Case Fans- 4pin, 3pin, molex

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wrenaudrey

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Mar 6, 2012
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I understand that a fan with a molex power connector will make it run @ 12v and molex is in my opinion the easiest way to power up fans.

But what about 3pins-What voltage are they able to run at? Can you adjust the speed or the voltage?
And im aware that some motherboards come with several (2-4+ headers) in the board it self, but what if you had more fans than your mobo can be plugged into, where would you plug it in then?

And 4pins- What voltage are they able to run at? Im pretty sure you can adjust the speed on these but where?
and again, where would you plug in these 4pin fans apart from the CPU cooler pin (ofcourse), as im aware that not many or even none have 4pin headers apart from the cpu cooler on mobos
Is it ideal to use 4pin fans as case fans?

Last thing, can you guys send me link to some fans that you think are good? Preferably, there has to be a balance between performance and quietness.

Thank you all in advanced
 
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Start with: all case fans are designed to run at 12 VDC for full speed, but will run slower under the right conditions. Details below.

A 4-pin Molex connector from the PSU will supply 12 VDC to the fan at all times over 2 wires, so it always runs at full speed. Such a system has no way for the fan's speed to be sent to the mobo.

One IMPORTANT note: it is advisable to plug your CPU cooler fan into the CPU_FAN port of your mobo, and let the mobo's automatic systems control the CPU fan speed. This ensures that the CPU cooling fan (assuming it's working properly) will run fast enough to keep the CPU at the right temperature, but not too fast so it makes more noise than necessary. It also allows the mobo to check that the fan is working - it will shut the system down fast if that fan suddenly stops. But because of that checking feature, if you opt to run your CPU fan straight from a Molex PSU connector at full speed, you must tell your mobo's BIOS NOT to watch that fan, or it will get very upset that there is no fan speed signal to watch.

Do NOT plug into the mobo CPU_FAN connector ANY other fan. If you don't plug the CPU fan in there, leave that fan port unused.

A 3-pin fan plugs into EITHER a 3-pin or a 4-pin fan port on the mobo. Fan connectors and the mating mobo ports have been designed, physically and electrically, so that they always will fit together with reasonable electrical connections, but the details of fan speed control are not always the same. If you plug a 3-pin fan into a 3-pin fan port of the mobo and allow the mobo's automatic systems to control the fan speed, here's what happens. The fan's power is on the Black (Ground) and Red (+12 VDC) wires, and the mobo lowers the voltage on the Red wire to reduce fan speed as needed. The Yellow wire carries a pulse train (2 pulses per revolution) signal generated in the fan motor back to the mobo for display and monitoring. This is how the mobo can warn you if the fan stops. The basis for speed control is what's called a feedback loop. In that system, the result of the loop's control action (a measured actual temperature) is fed back into the mobo controller and compared to the target. As the actual temp changes from the target, the control loop changes its output (the voltage supply to the fan) to bring it back to target. Note that the actual measured fan speed is NOT used to control the fan speed - that control is based only on measured temperature. For the CPU, the actual temperature measurement is done with a sensor built into the CPU chip itself and fed to the mobo on one of the CPU's pins. For the Case Fans, the mobo has its own temp sensor built in and uses that to measure the actual inside-the-case temp.

A 4-pin fan plugged into a 4-pin fan mobo port works very similarly, but the details of how the fan speed is controlled are different, and the wire color codes are different, also. In this system, the Ground and +12 VDC power supply lines and the speed pulse return line are all there still, but there's a 4th line carrying the PWM (Pulse Width Modulation) signal. The +12VDC supply line in this system is always at that full voltage (does not get reduced by the controller). Inside the fan motor is a small chip that uses the PWM signal to control how much of the time the +12 VDC supply is actually fed to the motor, effectively reducing the average current flowing through the motor, and thus its speed.

Now, what about "mis-matched" fans and ports? As I said, they will work because of the backwards compatibility designs. BUT ... If you plug a 3-pin fan into a 4-pin port, that fan will receive the first three signals, and not the PWM signal it can't use, anyway. However, the +VDC line is always at +12 VDC on a standard 4-pin port, so the fan always runs at full speed. To handle this situation, SOME mobo makers allow you in BIOS to change the mode of operation for the fan controller for that port, and make it behave like a standard 3-pin port with varying +VDC supply, accomplishing fan speed control. Some mobos even are smart enough to figure this situation all by themselves and make that mode adjustment for you.

