How does a pwm splitter work with 3 pin fans?

samkanga

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So Im going to get one of these:
https://www.amazon.co.uk/Akasa-AK-CBFA03-45-Flexa-Splitter-Cable/dp/B005EKU5CO

But how does it work?

What I belive is that you plug the 4 pin into the cpu fan header. And then all your other fans into the other connectors on the splitter cable. Now all fans will follow the temp on the cpu. So if the cpu is under load all fans will spin faster and if it is on idle they will spin slower.

But all my case fans are conncet via a 3 pin cable. And all the connecters on the splitter are 4 pin. Will my case fans work togheter with the cpu temperature, even if they are 3 pin?

 
Solution
With that mobo info I can tell you how to make it work. There are two factors at play here. First, the mobo manual on p. 13 shows labels for the SYS_FAN1 and SYS_FAN2 headers indicating clearly that they do NOT use PWM Mode, they use only Voltage Control Mode. Thus, you can NOT use a Hub that relies on having a PWM signal. But you CAN use a SPLITTER to connect a few fans to each of these headers. NOTE that you should not try to use the SYS_FAN3 header - its labels say it makes NO attempt to control fan speed and always supplies the full 12 VDC.

The second factor is that a header using Voltage Control Mode (as your two do) CAN power and control the speed of BOTH 3-pin and 4-pin fan types. (Technically, when used for 4-pin fans, this is...

Paperdoc

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Actually, that device I would call a HUB. To me, a SPLITTER is a set of wires that just connects several fans in parallel to the power supplied by the mobo header, with additional connections to allow for PWM signal sharing and one speed signal. With a SPLITTER, all power for all the fans must come from the mobo header, and that is limited to max. 1 amp, which limits how many fans you can use.

A HUB, on the other hand, has one extra lead set on it, as does the item you linked. This extra set connects directly to a power output connector from the PSU. In the case of your link, OP, note that, of the two connectors in the foreground, one is much larger and contains two round pins plus two empty spaces. This plugs into a PSU 4-pin Molex output. The wiring of the HUB is set so that all of the fans get all of their power from this PSU connection, and NONE is drawn from the mobo header, thus eliminating the header's current limit. The HUB also does pick up a proper PWM signal from Pin #4 of the mobo header and simply shares it to all of the fans - this does NOT overload the header capability. And lastly, the HUB, just like any decent splitter, sends back to the mobo header the speed signal from only ONE of its fans.

A HUB really can only work when it is connected to a mobo header that is a real 4-pin header that uses PWM Mode for control of fans. There are now MANY mobos that have 4-pin headers for CHA_FAN or SYS_FAN uses BUT actually use them only like older 3-pin headers in Voltage Control Mode. Such headers can power and control both 3-pin and 4-pin fans individually, or even a few fans per header using SPLITTERS, but they can NOT be used with a 4-pin HUB because they do not put out a PWM signal.

Here's the dilemma you are facing. If you mismatch by plugging a 3-pin fan into a 4-pin header that actually does use PWM Mode, that fan can only run full speed all the time. Neither a Splitter not a Hub can change that. Now, IF your mobo's headers have 4 pins but actually use Voltage Control Mode, then you can connect a few fans of EITHER type to each such header using SPLITTERS, but not a HUB as you linked. So, how would you know about the headers on your mobo? Post back here the exact maker and model number, and we can look up its details and advise.

Your initial proposal is partly correct. You CAN use the HUB you linked to if it is connected to the CPU_FAN header because virtually ALL such headers do operate in PWM Mode, and hence do supply the PWM signal a Hub needs. The stumbling block, though, is that any 3-pin fan you connect into this 4-pin fan control system can only run full speed.

However, you should realize that your mobo has SYS_FAN or CHA_FAN headers also, and these are designed to control those case ventilation fans according to a temperature sensor in the mobo itself, not according to the one inside the CPU chip. So these are the right headers to use for case ventilation fans. They still are subject to the problems of mismatching header and fan types. But if you post your mobo details we can advise the best arrangement.
 

samkanga

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Thanks for your reply!

The mobo I am using is a Gigabyte z170 hd3p.
 

Paperdoc

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With that mobo info I can tell you how to make it work. There are two factors at play here. First, the mobo manual on p. 13 shows labels for the SYS_FAN1 and SYS_FAN2 headers indicating clearly that they do NOT use PWM Mode, they use only Voltage Control Mode. Thus, you can NOT use a Hub that relies on having a PWM signal. But you CAN use a SPLITTER to connect a few fans to each of these headers. NOTE that you should not try to use the SYS_FAN3 header - its labels say it makes NO attempt to control fan speed and always supplies the full 12 VDC.

The second factor is that a header using Voltage Control Mode (as your two do) CAN power and control the speed of BOTH 3-pin and 4-pin fan types. (Technically, when used for 4-pin fans, this is not the very best way, but the difference is really small.) So, if you have 3-pin fans for case ventilation, you are in a good place.

Now, the limit you must deal with is this: a mobo fan header can supply up to 1.0 amps total current to ALL its fans. So, you must check the specs for your fans for what their max. current draw is. Often it falls between 0.1 and 0.25 amps per fan, so you can safely connect three or four fans to one header. How? By using a SPLITTER, and not a Hub.

