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Fans, PWM, 3Pin, Fan Controller

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April 3, 2012 10:00:38 PM

So a fan with 3pin connector can be controlled BUT with a fan controller? Like the one linked above?

A case fan with 4pin connector so a pwm connector, where can this be plugged in?
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April 3, 2012 10:09:40 PM

mcnumpty23 said:
a 3 pin fan can also be controlled by the motherboard

a 4 pin pwm fan can be connected to a 4 pin header on some motherboards or fan controller with 4 pin pwm

connector

this may explain it clearer

http://en.wikipedia.org/wiki/Fan_control#Pulse-width_mo...


Would you also happen to know a link to one of these 4pin pwm fan controllers?
a b ) Power supply
April 3, 2012 10:19:17 PM

how many fans do you need it to control?

heres one but it does up to 8 fans so may be more than you need

just google the model number

NFS-2108S/B
April 3, 2012 10:51:07 PM

Lookup speedfan you might find that very helpful if your motherboard manufacturer allows communication on SMB or ISA bus to your 3pin fan connectors. Some boards do not have the internal circuitry to handle this as they may be "hard wired" to a voltage source instead of some logic controller. Most boards manufactured recently support communication over one or both and may even have multiple channels so you can control several of the connectors on your board.
a b ) Power supply
April 4, 2012 5:07:12 AM

BOTH 3-pin and 4-pin fans CAN be controlled by a motherboard (mobo) OR by a separate fan controller. The differences are in the hows and whys, so let's review.

First, you should recognize that "Control" can have several meanings, although there are only two of particular interest here. The simplest form of control allows you to manually set a fixed fan speed, and it will stay there until you change it. This could be done either by controlling the voltage of the power supplied to the fan (the 3-pin design, see below), or by altering the PWM signal for a 4-pin fan. This is the type of control available from most separate fan controllers, and MAY also be an option for a fan connected to a mobo port.

The other main type is automatic control, more properly a negative feedback automatic control loop, which is what almost all motherboard fan ports offer. In this system there is a temperature sensor that actually measures the temperature of some important point and feeds the information into a fan controller (actually, a software loop contained in the BIOS chip). In addition the controller loop has a Setpoint (the target temperature to reach at the sensor), a Gain setting, and a Zero Offset setting. (These last two may be apparent to the user as something more useful, however. For example, on my machine I get to specify the low temperature below which the fan will shut off, and the high temperature at which the fan will be running full speed.) This feedback controller system constantly compares the actual measured temperature from the sensor to the Setpoint. As the temperature changes, the fan speed is changed to bring the temperature back to Setpoint. It's called a "negative feedback" control loop because the result of the controller's action (the actual measured temperature) is fed BACK to the controller, and its response is to generate an action in the OPPOSITE direction from the changes in the measured variable (higher temperature generates more cooling).

So, the automatic controllers built into mobos constantly change the fan's speed according to what is required by actual measurement. Manual controllers do not do this. Of course, IF you have temperature sensors and readout devices available, you yourself can monitor the temperature you have chosen to watch, and reach down and turn the fan speed control knob. But you probably won't do this every second!

The particular fan controller you linked to has six separate fan control channels, each for one fan and using one manual speed knob. It also has several temperature sensors included that you can mount on your mobo or inside your case, and it will show you those temps. But as far as I can see, it does not provide any automatic control loops - it just shows you the temps, and allows you to adjust fan speeds. NOTE that this system can NOT show you the temperature INSIDE the CPU, which is what most mobos CAN give you. The mobo does this by monitoring a temperature sensor already built into the CPU case by the chip's manufacturer.

So, given that we want to control a fan's speed, how is that done? 3-pin and 4-pin fans accomplish this differently. Hence, the controller system needs to know what kind of fan is being used, so it can send the proper signals.

A 3-pin fan has 3 wires running to it. Pin 1 (Black wire) is Ground of the power supply. Pin 2 (Red) is the + side of the DC supply, and it varies from 0 to +12 VDC. Pin 3 (Yellow) actually takes a signal generated inside the fan motor and carries it back to the controller (mobo or separate controller unit) to be monitored. This signal is a series of pulses - 2 pulses per motor revolution - so just counting the pulses in a fixed time tells you the rotational speed (rpm) of the fan. To control the fan's speed, the controller just changes the voltage supplied to Pin 2, somewhere within the range 0 to +12VDC. Actually, it rarely goes down to 0VDC unless the controller really wants to shut the fan off. You see, a small DC motor like this that is running will probably stall if the supply voltage drops below about 3 VDC. And then, to get it started up again, it will probably require at least 5 VDC. NOTE that, even though the controller has access to the actual fan speed signal, it does NOT use this in any automatic speed control strategy. Fan speed is based on the measured TEMPERATURE of the device being cooled, and not on the actual fan speed. For example, the CPU cooling fan's speed, when controlled by the automatic controller in the mobo, is adjusted according to the actual temperature inside the CPU case, as measured by the sensor inside there.

