Fan splitter with different sized fans

[TeeCee]

- I have a B450M mobo with only one system fan header. For the case I bought two fans, be quiet!'s PURE WINGS 2 80- and 120mm. Both are 4 pin fans, the 80mm is 1900 rpm and the 120mm is 1500 rpm.

- To remedy the one fan header, I bought a 4 pin fan splitter. They both have the same volt range (5-12V) but the larger fan (to no-ones surprise) uses more power (W) and current (A).

 

QUESTION: should I be concerned that they are different sized fans? I've read that different voltages can be an issue with different fans, considering they have the same specs when it comes to voltage (and are the same brand) this shouldn't be a concern.

 

I was planning to put the 1500 rpm 120mm fan in the 4 pin connector and the 1900 rpm 80mm fan in the 3 pin connector on the splitter (since the third pin measures rpm).

[samcool55]

No problem, all good!

There is always a difference, even if you use 2 identical fans (manufacturer tolerances).

 

You do run into issues if you use a 5V fan and push 12V through it, but case fans are almost always 12V so no problem here.

[TeeCee]

1 minute ago, samcool55 said:

No problem, all good!

There is always a difference, even if you use 2 identical fans (manufacturer tolerances).

 

You do run into issues if you use a 5V fan and push 12V through it, but case fans are almost always 12V so no problem here.

Thank you, Sam!

I'll continue assembling my lego for grown ups now!

[mariushm]

15 minutes ago, TeeCee said:

- I have a B450M mobo with only one system fan header. For the case I bought two fans, be quiet!'s PURE WINGS 2 80- and 120mm. Both are 4 pin fans, the 80mm is 1900 rpm and the 120mm is 1500 rpm.

- To remedy the one fan header, I bought a 4 pin fan splitter. They both have the same volt range (5-12V) but the larger fan (to no-ones surprise) uses more power (W) and current (A).

 

QUESTION: should I be concerned that they are different sized fans? I've read that different voltages can be an issue with different fans, considering they have the same specs when it comes to voltage (and are the same brand) this shouldn't be a concern.

 

I was planning to put the 1500 rpm 120mm fan in the 4 pin connector and the 1900 rpm 80mm fan in the 3 pin connector on the splitter (since the third pin measures rpm).

 

My advice would be to pick one fan and pull out the rpm wire (3rd wire) from the connector. You can use a needle to lift the plastic bit that retains the wire inside the connector. 

This way, you'll have only one fan reporting the rpm speed. If you leave it like this, nothing bad will happen but the reported speed may be incorrect.

Basically a fan sends two pulses during one rotation, so each pulse is half a rotation.

With two fans, both fans may send a pulse at the same time, so you'd have 3 pulses or you may have four pulses in that  

The motherboard will then show more than 1900 rpm because it just divides the number of pulses by 2.

 

As for the PWM wire, yes you could wire it to just one fan but it's not a problem if the signal goes to both fans at same time.

The signal tells the fan to adjust speed to a percentage of maximum rpm of fan... I think it's between 30% and 100%

You have different max rpm so your 80mm fan will be ~600rpm at min speed, and your 120mm will be 450fpm

 

It's up to you which fan you want motherboard to control - for example, maybe the 120mm fan is less noisy so you wouldn't mind staying at 100% all the time, and it would make more sense to adjust the 80mm dynamically, keeping it at lower rpm most of the time.

Or just leave them both.

 

[TeeCee]

37 minutes ago, mariushm said:

 

My advice would be to pick one fan and pull out the rpm wire (3rd wire) from the connector. You can use a needle to lift the plastic bit that retains the wire inside the connector. 

 

This is already done by the manufacturer of the splitter. One of the connectors has 4 pins, the other one has the third one missing. I thought I had a defective unit, for a minute, after opening the package.