Compatibility between 3 pin and 4 pin fan connectors. Ask Question Asked 6 years, 5 months ago. Apparently a 3-pin fan can plug directly into a 4-pin socket. Two of the pins provide power to the fan, the 3rd provides an RPM pulse to the motherboard to read the speed. Case fan connectors.
Author: Giorgos LazaridisThe vast majority of PCs has at least one of them. They carry the heavy load to keep your PC cool and functional, either by providing fresh air in the box, or by forcing the hot air to leave a hot surface by pushing cool air.
Read the following article to learn how the BLDC PC Fans operates.What is inside a PC fan?There are may types of PC fans that are assembled in different ways. In this article, i will explain the basic and most common fan type. The fan that i study is a 3-wire 4 coils 80mm fan rotating at 2200 rpm. Then i will explain some other common fans.First of all i had to disassemble the fan. I am not the right person to disassemble something for the first time due to lack of patience. During the disassembling, i broke some parts of the housing and a fin.
Still i did not find any way of easy disassembling. I suppose that the fan i chosen (and maybe many others) are NOT to be disassembled and re-assembled. Anyway, let's see what's inside a PC fan:A victim in the name of scienceRemoving the fins from the housing, the controller is revealedThe rotor, the stator and the controllerIt is more than obvious that the PC fan is not rotated from a simple DC motor. It has the permanent magnets fixed on the rotor, the stator carries the coils, there are no brushes, it has a controller.
The sun is shining. It is of course a brushless motor.
I have written a detailed theory about brushless motors. You can find it in the ' page.Some different PC fan typesAs long as the motor is concerned, i suppose that all PC fans use brushless motors. There are several reasons that a brushless motor should be used, among them is the reliability, the power efficiency and the rpm feedback. So the motor type would not be the proper way to categorize PC fans.
Instead, i will categorize them with the most obvious characteristic: their connector.There are actually 3 different types of PC fans. Those with a 2-pin connector, those with a 3-pin connector and those with a 4-pin connector. Let's see them one by one:2-wire PC Fans.
These fans have usually a male-female molex 4-pins connector from where their power supply is drawn.These are the oldest and most simple PC fans. Only two wires comes out out of the fan controller, the positive and the negative. Giving power to the fan, it will rotate at full speed. The internal diagram of a typical two-wire fan is as follows:The connector of a 2-wire fan has a red and a black cable. The red cable goes to the positive of the power supply and the black to the negative. Usually, for more flexibility, they have a male-female 4-wire molex power connector. In one end of the connector the fan is connected in parallel with the 12V (YELLOW - BLACK).
Therefore, the fan is powered normally and the cable of the PSU can be used to power another device.3-wire PC Fans. Yet another 3-wire PC fan with different wire colorsA very common type of PC fan. These fans introduced the 'tacho' for the first time. The first two wires are the power supply of the fan.
![Pin Pin](/uploads/1/2/5/5/125505424/133686459.png)
The third wire, comes directly from the output of the. This output generates 2 pulses per one revolution of a fan. The fan is then connected to the motherboard.
From the third wire, the motherboard can 'read' the tacho of the fan and see if the fan is running and with how many RPMs! It is a great innovation! If the motherboard sees no pulses or very low rpm, then the characteristic buzzer sounds to inform the operator that something is not ok. The internal diagram of a typical three-wire fan is as follows:It seems that for once more, the manufacturers did not have the same wire provider, or their wire providers did not have the same colored-plastic provider. Two fans with 3-wire connectors may not have the same wire colors.
Thus, instead of using the colors to distinguish the function, better go with the connector that is standard. No matter what color the cable has, it will be plugged in the same motherboard connector! So, as you look from the key-side of the connector, number 1 is the most left pin:.
1: Negative power supply. 2: Positive power supply. 3: TachoBLACK: NegativeRED: PositiveYELLOW: TachoBLACK: NegativeYELLOW: PositiveGREEN: Tacho4-wire PC FanThis is the most modern type of PC fan. This fan is designed to be controlled with a PWM signal and increase or decrease its RPM. All fans actually can be controlled with PWM, but this particular type can also provide tacho feedback simultaneously, something that the 3-wire fan cannot do -under normal circumstances.
The 3-wire fan powers the Hall sensor and the controller from the same line that the coils are powered. Thus, if someone tries to send PWM pulses to the coils of a 3-wire fan, the same pulses will arrive at the controller. The controller will then malfunction, because it needs constant current to operate.
As a result, the third wire will not provide correct readings.Unlike the 3-wire fans, the 4-wire fans have a slight change that eliminates this problem. The controller and the Hall sensor are always powered with constant current. A transistor (fet) is placed before the coils. The base of the transistor is actually the fourth wire. So, the PWM pulses are driving the transistor.
