Fan Speeds - I'm confused

[Hogan773]

Pls help me out

I have Rosewill Challenger. Comes with 3 fans, plus my Hyper 212+ has its own PWM fan.

I have ASRock mobo which has a mix of 4 pin and 3pin fan headers.

Put aside the 212+ for now - it works fine and the mobo can turn it up or down according to temp limits.

on TWO of my 3 Rosewill fans, they just have 4 pin MOLEX connectors and I currently have them connected directly to the PSU. So they run full speed all the time.

What I WANT is to be able to slow down those case fans to lower noise. I don't have a big GPU and my case is plenty cool already. What I am CONFUSED about is what are my options besides just buying new fans, which seems a waste. If I buy some Molex to 3pin connectors, then I can connect those fans to the mobo. But my question is, once connected to the mobo, can I actually slow down a "single speed" fan through the mobo? My ASRock tools does show some fan settings for the various headers.....1 has a 1-10 setting and another has a 1-4. But will the FAN itself slow down appreciably if the mobo is adjusting the voltage? Part of the reason why I'm confused is looking at fan specs on Newegg, some of the fans show a voltage operating range and then say "1800 rpm +/- 10%" Does that mean that at best, they can only slow 10%? Or is that something different, just a margin of error to cover the fan manufacturer when stating his fan speed due to manufacturing variances?

Hopefully my question is clear. If the answer is that any single speed fan with 2 wires CAN still be slowed down via the mobo, then I'll buy some Molex to 3 pin connectors. I just don't want to buy them, wait for them to come, then find out that I'm just powering a single speed fan through a different power source (mobo vs PSU) but still can't adjust speed at all.

Thanks for advice

 

[piasabird]

So what size is fan/fans?? Fans should have ratings other than RPM's. Look at the CFM (Cubid feet per minute) rating 12 cm fan can move more air at slower speeds. They make these adapters you can use to go from the 8cm to 12cm fan that forces the 12cm fan through the opening of a 8cm fan. Also if you have hot air and blow it around it is not much use. Cool air from outside the case and improved airflow works better. So the Case itself is actually part of the equation. If you buy a case with bad airflow, fans will not help much.

 

[Hogan773]

So what size is fan/fans?? Fans should have ratings other than RPM's. Look at the CFM (Cubid feet per minute) rating 12 cm fan can move more air at slower speeds. They make these adapters you can use to go from the 8cm to 12cm fan that forces the 12cm fan through the opening of a 8cm fan. Also if you have hot air and blow it around it is not much use. Cool air from outside the case and improved airflow works better. So the Case itself is actually part of the equation. If you buy a case with bad airflow, fans will not help much.

Rear is 120mm and top is 140mm. The front 120mm has a 3pin connector already. Its the top and rear that just have Molex connectors.

My question is more about the actual electrical ability for a mobo to slow down a "single speed" fan.......I'm not really worried about maintaining certain airflows as my CPU is currently cool as ice and the primary cooling power also comes from the Hyper 212+ which already has the ability to throttle up to 2000 rpms when temps rise, and then throttle back down to as low as 600rpms if I were to set it that way (I actually keep it running faster just because my ear can't detect extra noise going from 600rpm to 1000 rpm on that fan)

 

[WildW]

Fan speed can be controlled in two ways - either by changing the voltage going to the fan (two or three wire connection) or with PWM (4 wire connection) which always applies 12V but not all the time - it's pulsed on and off rapidly.

A fan with a 4-pin molex is just connected to the 12V wire all the time, so it will run at full speed.

I've never seen adaptors that can connect a fan with a 4-pin molex plug to a 3-pin female fan plug, but if you think you can do that, fair enough, maybe you've seen something I haven't. If that's the case, plugging those fans into the motherboard may give you controllable speed if the motherboard supports varying fan speed by voltage. It comes down to how well designed the motherboard is and unfortunately its a bit hit-and-miss in my experience. Sometimes you can control speed, sometimes you can't.

If it is supported, there may be fan speed control options in the bios, or you may need to try a program such as Speedfan to control the fan speeds.

The alternatives are to go to a fan speed controller, an inline resistor to slow the fan down, or swapping some wires to the fan so that instead of 12V it gets 5V or 7V.

 

[Hogan773]

What I'm referring to looks like this........

 

[WildW]

Neat. I've never seen one of those =)

Looks a little dangerous, in that I wouldn't try to power more than one fan through a motherboard connector.

 

[BoomerD]

Depending on the fans, you SHOULD be able to power 2 of them from a single motherboard fan header.
I have 2 Noctua fans (with a "Y" splitter) on the CPU header, one 140 MM fan on one case fan header, one 200 MM fan on the other case fan header, and one 200 MM fan on the board's power fan header.
The CPU fan header and case fan header are controlled by the board and the fans vary in speed according to temperatures. The fan on the power fan header runs at 100% all the time.
Currently, CPU fans are at 1258 RPM, (1300 is full speed) case fan 1 is at 784 (1200 RPM Max) case fan 2 is at 490, (700 RPM max) and the power fan is at 732 RPMs. (that's max)

 

[Concillian]

Most fans will run from 5v. This dramatically reduces noise (and airflow, obviously). The super budget way is to make a molex connector that routes the 5v wire of the molex (red) to the fan's +12v wire (usually yellow on a 4 pin molex).

5v works for most fans, some want a little more voltage, you can try 7v by hooking the fan's black / ground to 5v (red molex) and +12v to +12v molex (yellow). This works but is not technically the "correct" way to do it.

What you can do with the 5v, 7v, 12v options from the molex connector is get an idea of what voltage is going to work best for you. Then you get a zener diode for the right voltage (12v minus zener diode voltage = ouput voltage). Put that in series somewhere on the +12v side. You just made your own fan controller.

If you have an electronics supply place nearby, zener diodes are usually (much) less than $1 each. Needs to be rated high enough for the fan. Dropping the voltage will drop the fan current. 5W Zener is enough for most fans, but you can put 2 in parallel if you want to be sure. Stripe goes towards the PSU side.

4.7v is a popular size to use with fans.
http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=1N5337BRLGOSCT-ND

Obviously due to shipping, it's preferred to go to Fry's or whatever you have nearby for electronic parts like this instead.

You can also do this with a resistor, but it's not as simple to figure out the size needed.
There are retail products that do this with either resistors or diodes also:
http://www.svc.com/nrc-1000.html
http://www.svc.com/zmrc100.html

nrc-1000 uses multiple regular (non-zener) diodes in series, each one in series drops about 0.75v. These are even cheaper than zeners, but you'll need more of them. Will be less than 10 cents each if you have an electronics supply house that doesn't price gouge. They'll be called 1N4001.

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=1N4001FSCT-ND

 

[Sephire]

Can't you just buy an aftermarket fan controller like Zalma or Silverstone?

 

[WoodButcher]

If your mobo will control the fan speed via voltage you need this- 1 fan = 1 mobo header.
http://www.performance-pcs.com/catal...roducts_id=608

At that site you can get cables w/ resistors to give different voltages right from the power supply as well.