View Full Version : Fan control, 3 pin vs 4 pin

05-19-2013, 08:46 AM
I am building a new machine. I believe I screwed up in my case selection. Fractal includes 3 fans with an integrated controller. Unfortunately the fans are all 3 wire and their "controller" is a simple 3 voltage fixed divider. Switch for low/medium/high.

Looking at the documentation for fan wiring, it appears that the pins functions starting at pin 1 are gnd, power, speed sense, and PWM control.

How will the controller on a P8Z77-V Deluxe board handle these fans. Can they actually be controlled in respnse to some measurement of temperatures inside the case or do they need access to the PWM signal? Do I need to replace these fans with a 4 wire version for proper control?

If the motherboard controller can control the voltage on pin 2 in relation to the speed that might work, but I really am not sure.

05-19-2013, 11:37 AM
It's really impossible to tell if the chassis fan headers work only in PWM mode, or are capable of voltage control. I checked the manual and it does not explain that at all. Only an owner of this board could provide that information. You'd need to know if the AI Suite II software can control three pin fans on the Chassis fan connectors.

Regarding a "screwed up" case selection due to the fans, I am not aware of ANY PC case that comes with four pin PWM fans. I doubt you can find a PC case that comes with even one four pin PWM fan.

Basing a case selection on the type of fan connectors it comes with would be a poor method to use. PWM controlled fans are still rare compared to three pin fans. Most PC cases come with quiet but weak air movement fans. The Fractal R4 has above average fans. If you bought the R4 in order to build an extra quiet PC, then you've made a good choice, but if you need a case with the best possible cooling, other cases would do a better job.

05-19-2013, 03:06 PM
Yes, in keeping with the RTFM rule, I could see no explanation of capabilities. My old case and fans use only 2 wire and seem to do some sort of control with a Gigabyte MB.

I am indeed after quiet. I have an absurdly large CPU cooler to get low fan speeds. Same thing I did with the last one. Fans are mostly at a low idle or off on my old system. I will see how these new case fans and MB work out before I get any other fans. Oddly, the new cooler uses 4 wires for the fan inside the heat exchanger core but only 3 wires for the outside fan. I am not exactly sure why they did that. There are two different fan sizes, but I would have thought they would control them the same way. When I get the system running I will look at what the monitoring software says about speeds and temperatures. The two cpu cooler fans are split from the same connector. I will try the three wire fan to the other cpu fan connection on the MB when things are stable and see what that does.

On the new Fractal case they are set up to use a low/medium/high switch that controls all chassis fan speeds. So using that feature there is no temperature feedback. I was in a hurry when I made the order and I did not understand that the Fractal "controller" was simply a 3 speed switch. But that may be OK.

I have a way to go. Prepping to move the OS image from a failed computer to my current computer, and my current computer's image to the new machine, something went horribly wrong with my backups. I have to figure that out before I can do most anything.

05-22-2013, 09:42 AM
It sounds like your CPU cooler's fans may both be controlled by the PWM speed signal. Splitter cable adapters for use with two PWM fans (if designed correctly) only have one four pin connection for the fans, the other is a four pin connector with only three wires/pins on it. That is necessary so only one fan speed signal is sent to the motherboard's fan controller. If both fans sent their speed signal to the board through one common wire, the resulting signal is a mess that cannot be interpreted correctly. The missing wire on the other connector is the speed/RPM signal wire. The fan on the three wire/pin connection still receives the PWM speed regulation signal from the board, so its speed changes along with the other fan.

After thinking about it, I doubt that your ASUS board is designed for use only with PWM fans. In my experience, ASUS has the best fan control software of any mother board manufacture. I would be very surprised if the chassis fan connectors, even being four pin types, would not control three pin fans. That would be a big change compared to all chassis fan connectors and control software used in the past. I've also have not seen anyone commenting about needing all PWM fans with their new ASUS boards, and believe me, most users would not be happy about that.

I have an R4 case, so I am familiar with the fan speed switch. If you want quiet, and constantly quiet, I predict you will like the R4's fan controller.

I have never seen a PC case that includes temperature regulated fan speed control. All built in PC case fan controllers are manual controllers, either a two or three speed switch, or a continuously variable control. The continuously variable controls are usually not that good, they don't allow precise speed control of any fan, since all fans are different and there is no standard for a fan's starting voltage, speed, etc.

Actually, people that want quiet PCs usually prefer manual fan speed settings, rather than variable by temperature. They trade higher component temperatures, which are usually temporary, for a constantly quiet PC. Otherwise the noise level goes up and down constantly, which they find annoying.

Check out the noise level of an all in one pre-built desktop PC, it will be quiet and never gets louder, since it's two or three fans never change speed, or change very little. A non-PC enthusiast friend of mine thinks my PCs are weird since the fan speeds change, and you can hear them. Of course, he does not know that his CPU, etc, are running at 50C+ most of the time, nor does he care.

05-30-2013, 02:53 AM
Thanks, you may well be correct about the heat sink fans. I makes sense. They would not be attempting to bring back the rpm wire from the slaved fan. I did not think hard enough about it.

So far it is my understanding that the Asus MB does act to control the fans based in some way from the temperature in the cabinet. I have the system together (but having a fairly terrible time getting the OS ported) and even with both sides off the case it is hard to hear sitting next to it. So it appears I have met my goal. The reason I felt it would be better to have PWM control rather than voltage control is range of control. PWM should be able to control the fan over a wider speed range. Mostly at the low end. The lower limit for motor starting should be lower with PWM. By its' nature, it should provide a higher voltage across the motor even at starting conditions.

05-30-2013, 01:32 PM
I agree about PWM fan control, much better low speed control, finer range of adjustment, and better automatic speed control. But PWM controlled fans are still outnumbered by about 10 to 1 over three pin fans.

You would not think that fan speed control of three pin fans would be that difficult, but it is for several reasons. One is there is no standard for even the starting voltage of a three pin fan. But given the range of sizes of fans, ~25mm - ~200mm+, and the range of speeds, ~500RPM to 4000RPM+, a standard is just impossible. Three pin fans are just... dumb fans, they are more dependent on the voltage they receive, and there are multiple methods of implementing three pin fan voltage control. Three pin PWM speed control exists, but is provided only by the mother board or fan controller, a three pin fan does not know how it is being controlled, and contributes nothing to speed control besides its RPM signal back to the board or fan controller.

The main problem with three pin fan speed control on mother boards is the board manufacture cannot predict what fans will be used with the board. They are worried that at the lowest three pin fan speed setting, will the fan actually spin up and run. If it doesn't, users will complain, no surprise there. So the lowest speed setting for three pin fans will be set so 99% of fans will start and run. The compromise is many fans will be running at 50%+ of their top speed at the lowest setting. So what is right or wrong?

My ASRock board has both three pin and four pin PWM chassis fan headers, but only one PWM chassis fan header. The PWM header has automatic and manual control, the three pin headers are all manual.

There are PWM fan adapter cables that use the board's PWM speed control, but allow you to connect three or more PWM fans. They connect directly to your PSU for power, so don't over draw power from the board.