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Connecting a 4 pin CPU Fan to a Fan Controller

Hey all,

I'm trying to connect the fan that came with my i5 760's cpu cooler to my NZXT Sentry 2 fan controller. The cpu fan uses a 4 pin connector, while the fan controller only has a 4 pin molex and a 3 pin connector (with only 2 wires on either, ground and 12VDC)

I tried cutting away the side of the 3 pin plug such that the 4 pin would then fit in (matching black to black, yellow to yellow, and the slots on the connector) but when I booted back up the fan just sat there and wobbled like it wasn't getting enough power. The label on the fan states that it uses 12VDC and 0.60A (V*I=7.2W), while the fan controller supplies up to 10W, so it should be ample. I think I read somewhere that the fan controller supplies an 8W minimum, but I would expect this to mean it just wouldn't slow down the fan, rather than not starting it.


P.S. I love this fan controller, the beeps aren't nearly as loud as the reviews lead me to believe.
12 answers Last reply Best Answer
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  1. That was a 4-pin PWM connector that is intended to connect to your mobo so that your mobo can regulate its speed automatically, without an additional fan controller.

    What make/model of motherboard are you using?

    You may have to get another fan to do what you want to do.....
  2. Your fan controller is controlling the fan speed by lowering the 12v supply. PWM fans do not work that way.
  3. The 4 pin CPU cooler fan is required to be connected to the MoBo. The 4th wire provides feedback to the BIOS for fan speed control. It also lets the BIOS know that the fan is in fact spinning and thereby allows the boot process to continue. You can usually turn this safety feature off but why one would do such a thing and risk CPU damage is something I'd find hard to understand.

    Now if you are saying that you have an aftermarket cooler and therefore are trying to make use of the fan from the "unused" heat sink, my suggestion would be to connect that fan to the fan header on the MoBo labeled "CHA" and set up chassis fan control via the BIOS.

    By trying to connect the CPU / chassis fan to the fan controller, you are trying to the same thing in a more cumbersome way a surgeon using a meat cleaver instead of a scalpel :)
  4. Unfortunately it is a very basic Biostar board (T55?) which seems to only run the fan at full speed rather than regulate the speed, despite having the 4 pins.

    I'm really not running any sort of risk of frying components due to temperature. The fan controller has temperature sensors which I have placed at various locations throughout the case, adn an alarm which sounds if the temperature reaches a point which I can set manually. Thus far the CPU has only bridged 40 celsius once.

    I guess I'll just have to leave it for now, or replace the fan with another which will work with my controller.
  5. here's the way 4-pin fans are wired, and how to connect to a 3-pin output.

    What you did makes sense - black to pin #1, yellow to pin #2. BUT do you have the FIRST system - Black, Yellow, Green and Blue? NOTE that if you have the second system with RED as the +12 VDC line to pin #2, then the YELLOW on that system is the fan's speed output to connect to pin #3!

    IF you have the first system that uses Black as Ground and Yellow as +12 VDC it should work. However, be aware that, when connected that way, the fan motor may NOT start up if your controller is set to a low speed (low voltage). It needs a full voltage (speed setting) to start, THEN turn the speed down to what you want.

    Here's how 4-pin fans work. They are supplied with Ground (pin #1), a constant +12 VDC (pin #2) and a PWM signal (pin #4). Pin #3 is the fan motor's speed pulse signal (2 pulses per revolution) fed back to the mobo for monitoring fan speed. The PWM (pulse width modulation) is a signal that looks like a "square wave" except that it is NOT a plain 50% on / 50% off waveform. Its "% On" value is varied according to the motor speed required. The circuit that does this work is built into the fan motor case. It uses the PWM signal to control how much of the time the full +12 VDC is applied to the fan motor. So the motor receives a voltage that is either full 12 V or nothing, but it does not get any reduced voltage. That way it can start up well even when the PWM signal is only 50% on, because it starts at 100% on, then coasts while the voltage is off.

    A 3-pin fan system works differently. In that system the +VDC voltage is varied but ALWAYS on, so that the motor runs at a speed determined by the voltage available. However, if that voltage is set very low, it is hard to start up a stationary motor.

    The wiring system is backwards compatible. So, if you plug a 4-pin fan into a 3-pin fan outlet it will work because the +12 VDC signal is present, but reduced for lower speeds, and the PWM signal is absent so it cannot cut off the supply to the fan motor. It's not ideal but should work if you "kick it" to start up.