The coils receive these pulses through the transistor, but the controller along with the Hall sensor are not affected at all. This change can be seen in the internal diagram of a typical 4-wire fan:Usually, the diagram is more complicated than this. This is to give you an idea about the principle of operation of the PC PWM Fans (as used to be called). The controller actually checks the PWM input pulses and sends pulses to the transistor accordingly.
If the PWM Duty cycle is bellow a threshold value, then the fan either shuts down, or it remains in a stable 'LOW' rpm. There are also fans that even with 0% duty cycle, they keep on running at this 'LOW' speed. This is usually done in critical applications that even if the external controller fails to operate, the internal fan controller will bypass the signal and will keep the fan running.As for the pinout.
Just do not trust the colors. As you look from the key-side of the connector, number 1 is the most left:. 1: Negative power supply. 2: Positive power supply.
3: Tacho. 4: PWM controlBLACK: NegativeYELLOW: PositiveGREEN: TachoBLUE: PWM ControlBLACK: NegativeRED: PositiveYELLOW: TachoBLUE: PWM ControlCan I connect a 3-wire fan to a 4-wire connector?Yes you can. If you notice the pinout of the fans, the 3 first pins are the same for the 3 and 4 wire fans. Also, the keys are the same for both connectors. The 4-wire connector has smaller back-key to accept the smaller 3-wire fan connector keys.
The fan will always run at full speed (as the control pin will not be used), but the rpm feedback (tacho) of the fan will operate normally and the motherboard will read the rpm normally.Can I connect a 4-wire fan to a 3-wire connector? A 4-wire fan connected to a 3-wire connector. No problem!Yes (and no) and Yes. Although the connector is larger, the keys of the 4-wire fan have the same distance as the 3-wire connector. The fan will operate at full speed all the time, as the 4 th wire from the PWM control will be on air.
The motherboard will normally read the rpm feedback from the fan tacho.Now, i am not quite sure about the internal connectivity of the 4-wire fans. No matter how may fans i tested, and no matter how many sites i visited, i found no clue that this configuration will fail. This means that the PWM control line must have an internal pull-up resistor, so that when the pin is unconnected, the control FET will be kept always ON. There could be a manufacturer though that maybe felt like making something different, and either he removed this resistor or replaced the FET with different channel than normal. I do not know why anyone would do this!
But i have not find anywhere a norm that declares if the fan MUST operate or not with the 4 th wire unconnected. A site-reader sent me which definitely shows that a 4-wire fan can be connected to a 3-pin connector, so i suppose that this is the norm i was looking for. Thanks a lot Mysteron347.Anyway, what you only have to do is to test it.
Either plug it in and see what happens, or give power yourself to the first 2 pins (negative and positive). If it rotates, then no problem!NameEmail (shall not be published)WebsiteNotify me of new posts via emailWrite your comments below:BEFORE you post a comment:You are welcome to comment for corrections and suggestions on this page. But if you have questions instead to post it. Thank you.
At 30 March 2016, 10:02:26 user Adam wrote:@Giorgos Lazaridis Hi and thank you for the very informative read! I've just read through all the comments to check that this hasn't been asked.
Long story short: Can I fit a resistor to either the 12v or PWM wire on a 4-pin CPU fan to retain the automatic PWM control, yet reduce the maximum speed? The fan is 12v 0.75A and spins at 6000rpm at 100% which makes quite a bit of noise. If so, which wire should I fit the resistor to. Whether reducing the 12v would effect power to the inbuilt fan controller. Or whether the resistor would even make a difference to the PWM considering its the pulse width that matters and (possibly) not the voltage of the pulse?More info if required - The computer is an Alienware x51 and the cpu fan is a slim 80x80x20mm fan (almost all are 25mm high - which doesn't suit the Small form factor case and its plastic deflector to push air out the back of the case). I have searched long and hard and found a.45A fan which would cost $20 and take about a month to arrive, or I could fit a $0.50 resistor of 12 ohm 5w and reduce the max speed that way. Plus you get a sense of achievement, heh.Cheers from Australia!.
At 28 March 2016, 5:39:41 user Sherif Omran wrote:does the 2/3/4 fan operate as a dynamo if we rotate the fins per hand? Or is there a diode that stops current output?thanks. At 21 March 2016, 16:04:05 user Lyle Stotz wrote:I simply used too much thermal compound and my cpu fan ran at full speed. After removing some of the compound all is well. At 13 March 2016, 17:04:41 user Bryan wrote:I have a Delta AFB 048EH cooling fan with four wires.
The colors, however, are not the normal ones. This fan has red, blue, white and yellow! Want to use just the and - and run the fan all the time.
I don't know which wires are. Usually it is red and black or on some fans yellow and black. Neither of these combinations exist on my fan. Can anyone help.
Thanks. At 14 February 2016, 17:40:26 user Luiz Fernando wrote:Very usefull page helped me a lot. Thanks for write this instructive article. At 21 January 2016, 17:50:23 user Johan wrote:Hi! If I cut the cables from 4-wired fan and just connect it to a power source, will it run at full speed then? If not, can I make it run at full speed in some way? I'm not using it in a computer.Regards, Johan.
