How does a Fan Controller control the fans?

[shadoweye14]

Okay so, I am planning to build a new PC and I came across the issues of cooling your case. I had a look at many different fans and many different controllers, but did not understand how it all worked. Apologies if these queries look stupid but I honestly have no clue xD.

So you get a fan controller, say the NZXT GRID+, you connect all your fans to it. Connect the GRID+ to your PSU directly and your Mobo using a USB Header to control with your cam software. The Grid has a total 30W power limit (I think..). My questions at this stage would be:


How does the GRID control the fan? When we specify a setting of 50% to the GRID is that a setting for VOLTAGE or RPM?

If RPM then how does the Controller know what RPM the fan is capable of? (Not the current RPM, the total RPM)

And if its controlled by altering voltage then If I have only 3 fans instad of six does each fan still get only (30/6=) 5W or (30/3=) 10W

 

[Darkbreeze]

Voltage controlled fans use higher or lower voltage to adjust fan speed according the the RPM signal sent to the controller, which in most cases is the motherboard bios and is the recommended method rather than a third party fan hub, which is obtained via the tach signal on the third wire. PWM, or Pulse width modulation fans use an on and off method of controlling the speed, which is generally quieter and more efficient as well as more precise. Most of what you want to know about voltage and PWM controlled fans can be found here:

https://en.wikipedia.org/wiki/Computer_fan_control


When possible, I highly recommend using the motherboard fan headers for fan control rather than a hub or external controller. It's more efficient and thermally accurate and eliminates unnecessary additional wiring inside the case. It's also cheaper since it's already built into all modern motherboards. The only time I'd do it differently is if the motherboard has only a single chassis fan header and you need more than two fans in which case these:

http://www.newegg.com/Product/Product.aspx?Item=N82E16812162026

won't give you enough fan headers to run the required number of fans. Most motherboards have at least two fan headers, so with two of those splitters you can easily run at least four case fans and if you also have a CPU OPT secondary CPU fan header in addition to the primary one, you can also run the rear case fan off of that. It will run faster depending on CPU temperature rather than motherboard temperature sensor readings, if you use that CPU OPT header, but that's actually beneficial since when the CPU cooler is running faster, it's nice to have that fan also running faster to remove more of the heat exchanged by the CPU cooler, out of the case faster. It does make for a slightly louder configuration under heavy loads though.

 

[smorizio]

also with fan controllers look at there current limit and the fan start up current. some of the older led fans may draw to much current for some of the fan controllers. last thing you want is magic smoke coming from your new pc.

 

[Darkbreeze]

That's for sure.^^^^^

 

[Paperdoc]

A few corrections.

When you connect your fans to mobo ports and allow it to operate in default automatic mode, the mobo controls the fans according to TEMPERATURE as actually measured by at least two sensors. There is always a sensor built into the CPU chip that sends its signal out on one pin for the mobo to measure. This temperature is used to control the fan connected to the CPU_FAN port. The mobo CPU_FAN system also does a couple of other checks on its fan operation for safety to prevent disastrous overheating of the CPU in abnormal situations.

The mobo maker also places a second temperature sensor (sometimes more than one) on the mobo in a spot the maker has decided is important, and this temperature is used to guide the fans connected to the (one or several) SYS_FAN or CHA_FAN port(s).

All mobo fan ports also allow the fan motor to send back to the mobo a speed signal that the mobo can measure and display for you. However, it is interesting that this speed is NOT used for any control purpose - it is only for your interest. (Well, the mobo also checks this signal for the CPU_FAN to be sure it is not stalled.) Control is based solely on temperature as measured by the sensors.

If you choose instead to buy and install a Fan Controller from a third party, it will allow YOU to control fan speeds, either by setting voltage or the PWM signal. But the speeds are ALL controlled by you manually. You set the speed, and you decide when to change it. You are responsible for ensuring that the components on the mobo and the CPU keep at a good temperature at all times. There is no automatic control. You also should know that these controllers have no way to forward the fan speeds to the mobo for display and monitoring. Unless the Fan Controller also has a feature to display the speeds of its fans, you will not see those speeds.

There are two basic types of fan systems. 3-pin fans (aka Voltage Controlled fans) have their speed controlled by varying the voltage of the DC power supplied to them. 4-pin fans (PWM fans) receive a constant 12VDC supply, but they also receive from the mobo a PWM signal. Inside the fan motor there is a small chip that uses the PWM signal to control how much of the time that constant 12VDC supply is actually flowing through the fan motor, and that is how this system adjusts fan speed. While the two systems have some backwards compatibility aspects to allow you to mix fan and port types (this is allowed electrically and mechanically), the results are not always what you'd want. So the best rule is to buy fans that match the fan port type you will connect to.

Personally, I prefer to use the automatic control systems built into the mobo by connecting fans to mobo ports. If you find you have more fans than ports, you can buy Y-splitters that allow you to connect two fans to one port. Do not try to use more than two fans per port, though. Splitters for 3-pin and 4-pin fans are different, so buy according to the fan and port type you are using. If you need even more fans, there is another way to connect several 4-pin fans to one mobo port, but this does not work for 3-pin fans.