Now the other way - a 4-pin fan plugged into a 3-pin port. The fan will receive the first three signals, but no PWM signal to use. So it will not do anything to alter the flow of current from the supply through the motor. But since this is a standard 3-pin port, the +VDC line is varying, not fixed at +12 VDC, so the fan speed CAN be controlled by the mobo.

To complete the picture, SOME mobos have a port labelled "PWR_FAN", and SOME PSU's have a set of wires coming out of them the obviously fit onto a standard 3-pin fan port. If you have both of these, you plug one into the other. All it really does is allow the mobo to receive the PSU fan's speed signal and monitor / display it for you. This mobo port does NOT control the PSU fan's speed. IF that fan's speed is under control, that is entirely done inside the PSU itself. Now, if you do not have such a signal wire set coming out of your PSU, you just don't plug anything into that mobo port. EXCEPT ... some mobos apparently do have the Ground and +12 VDC signals on that port so it CAN be used to power a 3-pin or 4-pin fan, but it will not have any speed control - it will run at full speed at all times.

Too many fans to connect, and not enough mobo ports? Well, you can do a few things to deal with this. First, it appears that most mobo fan ports can supply enough current to power TWO fans per port, but not more. The limit is mainly in the heavy momentary current as the fans start up from stopped. If you are going to strip fan wires and solder them together to accomplish this, note this. For 3-pin fans you should connect together the two Black (Ground) wires, and then the two Red (+VDC) wires. But leave only ONE Yellow (speed pulse) wire connected to the connector - leave the second fan's Yellow wire disconnected. You should not feed two pulse train signals into one fan port - the mobo pulse counting system will get totally confused. If you're doing this with 4-pin fans, follow the same rule, plus tie together the two PWM signal lines - two motors can share use of that signal. Check the web for color coding on 4-pin fans.
 
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dude,,awesome explanation.
been wondering over the net looking for this explanation.
and i found it in 2012 comment..lol

thanks
 
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Wow! I do not think I can find such a comprehensive explanation somewhere else on the web. It's March 2015 and you explained everything I need. Thank you so much!
 
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All fans come with a label that states their specs. For example: (12V=DC 1.34A) If you have an older computer like I do (Dell Optiplex GX270) then you have a floppy drive. I personally have removed that drive because it's a waste of space and with it gone i have mounted a blower fan which pulls cool air through the floppy port hole to add extra cooling to all internals. If your pc is running a little warm it is not a bad idea to run a 4 pin Molex to 3 pin or 4 pin fan adapter. Doing so (like Paperdoc explained) will NEVER run under full speed. In other words, your pc internals will ALWAYS have cool air flowing.
 
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Paperdoc I wonder if you are around and if you or anyone reading this has any knowledge of what I am about to try to do with fans. I have a powerful MB and case that controls all my fans nicely. But I want a redundant readout in a 5.25 slot on the front. I am going to try to use fan Y adapter's in reverse. Therefor letting the cpu fan and everything still have it's control of the fan. but use the second have of the y to go to another separate fan controller. I'm not sure if the voltages will interfere. I really want to do this. How awesome would it be if your fans are all automatically controlled yet I have a redundant double temp verification in plain view on the front and if I am about to do some hard gaming I would have the ability to juice up the fans a bit more manually. Will this work??? Anybody???
 
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Yes, it can work IF you re-wire things carefully. At least, I think it will. The question I cannot answer is whether two devices (the mobo port and the fan controller inputs) can share the speed pulse signal coming out of each fan on its Pin #3, but I expect the answer here is yes, they can share. Of course you will need to buy and install a third-party fan controller module in the front, and then not even try to use its control features and not output any power to the fans. And of course, this will have to be a controller designed to accept fan speed signals from several fans and allow you to choose which to view, which means it needs to be designed with fan connections for 3- or 4-pin fans. It does not matter whether these connectors are for 3- or 4-pin fans, since you are not sending power to the fans from them. The only connections you will use between fan controller and fan are the Ground and Speed Pulse lines.