At 22 December 2015, 5:25:09 user khaled ahmed wrote:very usefull page. At 3 December 2015, 15:06:00 user Niels Vrijland wrote:Dearest,I use stand-alone 3-wired fans for ventilation of a room. How could I connect the third wire to control the speed of the fan?Kind regards, Niels. At 20 November 2015, 10:50:02 user Max wrote:this helped me a lot. Thanks for writing stuff like this. At 29 October 2015, 23:10:59 user Chris wrote:I cannot find the exact same 24V 1.4W two pin fan.
I found a 24V 1.7W fan that is three wire and I figured it was close enough. Can I simply tape off the tacho wire and will the 0.3 Wattage difference likely be a big problem? This is for a Viking refrigerator.basically I'm looking for any comparable fan to replace the existing Sunon KDE2406PTB3 DC24V 1.4W fan.
At 25 October 2015, 6:57:55 user Giorgos Lazaridis wrote:@Louis most likely yes. At 24 October 2015, 10:25:59 user Louis wrote:Will I damage the fan if it connect 12v to the wrong pin? 3pin version. At 4 September 2015, 16:04:49 user jaco wrote:Hi I have a 4 wire cpu fan and I find that if I power it up and put a second supply pos to green and com yo blue but using a resistor. It spins at max speed. At 19 August 2015, 21:23:56 user Giorgos Lazaridis wrote:@john copertino Yes you can, no problem. At 13 August 2015, 13:24:41 user john copertino wrote:Can I connect a 3 wires fan just using the positive and negative and leave the Tach wire unconnected.
Would this be harmful to the fan. At 8 August 2015, 15:52:37 user Viggo wrote:Thanks for this instructive article.
It helped me:)It is argued, that the 3 wire interface makes it impossible to have both PWM-control and usable taco signal. I think it should be possible with some workarounds.
The fan manufacturers can include a diode and capacitor in order to maintain supply voltage to the hall element controller. Another possibility is by PC software. When you know the actual supply state (on and off) you can interpret the taco signal and it should be possible to find the right RPM value - just a little more complex software.But now the 4-wire interface has been introduced with the confusions to many people having now two kinds of interfaces.I did also find Intels 4-wire interface spec. From 2004:noticed a motherboard from ASUS having three 4-pin interfaces to fans.
Only one (for CPU cooler) made use of the interface. The two others had 5V constant to the PWM signal. I seemed like it was possible to make PWM control on the power supply pin as done on previous ASUS motherboards. At 7 August 2015, 10:38:31 user Viggo wrote:Thank you very much for this article.
It made me understand this issue.I do actually wonder about why the extra pin 4 has been introduced, because there should be possible workarounds. Making a new kind of interface will always create problems for many people.Workarounds for the fan manufactures can be a small circuit including a diode and capacitor able to keep supply voltage on the hall element controller. In this way you can have a stable taco signal independent of the PWM control. Another work around is by software in PC. If you measure the taco signal at the same time you know/control the output PWM-power signal (high or low), then this information should provide you the real taco signal information you want. With some proper software it should be possible.So perhaps some makers of fans or PC software for fan control already did this - I don't know.However someone in this business did decide to go make a new 4-pin standard.
At 3 August 2015, 1:38:33 user abc wrote:for the 3-wire fan, wire colours: you say the centre pin is always positive. Well it's not on my sony vaio laptop. Im glad i didnt do any damage following your instructions mate. At 2 May 2015, 2:39:17 user Steve Horvath wrote:Hello!Yesterday I bought a Hyper 212 EVO CPU Fan because the old Fan installed almost 3 years ago was nearing its lifetime with a few weeks to spare. Due to the fact the summer is approaching and the ambient temperature will get higher, I wanted to be sure that my CPU was being cooled off!! As additional cooling, I also installed two 3x3 Inch Fans onto the Chassis directly above the Hyper 212 EVO CPU fan to move the heat outside of the Chassis.
The installation was very simple as both of these Fans had a Molex connector, and they both work perfectly since their install with my AGS Series SATA ATX 450 Watt Power supply. I must say that I was fortunate to have small holes on my Chassis that made it easy to screw the fans into place and secure them.For those whose Chassis don't have any holes, the solution is to drill a hole or two where you could install small Fans to remove excess heat from your device and keep the CPU and it's environment cool for optimal performance.Best Regards, Steve, Chicago, IL. At 1 May 2015, 10:18:13 user Giorgos Lazaridis wrote:@Patrick Sure, you can simply make a PWM fan controller or linear voltage controller. Check out my circuit pages.
At 1 May 2015, 10:13:07 user Giorgos Lazaridis wrote:@Stephen get a 5V fan, stick it under the laptop power through usb.