ASUS Q-Fan and PWM-controlled fans

[mbf]

I'm not quite sure if I should have posted this in the Motherboard section in stead, but here goes.

On recent ASUS motherboards the Q-Fan feature can be set to two modes. The traditional one, where the speed of the CPU cooler fan is set by changing the voltage of the fan. The other mode is to let PWM control the fan speed.

Needless to say that the latter mode will only function with a PWM-controlled fan.

My question is this: can a PWM-controlled fan still be controlled/slowed by reducing the voltage as used by the traditional means of fan-control? Or would that damage a PWM-controlled fan?

I'd really appreciate some input on this, so thanks in advance!

 

[DerwenArtos12]

Originally posted by: mbf
I'm not quite sure if I should have posted this in the Motherboard section in stead, but here goes.

On recent ASUS motherboards the Q-Fan feature can be set to two modes. The traditional one, where the speed of the CPU cooler fan is set by changing the voltage of the fan. The other mode is to let PWM control the fan speed.

Needless to say that the latter mode will only function with a PWM-controlled fan.

My question is this: can a PWM-controlled fan still be controlled/slowed by reducing the voltage as used by the traditional means of fan-control? Or would that damage a PWM-controlled fan?

I'd really appreciate some input on this, so thanks in advance!

A PWM fan cannont be controlled due to the internal circuit design. IMHO and depending on the fan you won't see a real difference dropping a 12v PWM fan down to 10 volts but, at 10v or lower the fan will start to develop a tick as the internal capacitance of the circuit charges up then discharges into the motor. It won't be that significant, especially if the board uses analog PWM instead of the newer and more expensive digital PWM. At that point you're damaging the fan and you still won't see that great a reduction in the fan speed.

 

[mbf]

Thanks for your quick reply. So things are pretty much as I figured, or rather, I knew there would be a snag to using PWM-controlled fans.

Now with that issue off the table, what would be preferable these days; a normal or a PWM-controlled fan? PWM-controlled fans sound nice in theory because of the finer control, but that control is completely automatic (as far as I can tell). Also, because of the automatic control a "whining" cpu cooler fan (speeding and slowing incessantly as the temperature rises and falls) seems to be a distinct possibility. That's pretty annoying to listen to.

FYI, I'm asking these questions because I'm building a system for an elder couple. As this is going to be a cost-effective AMD-based system, I'm looking at either an Alpine64 or an Alpine64 PWM cooler. I just want the least annoying cheap cooler for them, and the boxed cooler isn't it.

 

[DerwenArtos12]

I'd go with the PWM, chances of them ever running the system to half it's capacity is highly unlikely. I might even just use the factory cooler to be honest. They're really not that loud at all, especially in the ears of old people.

 

[mbf]

Thanks for the input. I'm still wavering between the PWM and the traditional fan, but I'm leaning towards your suggestion. It's not really that they're an old couple. Both are in their fifties. Hearing probably isn't what it used to be, though. In any case, no overclocking will be going on, so as long as the cooler keeps the processor (we've settled on an A64 X2 4200+) reasonably cool while being as quiet as possible that's all that's needed.

 

[The Boston Dangler]

i suggest either of these asus motherboards to go with that chip.
http://www.newegg.com/Product/...x?Item=N82E16813131214
http://www.newegg.com/Product/...x?Item=N82E16813131172

 

[mbf]

Thanks for the suggestions.

Everything but the cooler has already been bought. We went with a variation on the 690G board, you recommended, namely the ASUS M2A-VM HDMI. I think it'll suit them fine...

 

[DerwenArtos12]

I honestly think they're going to be happy either way, the fans are designed to be comperable. I think it should depend on what style the case fans you're using are. I doubt the board can split headers so that one header on the motherboard is PWM and another is voltage regulated and I'm sure you want all the fans to be regulated, right?

 

[mbf]

Seems as if the only influence you have over PWM/non-PWM fans is for the CPU cooler. Either that or the CPU cooler fan type can be changed to either PWM or DC mode regardless of the Q-Fan setting. It's a bit hard to discern more information from the manual and later BIOS revisions might even change the feature list of the BIOS as it is listed in the manual. I'd guess temperature-controlled case fans would be the best option.