Fan Connection PRoblem

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ebab0204

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Jul 22, 2017
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So my motherboard has 2 case fan headers, so I was going to get a splitter cable because I'm getting a 4 pack of fans. IS it ok to plug 3 pin fans into the ends on the splitting cable which is 4 pin on all sides?
 
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We'll get a few facts straight here.

When 4-pin fans were introduced, they were designed with some backwards compatibility features with existing 3-pin systems. These include
(a) the female connectors all have ridges on one side just beyond Pins 1 and 3. The male connectors all have a "tongue" sticking up on one side aligned with those first 3 pins. The result is that you can only plug them together one way - the correct way to get the contacts right. BUT also you CAN plug any male into any female connector - they will fit mechanically, and the connections will be right. The exception is this: SOME male connectors are made not with exposed pins but with them inside a shroud. If it's a 3-pin male connector, that shroud may be too narrow...
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The whole idea around 4-pin fans is that they are controllable by the motherboard. Some motherboards also are able to control 3-pin fans by varying the DC voltage (Asus ROG for example).

But if you are going to use 3-pin fans, get a splitter that uses power directly from your power supply. They use a 4-pin Molex cable from the power supply. They can be either a simple splitter or a fan controller.

Here are some examples.

Controller:
https://www.newegg.com/Product/Product.aspx?Item=N82E16811992013&cm_re=fan_controller-_-11-992-013-_-Product

Splitter:
https://www.newegg.com/Product/Product.aspx?Item=9SIACJF5497353&cm_re=fan_splitter-_-9SIACJF5497353-_-Product

Plus there are some variants that use a a controlled 4-pin header and a Molex to control three or four fans from a single motherboard 4-pin header. So you have some options.

But to answer your question can a 3-pin cable go into a 4-pin header. It will probably go in, but it may or not work. One pin in the 4-pin header, is for the rpm sensor, which will be useless to the 3-pin fan. I have heard of people snipping off that fourth pin and using the fan in in a 3-pin header.

Also depending upon the quality of the connectors, the fan connector may be keyed (so the connector can only be plugged in the correct way).
 
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We'll get a few facts straight here.

When 4-pin fans were introduced, they were designed with some backwards compatibility features with existing 3-pin systems. These include
(a) the female connectors all have ridges on one side just beyond Pins 1 and 3. The male connectors all have a "tongue" sticking up on one side aligned with those first 3 pins. The result is that you can only plug them together one way - the correct way to get the contacts right. BUT also you CAN plug any male into any female connector - they will fit mechanically, and the connections will be right. The exception is this: SOME male connectors are made not with exposed pins but with them inside a shroud. If it's a 3-pin male connector, that shroud may be too narrow to allow insertion of a female 4-pin connector. In cases like that, you can modify the male connector's shroud to allow proper connection.

(b) The control method for the two fan systems is different, and the electrical connections differ as a result. However, they are still similar, and they are arranged to ensure that mixing systems will work, sort of. A 3-pin fan has these connections:
Pin #1 - Ground (Black wire)
Pin #2 - +DCV varying from 12 (max) down to 5 (min) (Red wire). Under 5 VDC may cause the fan to stall and require a higher voltage to start up again.
Pin #3 - Speed Pulse Signal (2 pulses per revolution) (Yellow wire) generated in the fan motor and sent on this line back to the mobo for counting to measure speed.
Its speed is changed by varying the voltage supplied on Pin #2. This method of control is called Voltage Control Mode, or DC Mode.
A 4-pin fan gets these signals:
Pin #1 - Ground (Black wire) (SAME as above)
Pin #2 - +12VDC constant (usually Yellow wire) - DIFFERENT
Pin #3 - Speed Pulse Signal (2 pulses per revolution) (usually Green wire) generated in the fan motor and sent on this line back to the mobo for counting to measure speed - (SAME as above)
Pin #4 - PWM signal (usually Blue wire) NEW additional line
The motor has a special tiny chip inside that applies the PWM signal to the supply voltage from Pin #2 to modify the current flowing through the motor and alter its speed. This method of control is called PWM Mode.