    I am intrigued, though, that you say you had to modify the connector to get it to fit on. The "standard" 3-pin male connector (on a mobo, for example) WILL accept a 4-pin female connector from the fan wires, with the 4th pin (for the PWM signal) not connected. This DOES allow the fan's speed signal on pin #3 to be fed back into the mobo or fan controller to be monitored.
  6. The fan controller plug, though intended for the 3 pin, has only 2 pins inside, pin 1 and pin 2 (12VDC and GRD). It has the 2 pins, and a surround that would accomodate a typical 3 pin female connector, but the surround will not fit over a 4 pin connector, thus the 'modification'.

    With the 12VDC and GRD connected, and the controller at 100%, it would still not kick start, so I'm wondering if in fact, the control wire should be connected to the 12VDC as well (if it is only on when the control line is on, then this would make sense)

    I'm tempted to try it, but I'll feel stupid if it doesn't work after I've hacked the wires... Of course the site you linked (which I had viewed before actually) shows that a 4 pin fan should work when plugged into a 3 pin connector, which would also have the control not plugged in...
  7. Just as a test of the fan itself, can you plug it into another power source, like a 3-pin or 4-pin output on the mobo? Even though you've modified the plug by eliminating the speed feedback and PWM signal lines, it should still work at full speed when connected.
  8. I modified the connector from the fan comtroller (just cut some plastic away). The fan is currently plugged into the mobo (4 pin) and is functioning, I just wanted some speed control to slow it down and reduce noise... I have not done anything to the fan or it's connector or wires.
  9. Best answer
    If you have the CPU fan plugged into the mobo and still cannot get speed control, check two things. First and foremost, make sure it is plugged into the mobo pinout identified for the CPU_FAN. Only that pinout is connected to the actual temperature measured inside the CPU. Next, look closely in your BIOS Setup screens and find the place where the CPU Fan control is done. Some of these allow you to ignore the control system entirely and set it to run all the time at full speed. In your case you had the CPU fan NOT connected to the mobo at one time, so you (or someone else) may have set it this way just to avoid problems. Some of these CPU cooling fan controller systems get very upset if they receive no CPU fan speed signal - they think the fan has failed and shut down quickly. So they have an option to disable the controller function. You may have to Enable the CPU fan control IF you connect that fan to the CPU_FAN pinout.

    Now, once those are done, there still MAY be another step. Some of these systems allow you to set up controller parameters (such as temp settings for minimum and maximum fan speed) within the BIOS screen. Others show you no such options. In those latter cases, often the trick is that you have to install a utility that came with the mobo (on a CD) that runs as a Windows app and allows you to see fan speeds, mobo and CPU temperatures, and often to configure the fan speed controllers.
  10. Best answer selected by John_Doe823.
  11. hello i am new to this thread,my name is alon and i orginally looked at this thread to try to figure why my 4pin connector plugged into my 3pin connector to my motherboard would cuase all my fans to go max speed and not boot up my system.once that 4pin was unplugged the system would boot.

    anyway while i am here i can tell you guys a fix for the 4pin fan controller that you was looking at and how to get it to start and be controlled like a regular fan. that blue wire is a real pain to deal with,from what i can see it is designed to control the fan speed and with out it will either go at full speed or not work at all.but if you are useing a fan controller then you should be able to adjust that voltage and make it the way i have to fix will more or less have you mod the fan its self and convert it into a two pin for use with the controller.i have multiple of these 4pin fans and not enough connectors on the board so i wanted to use the fans on a molex to 2pin fan converter.what i found out is that it would just kinda wobble and not do anything.since i had multiple of the fans and converters i decided to experiment with a 9v battery.I cut the 4pin connector on the fan off,stripped the wires and touched each wire to the battery until i got it to work. the result is.....

    you can splice the red wire of the fan to the red wire of the molex converter.just cut the end off of the converter and twist the wires.i find hotglue to be really nice to hold the wires together once twisted :) just pull the trigger of the hot glue gun slightly until a tiny bit comes out and then stick the wires down the barrel an vola you got a nice solid connection. next take the black and yellow wires and twist them together and put them to the black wire of the 2pin converter.the blue wire can dangle(i do not know if you need to have the blue wire stripped in order for it to turn on,im sure it does for some reason) that is all to the mod :D theoretically you should be able to lower the fan speed with your controller due to the voltage,however if your doing this for the cpu of the machine i do not recommend this,its best to let the machine determine the speed of the fan for the proccessor with the 4pin connector,otherwise it may over heat and burn out. now the chasis fans i dont see a problem with controlling the speeds an such.

