Maximum fans for 3 pin splitter

[Stag1928]

From what I've seen, its safe to connect 2 fans to a single 3 pin header, but can you bounce 3 off a single header? Some reviews for this http://www.newegg.com/Product/Product.aspx?Item=N82E16812200855 said you can daisy chain them. I got a carbide Spec-03 with 3 120mm fans all with the 3 pin connectors, 2 of which are LED.

 

[Shaun o]

yes it is safe to use a splitter to connect 2 fans to the same motherboard fan header.
But the more you add in a chain the more likely it will effect how fast each of the fans will spin if in a chain.
as you will be dividing the 5v and 12v feed from the fan headder block of the mobo.

Think of it like a battery and a light bulb in a circuit with a battery. 1 bulb is nice and bright, add another both work but are not as bright as one bulb alone.
Add more and each time the light given off per bulb begins to dim in brightness again.

So there is a limit on how many fans you can chain before the rpm of them reduces due to shared power draw.

3 pin fans can have a set fixed rpm speed. You should also note when doing this that in the bios for fan monitoring there may be an alarm that triggers based on how low the rpm speeds are.

This would halt your boot process of the computer in most cases because it will think the fan has failed and as a precaution prevent a full boot of the system via your bios of the board. So you must turn it off, or lower the alarm trigger threshold value in the bios fan monitor settings in rate of rpm of the fans in such a case. Your not going to know the value but if you chain some fans and the bios halts at post after you have chained a few together then a trip to the bios of the board is needed to lower the alarm trigger point in rpm of the fans in a chain connected via the selected fan header on the motherboard ok.

 

[Stag1928]

So the long and short of it is it's probably not good to have more than 2 off a single header. I did notice my Toughpower 650 has a strip of molex connectors and a single 4 pin (for PWM fans presumably)- can I hook up one of the 3 pin leads to that? I'm trying to plan ahead for when the rest of the skylake parts come out. It seems like most of the H-xxx boards have a 3 pin and 4 pin header for the chassis fans

 

[Shaun o]

Yes you can use the one of the power supply if they fit. You should be ok
If you are intending to buy a sky lake and run a setup based around it.

 

[Paperdoc]

The first reply you got was very confused, treating fans on splitters as if they were in series. They are not. Let's get it straight.

Yes, you can use a splitter to connect two fans to one mobo fan port. This applies to 3- or 4-pin fans. However, more than two gets risky. The fans operate in PARALLEL this way, so they all get the same voltage but each tries to draw its full amperage as rated. BUT most mobos have a limited amperage available. This becomes important for a few seconds when the system first starts up, and those fans all demand over twice their "normal" amps just to get started. Loading too many fans on one mobo port could overload the port causing it damage.

On the subject of mixing fans with different pins, here's what happens: a 3-pin fan plugged into a 4-pin port will always run at full speed because the 4-pin port uses a speed control system (PWM Mode) the 3-pin fan knows nothing about. A 3-pin mobo port uses Voltage Control Mode. A 4-pin fan plugged into a 3-pin fan port WILL operate under speed control because it receives no PWM signal and then just behaves exactly like a 3-pin fan under voltage control.

Either fan type, using an appropriate adapter, can be plugged into a 4-pin Molex power output directly from the PSU. In fact, such an output can supply MUCH more power than a mobo fan port, so MANY fans can be daisy-chained to this source. However, there is NO speed control here, so all the fans connected to a 4-pin Molex output will run at full speed. Furthermore, since such a connection does not include a way to send the fan's speed signal output back to the mobo, you can never read the speed of any fan connected this way.

For 4-pin fans only there is a way to use several fans under the control of one mobo 4-pin port. You buy and install a 4-pin fan hub. It shares the PWM signal from the mobo port among all its fans (no heavy current draw on this line) but it gets power for all its fans from one of those 4-pin Molex outputs from the PSU. This does not work for 3-pin fans.