Now, the re-wiring details. First piece of info to settle is: are your existing fans 3-pin or 4-pin? The answer affects how you can identify the correct wires to modify. A 3-pin fan has a Black wire on Pin #1 for Ground, a Red wire on Pin #2 for the +VDC supply, and a Yellow wire on Pin #3 for the Speed Pulse signal. On a 4-pin fan, the functions of the first three pins are the same, but the wire color coding is different. The most common colors on 4-pin fans are: Pin #1Black (Ground), Pin #2 Yellow (+12 VDC), Pin #3 Green (Speed Pulses), Pin #4 Blue (PWM signal).

You cannot buy an adapter or splitter to do this job. Any good splitter does NOT connect wires to BOTH of the connectors from the fan's Speed Pulse line. So, you will have to go to the wires to each fan, bare off a short length of the Speed Pulse wire on Pin #3, and solder a second wire to that, then insulate the bared wire. At the same time, do the same for the Black wire on Pin #1 to establish the Ground connection to that fan. A two-wire cable for each fan will be suitable, and you can place a label on each such cable to identify the fan it comes from.

The second step then is to connect the pair of new wires from each fan to the input connectors of the fan controller. It will be designed with male inputs of 3 of 4 pins (does not matter which) and you will need female 3- or 4-pin connectors on the ends of your cables from each fan. Since you are NOT using the PWM signal, any standard 3-pin fan connector will do this job. For each cable end, connect the Black lead from the fan's Pin #1 to the Pin #1 of the connector at the fan controller end; likewise, connect Pin #3 to Pin #3. Make SURE these are done right. Then plug the new fan signal leads into the fan controller, and it should all work. You should be able to read the speed of each fan on the controller's front face, even though the actual control is being done by the mobo ports.

Now for your last statement, "if I am about to do some hard gaming I would have the ability to juice up the fans a bit more manually". NO, you can't do that readily. The fan controller on the front CANNOT send power to the fans, so it cannot control any fan at all. Since all control and power for the fans is being done by the mobo, you would have to use the mobo's fan control systems to accomplish this. In most cases that can be done in BIOS Setup, which means a reboot usually. BUT many mobos come with a fan control interface utility on their CD's of software. This is a small app you can run in Windows that lets you see and adjust the mobo's fan control systems. So using that you could choose one of three possibilities:
1. Leave it alone. The automatic system is already designed to increase fan speeds as heat generation increases due to workload;
2. Alter the automatic system settings so it is more aggressive and speeds up the fans more than "normal" if you think it does not do enough cooling already in heavy-use situations; or,
3. Change to a fixed manual fan speed setting (probably very high speeds) for gaming.
Of course, if you make changes, you'll need to do this for all your fans individually, and then un-do those changes when you're finished gaming.

A comment: Many gamers talk about speeding up the fans and cooling when they are gaming and using the system heavily. BUT that is because they do NOT use the mobo's automatic control system at all. They are using a third-party fan controller like the one you propose, and in that case they MUST speed up the fans manually. They do NOT have any automatic control system to do that for them. You don't have that situation if you plan to leave the fans all under mobo automatic control, so manually changing things for gaming should not be necessary.
 
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Thank you! I should have told you my fans were all 4 pin, my bad. Yes, I suppose you are right there is really no need to speed up the fans beyond what the MB does. Eliminating the voltage increase or whatever from the manual fan controller would also eliminate most of the risk I was worried about. Even if it worked, I guess I would only be able to add fan speed on top of the MB, and then even the idea of a fluid ability of finding a more silent sweet spot would be limited to adding voltage, therefore likely ineffective. Glad you helped me talk this out thanks again. So I guess I'll be splicing pin #1-ground/black and pin #3-speed pulse/likely green. The Y-cables I have coming say they are 4 pin I would think I'll just end up cutting wires 2 and 4, you are thinking this won't be the case? Either way I should be able to see by looking at them. I'll post a picture if it works and I think you will see why I wanted to do this. (Interesting so I'm guessing on 4-pin fans the voltage is constant and the PWM sort of limits the speed)
 
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What you should find when your 4-pin Y-splitters arrive is that, of the two male output connectors, only ONE has a wire from its Pin #3 to the female connector. So if you connect that splitter's female end to a mobo SYS-FAN port and the male output with 4 wires to the fan, then snip off the wires on the other male connector for Pins 2 and 4, there still is NO wire to carry the speed pulse back up to the second male output connector's Pin #3. That wire is missing in the first place! That is why a Y-splitter won't do the job. But even if you could get around that problem, you still need a two-wire line from that splitter up to the fan controller on the front panel, and that line would probably need a female 3-pin fan connector on each end - something I'm sure you cannot buy. So you're definitely into custom wiring and soldering. It is probably easier to get a set of wires from an old 3-pin fan (well, several since you have several 4-pin fans to connect) that already has the female connector on the end. Then you snip off the Red wire, and use the Black and Green ones to solder onto the leads from your fan, Pins 1 and 3 respectively.
 