    overall i hope this will help you with your fan controller problem,4pins are very annoying with how they are set up,but with my mod you should have a very nice control over it(the mod basically takes away the brain of the fan an gives it to the fan controller )
  12. I find alon944's post confusing. His "fix" may be based on the less-common color coding used on some AMD CPU fans with Black, Red, Yellow and Blue wires. For the more common system of Black, Yellow, Green and Blue, see again this link:

    Now, if you are trying to connect to one of these 4-pin connectors on the wires from a fan, you need to know the color coding of the standard 4-pin Molex connector (comes from the PSU) used to provide power to older IDE devices, etc. See this link:

    So, if you're trying to connect a 4-pin fan to some other power source connector, realize that the FAN's connector has Ground on Pin #1 (BLACK wire) and +12VDC on Pin #2 (normally Yellow). NOTE that this is NOT the same as the Yellow wire on a 3-pin fan's Pin #3, which is the speed pulse line. On a 4-pin fan's connector, the speed pulse line is still on Pin #3, BUT its color is normally Green.

    To get a 3-pin OR a 4-pin fan to run, you need to provide Ground to connector Pin #1 and +12 VDC to Pin #2. Then it will always run at full speed. If you want it to run a slower speed, you still supply the +VDC signal to Pin #2, but it should be reduced to a lower voltage. That is what all speed controllers for 3-pin fans do, whether they are separate third-party devices or mobo pinouts. You do NOT need to connect anything to Pin #3. It takes the speed pulse signal (2 pulses per motor revolution) generated by the motor back TO the mobo so it can be monitored and display the motor speed. This signal is NOT necessary for the mobo to accomplish fan speed control - that is done based on actual temperature measurement separately, and accomplished by changing the fan +VDC voltage. However, mobo's do monitor that fan speed signal to be sure the fan is still turning.

    A 4-pin fan NORMALLY receives +12 VDC on Pin #2 at all times, PLUS the special PWM signal on Pin #4 (normally a Blue wire). Within the fan there is a tiny controller chip that uses the PWM signal to control actual flow of current from the +12 VDC supply to the motor. The design is backwards compatible with 3-pin fan designs in two ways. First, the connector will fit on, connecting the first 3 pins to exactly the same signals in each case. Secondly, if the 4-pin fan receives NO PWM signal on Pin #4, it passes all the power available from Pin #2 to the motor. Now the power coming out of a 3-pin pinout on a mobo has the voltage on Pin #2 vary according to desired fan speed - it is NOT always +12 VDC. So a 4-pin fan plugged into a 3-pin mobo pinout WILL function and will change its speed.

    Now, what about trying to connect a 3-pin OR a 4-pin fan to a separate fan speed controller. The controller output connector only has TWO lines - Ground and +VDC (varying from 0 to 12). It has NO PWM signal for Pin #4, and many controllers have no use for the speed pulse signal coming back from the fan on Pin #3. So to make this work you should be connecting controller Ground to fan Pin #1 (Black), and controller +VDC to fan Pin #2 (normally Yellow, but sometimes Red). Do not twist any other fan wires to anything else - leave them unconnected. Now, IF your fan controller actually does have a way to use the fan's pulse speed signal on Pin #3, then you should connect that one, too.

    One small problem with these systems is the start-up situation. A +12 VDC fan motor needs a certain minimum voltage to start up - probably about 6 to 9 volts just briefly. When a mobo is doing the controlling, it is always set to provide full 12 VDC at start-up, and then drop it down a few seconds later as the actual measured temperature becomes available. BUT if you are using a less sophisticated fan controller unit pre-set to some low voltage, it may no be enough to start the fan. At start-up time you should briefly turn up each fan's speed (voltage) control to full, then reduce it to the desired setting.

    What about feeding power to a fan directly from a 4-pin Molex power output from the PSU? Well, look back at that drawing of it. The Molex has +12 VDC on Pin #1 with the YELLOW wire, and Ground on Pins 2 and 3 (Black wires). Pin #4 with the RED wire does NOT have 12 volts - it has +5 VDC. So you must connect fan Pin #1 (Black Ground) to either of the Black wires of the Molex, and fan Pin #2 (Yellow or sometimes Red on 4-pin fans, and always Red on 3-pin fans) to the YELLOW wire of the Molex. NOTE that, if you connect a fan's Pin#2 by mistake to the Molex's RED wire, you are giving it only +5 VDC and it may not start up!
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