(c) BOTH systems are designed to allow the signals on the male mobo header to power and control the speed of the fan, and to measure its speed. But if you mix systems, the results are a little different. If you plug a 3-pin fan into a 4-pin header, the fan receives a fixed 12 VDC supply on Pin #2, and no PWM signal from its non-existent Pin #4 (which it cannot use anyway, since it does not have the special chip). Thus the fan will always run full speed. This is what has produced the FALSE statements that the mobo cannot control a 3-pin fan. In truth, a mobo 4-pin header that uses only the PWM method of control cannot control the speed of a 3pin fan. The other mis-match: if you plug a 4-pin fan into a 3-pin header (such a header can ONLY use Voltage Control Mode) the fan will receive a varying voltage on Pin #2, and no PWM signal at all on Pin #4. So its chip cannot apply any modification to the voltage supply, and the fan motor's speed DOES change according to that voltage. Thus, a 3-pin header CAN control the speed of a 4-pin fan, although the method used is not what that fan was designed for and is not ideal.

(d) MANY mobos these days have only 4-pin fan headers on them, but that does NOT tell you what control method they use. Any 3-pin header can ONLY use Voltage Control Mode, although there are some that do not even do that - they supply a fixed 12 VDC on Pin #2, and these headers mainly are used to power a pump whose speed you do NOT want to slow down. On a 4-pin header. the mobo may use only the original design signals and apply the PWM Mode of control. Or, it may use only the Voltage Control Mode and not even supply any PWM signal to the fan. Note that, because of that backwards compatibility feature of the 4-pin fan design, this still means that the 4-pin fan's speed WILL be under mobo control (just not ideal). On some mobos you have an option in BIOS Setup to select whether a particular 4-pin fan header uses one Mode or the other. This option is almost always there for CPU_FAN headers, but often not for case fan headers. Some mobos claim that their 4-pin headers are "automatic' and will discover for themselves which fan type is plugged in and change their control Mode as required. However, note that this feature is easy to "fake" if the header uses only Voltage Control Mode, because BOTH fan types will appear to be under speed control.

(e) Most common fans for computer cases now consume at max 0.1 to 0.3 amps at full speed, although ones with LED's in them often consume 0.4 to 0.5 amps. Most mobo fan headers are limited to supplying a max of 1.0 amps total to whatever is connected. (There are some newer mobos that have a few headers able to supply up to 3.0 amps.) So, it IS permissible to connect more than one fan to a single header as long as you do not exceed its limit.

(f) A SPLITTER is a device that can allow connecting more than one fan to a single header. It merely connects all the fans in parallel to the mobo header. A SPLITTER consists of one arm of wires with a female connector that plugs into a mobo header, and two or more arms ending in male connectors for the fans. It has no other arm types. All the fans receive the same signals and do much the same thing. HOWEVER, the mobo header's system for measuring fan motor speed - counting the pulses coming in on Line #3 - can only deal with ONE pulse train signal. Feeding it two pulse trains that change will cause great confusion and errors. So any proper Splitter will arrange to send back to the header only the speed signal from ONE of its fans, and ignore the others. This may be done by having wires to Pin #3 on only one of its output male connectors, or by not having the actual pin in that position on some connectors. 4-pin Splitters can be used with both 3- and 4-pin fans and headers (yes, they fit), and the fans will be subject to the performance limits in (c) above. 3-pin Splitters really are useful only with 3-pin fans and headers that are using Voltage Control Mode. NOTE that, since all 3-pin fans can be speed controlled only by a mobo header using Voltage Control Mode (varying voltage on Pin #2), SPLITTERS are the only way to connect more than one of them to a single header. Such an arrangement is always subject to the current limits in (e) above.