A 4-pin fan works differently, and it has 4 wires running to it - surprise! Again, Pin 1 is Ground, Pin 2 is +12 VDC, Pin 3 is the speed pulse signal being returned, and the extra Pin 4 is the PWM signal from the mobo to the fan motor. For these fans, Pin 2 is ALWAYS at +12 VDC - it does not vary the way a 3-pin fan's Pin 2 does. (BUT, see later for the exception). Inside the fan motor housing there is a small controller chip that regulates the flow of current available from the Ground and +12 VDC supply lines to the actual motor according to the PWM signal. PWM stands for Pulse Width Modulation. The signal is a bit like a square wave - it is either fully on or fully off - but is different in that the time on / time off ratio changes, and that's what changes the fan speed. This PWM signal is used like an inhibitor - when it is on, the tiny in-motor chip cuts off the current to the motor. When the PWM signal is off, the tiny chip sends the full +12VDC supply to the motor. As the PWM signal switches rapidly on and off, the motor gets a current supply turned off and on, and the result is a speed less than the motor's maximum speed. The big advantage of a 4-pin fan is that it can be controlled to slower speeds than a 3-pin can. Why? because for very low speeds the PWM signal just restricts the current supply to the fan to very short pulses, BUT they are pulses of a full +12 VDC, so the fan keeps getting a strong "kick" every pulse and does not stall so easily. Likewise, a 4-pin fan can be started up at a low signal.

So, a 3-pin fan's speed is changed by altering the voltage of its Pin 2 supply line. A 4-pin fan gets +12VDC all the time on that Pin 2, but the little chip inside the motor case then regulates that according to the % time off of the PWM signal from Pin 4.

Now, the designers of these fans went to some trouble to build in backwards compatibility. 3-pin fans came first. (Actually, 2-pin fans came before that - they just had no Pin 3 Yellow wire to send back a speed pulse signal.) When 4-pin fans were introduced, two things were done. First, the connector on the end of the fan wires is designed so that it will plug into a standard 3-pin fan's port on a mobo, and the first 3 pins on the fan connector are exactly the same signals as the 3-pin system's outlet on the mobo. In this case, the second feature kicks in. The 4-pin fan just gets NO signal on its PWM line, and the Pin 2 signal is not a constant +12VDC - it varies the way a 3-pin fan expects. So the 4-pin fan operates exactly like a 3-pin fan, with no PWM "on" signal to inhibit current flow through the tiny chip inside the fan's case.

Now, how about the other way around? Plug a 3-pin fan into a 4-pin mobo outlet. Now we have that fan supplied with the same signals on the first 3 pins it always expected, EXCEPT for one thing. The supply on Pin 2 is always +12VDC, and the 3-pin fan does not ever receive the PWM signal on Pin 4 (because it could not use it, anyway!), so this fan will run at full speed all the time. Well, at least we get cooling this way, even if it's too much at times.

And here's where we get to the "it depends ..." stuff. A mobo with automatic feedback control supplying a 3-pin fan port will always do its job by varying the voltage on Pin 2, and both 3-pin and 4-pin fans can work with that. But consider the mobos with 4-pin fan ports. SOME of them do as I said above - they operate solely as 4-pin controller systems, and any 3-pin fan plugged into them will always run full speed. SOME mobo makers, however, offer you an option in BIOS Setup for that 4-pin fan port. You can set the controller for this port to use either 3-pin or 4-pin mode, thus making the controller send out the exactly right kind of signal for the fan you have plugged in. And a few mobo makers actually have this adjustment automated - the mobo controller itself figures out which type of fan is plugged in, and adjusts its control mode accordingly. Now that's smart!

For the user, figuring out which way a mobo maker set up a 4-pin fan port is not easy - I often find the mobo manual is unclear on this feature. Sometimes it becomes clear when you actually go into BIOS Setup and examine the port options. Sometimes the mobo maker's Tech Support people can tell you. Sometimes you gotta figure it out yourself.

So, what to do? If you want automatic fan speed control to keep certain parts to a particular temperature, you almost always do this via the fan ports on the mobo. That can become difficult if you have a lot of fans, and not enough mobo ports, but that's a different discussion. On the other hand, if you prefer to do your own fan speed settings and not have them change by themselves, then you probably want a separate fan controller module, and that may allow you more fan control channels.

Which mobo ports to use? First, the one marked CPU_FAN should ONLY be used for the fan cooling the CPU chip. Its control loop is using the sensor built into the CPU case, and it will always adjust the fan speed according to that internal temp. Moreover, SOME mobos add an extra precaution on this control loop. They check the CPU_FAN speed and, if it ever drops to zero (or if there is no fan connected here), they send out an alarm and may shut down the entire machine in a very few seconds! This is to prevent severe overheating of the CPU with no cooling fan running, and the system does not wait for the measured CPU temp to rise suddenly. On systems like this, if you do NOT run your CPU fan from this port, you should go into BIOS Setup for the CPU fan and tell it NOT to monitor that fan and activate alarms based on it.

You will find one or two (occasionally more) mobo ports called SYS_FANx. These are intended for case fans, and they usually are linked to a separate temperature sensor built into the mobo. However, I have seen mobos in which ONE of these was set up with feedback control based on the mobo temp, and the other had no fan speed control - it just ran full speed.

