Hardware Secrets are my picks, and the hardware secrets review does not mention anything about the fan getting loud and they test in a hotbox. For the most part, once you put a PSU with a top mounted fan into a case, you arent going to hear it over the CPU or GPU cooler so i wouldn't worry about its noise level.


The FSP Aurum Gold 700 does NOT have a PWR_Fan connector so the fan speed is controlled inside the PSU by the PSU itself and cannot be adjusted by the motherboard or user.
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November 4, 2011 12:51:40 AM

clutchc said:
Does the PSU provide a seperate fan power cable designed to be connected to an external +12V source? I didn't see any mention of that in the review or the manufacturer web page.
That is literally what I am trying to find out in this thread. I am yet to find a screenshot or description of that connection.

hunter315 said:
The FSP Aurum Gold 700 does NOT have a PWR_Fan connector so the fan speed is controlled inside the PSU by the PSU itself and cannot be adjusted by the motherboard or user.
But "120mm PWM CONTROLLED FDB FAN" is one of the features listed on its website (link). By the way, I am not shouting - that is a direct quote from their website. :) 
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Best solution

a c 157 ) Power supply
a c 487 V Motherboard
November 4, 2011 1:04:02 AM

I believe what the website is trying to convey, is that the automatic speed control of the 'Pulse-width modulation (PWM) Fluid Dynamic Bearing (FDB) fan' is done internally by the power supply's controller. You will have no external fan power cable to connect to the motherboard.
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November 6, 2011 10:05:37 PM

Brilliant! Thank you both for your patience. It took me a while to wrap my head around it, but we got there in the end. :D 
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November 6, 2011 10:05:57 PM

Best answer selected by orc.
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a b ) Power supply
a c 136 V Motherboard
November 7, 2011 5:47:41 AM

This topic has been closed by Maziar
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