(g) A HUB is a different device and (with few exceptions) is suitable only for 4-pin fan systems. A HUB has one arm with a female 4-pin connector to plug into a mobo 4-pin header that uses PWM Mode for control. It has two or more arms ending in 4-pin male connectors for the fans. Then it has one additional arm, one that must plug into a power output from the PSU (either a 4-pin female Molex or a SATA power output). The Hub gets all power for all its fans from the PSU and does NOT draw power from the mobo header, thus avoiding the current limit of the header. It does merely share the PWM signal from the mobo header to all its fans, but that does not overload the header. And like a Splitter, it sends back to the mobo on Pin #3 ONLY the speed signal of ONE fan. A HUB may look just like a group of wires in arms, or it may be a box with connecting arms and male output ports. Because a HUB depends on each fan to use the PWM signal to adjust its voltage, it can ONLY operate using a mobo header that is using PWM Mode to control, and it can ONLY control 4-pin fans. There are a very few Hubs that are different in one important way. These do not merely share their signals out to the fans. They use the PWM signal from the mobo to create their own internal group of male output headers that use Voltage Control Mode, and hence can control BOTH 3-pin and 4-pin fans in any mix. Typically these have that limit of 1 amp per output port (NOT 1 amp total for ALL fans on the Hub). So, a HUB can work only with a mobo 4-pin header that IS using PWM Mode, and can power AND control many fans from one common signal from a single header. BUT most Hubs can work only with 4-pin fans. Note that, because any Hub MUST have a PWM signal to operate, it can NOT be used with any fan header (3- or 4-pin) that is NOT using PWM Mode to control.

(h) We speak of fan SPEED controls. But the real truth is that the automatic controls of fans by the mobo are TEMPERATURE control systems. Each has a TEMPERATURE target to be met at a sensor, and the control system will change the signals it sends to the header fans to whatever it takes to get that temperature on target. It really does not care about fan speed - and in fact DOES NOT USE the speed signals from the fans to control them. Those signals are measured and available for you to "see". They ARE used by the mobo headers for a different function: FAILURE detection. The mobo monitors the speed signals on each header and will send out a warning if there is no signal coming in. For the case of the CPU_FAN header, extra attention is devoted to this to ensure that the mobo NEVER is without a cooling source. Most mobos have two such systems. One is for cooling the CPU chip, based on a sensor built into the CPU chip itself and sent out on one of its pins. The second is based on a different sensor built into the mobo at a place the maker judges most suitable to represent the entire boards' cooling needs. Some mobos now offer more than one mobo sensor, and the option to select which of those is used for each of the case fan headers.

With all that background, OP, you want to use four 3-pin fans with a mobo that has only two headers for case fans. That CAN be done and still use the mobo's ability to control all those fans' speeds automatically according to the processing load. You do not HAVE to switch to a third-party fan controller module, although that also IS an option. The details of how to do that depends on what fan type you have - you have settled on 3-pin - on the current draw specs of your fans, and on the details of what method of control your mobo uses on those two headers. If you tell us what maker and model of fans you have, and also what maker and exact model number of your mobo, we can advise exactly how to get it connected.
 
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Solution
As I said above some motherboards are able to control 3-pin fans (using the 4-pin header which I didn't specify). I have one doing so right now and it has no 3-pin headers.

The 4-pin motherboard headers are keyed that I've seen. But not all fan connectors are keyed (particularly the splinters and extensions, which is what I had on my mind).

I have read warnings about damaging motherboards with too many fans on one fan header. But the point was not to tie the two 4-pin headers that you have especially when they are so cheap. The fan controllers are on the order of $30, but you can control a half dozen fans with one controller.
 
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The warning of too many fans on one header is REAL. But you need to understand why, and how to avoid the problem. A single header has a limit (1.0 amp in most cases) to how much current it can supply - you have trouble if you exceed that. But if you use a HUB to connect many fans to a single header, the HUB gets all the fan power from the PSU directly, and NONE from the header, eliminating that problem. The tricks are: any Hub MUST have a connection to a mobo 4-pin header that actually does use PWM Mode for control; and most Hubs can only control 4-pin fans (there are a few exceptions). Note that a SPLITTER can NOT get extra power from the PSU - it is limited to the header's 1 amp.
 
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In the US, fan splitters ARE available with additional power from a molex power cable (I even found some with power from a SATA power connector). And just for your information here is a commercially available example from Gelid.

https://www.quietpc.com/gel-pwm-1-4-pwmcable

This is a "Gelid Solutions 1-to-4 PWM Fan Splitter". It is not a "HUB".

Is that clear enough?
 
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Unfortunately we are dealing with terminology, and to some extent with personal preferences in labels. I see lots of devices like the Gelid one you linked called Splitters. I disagree.

To me, a SPLITTER is a device that does only one thing. It SPLITS the lines from the source (a mobo fan header) into a group of parallel connections to output devices (e.g., several fans). All the output devices are in parallel with each other and sharing the signals from the source equally. There is NO access to other resources (such as additional power) provided by a SPLITTER in my view.

