[SOLVED] Controlling fans speed connected through fan splitter

daweking

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Oct 25, 2016
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Hi.

I have my two case fans connected directly to my motherboard sysfan connectors. Both are only 3pin (non-PWM), connected to 3pin connectors sysfan1 and sysfan2.
To prevent the fans running at full speed all the time, I figured how to control their speed. I can set them to static speed in BIOS (for example 50%), or dynamically control them from SpeedFan application - for example based on my PHC/chipset temperature the fans can run from 0% to 100%.

I wanted to have even more airflow in my case so I bought two new Noctua fans (also 3pin non-PWM) and connected them to two remaining motherboard fan connectors - sysfan3 and sysfan4. But I cannot control them same as those first two fans. It seems like my motherboard allows to control fans connected to sysfan 1-2, but not 3-4. I have an older MSI P67A-C45 (B3) and another thread in some forum confirms that.

So my question is, if use a "Y" shape fan splitter (two 3pin to one 3pin), how it will appear to BIOS or SpeedFan?




Let's say I will connect two front fans over the splitter to sysfan1 connector.
Will the system ignore the fact there are actually two fans connected to one port and let me configure the port like before?
For example if I set 50% on sysfan1 in BIOS, will both run at 50%?
In case of SpeedFan, where I can configure sysfan1 to increase speed based on chipset temperature. Will both fans dynamically change speed like one (mirroring)?

Or will the speed I set be divided by two, because there will be two fans connected to one motherboard connector?

Thank you.
 
Yes, this will work. Almost all mobo SYS_FAN headers can supply up to 1.0 A current to the total load connected to that header. Most modern fans consume at max 0.1 to 0.25 A, so 3 or 4 fans could be connected to a single header. Two per header is surely OK. When you connect two fans in parallel to a header as these Splitters will do, they both receeive exactly the same voltage supply and do the same thing. One small detail. If you connect two different fans to the same header (for example, one Noctua and one other older fan) they will not necessessarily run the SAME speed, but both certainly WILL have their speeds controlled by the header. And no, they will not run "half speed" if the header tells them to run full speed. Your system to use Speedfan to set up automatic fan control based on system cooling needs will contiune to work.

Any fan header can deal with the speed signal coming back to it from only ONE fan. So the Splitter will not send back the speed signals from both fans. If you look closely at those Splitters you will see that one output has all three wires coming to it, but the second output does NOT have the Yellow wire coming to its Pin#3, the speed signal pin. This has NO impact on ability to control the speed. It only means that you will never "see" the speed of the second fan on each header in BIOS Setup or anywhere else.
 
Yes, this will work. Almost all mobo SYS_FAN headers can supply up to 1.0 A current to the total load connected to that header. Most modern fans consume at max 0.1 to 0.25 A, so 3 or 4 fans could be connected to a single header. Two per header is surely OK. When you connect two fans in parallel to a header as these Splitters will do, they both receeive exactly the same voltage supply and do the same thing. One small detail. If you connect two different fans to the same header (for example, one Noctua and one other older fan) they will not necessessarily run the SAME speed, but both certainly WILL have their speeds controlled by the header. And no, they will not run "half speed" if the header tells them to run full speed. Your system to use Speedfan to set up automatic fan control based on system cooling needs will contiune to work.

Any fan header can deal with the speed signal coming back to it from only ONE fan. So the Splitter will not send back the speed signals from both fans. If you look closely at those Splitters you will see that one output has all three wires coming to it, but the second output does NOT have the Yellow wire coming to its Pin#3, the speed signal pin. This has NO impact on ability to control the speed. It only means that you will never "see" the speed of the second fan on each header in BIOS Setup or anywhere else.
 

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