Connecting fans using a shared 3 pin

almoststew1990 · 11 May 2015 at 17:18

I'm running a front fan and rear fan from a single 3 pin motherboard. The problem is the rear fan runs flat out all the time (but the front fan seems fine).

If I the rear fan on the 3 pin on its own it still runs flat out.

So I take it I'll need a new 92mm fan? Or is it some other problem?

ttaskmaster · 11 May 2015 at 17:27

It might depend on the motherboard.
Some fan headers cannot cope with multiple fans, which more often results in just one spinning in my (limited) experience, but can sometimes result in other weirdness.

Also, is this rear fan a 3-pin model (ie does it have 3 wires) designed for variable RPMs?

almoststew1990 · 11 May 2015 at 17:32

Both fans are three pin. The connector on the motherboard is a PWM though.

MrMD · 11 May 2015 at 19:24

Often 3 pin fans just dont like PWM signals

I was tryin to hook up a 3 pin fan to a pwm PCB splitter the other-day,same thing just runs it a full speed regardless.

You could try connecting the fan to the splitter with an LNA/stepdown cable rather than replaceing the fan.

DavidS14 · 11 May 2015 at 19:56

If you are trying to control multiple fans from a single header then you should only have one of the fans with the tacho signal connected otherwise the multiple tacho inputs will cause issues.

If the one fan runs ok on the header and you can control the speed but the other one will not control I'd be looking at another fan if you are looking at controlling the speed or stepping the voltage down if you're happy with a set slower speed.

Are they the same make/model ?

almoststew1990 · 11 May 2015 at 20:31

What do you mean by tacho signal? As in rpm?

I think the splitter only actual connects two of the three pins of each fan, so it may already not use the tacho signal.

I've sourced a 92mm fan to try out from the clearance section for a quid, can't hurt to try it with a new fan!