Your comment about the Toughpower 650 makes me suspect you are confused about connectors and sources, which is understandable. That unit is a PSU for the entire machine. As such its output cables probably include one (or more) connectors called "4-pin Molex". These are about ¾" wide with four round holes in a straight line. They are female connectors. They were originally used to supply power to 5¼" floppy drives, hard drives, optical drives, backup tape drives, fans, etc. Many of those have almost disappeared or been replaced with newer designs that use different power input connections, so there is less use for these PSU outputs now, and hence fewer of them. These are NOT the normal connections for case fans or CPU cooling fans. The "standard" cooling fans now use either 3- or 4- pin connections to power. The wires from the fan end in a female connector with holes in a straight line, but this is much smaller than the PSU's "4-pin Molex". Moreover, they plug into a male connector (with pins) that supplies the power.

A 3-pin fan female connector has a slot or groove on its side aligned with its 3 holes, and that fits onto a plastic "tongue" on the male connector beside its pins; that way you can't plug it in backwards. A 4-pin connector system uses the same first three pins and electrical connections, and also has the tongue and groove system aligned with those 3 pins. It just has an additional 4th pin on one end. But this 4-pin fan connector (female) cannot possibly plug directly into a PSU's 4-pin Molex (also female) output connector.

For fans, good general rules:
1. Use 3-pin fans on 3-pin mobo fan ports; use 4-pin fans on 4-pin ports. If you have to, plugging a 4-pin fan into a mobo 3-pin port will work well.
2. You can use splitters to connect two fans of the same type to one mobo port of that type with no trouble. More than 2 fans on one port may be risky.
3. You can connect many 4-pin fans to a 4-pin fan hub that gets its control signal from one mobo 4-pin port. The power is drawn from a 4-pin Molex PSU output, not from the mobo port. All fans on this hub will run at about the same speed, and that will be controlled by the mobo port.

 

[Stag1928]

The first reply you got was very confused, treating fans on splitters as if they were in series. They are not. Let's get it straight...

Thanks for the detailed reply. However the Toughpower does have one of those 4 pin PWM female connectors (I wish I could upload a picture) nestled in with the 4-pin molex plugs. In the user guide it's labeled as an "FDD connector," maybe it's for a different application but to me it looks like they attached it rather than making you buy a 3/4 pin to molex connector. One other question though- if you look at this MoBo http://www.newegg.com/Product/Product.aspx?Item=N82E16813157512 it has a "power fan connector" 3-pin header. I did some googling before and what I found (which were old posts circa 2007) were saying they were for the PSU but if the PSU didn't use it, then you could bounce another case fan off of it. Is that the case?

Update- so after some intense googling, FDD = Floppy disc drive so while there is a 4 pin, its for a floppy lol. (Also didn't realize two female plugs can't connect..) but that does leave my other question- can a case fan connect to a "power fan connector"?

 

[Paperdoc]

OK, you got the power connector for a 3½" floppy drive figured out. Now for the PWR_FAN connector.

That is designed for a particular purpose. SOME Power Supply Units (PSU's) have, among their many cables, a set of three wires coming out that look just like the leads for a 3-pin fan. These wires actually end in a female 3-pin fan "standard" connector so it can be plugged into the mobo's PWR_FAN male connector. In fact it has only one function - to send back to the mobo the speed pulse signal generated inside the PSU's internal fan so the mobo can show you that fan's speed. It does not actually provide the power for that PSU fan, nor does it control that fan's speed. Many PSU's do control their own fan's speed, but they never allow the mobo to do that. Thus, the intent is that IF your mobo has these wires you plug them in here. If not, then you plug in nothing.

Now the minor exception. Most mobo makers actually connect the Ground and +12 VDC signals to Pins 1 and 2 of the PWR_FAN connector even thought the PSU fan does not need them. Thus you CAN plug a standard 3-pin fan in there and it will run. BUT since there is no attempt to control the voltage on Pin 2, that fan will always run at full speed. This is the same result as if you had connected that fan to a 4-pin Molex output from the PSU. But if you happen to want an always-full-speed fan powered from a mobo port, this does the job.