Connecting different size fans to the same header?

[thefiend1]

Hey guys!

I have a question about adding more fans into my ncase. I’m out of motherboard fan headers! So my plan is to buy a small fan hub that can allow me to add more than 2 fans into one port

The real question though is these four fans aren’t all the same size or spec. All of them are Noctua, 4 pin fans, but they range from 20mm to 92mm. Is it ok to have that kind of range in one port? I was just going to set the profile in the bios and leave it alone, but something tells me doing this might be a problem.

Currently I have a 92mm and a 20mm Fan connected via the Noctua splitter and then connected to the motherboard fan header and it seems to be ok. Just want to make sure I’m doing things right! Thank you!

 

[tinyitx]

A typical motherboard fan header is rated at 1A (12W), while a few will have a 2A rating.
So, you need to check this per the motherboard's user manual.

Then, you need to find out the current (in A) rating for each fan.
Usually, a 92-120mm fan has 0.12-0.15A. This is usually the 'working' current (ie the current pulled by the fan while it is spinning). However, a fan will draw more current while being started up. If you can find this 'startup' current specified by a fan, then use that figure. If not, assume 2-3 times the 'working' current.
Then, add up all the fans' current and make sure the total is less than the fan header's rating.

After this current consideration, you will now need to consider the fan speed/pwm aspect.
If fans (does not matter if they are of the same size or of different sizes) are connected to the same port, then only one pwm signal is used/shared by them all. This means, they all spin according to the same fan curve/profile (speed in % vs temp in C). This characteristic may or may not be advantageous and it largely depends on the airflow design of a particular PC system inside a particular case.

Say, the 20mm fan is for cooling an onboard M.2 SSD while the 90mm fan is for exhaust at the case rear. Current wise, it looks OK. But whether or not the air flow of these 2 fans following the same fan curve is advantageous, it is not a straight 'yes' or 'no'.

Usually, it is more ideal to connect fans of same cooling purpose (or at least similar) to the same fan header.
For example, 2 fans doing push-pull on a heatsink or radiator, 2 fans as case rear exhaust, 1 fan as intake in case front + 1 fan as exhaust in case rear...etc