To me, a HUB is a different device that connects SOME of the source's signals in parallel to the output devices, but ALSO provides additional resources (like power) from a different source. It does not matter whether the appearance of the HUB is as several arms each containing a group of wires for a fan, or as a printed circuit board with connectors, or as a box with enclosed connectors and attached cables. I define a HUB in terms of the FUNCTIONS it delivers, and thus of the resources it needs to do that.

In most designs, a HUB for fans works ONLY in 4-pin fan systems. That is for two reasons. First, it connects the mobo header's Ground, Speed, and PWM lines to all the output fans in parallel. (There is an important exception here for both HUBS and SPLITTERS. In each case, the device should connect back to the mobo header only ONE fan's speed signal. because the mobo can only deal with a single incoming pulse train. So really, in neither case are all of the speed signals connected in parallel.) The important clue here is that the circuitry inside a 4-pin fan that uses the PWM signal draws VERY little current, and hence connecting many fans' PWM input lines in parallel to a single mobo PWM output signal does NOT overload that part of the header circuits. But finally, to avoid the limit of how much power a single header can supply to fans, a HUB gets all power for its fans directly from the PSU (normally through either a SATA power output or a female 4-pin Molex output), and feeds that power source in parallel to all its fans on Pin #1 (Ground) and Pin #2 (fixed +12 VDC) of each fan. In fact, to avoid some problems, a good HUB will NOT connect the power source from the mobo header's Pin #2 to any fan so that the header does not experience a connection to the +12 VDC coming from the PSU. The advantage, of course, is that those PSU power outputs can supply many amps at a fixed +12 VDC, whereas a mobo header normally is limited to 1.0 amp. So using a HUB, all the fans are provided with power from the PSU, and with a separate control signal (the PWM signal) from a single mobo header.

From that design it is clear why a HUB normally can work only with 4-pin fan systems. It MUST have a PWM signal source, and it MUST be feeding fans that can accept a fixed 12 VDC supply and then use the PWM signal internally to accomplish control. This latter requirement is why it can't work with 3-pin fans. There are a few exceptions to this "rule". There are a few PWM Hub designs that do not simply share the PWM signal from the mobo to all their fans. Instead, these units use the mobo's PWM signal to create internally their own group if new 3-pin headers that use Voltage Control Mode, and supply to the fans a varying voltage on Pin #2 of each Hub port. The still get the fans' power from the PSU, but they do the change from fixed 12 VDC to varying DC internally, and they do not send out the PWM signal.

All Hubs do their sharing of control signal and "out-sourcing" of power supply in the same way (with few exceptions) irrespective of their construction and appearance. All Splitters do their functions differently and have no access to an outside power source. That is how I use the two terms - by function, not by appearance. Some may disagree with me on those views.
 
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The manufacturers refer to these devices that way. That is how they are labeled. And lastly if you are looking for them in online stores, that is the category they are located in.

The term (hub) that you use (until I started looking into this matter) is used in networking. But in this area that is about the only use I've heard for hub.

Apart from a few fans with inline controllers, accomplish the same thing . But they offer the ability control the rpm of PWM fan or can control regular 3-pin fans by means of varying the voltage.
 
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Yes, the term "hub" is used widely to refer to a device where several similar items can be attached to share a group of resources. I suspect it comes from the use of "hub" as the centre of a wheel where the spokes are attached to extend out to the rim to support it. So we see network hubs and USB hubs in computer systems, transit hubs where buses converge to exchange passengers, and cities called "financial hubs" because many companies locate there to have quick and easy communication and meetings with each other.

My view is that many makers use the label "Splitter" for anything that looks like a collection or arms with wires because that is what the original Splitter design is. From my perspective, the problem is that a new similar-looking device called a "Hub" (in my view) will not do the same job when used in that position, and the user is left very confused with a system that does not do what was hoped. Anyway, as I said this is a preference in use of labels, not an industry standard. Some makers and sellers use terms the way I do, and some do not. For that reason, when I offer advice in these forum threads, I always provide a BRIEF description of how to identify the two different device types so the reader will know exactly which one I recommend for a particular use. (In my long post above, the items (f) and (g) are complete explanations, and FAR from being brief!)
 
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