Help. Trying to control non-PWM fan speeds.

[JVIPER88]

Hey guys. I'm trying to reduce the noise of my PC by slowing down the RPM of the fans in the case. I thought I had a solution figured out, but i was wrong.

The case I'm using is the FT02. The AP181 fans are only 3-pin fans, but on my mobo, I was able to control one of them through the BIOS because it was connected to a 4-pin header. I wanted to control the other two fans, so I thought I could buy a 3-way splitter with molex for power. So I plugged all three fan headers into the splitter, connected it to the 4-pin header on the mobo, and now all three fans spin at their max speed, and I can't control them.

Why did this happen? Why could I control one when it was plugged in directly, but not all three, even though they are identical?

Similarly, on my CPU fan header, I added a simple Y-splitter for my two CPU cooler fans. One is a 4-pin, the other is a 3-pin. The splitter also had a 4-pin header and a 3-pin header. I plugged them in accordingly, but it didn't work. The PWM fan can be controlled, but the 3-pin doesn't react at all.

Clearly, I'm not understanding how controlling fan speed works. If someone could help me understand what I'm doing wrong here, I'd appreciate it!

 

[bradly1101]

To control 3 pin fans you must adjust the voltage; the third pin just reports speed. I guess the mobo can't do that. I don't know why the splitter doesn't work.

 

[Jovec]

3-pin (sometimes called DC) fan speed is controlled by voltage. The third wire (yellow) can report the RPM, but does not control it. AFAIK, you cannot mix PWM and DC fans off of the same header with a Y-adapter due to how the voltages are applied for each.

There are fan controllers you can buy. 3-pin fans generally run on 12v. You can buy 7v and 5v resistors to place in-line.

Some motherboards will allow for 3-pin fan speed to be controlled via CPU temp (i.e. speed up when the CPU gets hot). Depending on the board, this may not be possible, may only be possible for the CPU fan header, or may be possible on some or all of the additional fan headers. Generally, the more expensive the board, the more likely it is to have voltage control on all headers. Refer to your BIOS/manual. You can also check your motherboard manufacturer's software downloads, as they often make available fan-speed software. Finally, you can also look it buying new fans that may be quieter and/or better that what came with your case.

 

[Jovec]

Similarly, on my CPU fan header, I added a simple Y-splitter for my two CPU cooler fans. One is a 4-pin, the other is a 3-pin. The splitter also had a 4-pin header and a 3-pin header. I plugged them in accordingly, but it didn't work. The PWM fan can be controlled, but the 3-pin doesn't react at all.

The 4th pin on one of the ends of the Y-adapter is missing, so that only 1 fan reports it's RPM to the mobo. It is still meant for 2 PWM fans. Just like on 3-pin Y-adapters, one end will only have 2 pins. PWM and DC fan speed is controlled via different methods, so you cannot mix fan types on a single header.

 

[JVIPER88]

Some motherboards will allow for 3-pin fan speed to be controlled via CPU temp (i.e. speed up when the CPU gets hot). Depending on the board, this may not be possible, may only be possible for the CPU fan header, or may be possible on some or all of the additional fan headers.

Thank you for your response.

It seemed that my motherboard DID have this ability. I was able to go into the BIOS and select Smartfan options that slowed down the speed of the fans. It worked on my CPU header, as well as the SYS1 and SYS2 headers (but not SYS3 and SYS4).

I can accept that I won't be able to plug in a PWM fan and a DC fan into the same splitter for my CPU cooler, as you mentioned. So I will have to find two matching PWM fans for that. But what I don't understand is why it seemed I was able to control the speed of ONE 3-pin fan off of the SYS1 header, but when I use a splitter (with Molex) to connect three of them, which are all identical, I can't control any of them. Does getting power from the Molex connector cause them to all spin at max RPM regardless of the settings I select or something?

 

[Flapdrol1337]

3 pin fans are controlled by voltage, the motherboard header lowers the voltage, but if you use a splitter the power comes from the molex, which is 12V. The fan connector is most likely only the wire to report rpm.

You have to use the header alone if you want to control the fan. If you're not using powerful fans you should be able to power multiple off a single header.

 

[BonzaiDuck]

I think I went through several years experimenting with controllers and on-board fan-plugs while the motherboard options became "better."

The best strategy requires thinking about airflow and fans before completing your DIY build. In this process, you might inventory your motherboard fan plugs and determine which are thermally controllable, and which are not. However you choose to cool your system, try use the minimum number of fans necessary to get the optimum airflow you need, and try to focus the airflow on the components that need it.

On my ASUS boards over the last couple generations, you could control at least one SYS_FAN 3-pin and as many as two, while using the PWM headers "CPU_FAN" and "OPT_CPU_FAN." In fact, the PWM headers include the SYS_FAN1, and you could mix and match. However, under those circumstances, the last thing I would attempt to do is using a splitter device.

There are PWM splitters which take the burden of DC power off the motherboard while providing total thermal control. The Swiftech 8W-PWM-SPL units ($10) will control eight PWM fans with the signal from the CPU_FAN header (or any PWM plug that allows for thermal control). But you can only monitor one of the devices attached to it. Further, you can mix or match the devices -- fans and pumps that run on 12V of different amperages.