 

[Guest]

Your post doesn't say anything really that hasn't already been said. Setting fixed speeds is useless. You end up with either a rig that's loud all the time, or having to constantly monitor and change your fan settings. Automatically controlling the fan settings, by specific and desired profile in the BIOS according to thermal readings is a far better method of control, as even you agree to.


Personally, I've never once seen there be an issue using a three pin fan on a PWM header or using a PWM fan on a three pin header. Of course it makes more sense to use matching headers and connectors when possible, but I've seen no detrimental effects from using one with the other aside from a lack of PWM function when using a PWM fan on a 3 pin header. And three pin fans work fine with PWM fan splitters. The first three pins are the same anyhow. There is no difference. The fourth pin is simply not used.

 

[Paperdoc]

OK, here are the details of mis-matching.

If you plug a 4-pin fan into a 3-pin header, it will work, including speed control. The only difference is that now the 4-pin fan is acting as a 3-pin fan. That means you lose the two main advantages of the PWM control system: more reliable operation at low fan speeds, and easier to start at a low speed setting. Not big losses, I agree.

If you plug a 3-pin fan into a 4-pin port, it will always run at full speed. The 4-pin port sends out a fixed 12 VDC on Pin #2 and relies on the mini chip in the motor to use the PWM signal to alter fan speed. But a 3-pin fan cannot use such a signal, and does not even get it from Pin #4. This is one of the backward compatibility design features - this particular mis-match DOES give you good cooling (onstead of none), but no fan speed reduction at all.

There are two ways to avoid this situation for 3-pin fans on 4-pin ports. SOME mobo BIOS's allow you to alter a fan port's mode to either 3-pin or 4-pin. Some even do this for you automatically. Most often this feature is found in the CPU_FAN port system but not on the SYS_FAN or CHA_FAN ports. The other is a "trick" in some mobos. They install 4-pin connectors for all their ports, but electrically in BIOS they actually operate them as 3-pin ports all the time, ignoring the PWM signal. This takes advantage of the ability of a 4-pin fan to appear to work just fine on a true 3-pin port (above).

You are right to say that 3-pin fans work OK with 4-pin Y splitters, subject to the comments above. IF the splitter is plugged into a 3-pin port, then both its fans are being controlled via Voltage Control Mode, and it's all good. IF the splitter is plugged into a true 4-pin port, then the 3-pin fan will always run at full speed.

 

[Darkbreeze]

That is NOT true. I have used three pin fans on PWM headers and they do NOT run at full speed. I personally have a Storm Enforcer case with the 3 pin 200mm megaflow fan connected to a PWM header and it IS still voltage controlled with variable speed. I don't know where you got that idea from but it's definitely unsound. And there are NO 3 pin versus 4 pin settings on my Sabertooth board, so that's not the reason either. I just tried them on every fan header on the board, and they all provided the same behavior aside from the CPU and CPU OPT headers which of course react to different sensors.

 

[Paperdoc]

If you have a 3-pin fan for which the speed is varying, then certainly it is being fed a variable DC supply voltage on Pin #2. That is not what a true 4-pin (PWM Mode) port does. It means that, although the port connector may have 4 pins, it is operating as a true 3-pin (Voltage Control) port. That can come about in either of two ways - see my fourth paragraph above. Such behavior by a port with four pins is not "standard", although it does exist on some mobos.

 

[Darkbreeze]

Anyhow Shadoweye, I think you have a good amount of information on how fans function how, if you have further questions just ask and somebody will help you out.

 

[Darkbreeze]

If you have a 3-pin fan for which the speed is varying, then certainly it is being fed a variable DC supply voltage on Pin #2. That is not what a true 4-pin (PWM Mode) port does. It means that, although the port connector may have 4 pins, it is operating as a true 3-pin (Voltage Control) port. That can come about in either of two ways - see my fourth paragraph above. Such behavior by a port with four pins is not "standard", although it does exist on some mobos.

I'd be willing to venture that what you say holds true for most if not all OEM boards, but every recent aftermarket board, say the last gen and this gen, both AMD and Intel chipsets, have worked both ways. I'm sure you're right about some boards, but to my experience the number of boards that have no support that way is surely outnumbered by the number that do. At least for aftermarket hardware since the last two gens.

 

[Paperdoc]

Interesting info. I don't have a good way to survey lots of recent boards, so I did not know that a large majority coming out now have dual-mode 4-pin fan ports. From a technical perspective it would be interesting to know how many have automatic detection and use true 3-pin and 4-pin modes, and how many take the shortcut route of making them true 3-pin only and relying on backwards compatibility by 4-pin fans. But for most users that question does not matter, anyway.

 

[Darkbreeze]

True enough. I think I'll look into this further as it actually has me piqued about it.