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Holy all-embracing, in-depth explanations Batman, thx a million Paperdoc.

And so armed with his new-found knowledge, courtesy of Paperdoc, our hero put his phone down, picked up his trusty screwdriver again, and returned to work.
 
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Paperdoc I wonder if you might be able to help me. I have mono with a single 4 pin sys fan header. My thermaltake v1 case has a 200mm fan (0.2amp) that spins at about 800rpm and I want to install 2 80mm fans that max at 2000 rpm at the back. If I use a 4 pin splitter will these fans with different speeds go hay wire or will they work as they would if they. We're all connected individually? I have a post about this on these forums but I'd like s second opinion
 
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First I'll address your question, then ask for more info.

When you use a splitter or a 4-pin fan Hub to connect more than one fan to a single mobo fan header, all the fans will work under the same controls (see my questions below). The mobo may be using either Voltage Control Mode or PWM Mode, and all the fans on that splitter or Hub receive exactly the same signals. IF all those fans were identical, they would operate at very nearly the same speed. But if they are different designs, as you plan, they will operate at different speeds. However, that does NOT matter at all. Although a mobo header can display the speed of ONE of the fans connected to it, it does not actually use that speed information to do its control functions. So if several fans on one splitter operate at different speeds that does NOT affect or harm the control system in any way.

The issue that you have not mentioned is this: a true 4-pin mobo fan header operating in PWM Mode can NOT control the speed of a 3-pin fan. Now, I suspect strongly that the 200mm fan built into your case front is 3-pin. So we are left wondering whether your mobo's 4-pin header does actually change the speed of that front fan. It is possible that it does, in one of two ways. SOME mobo BIOS's allow you to configure a 4-pin SYS_FAN header specifically for either 4-pin (PWM Mode) or 3-pin (Voltage Control Mode or DC Mode) so either type of fan can be controlled. A lot of current mobos actually have "fake" 4-pin headers that really act only as 3-pin headers in Voltage Control Mode with a useless 4th pin, and these also CAN control a 3-pin fan. Moreover, because of the backwards compatibility designed into 4-pin fans, they also can be controlled by such a header. The only problem with this type of "fake" header is that it cannot be used with a true 4-pin fan HUB, although it CAN be used with a 4-pin fan SPLITTER.

So, important questions to you: as you use your system, does the speed of that front fan change as you do more or less work? Or, does it run at one speed all the time? AND, is it really a 3-pin fan? A 3-pin fan has a female connector on the end of its wires with 3 holes, and the standard wire colours are Black, Red and Yellow.

IF you have a 3-pin front fan AND if its speed really does change under mobo control, then your mobo's header is using Voltage Control Mode (aka DC Mode). This means three things for how you choose your new fans:
(a) You should buy only 3-pin fans to add.
(b) Adding two "normal" 80 mm fans that each draw less than 0.2 amps is quite acceptable, but I'd start to worry about more than 3 fans on a single header.
(c) You will need to buy a 4-pin fan SPLITTER with 3 output arms. I say 4-pin because it's getting hard to find 3-pin splitters, and you can always plug 3-pin fans into 4-pin splitters. You need 3 output arms for 3 fans. Now, splitter versus Hub. A SPLITTER has one arm with a female plug on the end to connect to your mobo header, and (in this case) three arms with male output connectors for your fans. It does NOT have any other arms. A Hub has those, PLUS it has one additional arm that must connect directly to a power output connector from the PSU to supply power to the fans. You should not try to use a 4-pin HUB when you are using 3-pin fans because that would NOT give you automatic fan speed control.

If you have further questions, or if your front fan is 4-pin actually, or if it always spins at one speed, post back for more advice.
 