You may find a port called PSU_FAN. The original design here was NOT to control a fan. SOME (not all) PSU's have a set of wires coming out just like the 3 leads from a 3-pin fan, and these should connect to the mobo PSU_FAN port. All this really does is allow the fan inside the PSU to send its speed signal (on the Pin 3 Yellow wire) to the mobo for monitoring. The port does not control the speed of the PSU's fan. IF that fan's speed is under some control, that is done entirely within the PSU itself. However, on many mobos it appears that this PSU_FAN port on the mobo actually has the Ground and +12 VDC lines connected. So, if you do NOT plug into it the leads from the PSU, you can plug in instead a standard 3-pin (or even a 4-pin) fan and it will simply run at full speed all the time.
a b ) Power supply
April 4, 2012 10:55:07 AM

wrenaudrey said:
very nice finds mcnumpty23, thank you.
so from the things you've been saying, these fans are compatible with a fan controller to be controlled then?

http://www.ebuyer.com/206654-coolermaster-120mm-sicklef...
http://www.ebuyer.com/225778-casecom-140mm-blue-led-cas...



yes

though if you want good led fans then i would go for these--they give a much better light than the

coolermasters because the leds are in the hub not the frame

http://www.scan.co.uk/products/120mm-silverstone-sst-ap...

the coolermasters tend to give lines of light--these give a full circle


heres my new build with 2 of these on the left and the coolermaster fan on the right

http://i1184.photobucket.com/albums/z330/mcnumpty23/sto...

http://i1184.photobucket.com/albums/z330/mcnumpty23/sto...

http://i1184.photobucket.com/albums/z330/mcnumpty23/air...

not a great photo as i only had my phone handy but should clearly show the difference
September 25, 2012 4:22:01 PM


Thank you so much..That is really helpful.


Next question. I just built a MSI Z77A-GD65 system last night. And, I thought that I was buying 2 4 pin PWN case fans. But, I bought 2 3 pin fans (with 4-pin adaptor...which meant Molex it turns out). Now I am trying to determine if this is a "problem" or not since one of my goals was a high efficiency system.

One of the reasons I bought the MSI board is that it supposed to have great Power management control.

So, would a motherboard which can manage the voltage to a 3-pin connector be as effective at managing power consumption as a 4-pin PWN fan...especially since there would not be a constant 12V feed going to the fans. Like wise..wouldn't a motherboard like this one potentially also reduce that constant 12V to 4-pin PWN fans?

Thanks for any response :) 
a b ) Power supply
September 26, 2012 1:59:31 AM

A mobo can manage fan speeds in either of two ways, but not both simultaneously. For a 3-pin fan, it varies the voltage supplied from 0 to 12 VDC. Actually, however, that system has a small problem at low voltages (and speeds). If the voltage for a fan already running is run too low, the fan will stall. After that it will remain stalled until the voltage is increased above some threshold (about 5 or 6 volts) necessary to start it up again. Once the fan is running, the supply voltage can be reduced below this threshold, but at some lower voltage it will stall again. For initial start-up from the no-power state, all mobos supply the full 12 VDC at first, then reduce it after the fan speed control system is active, and by then the fan is already running.

A 4-pin fan's port supplies the full 12 VDC to the fan at all times, BUT it also sends it the special PWM signal. Inside the fan motor case there's a small regulator chip that uses the PWM signal to switch the full 12 VDC signal on and off very rapidly. The less time "on", the slower the fan motor turns. But when it is "on", the fan motor gets a brief but powerful "kick" to keep it going, or to start it up if it is stalled. Because of this the fan can keep running at a slower speed, and can be started at a slower speed, than a 3-pin fan can.

Some mobos' 4-pin fan ports can be set manually to either 3-pin or 4-pin mode; some even can adjust themselves automatically depending on what fan type is connected. (This cannot be done for a 3-pin port - it can only operate in 3-pin mode.) But when in 4-pin mode, the +12VDC supply is never reduced - it is always 12 VDC. In that mode, the power consumed by the fan depends on the PWM signal, NOT solely on the +12 VDC supply. Be aware, also, that not all mobos have this flexibility on any or all of their 4-pin fan ports - some merely work as 4-pin ports only, meaning that any 3-pin fan plugged into them can only run at full speed all the time.

As far as managing the power consumed by the fans, I suspect that it is possible that a 4-pin fan might be more power-efficient than a 3-pin, especially when cooling requirements are low and slow fan speed is sufficient. HOWEVER, the difference in power consumption between 3- and 4-pin fan motors for the same amount of air moved is bound to be VERY small. I doubt very much that this would have any significant impact on overall system power efficiency.
September 26, 2012 2:19:49 AM

Thanks again, I got a hold of MSI today, and they let me know that in fact, the Z77A-GD65 MB "Active Phase Switching" will do voltage regulating to drop that 3-pin fan's speed and consumption when the core temp is low enough. And likewise, APS will treat the 3-pin the same as the 4-pin. Of course, I think they were glossing over the stalling...But, I bet if the temp is low and u dont need the fan. Then who cares.
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