3x 140mm fans on one motherboard header?

masumo · Post by **masumo** » Mon Aug 30, 2010 5:43 pm

This is more a safety question than a cooling/silence one...but is it safe to connect three 140mm fans to a splitter, and then connect the splitter to one of the fan headers on the motherboard? I have it setup this way right now, but reduced the speeds in the BIOS. What's the worst that can happen? The fans just not getting enough juice and not powering on?

Fans in question (Noiseblocker Black, 140mm, 1700 rpm): http://www.noiseblocker.de/en/BlackSilentPro140.php
(went with 1700rpm because I was thinking of getting a fan controller, but the cable management is turning me off)

Motherboard in question (Biostar 890FXE): http://www.biostar.com.tw/app/en/mb/con ... p?S_ID=482
(only two SYS fan headers

- the other header is reserved by my H50)

Edit: I'm running a Seasonic X650 PSU

swivelguy2 · Post by **swivelguy2** » Mon Aug 30, 2010 6:54 pm

I had trouble running even 2 nexus 120mm fans from 1 MB header. They ramped up and down seemingly randomly, even on a header that supposedly could not be controlled or varied at all. In fact, I pretty much don't trust MB headers at all, all of my fans are off fanmates connected to 12v, so maybe I'm just paranoid.

Lawrence Lee · Post by **Lawrence Lee** » Mon Aug 30, 2010 8:15 pm

Back in 2005ish, I had sweet board with 3 controllable headers (unheard of back then). I was using Y-splitters on all of them to power 6 x 80/120mm fans with them, one pair each. 2 of the headers blew out and suddenly my board wasn't so sweet. Needless to say, I don't do that anymore.

lodestar · Post by **lodestar** » Mon Aug 30, 2010 11:23 pm

The best way to run three fans, if they are 3-pin fans, is to use a 3-pin to 4-pin adapter with rpm monitoring for each fan. The 4-pin refers to a molex connector, so you draw the power for the fan direct from the PSU and not from the motherboard. The adapter comes with a separate yellow (fan rpm sensing) cable with a plug on the end which can fit into any motherboard fan header, including SYS etc. This will give you rpm monitoring for each fan. The adapters are not expensive, around $3 US.

While this will remove power draw from the motherboard, it does not allow any motherboard control over fan speeds. The options are to use resistor cables to drop voltage to 9v or 7v and reduce fan rpm that way. Or to use a fan controller. All of these options tend to lead to a lot of wiring but I would still say that, if you can, you should avoid pulling the power for three fans from a single motherboard header.

datapappan · Post by **datapappan** » Tue Aug 31, 2010 12:27 am

As per above, you can blow a MB fan header if you overload it - happened to me, of course on the only one that could be controlled (except for the CPU fan header).

/ d

Parappaman · Post by **Parappaman** » Tue Aug 31, 2010 3:15 am

Well, if you are planning on using a fan controller, this problem doesn't exist: all of them get their power off a normal 4-pin molex and power each fan on a single header.