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You are quite right of course. The 200mm is a 3 pin 800 rpm fan so I'll just connect this to a Molex connector on the PSU and run the two PWM's off a splitter as I'm not sure that the 200mm needs modulating.



 
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OK, that will work fine. Then you STILL need to know how the mobo header tries to control fans. IF the mobo header IS able to control the speed of your 3-pin 200mm fan, then it must be using Voltage Control Mode. In that case, you could use either 3-pin or 4-pin fans with a 4-pin splitter and it will work. Often you find that 3-pin fans are a little cheaper than 4-pin.

BUT if your existing fan cannot be controlled by the header and thus that fan always runs full speed, then VERY likely the mobo header is using PWM Mode for control. In that case, you MUST buy 4-pin fans and a splitter to be able to control them from that mobo header.
 
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Thanks for your kind words.

I'd like to update my earlier posts (July 13/12 etc.) with info I've learned since then.

1. Mobo fan headers types and modes.
There are three basic designs of mobo headers in use now:
(a) Headers that are strictly 3-pin or 4-pin, and have the appropriate number of pins. 3-pin headers always operate in Voltage Control Mode only (excepting the 3-pin PWR_FAN headers for their special application that offer no control of fan speed);
(b) Headers with 4 pins that can be manually configured in BIOS Setup to operate either in PWM Mode or in Voltage Control Mode (sometimes called DC Mode). It is necessary for the user to ensure the configuration matches the type of fan connected; and,
(c) Headers with 4 pins that actually operate only in 3-pin Voltage Control Mode with a useless 4th pin. These are there to help the user not worry because they are "universal". That is, they CAN control the speed of any 3-pin or 4-pin fan, because all 4-pin fans can be controlled by Voltage Control Mode due to their design. This only becomes a problem if you are trying to use such a port with a 4-pin fan HUB, because that Hub will require a PWM signal from Pin #4, and these "fake" 4-pin headers do not provide that. It can be very difficult to discern from mobo manuals whether or not your mobo has this type of fan header.

NOTE that virtually all mobos use the configurable header type (b) above for their CPU_FAN header so that they can always be set correctly for whichever fan type you use there. A few still have the single-configuration type (a) above, but VERY few have the confusing type (c).

2. As I said, a SPLITTER can be used to connect more than one fan to a single mobo header. Lately, 3-pin splitters are hard to find, but BOTH 3- and 4-pin fans can plug into a 4-pin splitter. Either way, the Splitter will return to the mobo the speed signal of only ONE of its fans (to avoid confusing the mobo with overlapping pulse trains), and it usually does this by NOT having a Pin #3 on most of its output arms. I said earlier that one should not try to connect more than two fans to one header, but that is no longer true. Some posts here have maintained that one does NOT need to worry about heavy brief start-up current draw, so the only concern is the total normal running current of all the fans on one header. Almost all mobo headers can support up to 1 amp. Most common fans today use less than 0.2 amps. So it should be OK to use from 1 to 5 fans on a single header - maybe even more, but the more you use the closer you are to the limit. HOWEVER, if you are using heavy-duty fans with higher current draws, you MUST take that into account. Every fan has a current draw spec you can use for this.

3. HUBs are different devices. Further, for these purposes a Hub can only be for a 4-pin fan systems; there are no 3-pin Hubs. What distinguishes a Hub from a Splitter is that the Hub also has a connection directly to a power output from the PSU (either a 4-pin Molex or a SATA power output). It uses that high-power source for the power to all its fans, thus eliminating the 1 amp limit of a mobo header. It then shares the PWM signal it gets from Pin #4 of its connection to one mobo true 4-pin header to all its fans so they all are under the same control signal, and it returns to the mobo ONE fan's speed signal, as above. Most Hubs are for 4-pin fan systems only because they merely share the PWM signal out to their fans. Right now (mid-2016) I am aware of two Hubs that do this differently because they use the PWM signal to create their own group of 3-pin ports operating in Voltage Control Mode. Thus they can control both 3-pin and 4-pin fans, and any mix of them. Normally each port of this Hub type is subject to the limit of 1 amp max current so it is possible to use splitters on such ports, but the limit on the total number of fans connected to all of the Hub ports is much higher - often specified as two fans on each port.
 
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