As I said before, a Splitter looks like a bunch of wires with several connectors, much like the item you linked to originally, but it is different. A Splitter has one arm with a female connector to plug into a mobo SYS_FAN header. Then it has two or three other arms each with a male connector (with pins) to connect your fans to. Of these, only ONE of the output arms will have all its pins, and the others will be missing Pin #3. These days, it is hard to find 3-pin Splitters, but that's no problem. 4-pin Splitters work with both 3-pin and 4-pin fans. Here is one example of a 4-pin Splitter with 3 output arms.

https://www.amazon.co.uk/EK-Waterblocks-3831109867914-Blocks-3831109867914%C2%A0Black/dp/B00L6M2OSC/ref=sr_1_9?ie=UTF8&qid=1480733334&sr=8-9&keywords=fan+splitter+cable

Note that this device has NO extra arm to connect to a power output connector from the PSU. Also note that this particular one has a label attached to the one output that has all its pins, to indicate that THIS particular fan will have its speed signal sent back to the SYS_FAN header for measurement and display.

I don't know how many fans you have. With two of these units and two SYS_FAN headers to use, that would cover 6 case ventilation fans easily.
 
Solution

samkanga

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Ok! That sounds great!
But which program do I use to control the fans? I tried with Gigabyte App center but it doesnt work since it crashes all the time. I tried with SpeedFan but none of my fans shows up. So is it BIOS that I want to use? In BIOS I can set fans speed to normal, quiet, max and manual I think. But I'm not sure if this affects my fans at all. If i set it to manual nothing about voltage control pops up, just pwm. It says 0.75 pwm or something.

Im going to use five fans in total. Two of them are preinstalled in my case and the other three ar after market fans.

Im going to get two corsair AF120 and one SP120.

 

samkanga

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Also. These werw the only ones i could find, from my local store.

http://images.webhallen.com/product/24569/large

Will it work or should i order these instead:

https://inetimg.se/img/800x600/8906148_0.jpg

The differnece is that on the first one, 1 of the Cables are 2 pin but one the second one both Cables are.
 

Paperdoc

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I would expect Gigabyte App Centre to do this job for you, but you've been having trouble with it. I note on the Gigabyte website that you MUST install Microsoft .NET Framework 4.5 BEFORE you install the App Centre. So if you did not do that, first UN_install the App Centre, then follow the sequence of installing that .NET thing, THEN the App Centre.

Speedfan is a free third-party utility, and often those tools require that you custom configure them to match your mobo so they work. I don't know the details - maybe check the web for more info if you want to use that tool.

You can always make such configuration changes in BIOS Setup, and I normally recommend that you set it to "Normal", which puts the control system into a configuration that the mobo maker has found to be optimal. I realize, however, that doing it through BIOS Setup means you cannot monitor and adjust while actually using the machine, and that is why the App Centre thing is more convenient if you can get it to work.

In BIOS Setup I don't like using fixed "Silent" or "Full Speed" settings - that completely cancels any automatic control. "Manual" is much like "Normal", except that you get to set your own control loop Gain. You see, the headers are operated by a TEMPERATURE control loop. It has its own target temperature for the sensor built into the mobo, and constantly compares the actual measured temperature to that target, which generates a value for the difference or "Deviation" of actual from target. This is multiplied by the loop gain to generate the actual signal that is sent out to the fans to try to bring the actual temperature back to target. Setting this too low results in a system that does not increase fan speed enough when the measured temperature rises, so it can take a long time for the system to get the case temperature under control. Setting it too high makes the fan speed change too much, causing the speeds to change constantly up and down too far and over-correcting for temperature changes. Just the right value of Gain and another parameter, damping, will allow the system to correct temperature changes pretty quickly with almost no lag or overshoot. You can experiment with this if you are interested, but it is likely that the optimal value is already set by default in the "Normal" configuration.

PWM is a "% ON" kind of signal that can range from 0% to 100%. So setting the "PWM Value per C" to 2.5, for example, means that if the Deviation of measured temperature from target increases to 10 degrees, then the PWM signal sent to the fan will be increased by 25%.

Those two splitters you linked work exactly the same. Both connect the Yellow lead to Pin #3 for only ONE of the two fans. The fact that the first one is missing the Pin #3 as well as the Yellow wire to that pin makes no difference.

Now, using splitters with two outputs to power 5 fans from 2 headers will require one adjustment. Buy 4 splitters, not 2. Take 2 of them and plug them into the two output arms of one other splitter. This "stacked" arrangement results in four output arms from one header. You can use this to connect three fans to one CHA_FAN header, and use the last splitter to connect the other two fans to the other header. For the unused male output connector, just put tape around the connector so it won't short out against the case.
 

samkanga

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Apr 2, 2016
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Thanks, bro!

I solved the problem with App centre by downloading it from my motherboards page on gigabyte. So i got the intel 100 series version, which i didnt get before. Now it works perfectly.

Just to make sure:

I will be able to control my fans when using this adapter, right?

http://images.webhallen.com/product/24569/large

And i need to connect to the 4 pin fan outputs on my motherboard to make it work. I just noticed that this cable ^^ is 3 pin and not 4 pin as the one u linked from amazon was to connect the fans from. But that doesn matter since I wont' be using that pin for any of my fans, right?

Anyways, thank you so much for all your answers! They were really helpfull and I learned a lot thanks to you!
 

Paperdoc

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Yes, that splitter is just fine for your use. Although it is a 3-pin type, it will fit perfectly onto the mobo 4-pin headers (with one pin just sicking up bare) and connect properly to your fans. Since your mobo headers do not use their Pin #4, not having a wire for that in the splitter is OK.

Thanks for Best solution.